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101. Public and Government Services

Chapter Editor: David LeGrande

Table of Contents

Tables and Figurs

Occupational Health and Safety Hazards in Public and Governmental Services
David LeGrande

     Case Report: Violence and Urban Park Rangers in Ireland
     Daniel Murphy

Inspection Services
Jonathan Rosen

Postal Services
Roxanne Cabral

David LeGrande

Hazards in Sewage (Waste) Treatment Plants
Mary O. Brophy

Domestic Waste Collection
Madeleine Bourdouxhe

Street Cleaning
J.C. Gunther, Jr.

Sewage Treatment
M. Agamennone

Municipal Recycling Industry
David E. Malter

Waste Disposal Operations
James W. Platner

The Generation and Transport of Hazardous Wastes: Social and Ethical Issues
Colin L. Soskolne


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1. Hazards of inspection services
2. Hazardous objects found in domestic waste
3. Accidents in domestic waste collection (Canada)
4. Injuries in the recycling industry


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Public and government services encompass a wide variety of industrial and occupational categories. For example, included are workers employed within telecommunications and postal services, inspection and field services, as well as sewage treatment, recycling, landfill and hazardous waste operations. Depending on the individual country, industrial categories such as telecommunications and postal services may be located within either the public or private sector.

Occupational and environmental safety and health hazards in public and government services include exposure to chemicals, ergonomics, blood-borne pathogens, tuberculosis, machinery hazards, violence, motor vehicles and flammable materials. In the future, as public and government services continue to grow and become more complex, it is anticipated that occupational safety and health hazards will increase and become more widespread. In turn, led by tripartite (labour, management and government) initiatives, improvements in occupational safety and health hazard recognition and control will provide improved resolution of identified hazards.

Health Problems and Disease Patterns

Patterns or identifiable trends of occupational health problems have been associated with the type of work (i.e., use of visual display units (VDUs) or chemicals), as well as where the work is performed (i.e., indoors or outdoors).

Indoor work

The primary hazards associated with indoor work are poor or inadequate physical and work organization ergonomics, inadequate indoor air quality or heating, ventilation and air conditioning systems, chemicals, asbestos, workplace violence and electromagnetic fields (low-level radiation).

Health symptoms and disorders or illnesses have been associated with exposure to these hazards. Since the mid-1980s, a large number of ergonomic-related upper extremity physical illnesses have been reported. Disorders include carpal tunnel syndrome, ulnar deviation, thoracic outlet syndrome and tendinitis. Many of these are related to the introduction of new technology, particularly VDUs, as well as the use of hand tools and equipment. Causes of identified illnesses include physical and work organization factors.

Since the engineering and construction of “tight-buildings” in the 1970s, a pattern of increasing incidence of upper respiratory and dermatological health symptoms and illnesses has been observed. Such health problems are associated with improper maintenance of the heating, ventilation and air conditioning systems; chemical contaminants and microbiological agents; and the inadequate provision of fresh air and air flow.

Exposure to chemicals in indoor work environments has been linked to upper respiratory and dermatological health symptoms and illnesses. A variety of different chemical contaminants are emitted from copying machines, furniture, carpets, cleaning materials (solvents) and the heating, ventilation and air conditioning system. One particular syndrome, multiple chemical sensitivity, has been associated with chemical exposures in indoor work environments.

Asbestos exposure may occur when building renovation and service work are performed and asbestos products or materials are deteriorated or damaged, thus causing asbestos fibres to become airborne.

Since the 1980s, workplace violence and associated safety and health problems have become increasingly widespread. Work environments where increasing rates of workplace violence have been documented are characterized as follows: handling money, working with the public, working alone, coming into contact with patients or clients who may be violent and dealing with customer or client complaints.

Health concerns include physical harm and death. For example, homicide was the second leading cause of death in the US workplace in 1992, accounting for 17% of all workplace deaths. In addition, from 1980 to 1989 homicide was the leading cause of death in the workplace for women, as discussed in more detail in the chapter Violence in this Encyclopaedia.

Work with and exposure to electronic equipment and related electromagnetic fields or non-ionizing radiation has become commonplace, as is exposure to high frequency non-ionizing radiation emitting products such as laser and microwave transmission equipment, radio-frequency heat sealers and electric tools and generation equipment. The relationship between such exposures and consequent health effects such as cancer, visual and skin disorders is not yet clear and much research is still needed. Several chapters in this Encyclopaedia are devoted to these areas.

Outdoor work

Outdoor work environment occupational hazards include exposure to chemicals, lead, hazardous and solid waste, environmental conditions, inadequate ergonomics, motor vehicles, electrical and mechanical equipment and electromagnetic field emissions.

Exposure to chemicals occurs in several identified occupational categories including waste disposal operations, water and sanitation services, sewage treatment, domestic waste collection, postal collection and technician jobs in telecommunications. Such exposure has been related to upper respiratory, dermatological, cardiovascular and central nervous system illnesses. Exposure to lead occurs among telecommunications workers while performing splicing operations with and removing lead telecommunications cables. Such exposure has been liked to a variety of health symptoms and illnesses, including anaemia, peripheral and central nervous system disorders, sterility, kidney damage and birth defects.

Hazardous work environments are common to waste disposal operations, water and sanitation services, sewage treatment and domestic waste collection. Occupational safety and health hazards include microbiological and medical waste, chemicals, inadequate ergonomics, motor vehicles, confined spaces and electrical and mechanical equipment. Identified health symptoms and illnesses include upper respiratory, dermatological, upper and lower extremity musculoskeletal, cardiovascular, central nervous system and visual problems. Additional concerns include lacerations, heat exhaustion and stroke.

Inadequately designed workplace tools and equipment are common to all outside public and government service occupations. Hazards comprise poorly designed hand and power tools, machinery and motor vehicles. Associated health problems include upper and lower extremity musculoskeletal symptoms and illnesses. Safety-related concerns include visual problems, strains, sprains and fractured and broken bones.

Hazards associated with motor vehicles include poorly designed equipment (e.g., hoppers, compaction boxes and aerial equipment), as well as improperly operating machinery and equipment. Associated health problems comprise musculoskeletal injuries and death. Motor vehicle accidents account for the greatest number of injuries and fatalities outdoors.

Hazards associated with electrical and mechanical equipment include poorly designed equipment, electrical shock and electrocution, as well as chemical exposures. Health problems include strains, sprains, broken bones, central nervous and cardiovascular system disorders, as well as upper respiratory and dermatological disorders and death.

Work with or in close proximity to electrical transmission equipment and the associated electromagnetic fields of non-ionizing radiation emissions has been linked with the occurrence of certain central nervous system symptoms and disorders as well as cancer. However, scientific and epidemiological research has, as of yet, not clearly defined the degree of harm posed by electromagnetic fields.

Outdoor public and government services activities present several environmental and public health problems. For example, chemicals, microbiological agents, sewage and domestic waste may be used and disposed of improperly, thus finding their way into the water table as well as streams, lakes and oceans, causing environmental contamination. In turn, such waste may lead to the contamination of public water supplies as well as the creation of toxic dumps or sites. Such contamination has been related to the deterioration and destruction of the environment as well as public health. Associated human health effects include dermatological, central nervous and cardiovascular system health symptoms and disorders, as well as certain types of cancer.



Rangers in parks in large Irish cities are employed to “keep the peace”, to “liaise with the public” (i.e., discourage vandalism and respond to any complaints that might be made) and to perform “light cleaning duties” (i.e., cleaning up rubbish and garbage such as broken bottles, needles and syringes discarded by drug abusers and used condoms). Their hours are unsociable: they report around mid-day and remain on duty until dusk when they are supposed to lock the park gates. This means long hours in the summertime that are somewhat compensated for by the shorter days in winter.

The majority of the parks have only one ranger who works alone, although there may be other local authority employees doing landscaping, gardening and other jobs in the park. Usually the only building in the park is the depot where gardening equipment is kept and where the staff may go for shelter in very severe weather. To avoid spoiling the ambiance, the depots are usually located in sequestered areas out of the public view where they are subject to misuse by vandals and marauding gangs of youths.

The park rangers are frequently exposed to violence. An employment policy that favoured the hiring of individuals with mild disabilities as rangers was recently supplanted when it was realized that public knowledge of such problems made these rangers ready targets for violent assault. Public authorities were not covered by the Irish health and safety legislation which, until recently, was applicable only to factories, building sites, docks and other process industries. As a result, there were no formalized arrangements for dealing with violence against park workers who, unlike their counterparts in some other countries, were not provided with firearms or other weapons. Nor was there any access to post-violence counselling.

The tendency to assign rangers who lived in the immediate neighbourhood to a particular park meant that they were more likely to be able to identify the trouble-makers likely to have been the perpetrators of violent acts. However, this also increased the danger of reprisals to the ranger for having “fingered” the culprits, making him or her less inclined to make formal complaints against their assailants.

Lack of an adequate police presence in the parks and the very early release from prison of convicted perpetrators were often crushing blows to the morale of the victims of the violence.

The trade unions representing the rangers and other public authority personnel have been active in promoting efforts to deal with violence. They now include training in recognizing and preventing violence in the courses they sponsor for safety representatives.

Even though the Irish health and safety legislation now covers public authority workers, the creation of a national committee to deal with both the control of violence and the provision of aftercare for its victims would be beneficial. While guidelines on preventing violence are now available to assist those engaged in assessing the risks of violence in workplaces, their use should be made mandatory for all occupations where violence is a risk. Furthermore, increased resources for and enhanced coordination with the city’s police force are desirable for dealing with the problem of violence and assault in the public parks.

Training in how to deal with individuals and groups likely to be violent should be make available to all workers who face this risk in their jobs. Such training might include how to approach and deal with individuals presenting indications of violent assault as well as self-defence manoeuvres.

Improved communications for reporting problem situations and requesting help would also be helpful. Installing telephones in all park depots would be a useful first step while “walkie-talkie” radios and cellular telephones would be useful when away from the depot. Video camera systems for surveillance of sensitive areas, such as the park depots and sports facilities, might help to deter violence.



Monday, 28 March 2011 19:19

Inspection Services

National, state or provincial, municipal and other local government units employ inspectors in a variety of agencies to verify compliance with laws, ordinances and regulations intended to promote and protect the health and safety of both workers and the public. This is government’s traditional role of enacting laws to address socially unacceptable risks and then to assigning agencies to establish programmes to achieve conformance with the regulatory standards. The inspector or investigator is the key person on the front-line in enforcing regulatory standards.

An example of such a legislative mandate is the role of inspection of workplaces for health and safety practices. Worksite inspectors visit workplaces to verify compliance with regulations governing the workplace, potential occupational and environmental hazards, the tools, machines and equipment being used, and the way the work is done, including the use of personal protective equipment (PPE). The inspectors have the authority to initiate penalties (citations, monetary fines and, in egregious cases, criminal prosecution) when deficiencies are encountered. Under laws enacted in some localities, regional authorities share responsibilities for carrying out inspections with federal powers.

Other areas in which governmental agencies have inspection responsibilities include environmental protection, regulation of food and drugs, nuclear energy, interstate commerce and civil aviation, public health and consumer protection. Engineering and building inspections are generally organized at the local level.

Throughout the world the basic functions and protections addressed by inspection services are similar although the particular legislation and governmental structures vary. These are discussed elsewhere in this Encyclopaedia.

To protect workers and property, to avoid statutory penalties and the adverse publicity that accompanies them and to minimize legal liability and the costs of workers’ compensation benefits, private sector enterprises often conduct in-house inspections and audits to ensure that they are complying with the regulations. These self-audits may be conducted by appropriately qualified staff persons or outside consultants may be retained. A notable recent trend in the US and some other developed countries has been the proliferation of private consulting organizations and academic departments which offer occupational health and safety services to employers.


In general, inspectors are faced by the very same hazards they are charged to identify and correct. For example, workplace health and safety inspectors may visit worksites that have toxic environments, harmful noise levels, infectious agents, radiation, fire or explosion hazards and unsafe buildings and equipment. Unlike workers in a fixed environment, the inspectors must anticipate the kinds of hazards they will encounter on a given day and make sure that they have the tools and PPE they might need. In each instance, they must prepare themselves for a worst-case scenario. For example, when entering a mine, inspectors must be prepared for an oxygen-deficient atmosphere, fires and explosions and cave-ins. Inspectors checking isolation units in health care facilities must protect themselves against contagious organisms.

Occupational stress is a prime hazard for inspectors. It stems from a number of factors:

  • Work stress is increasing as fiscal retrenchments cause reductions in agency budgets, which often results in understaffing. This brings pressure to manage an increasing work load that inevitably affects the ability to maintain the quality and integrity of inspections.
  • There is also the stress of having to enforce the minutiae of guidelines and regulations which the inspector may acknowledge to be unwarranted in particular situations. And, when circumstances do not allow them to be overlooked, the inspector may bear the brunt of abuse for enforcing unpopular rules and regulations.
  • Employers, and sometimes the workers as well, may resent the “intrusion” of the inspector into the workplace and his or her need to maintain a high level of suspicion with respect to subterfuges and cover-ups. This often makes the job unpleasant and stressful for the inspector. This antagonism may escalate into threats and actual violence.
  • The inspector may suffer from feelings of responsibility when neglected or unrecognized hazards in the workplace result in a worker’s loss of life or limb or, even worse, in disaster involving many individuals.
  • Like many employees who work in the field on their own, inspectors may suffer from such bureaucratic ills as distant and/or inadequate supervision, lack of support, endless paperwork and separation from home, family and friends.
  • The necessity of entering unsafe neighbourhoods may expose them to crime and violence.
  • Finally, particularly when they are required to wear uniforms, they may be seen as enemies by those who bear a grudge against the particular agency or the government as a whole. This can culminate in abuse or even violent assaults. The 1996 bombing of the federal office building in Oklahoma City, Oklahoma, in the US is an indication of such hostility to government.


Agencies employing inspectors must have clearly written health and safety policies describing appropriate measures to protect the health and well-being of inspectors, particularly those working in the field. In the US, for example, OSHA includes such information in its compliance directives. In some instances, this agency requires inspectors to document their use of the appropriate protective equipment while performing an inspection. The integrity of the inspection may be compromised if the inspector himself or herself violates health and safety rules and procedures.

Education and training are the key to preparing inspectors to properly protect themselves. When new standards are promulgated and new initiatives or programmes undertaken, the inspectors should be trained in preventing illness and injury to themselves as well as being drilled in the new requirements and enforcement procedures. Unfortunately, such training is rarely offered.

As part of programmes for learning to cope with work stress, also rarely offered, inspectors should be trained in communication skills and contending with angry and abusive people.

Table 1 lists some of the categories of government inspectors and hazards to which they may be exposed. More detailed information about the recognition and control of such hazards is to be found elsewhere in this Encyclopaedia.

Table 1. Hazards of inspection services.



Associated hazards

Occupational safety and health compliance officers

Investigate and cite safety and health hazards

A wide variety of safety and health hazards

Agricultural inspectors

Investigate agricultural and farmworker health and safety

Agricultural equipment, chemicals, pesticides, biological agents and
outdoor environment

Environmental inspectors

Investigate industrial and agricultural sites for contaminated air, water and soil

Chemical, physical, biological and safety hazards

Health inspectors

Investigate nursing homes and hospitals for compliance with hospital safety and health standards

Infectious, chemical, radioactive and safety hazards

Food inspectors

Investigate and cite food product safety and establishments

Insects, vermin and associated microbiological agents; chemical agents; violence and dogs

Engineering and building inspectors

Investigate for compliance with building construction and fire operation and maintenance codes

Unsafe structures, building and construction equipment and materials

Customs inspectors

Investigate for contraband and hazardous materials entering territorial boundaries

Explosives, drugs, biological and chemical hazards


A recent phenomenon in many countries that is disturbing to many is the trend toward deregulation and decreased emphasis on inspection as an enforcement mechanism. This has led to the under-financing, degrading and downsizing of agencies and erosion of their inspection services. There is a growing concern not only for the health and safety of the cadres of inspectors but also for the health and well-being of the workers and the public they are charged to protect.



Monday, 28 March 2011 19:22

Postal Services

Although the social obligation of most postal administrations—domestic mail collection, sorting, delivery and international mail processing while preserving the security of mail—has remained unchanged over the last century, the methods by which this obligation is carried out have been transformed due to the rapid advances of technology and increases in mail volumes. Australia, France, Germany, Sweden, the United Kingdom and other industrialized countries each process billions of mail pieces each year. In 1994 the US Postal Service delivered almost two hundred billion pieces of mail, an increase in mail volume of 67% since 1980. Competition by private carriers entering the market, particularly for parcel delivery and express delivery service, as well as from other technological advancements, such as facsimile (fax) machines, computer modems, electronic mail, electronic transfer of funds and satellite systems, have also changed personal and business communications. Since private carriers carry out many of the same operations as postal services, their workers face many of the same hazards.

Most postal administrations are government-owned and operated, although this is changing. For example, Argentina, Australia, Canada, Germany, the Netherlands, Sweden, the United Kingdom and the United States have, to varying degrees, privatized their postal operations. The franchising or contracting of work and services is becoming increasingly common among the postal administrations in the industrialized world.

Postal administrations, especially in industrialized nations, are often one of the largest employers in the country; they employ up to several hundred thousand people in some countries. Although advances in technology have not dramatically changed how postal administrations are structured, they have altered the methods by which mail is sorted and delivered. As postal services have long been highly labour intensive (with wages and benefits accounting for up to 80% of total operating costs in some countries), efforts to reduce these costs as well as to improve productivity and increase operating efficiency have promoted technological advancement through capital investments. For many industrialized nations the objective is to fully automate the processing of mail up to the point of delivery.


Postal operations are divided into three main phases: collection, sorting and delivery. Administrative and maintenance services are also integral aspects of postal operations. The technological changes in operating methods, especially for the sorting phase, have led to a declining demand for workers. As a result, workers are more isolated because less staffing is required to operate the newer postal equipment. Enhanced technology has also led to a reduction of requisite skills in the workforce as computers have replaced such tasks as memorizing postal codes and performing diagnostic tests on mechanical equipment.

Shift work is still a common practice in postal operations as most mail is collected at the end of the day and then transported and sorted at night. Many postal administrations provide home and business mail delivery six days a week. The frequency of service requires most postal operations to run twenty-four hours a day, seven days a week. Consequently, the psychological and physical stress from shift work and night work still remain problems for many postal workers, particularly during the busy night shift in large processing centres.

Most postal administrations in the industrialized world are organized with large processing centres supporting small retail and delivery offices. Often several stories high and occupying several thousands of square metres, processing centres are equipped with large pieces of machinery, material handling equipment, motor vehicles and repair and paint shops similar to work environments in other industrial workplaces. Smaller retail offices, however, are generally cleaner and less noisy and more akin to office environments.

Hazards and Their Prevention

While technology has eliminated many dangerous and monotonous tasks performed by postal workers, different hazards have emerged that, if not properly addressed, may jeopardize the health and safety of postal workers.

Retail services

For employees who work at retail postal counters, job tasks depend on the size of the post office and the type of services offered by the postal administration. General duties of the retail employee include selling stamps and money orders, weighing and pricing letters and parcels and providing postal information to customers. Since retail personnel are directly involved in the exchange of money with the public, the risk of violent robbery is increased for these workers. For retail personnel who work alone, in proximity to high crime areas or late at night or early in the mornings, workplace violence can be a major occupational hazard if appropriate protective measures are not taken. The potential for such workplace violence also contributes to undue mental stress. Also, the day-to-day pressure from dealing with the public and the responsibility for relatively large amounts of money are contributing stress factors.

Environmental conditions and the physical layout of the retail employee’s workstation may also contribute to health and safety hazards. Indoor air quality problems, such as dust, the lack of fresh air and temperature variations may cause discomfort for the retail clerk. Poorly designed work stations that require the operator to work in awkward postures due to the placement of retail equipment (e.g., cash register, scale, mail and parcel containers), prolonged standing postures or sitting in uncomfortable and unadjustable chairs, and lifting heavy parcels can lead to musculoskeletal disorders.

Preventive measures that address these hazards include improving security by installing bright external and internal lighting, doors, windows and partitions of bullet proof glass and silent alarms, ensuring that clerks do not work alone, providing emergency and defensive response training and ensuring that the public has limited and controlled access to the facility. Ergonomic and indoor air quality assessments may also contribute to the improvement of the working conditions for retail personnel.


The transition from manual operations to mechanized and automated systems has greatly affected the handling and sorting phase of postal operations. For example, whereas postal workers were once required to memorize various codes that corresponded to address delivery routes, that task is now computerized. Since the early 1980s, technology has improved so that many machines can now “read” an address and apply a code. In the industrialized countries, the task of sorting mail has shifted from humans to machines.

Material handling

Although technology has reduced the amount of manual letter and small parcel sorting, it has had less of an impact on the movement of containers, bundles and sacks of mail inside a postal facility. Mail that is transported by trucks, planes, rail or ship into large processing and sorting centres may be internally transferred to different sorting areas by complex conveyor or belt systems. Fork-lift trucks, mechanical dumpers and smaller conveyors assist postal employees in unloading and loading trucks and placing the mail onto the complex conveyor systems. Some material handling tasks, however, especially those performed in smaller postal facilities, must still be performed manually. Culling operations that separate mail to be processed by machine from mail that which must be sorted by hand is one task that has not been fully automated. Depending on the postal administration’s regulations or national health and safety regulations, limits on load weights may be imposed to prevent employees from having to lift and carry containers of mail and parcels that are too heavy (see figure 1).

Figure 1. Manual lifting of heavy parcels is a serious ergonomic hazard. Weight and size limits on parcels are necessary.


Material handling tasks also expose postal workers to electrical hazards and machine parts that may injure the body. Although paper dust is a nuisance to almost all postal workers, employees who primarily perform material handling tasks commonly inhale dust when they first open mailbags, containers and sacks. Material handling workers are also the first employees to come into contact with any biological or chemical materials that may have spilled during transport.

Efforts to reduce fatigue and back injuries include automating some of the manual lifting and carrying tasks. Transporting pallets of mail by forklifts, using rolling containers to transport mail inside a facility and installing automatic container unloaders are methods of automating material handling tasks. Some industrialized nations are utilizing robotics to assist in material handling tasks such as loading containers onto conveyors. Regulating the amount of weight                                                                                               workers lift and carry and training workers in proper lifting techniques may also                                                                                           help to reduce the incidence of back injury and pain.

To control exposure to chemicals and biological matter, some postal administrations place prohibitions on the type and amount of hazardous materials that can be sent by mail and also require these materials to be identifiable to postal workers. Since some mail will undoubtedly be sent without proper warnings affixed, workers should be trained in responding to releases of potentially hazardous materials.


As sorting technology improves, manual letter sorting is rapidly being phased out. Some manual letter sorting, however, is still necessary in many postal administrations, particularly in the developing countries. Manual letter sorting involves workers placing individual letters into slots or “pigeon holes” in a case. The worker then bundles the mail from each slot and places the bundles into containers or mail bags for dispatch. Manual sorting is a repetitive activity that the worker performs while either standing or sitting on a stool.

Manual parcel sorting is also still performed by postal workers. Since parcels are generally larger in size and much heavier than letters, workers must often put the parcels into separate hampers or containers that are arranged around them. Workers who perform manual parcel sorting often are at risk for cumulative trauma disorders affecting the shoulders, arms and back.

Automation has addressed many of the ergonomic hazards associated with manual letter and parcel sorting. Where automation technology is not available, workers should have the opportunity to rotate to different tasks to relieve fatigue from one particular body area. Appropriate rest breaks should also be provided to workers performing repetitive tasks.

In modern, mechanized sorting systems, workers sit at a keyboard while letters are mechanically passed in front of them (figure 2). Coding desks are arranged either side-by-side or behind one another in a line. Operators must often memorize hundreds of codes that correspond to different zones and enter a code for each letter on a keyboard. Unless adjusted properly, the keyboards may require the operator to use more force to depress the keys than modern computer keyboards. Approximately fifty to sixty letters each minute are processed by the operator. Based upon the code entered by the operator, the letters are segregated into different bins and then removed, bundled and dispatched by the postal workers.

Figure 2. Coding desk operators sorting letters with the aid of computerized machines.


Ergonomic hazards that lead to musculoskeletal disorders, particularly tendinitis and carpal tunnel syndrome, are the biggest problem for mechanized sorting operators. Many of these machines were designed several decades ago when ergonomic principles were not applied with the same degree of diligence as they are today. Automated sorting equipment and VDUs are quickly replacing these mechanized sorting systems. In many postal administrations where mechanized sorting is still the primary system, workers may rotate to other positions and/or take breaks at regular intervals. Providing comfortable chairs and adjusting the keyboard force are other modifications that can improve the job. Although a nuisance and discomfort to the operator, noise and dust from the mail are generally not major hazards.





Visual display units

Visual display unit-based sorting terminals are beginning to replace mechanized sorters. Instead of the actual mail pieces being presented to the operator, enlarged images of the addresses appear on the screen. Much of the mail that is processed by VDU sorting has been previously rejected or culled as not machineable by the automatic sorters.

The advantage of VDU sorting is that it does not need to be located in close proximity to the mail. Computer modems can send the images to the VDUs that are located in another facility or even a different city. For the VDU operator, this means that the work environment is generally more comfortable, with no background noise from sorting machines or dust from mail. However, sorting with the VDU is a very visually demanding job and often involves only one task, keying from images of letters. As with most sorting tasks, the job is monotonous but at the same time requires intense concentration from the operator in order to maintain the required productivity levels.

Musculoskeletal discomfort and eye strain are the most common complaints of VDU operators. Steps to reduce physical, visual and mental fatigue include providing adjustable equipment, such as keyboards and chairs, maintaining adequate lighting to reduce glare and scheduling regular breaks. In addition, since VDU operators often work in an office-type environment, consideration should be given to indoor air quality complaints.


The most advanced type of sorting reduces the need for workers to be directly involved in the coding and segregation of individual mail pieces. Generally only 2 or 3 workers are required to operate an automatic sorter. At one end of the machine, a worker loads mail onto a mechanical belt that feeds each letter in front of an optical character reader (OCR). The letter is read or scanned by the OCR and a bar code is printed on it. The letters are then automatically segregated into dozens of bins located at the other end of the machine. Workers then remove the bundles of segregated mail from the bins and transport them to the next stage of the sorting process. Larger automated sorters can process between 30,000 and 40,000 pieces of mail per hour.

Although such automation no longer requires a keyboard to encode mail, workers are still exposed to monotonous, repetitive tasks that put them at risk for musculoskeletal disorders. Removing the bundles of segregated mail from the different bins and placing them into containers or other material handling equipment puts physical stress on the operator’s shoulders, back and arms. Operators also complain of wrist and hand problems from constantly grasping handfuls of mail. Dust exposure is sometimes more problematic for automated sorter workers than other postal employees because of the larger volume of mail processed.

Many postal administrations have only recently acquired automated sorting equipment. As complaints of musculoskeletal discomfort mount, equipment designers and engineers will be forced to incorporate ergonomic principles more thoroughly in their attempts to balance productivity needs with the well-being of employees. For example, in the United States, government safety and health officials have concluded that some of the automated mail-sorting equipment poses serious ergonomic deficiencies. While attempts can be made to modify either the equipment or work methods to reduce the risks of musculoskeletal discomfort, such modifications are not as effective as the proper design of equipment (and work methods) in the first place.

Another problem is the risk of injury during the clearing of jams or during maintenance and repair operations. Proper training and lockout/tagout procedures are needed for these operations.


Postal operations rely upon many methods of transportation to distribute mail including air, rail, water and highway. For short distances and local delivery, mail is transported by motor vehicles. Mail travelling generally less than several hundred kilometres from large processing centres to smaller post offices is usually carried by trains or large trucks, while air and sea travel is reserved for the longer distances between large processing centres.

As the use of motor vehicles for delivery services has increased dramatically during the past two decades, accidents and injuries involving postal trucks, jeeps and automobiles have become for some postal administrations the biggest and most serious occupational safety and health problem. Vehicular accidents constitute the main cause of workplace fatalities. Additionally, while the increased use of motor vehicles for delivery and the installation of more street mail storage boxes have helped to reduce the amount of time letter carriers spend walking, musculoskeletal discomfort and back injuries still are problematic due to the heavy bags of mail that they must carry on their routes. Also, robberies and other violent attacks against letter carriers are on the rise. Injuries caused by slips, trips and falls, particularly during adverse weather conditions, and dog attacks are other serious hazards experienced by letter carriers. Unfortunately, other than increased awareness not much can be done to eliminate these particular hazards.

Steps designed to reduce the likelihood of vehicular accidents include installing anti-lock brakes and extra mirrors to improve visibility, increasing seat belt usage, improving driver training, conducting more frequent vehicle maintenance inspections and improving roadways and vehicle design. To address the ergonomic hazards associated with lifting and carrying mail, some postal administrations provide carts with wheels or specialized mail bags where the weight is more evenly distributed across the worker’s shoulders instead of concentrated on one side. To reduce the risk of workplace violence, letter carriers may carry two-way communication devices and their vehicles may be equipped with a tracking system. In addition, to address environmental concerns and concerns of exposure to diesel exhaust, some postal vehicles are powered by natural gas or electricity.

Repair and Maintenance

Workers that are responsible for the day-to-day upkeep, cleaning and repair of postal facilities and equipment, including motor vehicles, face similar hazards as maintenance employees in other industrial operations. Exposure to welding operations, electrical hazards, falls from scaffolding, chemicals found in cleaning fluids and machine lubricants, asbestos from brake linings and dust are examples of hazards associated with maintenance tasks.



Monday, 28 March 2011 19:29


Telecommunications is the act of communicating with others through the use of electronic equipment like telephones, computer modems, satellites and fibre optic cables. Telecommunications systems comprise telecommunications cables from the user to the local switching office (local loops), the switching facilities which provide the communications connection to the user, the trunks or channels that transmit calls between the switching offices and, of course, the user.

During the early to mid-twentieth century, telephone exchanges, electromechanical switching systems, cables, repeaters, carrier systems and microwave equipment were introduced. After this occurrence, telecommunications systems spread to the industrialized areas of the world.

From the 1950s to 1984, technological advances continued to appear. For example, satellite systems, improved cable systems, the use of digital technology, fibre optics, computerization and video telephony were introduced throughout the communications industry. These changes allowed for the expansion of telecommunications systems throughout more areas of the world.

In 1984 a court ruling in the United States led to the breakup of the telecommunications monopoly held by American Telegraph and Telephone (AT&T). This breakup coincided with many rapid, major changes in the technology of the telecommunications industry itself.

Until the 1980s telecommunications services were considered to be public services operating within a legislative framework that provided monopoly status in virtually all countries. Along with the development of economic activity, the advent of new technologies has led to the privatization of the telecommunications industry. This trend culminated in the divestiture of AT&T and the deregulation of the US telecommunications system. Similar privatization activities are underway in a number of other countries.

Since 1984, technological advances have produced and expanded telecommunications systems that can provide universal service to all people throughout the world. This occurs as telecommunications technology is now converging with other information technologies. Related fields such as electronics and data processing are involved.

The impact of the introduction of new technology on employment has been mixed. Without question, it has reduced levels of employment and produced the de-skilling of jobs, radically altering the tasks of telecommunications workers as well as the qualifications and experience required of them. However, it is anticipated by some that employment growth will occur in the future as a result of the new business activity stimulated by the deregulated telecommunications industry that will produce many highly skilled jobs.

Occupations within the telecommunications industry can be categorized as either skilled craft or clerical work. Craft jobs include cable splicers, installers, outside plant technicians, central office technicians and frame technicians. These jobs are highly skilled, particularly as a result of the new technological equipment. For example, employees must be very proficient in the electrical, electronics and/or mechanical fields as they relate to the installation, service and maintenance of telecommunications equipment. Training is acquired through classroom and on-the-job training.

Clerical occupations include directory assistance operators, customer service representatives, account representatives and sales clerks. In general these tasks involve the operation of communications equipment such as VDUs private branch exchange (PBX) and facsimile machines which are used to establish local and/or long distance connections, perform business office work inside or outside the workplace and handle sales contacts with customers.

Hazards and Controls

The occupational safety and health hazards within the telecommunications industry can be categorized by the type of tasks or services performed.

Building and construction operations

In general, the same risks occur as in construction and building operations. However, several noteworthy activities which are specific to telecommunications include working at heights on poles or pylons, installing telecommunications wiring systems and excavating for cable laying. The usual means of protection, such as climbing gaffs, safety harnesses, lines and raise platforms and proper shoring for excavations, are applicable in telecommunications. Often, this work is performed during emergency repairs made necessary by storms, landslides or floods.


The safe use of electricity and electrical equipment is extremely important when performing telecommunications work. The normal preventive measures against electrocution, electric shock, short circuits and fires or explosions are fully applicable to telecommunications. Also, a serious source of danger may arise when telecommunications and electricity cables are within close proximity to one another.

Cable laying and maintenance

A significant safety and health concern is cable laying and maintenance. Work on underground cables, pipelines and jointing chambers involves handling heavy cable drums and pulling cables into pipelines with power-driven winches and cable equipment as well as cable splicing or jointing and insulation or waterproofing. During cable splicing and insulation jobs, workers suffer exposure to health hazards such as lead, solvents and isocyanates. Preventive measures include use of the least toxic chemicals, adequate ventilation and PPE. Often, maintenance and repair work is performed in confined spaces like manholes and vaults. Such work necessitates special ventilation equipment, harness and lifting equipment and the provision of a worker stationed above ground who is able to perform emergency cardiopulmonary resuscitation (CPR) and rescue activities.

Another health and safety concern is working with fibre optic telecommunications cables. Fibre optic cables are being installed as an alternative to lead and polyurethane-encased cables because they carry many more communications transmission and they are much smaller in size. Health and safety concerns involve potential burns to the eyes or skin from exposure to the laser beam when cables become disconnected or broken. When this occurs, protective engineering controls and equipment should be provided.

Also, cable installation and maintenance work performed in buildings involves potential exposure to asbestos products. Exposure occurs as a result of the deterioration or break-up of asbestos products like pipes, patching and taping compounds, floor and ceiling tiles and reinforcing fillers in paints and sealants. During the late 1970s, asbestos products were banned or their use was discouraged in many countries. Adherence to a worldwide prohibition will eliminate exposure and resultant health disorders for future generations of workers, but there are still large amounts of asbestos to contend with in older buildings.

Telegraph services

Telegraph workers use VDUs and, in some cases, telegraph equipment to perform their work. A frequent hazard associated with this type of work is upper extremity (particularly hand and wrist) musculoskeletal cumulative trauma. These health problems may be minimized and prevented with attention to ergonomic work stations, work environment and work organization factors.

Telecommunications service

Automatic switching and connecting circuits are the mechanical operations components of modern telecommunications systems. Connections are generally made by microwave and radio frequency waves in addition to cables and wires. Potential hazards are associated with microwave and radio frequency exposures. According to available scientific data, there is no indication that exposure to most types of radiation-emitting telecommunications equipment is directly linked to human health disorders. However, craft employees may be exposed to high levels of radio frequency radiation while working in close proximity to electrical power lines. Data have been collected that suggest a relationship between these emissions and cancer. Further scientific investigations are being conducted to more clearly determine the seriousness of this hazard as well as appropriate prevention equipment and methods. In addition, health concerns have been associated with emissions from cellular telephone equipment. Further research is being conducted to draw conclusions regarding potential health hazards.

The vast majority of telecommunications services are performed with the use of VDUs. Work with VDUs is associated with the occurrence of upper extremity (particularly hand and wrist) musculoskeletal cumulative trauma disorders. Many telecommunications unions, such as the Communications Workers of America (US), Seko (Sweden) and the Communication Workers Union (United Kingdom), have identified catastrophic rates of VDU workplace musculoskeletal cumulative trauma disorders among the workers they represent. Proper design of the VDU workplace with attention to work station, work environment and work organization variables will minimize and prevent these health problems.

Additional health concerns include stress, noise and electrical shock.



Without treatment of waste the current concentration of people and industry in many parts of the world would very quickly make portions of the environment incompatible with life. Although reduction of the amount of waste is important, the proper treatment of waste is essential. Two basic types of waste enter a treatment plant, human/animal waste and industrial waste. Humans excrete about 250 grams of solid waste per capita per day, including 2000 million coliform and 450 million streptococci bacteria per person per day (Mara 1974). Industrial solid waste production rates range from 0.12 tons per employee per year at professional and scientific institutions to 162.0 tons per employee per year at sawmills and planing mills (Salvato 1992). Although some waste treatment plants are exclusively dedicated to handling one or the other type of material, most plants handle both animal and industrial waste.

Hazards and Their Prevention

The goal of waste water treatment plants is to remove as much of the solid, liquid and gaseous contaminants as possible within technically feasible and financially achievable constraints. There are a variety of different processes that are used to remove contaminants from waste water including sedimentation, coagulation, flocculation, aeration, disinfection, filtration and sludge treatment. (See also the article “Sewage treatment” in this chapter.) The specific hazard associated with each process varies depending on the design of the treatment plant and the chemicals used in the different processes, but the types of hazard can be classified as physical, microbial and chemical. The key to preventing and/or minimizing the adverse effects associated with working in sewage treatment plants is to anticipate, recognize, evaluate and control the hazards.

Figure 1. Manhole with cover removed.


Mary O. Brophy

Physical hazards

Physical hazards include confined spaces, inadvertent energizing of machines or machine parts and trips and falls. The result of an encounter with a physical hazards can often be immediate, irreversible and serious, even fatal. Physical hazards vary with the design of the plant. Most sewage treatment plants, however, have confined spaces which include underground or below grade vaults with limited access, manholes (figure 1) and the sedimentation tanks when they have been emptied of liquid content during, for example, repairs (figure 2). Mixing equipment, sludge rakes, pumps and mechanical devices used for a variety of operations in sewage treatment plants can maim, and even kill, if they are inadvertently activated when a worker is servicing them. Wet surfaces, often encountered in sewage treatment plants, contribute to slipping and falling hazards.

Figure 2. Empty tank in a sewage treatment plant.


Mary O. Brophy

Confined-space entry is one of the most common and one of the most serious hazards faced by sewage treatment workers. A universal definition of a confined space is elusive. In general, however, a confined space is an area with limited means of entry and egress that was not designed for continuous human habitation and that does not have adequate ventilation. Hazards occur when the confined space is associated with a deficiency of oxygen, the presence of a toxic chemical or an engulfing material, such as water. Decreased oxygen levels can be the result of a variety of conditions including the replacement of oxygen with another gas, such as methane or hydrogen sulphide, the consumption of oxygen by the decay of organic material contained in the waste water or the scavenging of oxygen molecules in the rusting process of some structure within the confined space. Because low levels of oxygen in confined spaces cannot be detected by unaided human observation it is extremely important to use an instrument that can determine the level of oxygen before entering any confined space.

The earth’s atmosphere consists of 21% oxygen at sea level. When the percentage of oxygen in breathing air falls below about 16.5% a person’s breathing becomes more rapid and more shallow, the heart rate increases and the person begins to lose coordination. Below about 11% the person experiences nausea, vomiting, inability to move and unconsciousness. Emotional instability and impaired judgement may occur at oxygen levels somewhere between these two points. When individuals enter an atmosphere with oxygen levels below 16.5% they may immediately become too disoriented to get themselves out and eventually succumb to unconsciousness. If the oxygen depletion is great enough individuals can become unconscious after one breath. Without rescue they can die within minutes. Even if rescued and resuscitated, permanent damage can occur (Wilkenfeld et al. 1992).

Lack of oxygen is not the only hazard in a confined space. Toxic gases can be present in a confined space at a concentration level high enough to do serious harm, even kill, despite adequate oxygen levels. The effects of toxic chemicals encountered in confined spaces are discussed further below. One of the most effective ways to control the hazards associated with low oxygen levels (below 19.5%) and atmospheres contaminated with toxic chemicals is to thoroughly and adequately ventilate the confined space with mechanical ventilation prior to allowing anyone to enter it. This is usually done with a flexible duct through which outside air is blown into the confined space (see figure 3). Care must be taken to ensure that fumes from a generator or the fan motor are not also blown into the confined space (Brophy 1991).

Figure 3. Air moving unit for entering a confined space.


Mary O. Brophy

Sewage treatment plants often have large pieces of machinery to move sludge or raw sewage from one place in the plant to another. When repairs are made on this type of equipment the entire machine should be de-energized. Furthermore, the switch to re-energize the equipment should be under the control of the person performing the repairs. This prevents another worker in the plant from inadvertently energizing the equipment. Development and implementation of procedures to achieve these goals is called a lockout/tagout programme. Mutilation of body parts, such as fingers, arms and legs, dismemberment and even death can result from ineffective or inadequate lockout/tagout programmes.

Sewage treatment plants often contain large tanks and storage containers. People sometimes need to work on top of the containers, or walk by pits that have been emptied of water and may contain an 8 to 10 foot (2.5 to 3 m) drop (see figure 4). Sufficient protection against falls as well as adequate safety training should be provided for the workers.

Microbial hazards

Microbial hazards are primarily associated with the treatment of human and animal waste. Although bacteria are often added to alter the solids contained in waste water, the hazard to sewage treatment workers comes primarily from exposure to micro-organisms contained in human and other animal waste. When aeration is used during the sewage treatment process these micro-organisms can become airborne. The long term effect on the immune system of individuals exposed to these micro-organisms for extended periods of time has not been conclusively evaluated. In addition, workers who remove solid refuse from the influent stream before any treatment is begun are often exposed to micro-organisms contained in material splashing onto their skin and making contact with the mucous membranes. The results of encountering micro-organisms found in sewage treatment plants for extended periods of time are often more subtle than resulting from acute intense exposures. Nevertheless, these effects can also be irreversible and serious.

The three main categories of microbes relevant to this discussion are fungi, bacteria and viruses. All three of these can cause acute illness as well as chronic disease. Acute symptoms including respiratory distress, abdominal pains and diarrhoea have been reported in waste treatment workers (Crook, Bardos and Lacey 1988; Lundholm and Rylander 1980). Chronic diseases, such as asthma and allergic alveolitis, have been traditionally associated with exposure to high levels of airborne microbes and, recently, with microbial exposure during the treatment of domestic waste (Rosas et al. 1996; Johanning, Olmstead and Yang 1995). Reports of significantly elevated concentrations of fungi and bacteria in waste treatment, sludge dewatering and composting facilities are beginning to be published (Rosas et al. 1996; Bisesi and Kudlinski 1996; Johanning Olmstead and Yang 1995). Another source of airborne microbes is the aeration tanks which are used in many sewage treatment plants.

In addition to inhalation, microbes can be transmitted through ingestion and through contact with skin that is not intact. Personal hygiene, including washing hands before eating, smoking and going to the bathroom, is important. Food, drink, eating utensils, cigarettes and anything that would be put into the mouth should be kept away from areas of possible microbial contamination.

Chemical hazards

Chemical encounters at waste treatment plants can be both immediate and fatal, as well as protracted. A variety of chemicals are used in the process of coagulation, flocculation, disinfection and sludge treatment. The chemical of choice is determined by the contaminant or contaminants in the raw sewage; some industrial waste requires somewhat exotic chemical treatment. In general, however, the primary hazards from chemicals used in the coagulation and flocculation processes are skin irritation and eye injury due to direct contact. This is especially true of solutions which have a pH (acidity) less than 3 or greater than 9. The disinfection of effluent is often achieved by using either liquid or gaseous chlorine. Use of liquid chlorine can cause eye injury if splashed into the eyes. Ozone and ultraviolet light are also used to achieve disinfection of the effluent.

One way to monitor the effectiveness of sewage treatment is to measure the amount of organic material which remains in the effluent after treatment is complete. This can be done by determining the amount of oxygen that would be required to biodegrade the organic material contained in 1 litre of liquid over a period of 5 days. This is referred to as the 5-day biological oxygen demand (BOD5).

Chemical hazards in sewage treatment plants arise from the decomposition of organic material which results in the production of hydrogen sulphide and methane, from toxic waste dumped down the sewer lines and from the contaminants produced by operations performed by the workers themselves.

Hydrogen sulphide is almost always found in waste treatment plants. Hydrogen sulphide, also known as sewer gas, has a distinctive, unpleasant smell, often identified as rotten eggs. The human nose, however, quickly becomes accustomed to the smell. People who are exposed to hydrogen sulphide often lose their ability to detect its odour (i.e., olfactory fatigue). Furthermore, even if the olfactory system is able to detect hydrogen sulphide, it is not able to accurately judge its concentration in the atmosphere. Hydrogen sulphide biochemically interferes with the electron transport mechanism and blocks the utilization of oxygen at the molecular level. The result is asphyxiation and ultimately death due to the lack of oxygen in the brainstem cells that control the breathing rate. High levels of hydrogen sulphide (greater than 100 ppm) can, and often do, occur in the confined spaces found in sewage treatment plants. Exposure to very high levels of hydrogen sulphide can result in almost instantaneous suppression of the respiratory centre in the brainstem. The US National Institute for Occupational Safety and Health (NIOSH) has identified 100 ppm of hydrogen sulphide as immediately dangerous to life and health (IDLH). Lower levels of hydrogen sulphide (less than 10 ppm) are almost always present in some areas of sewage treatment plants. At these lower levels hydrogen sulphide can be irritating to the respiratory system, be associated with headaches and result in conjunctivitis (Smith 1986). Hydrogen sulphide is produced whenever organic matter decays and, industrially, during the production of paper (Kraft process), the tanning of leather (hair removal with sodium sulphide), and the production of heavy water for nuclear reactors.

Methane is another gas produced by the decomposition of organic matter. In addition to displacing oxygen, methane is explosive. Levels can be reached which result in an explosion when a spark or source of ignition is introduced.

Plants that handle industrial waste should have a thorough knowledge of the chemicals used in each of the industrial plants that utilize their services and a working relationship with the management of those plants so that they are promptly informed of any changes in processes and waste contents. Dumping of solvents, fuels and any other substance into sewer systems presents a hazard to treatment workers not only because of the toxicity of the material dumped but also because the dumping is unanticipated.

Whenever any industrial operation, such as welding or spray painting, is performed in a confined space special care must be taken to provide sufficient ventilation to prevent an explosion hazard as well as to remove toxic material produced by the operation. When an operation performed in a confined space produces a toxic atmosphere it is often necessary to equip the worker with a respirator because ventilation of the confined space may not ensure that the concentration of the toxic chemical can be maintained below the permissible exposure limit. Selection and fitting of a proper respirator falls within the purview of industrial hygiene practice.

Another serious chemical hazard in sewage treatment plants is the use of gaseous chlorine to decontaminate the effluent from the plant. The gaseous chlorine comes in a variety of containers weighing from 70 kg to roughly 1 tonne. Some of the very large sewage treatment plants use chlorine delivered in railroad cars. Gaseous chlorine is extremely irritating to the alveolar portion of the lungs, even in levels as low as a few ppm. Inhalation of higher concentrations of chlorine can cause inflammation of the alveoli of the lung and produce the adult respiratory distress syndrome, which has a 50% death rate. When a sewage treatment plant utilizes large amounts of chlorine (1 tonne and greater) the hazard exists not only for the plant workers but for the surrounding community as well. Unfortunately, the plants that use the largest amounts of chlorine are often located in large metropolitan centres with high density of people. Other methods of decontamination of sewage treatment plant effluent are available, including ozone treatment, the use of liquid hypochlorite solution and ultraviolet irradiation.



Monday, 28 March 2011 19:39

Domestic Waste Collection

In many locations domestic waste collection is performed by municipal employees. In others, by private companies. This article provides an overview of processes and hazards that are based on observations and experiences in the Province of Quebec, Canada. Editor.


Besides the few workers employed by municipalities in the Province of Quebec, Canada, that have their own waste collection boards, thousands of waste collectors and drivers are employed in hundreds of companies in the private sector.

Many private enterprises rely, either wholly or partially, upon jobbers who rent or own trucks and are responsible for the collectors who work for them. Competition in the sector is high, as municipal contracts are awarded to the lowest bidder, and there is a regular annual turnover of enterprises. The high competition also results in low and stable domestic waste-collection rates, and waste collection accounts for the lowest proportion of municipal taxes. However, as the existing landfills fill up, landfill costs rise, obliging municipalities to consider integrated waste-management systems. All municipal workers are unionized. Unionization of private-sector workers began in the 1980s, and 20 to 30% of them are now unionized.

Work Processes

Waste collection is a dangerous trade. If we recognize that garbage trucks are similar to hydraulic presses, it follows that waste collection is like working on a mobile industrial press under conditions much more demanding than those encountered in most factories. In waste collection, the machine travels through traffic in all seasons and workers must feed it by running behind it and tossing irregular objects of variable volume and weight, containing invisible and hazardous objects, into it. On average, collectors handle 2.4 tonnes of waste per hour. The efficiency of waste collection operations is entirely dependent on determinants of work rate and rhythm. The need to avoid rush-hour traffic and bridge line-ups creates time pressures at collection points and during transport. Speed is again of importance during unloading at landfills and incinerators.

Several aspects of waste collection influence workload and hazards. First, remuneration is on a flat-rate basis, that is, the territory specified by contract must be completely cleared of domestic waste on collection day. Since the volume of waste depends on residents’ activities and varies from day to day and from season to season, the workload varies enormously. Secondly, workers are in direct contact with the objects and waste collected. This is quite different from the situation in the commercial and industrial waste-collection sectors, where waste-filled containers are collected by either front-loading trucks equipped with automated fork-lifts or by roll-off trucks. This means that workers in those sectors do not handle the waste containers and are not in direct contact with the waste. Working conditions for these collectors therefore more closely resemble those of domestic waste drivers, rather than domestic waste collectors.

Residential collection (also known as domestic collection) is, on the other hand, primarily manual, and workers continue to handle a wide variety of objects and containers of variable size, nature and weight. A few suburban and rural municipalities have implemented semi-automated collection, involving the use of mobile domestic waste bins and side-loading collectors (figure 1). However, most domestic waste continues to be collected manually, especially in cities. The principal characteristic of this job is thus significant physical exertion.

Figure 1. Automatic, side-loading refuse collector.


Pak Mor Manufacturing Company


A study involving field observations and measurements, interviews with management and workers, statistical analysis of 755 occupational accidents and analysis of video sequences revealed a number of potential hazards (Bourdouxhe, Cloutier and Guertin 1992).


On average, waste collectors handle 16,000 kg spread out over 500 collection points every day, equivalent to a collection density of 550 kg/km. Collection takes almost 6 hours, equivalent to 2.4 tonnes/hour, and involves walking 11 km during a total work day of 9 hours. Collection speed averages 4.6 km/h, over a territory of almost 30 km of sidewalks, streets and lanes. Rest periods are limited to a few minutes precariously balanced on the rear platform, or, in the case of driver-collectors of side-loading trucks, at the wheel. This demanding workload is exacerbated by such factors as the frequency of truck dismounts and mounts, the distance covered, travel modes, the static effort required to maintain one’s balance on the rear platform (a minimum of 13 kg of force), the frequency of handling operations per unit time, the variety of postures required (bending movements), the frequency of tosses and twisting movements of the trunk and the high collection rate per unit time in some sectors. The fact that the Association française de normalisation (AFNOR) adapted weight standard for manual handling was exceeded in 23% of observed trips is eloquent testimony of the impact of these factors. When workers’ capacities (established to be 3.0 tonnes/hour for rear-loading trucks, and 1.9 tonnes/hour for side-loading ones) are taken into account, the frequency with which the AFNOR standard is exceeded rises to 37%.

Diversity and nature of objects handled

Manipulation of objects and containers of variable weight and volume interrupts the smooth flow of operations and breaks work rhythms. Objects in this category, often hidden by residents, include heavy, large or bulky objects, sharp or pointed objects and hazardous materials. The most frequently encountered hazards are listed in table 1.


Table 1. Hazardous objects found in domestic waste collections.

Glass, window panes, fluorescent tubing

Battery acid, cans of solvent or paint, aerosol containers, gas cylinders, motor oil

Construction waste, dust, plaster, sawdust, hearth cinders

Pieces of wood with nails in them

Syringes, medical waste

Garden waste, grass, rocks, earth

Furniture, electrical appliances, other large domestic trash

Pre-compacted waste (in apartment buildings)

Excessive numbers of small containers from small businesses and restaurants

Large amounts of vegetable and animal waste in rural sectors

Extra-large bags

Prohibited containers (e.g., no handles, excessive weight, 55-gallon oil drums, thin-necked drums, garbage cans without covers)

Small, apparently light bags that are in fact heavy

Excessive numbers of small bags

Paper bags and boxes that rip

All waste that is hidden because of its excessive weight or toxicity, or that surprises unprepared workers

Commercial containers that must be emptied with an improvised system, which is often inappropriate and dangerous


Workers are greatly helped by having residents sort waste into colour-coded bags and mobile domestic bins which facilitate the collection and allow better control of work rhythm and effort.

Climatic conditions and the nature of objects transported

Wet paper bags and poor-quality plastic bags that rip and scatter their contents over the sidewalk, frozen garbage cans and domestic bins stuck in snow banks can cause mishaps and dangerous recovery manoeuvres.

Work schedule

The need to rush, traffic problems, parked cars and crowded streets all can contribute to dangerous situations.

In an attempt to reduce their workload and maintain a high but constant work rhythm in the face of these constraints, workers often attempt to save time or effort by adopting work strategies that may be hazardous. The most commonly observed strategies included kicking bags or cardboard boxes towards the truck, zigzagging across the road to collect from both sides of the street, grabbing bags while the truck is in motion, carrying bags under the arm or against the body, using the thigh to help load bags and garbage cans, hand-picking of waste scattered on the ground and manual compaction (pushing garbage overflowing the hopper with the hands when the compacting system is incapable of processing the load rapidly enough). For example, in suburban collection with a rear-loading truck, almost 1,500 situations were observed per hour that could result in accidents or increase workload. These included:

  • 53 mounts and dismounts from the truck’s rear platform
  • 38 short runs
  • 482 bending movements
  • 203 tosses
  • 159 twisting movements
  • 277 potentially hazardous actions (including 255 work strategies aimed at reducing workload by saving time or effort)
  • 285 instances of increased workload, including 11 mishap- recovery activities
  • 274 dangerous or heavy objects or containers.


Collection with side-loading trucks (see figure 1) or small mobile domestic bins reduces the manipulation of heavy or dangerous objects and the frequency of situations that could result in accidents or an increase in workload.

Use of public thoroughfares

The street is the collectors’ workplace. This exposes them to such hazards as vehicular traffic, blocked access to residents’ waste receptacles, accumulation of water, snow, ice and neighbourhood dogs.


Rear-loading trucks (figure 2) often have excessively high or shallow steps and rear platforms that are difficult to mount and render descents perilously similar to jumps. Hand-rails that are too high or too close to the truck body only worsen the situation. These conditions increase the frequency of falls and of collisions with structures adjacent to the rear platform. In addition, the upper edge of the hopper is very high, and shorter workers must expend additional energy lifting objects into it from the ground. In some cases, workers use their legs or thighs for support or additional power when loading the hopper.

Figure 2. Back-loading enclosed compactor truck.


National Safety Council (US)  The packer-blade comes down within centimetres of the edge of the platform. The blade has the capacity to cut protruding objects.

The characteristics of side-loading trucks and the operations related to their loading result in specific repetitive movements likely to cause muscle and joint problems in the shoulder and upper back. Driver-collectors of side-loading trucks have an additional constraint, as they must cope with both the physical strain of collection and the mental strain of driving.

Personal protective equipment

While the theoretical value of PPE is beyond question, it may nevertheless prove inadequate in practice. In concrete terms, the equipment may be inappropriate for the conditions under which collection is carried out. Boots, in particular, are incompatible with the narrow utilizable height of rear platforms and the high work rhythm necessitated by the manner in which collection is organized. Strong, puncture-resistant yet flexible gloves are valuable in protecting against hand injuries.

Work organization

Some aspects of work organization increase workload and, by extension, hazards. In common with most flat-rate situations, the main advantage to workers of this system is the ability to manage their work time and save time by adopting a rapid work rhythm as they see fit. This explains why attempts, based on safety considerations, to slow down the pace of work have been unsuccessful. Some work schedules exceed workers’ capacities.

The role of the myriad variations of residents’ behaviour in the creation of additional hazards merits a study in itself. Prohibited or dangerous wastes skilfully hidden in regular waste, non-standard containers, excessively large or heavy objects, disagreements over collection times and non-conformity with bylaws all increase the number of hazards—and the potential for conflicts between residents and collectors. Collectors are often reduced to the role of “garbage police”, educators and buffers between municipalities, enterprises and residents.

Collection of materials for recycling is not without its own problems despite a low waste density and collection rates far below those of traditional collection (with the exception of the collection of leaves for composting). The hourly frequency of situations that could result in accidents is often high. The fact that this is a new type of work for which few workers have been trained should be borne in mind.

In several cases, workers are obliged to perform such dangerous activities as mounting the truck’s compaction box to get into the compartments and move piles of paper and cardboard with their feet. Several work strategies aimed at speeding up work rhythm have also been observed, e.g., hand re-sorting of the material to be recycled and removing objects from the recycling box and carrying them to the truck, rather than carrying the box to the truck. The frequency of mishaps and disruptions of normal work activity in this type of collection is particularly high. These mishaps result from workers doing ad hoc activities that are themselves dangerous.

Occupational Accidents and Prevention

Domestic waste collection is a dangerous trade. Statistics support this impression. The average annual accident rate in this industry, for all types of enterprise, truck and trade, is almost 80 accidents for every 2,000 hours of collection. This is equivalent to 8 workers of every 10 suffering an injury at least once a year. Four accidents occur for every 1,000 10-tonne truckloads. On average, each accident results in 10 lost workdays and accident compensation of $820 (Canadian). Indices of injury frequency and severity vary among enterprises, with higher rates observed in municipal enterprises (74 accidents/100 workers versus 57/100 workers in private enterprises) (Bourdouxhe, Cloutier and Guertin 1992). The most common accidents are listed in table 2.

Table 2. Most common accidents in domestic waste collection, Quebec, Canada.



Per cent of accidents studied

Back or shoulder pain

Tossing or twisting movements during collection of bags


Back injuries

Excessive efforts while lifting objects


Ankle sprains

Falls or slips while dismounting from the truck or moving in its vicinity


Crushed hands, fingers, arms or knees

Struck by containers or heavy objects, being caught between the vehicle and containers, or collisions with part of the vehicle or parked cars


Hand and thigh lacerations of variable depth

Glass, nails, or syringes, occurring during hopper loading


Scrapes and bruises

Contact or collisions


Eye or respiratory-tract irritation

Dust or splashes of liquids occurring during work near the hopper during compaction






Collectors typically suffer hand and thigh lacerations, drivers typically suffer sprained ankles resulting from falls during cabin dismounts and driver-collectors of side-loading trucks typically suffer shoulder and upper back pain resulting from tossing movements. The nature of the accidents also depends on the type of truck, although this can also be seen as a reflection of the specific trades associated with rear- and side-loading trucks. These differences are related to equipment design, the type of movements required and the nature and density of waste collected in the sectors in which these two types of truck are used.


The following are ten categories in which improvements could make domestic waste collection safer:

  1. management of health and safety (for instance, the development of accident-prevention programmes based on workers’ knowledge of occupational hazards which are better adapted to actual tasks)
  2. training and hiring
  3. work organization, organization of collection and workload
  4. vehicles
  5. training and work conditions of auxiliary, occasional and temporary workers
  6. collection contracts
  7. public management
  8. collaboration between employer associations (municipal and private), workers and municipal or regional decision-making bodies
  9. stability of the workforce
  10. research on personal protective equipment, ergonomic design of trucks, subcontracting jobbers and safety.



Domestic waste collection is an important but hazardous activity. Protection of workers is made more difficult where this service is contracted out to private sector enterprises which, as in the province of Quebec, may subcontract the work to many smaller jobbers. A large number of ergonomic and accident hazards, compounded by work quotas, adverse weather and local street and traffic problems must be confronted and controlled if workers’ health and safety are to be maintained.



Monday, 28 March 2011 19:50

Sewage Treatment

Adapted from 3rd edition, Encyclopaedia of Occupational Health and Safety.

Waste water is treated in order to remove pollutants and to comply with the limits set by law. For this purpose an attempt is made to render the pollutants in the water insoluble in the form of solids (e.g., sludge), liquids (e.g., oil) or gases (e.g., nitrogen) by applying appropriate treatments. Well known techniques are then used to separate the treated waste water to be returned to the natural waterways from the pollutants rendered insoluble. The gases are dispersed into the atmosphere, while the liquid and solid residues (sludge, oil, grease) are usually digested before being submitted to further treatment. There may be single or multi-stage treatments according to the characteristics of the waste water and to the degree of purification required. Waste water treatment may be subdivided into physical (primary), biological (secondary) and tertiary processes.

Physical Processes

The various physical treatment processes are designed to remove insoluble pollutants.


The sewage is made to pass through screens which retain coarse solids that may block or damage the treatment works equipment (e.g., valves and pumps). The screenings are processed according to local situations.

Sand removal

The sand contained in the waste water has to be removed as it tends to settle in the pipework on account of its high density and cause abrasion to the equipment (e.g., centrifugal separators and turbines). Sand is generally removed by passing the waste water through a channel of constant cross-section at a velocity of 15 to 30 cm/s. The sand collects on the channel bottom and may be used, after washing to remove putrescible matter, as an inert material, such as for road building.

Oil removal

Oils and non-emulsifiable fats have to be removed because they would adhere to the equipment of the treatment works (e.g., basins and clarifiers) and interfere with the subsequent biological treatment. Oil and fat particles are made to collect on the surface by passing the waste water at an appropriate velocity through tanks of rectangular cross-section; they are skimmed off mechanically and may be used as a fuel. Multi-plate separators of compact design and high efficiency are frequently used for oil removal: the sewage is made to pass from above through stacks of flat inclined plates; the oil adheres to the bottom surfaces of the plates and moves to the top where it is collected. With both these processes, the de-oiled water is discharged at the bottom.

Sedimentation, flotation and coagulation

These processes enable the solids to be removed from the waste water, heavy ones (greater than 0.4 μm in diameter) by sedimentation and light ones (less than 0.4 μm) by flotation. This treatment, too, relies on the differences in density of the solids and of the flowing waste water which is passed through sedimentation tanks and flotation tanks made of concrete or steel. The particles to be separated collect in the bottom or at the surface, settling or rising at velocities which are proportional to the square of the particle radius and to the difference between the particle density and the apparent waste water density. Colloidal particles (e.g., proteins, latexes and oily emulsions) with sizes from 0.4 to 0.001 μm are not separated, as these colloids become hydrated and usually negatively charged by adsorption of ions. Consequently the particles repel each other so that they cannot coagulate and separate. However, if these particles are “destabilized”, they coagulate to form flocks greater than 4 μm, which can be separated as sludge in conventional sedimentation or flotation tanks. Destabilization is obtained by coagulation, that is, by adding 30 to 60 mg/l of an inorganic coagulant (aluminium sulphate, iron (II) sulphate or iron (III) chloride). The coagulant hydrolyses under given pH (acidity) conditions and forms positive polyvalent metal ions, which neutralize the negative charge of the colloid. Flocculation (the agglomeration of coagulated particles in flocks) is facilitated by adding 1 to 3 mg/l of organic polyelectrolytes (flocculation agents), resulting in flocks of 0.3 to 1 μm diameter which are easier to separate. Sedimentation tanks of the horizontal-flow type may be used; they have rectangular cross-section and flat or sloping bottoms. The waste water enters along one of the head sides, and the clarified water leaves over the edge at the opposite side. Also vertical flow sedimentation tanks can be used which are cylindrical in shape and have a bottom like an inverted right circular cone; the waste water enters in the middle, and the clarified water leaves the tank over the top indented edge to be collected into an external circumferential channel. With the two types of tank, the sludge settles on the bottom and is conveyed (if necessary by means of a raking gear) into a collector. The solids concentration in the sludge is 2 to 10%, whereas that of the clarified water is 20 to 80 mg/l.

The flotation tanks are usually cylindrical in shape and have fine bubble air diffusers installed in their bottoms, the sewage entering the tanks in the centre. The particles adhere to the bubbles, float to the surface and are skimmed off, while the clarified water is discharged below. In the case of the more efficient “dissolved-air floating tanks”, the waste water is saturated with air under a pressure of 2 to 5 bars and then allowed to expand in the centre of the floating tank, where the minute bubbles resulting from the decompression make the particles float to the surface.

Compared to sedimentation, flotation yields a thicker sludge at a higher particle separation velocity, and the equipment required is therefore smaller. On the other hand, the operating cost and the concentration of solids in the clarified water are higher.

Several tanks arranged in series are required for coagulating and flocculating a colloidal system. An inorganic coagulant and, if necessary, an acid or an alkali to correct the pH value are added to the waste water in the first tank, which is equipped with an agitator. The suspension is then passed into a second tank equipped with a high-speed agitator; here, the polyelectrolyte is added and dissolved within a few minutes. The flock growth takes place in a third tank with a slow-running agitator and is carried out for 10 to 15 minutes.

Biological Processes

Biological treatment processes remove organic biodegradable pollutants by use of micro-organisms. These organisms digest the pollutant by an aerobic or anaerobic process (with or without supply of atmospheric oxygen) and convert it into water, gases (carbon dioxide and methane) and a solid insoluble microbic mass which can be separated from the treated water. Especially in the case of industrial effluents proper conditions for the development of micro-organisms must be assured: presence of nitrogen and phosphorus compounds, traces of microelements, absence of toxic substances (heavy metals, etc.), optimum temperature and pH value. Biological treatment includes aerobic and anaerobic processes.

Aerobic processes

The aerobic processes are more or less complex according to the space available, the degree of purification required and the composition of the waste water.

Stabilization ponds

These are generally rectangular and 3 to 4 m deep. The sewage enters at one end, is left for 10 to 60 days and leaves the pond partly at the opposite end, partly by evaporation and partly by infiltration into the ground. The purification efficiency ranges from 10 to 90% according to the type of effluent and to the residual 5-day biological oxygen demand (BOD5) content (<40 mg/l). Oxygen is supplied from the atmosphere by diffusion through the surface of the water and from photosynthetic algae. The solids in suspension in the waste water and those produced by microbial activity settle on the bottom, where they are stabilized by aerobic and/or anaerobic processes according to the depth of the ponds which affects the diffusion both of oxygen and sunlight. The oxygen diffusion is frequently accelerated by surface aerators, which enable the volume of the ponds to be reduced.


This type of treatment is very economical if space is available, but requires clay-like soil to prevent the pollution of underground water by toxic effluents.

Activated sludge

This is used for an accelerated treatment carried out in concrete or steel tanks of 3 to 5 m depth where the waste water comes into contact with a suspension of micro-organisms (2 to 10 g/l) which is oxygenated by means of surface aerators or by blowing in air. After 3 to 24 hours, the mixture of treated water and micro-organisms is passed into a sedimentation tank where the sludge made up by micro-organisms is separated from the water. The micro-organisms are partly returned to the aerated tank and partly evacuated.

There are various types of activated-sludge processes (e.g., contact-stabilization systems and use of pure oxygen) which yield purification efficiencies of greater than 95% even for industrial effluents but they require accurate controls and high energy consumption for oxygen supply.

Percolating filters

With this technique the micro-organisms are not kept in suspension in the waste water, but adhere to the surface of a filling material over which the sewage is sprayed. Air circulates through the material and supplies the required oxygen without any energy consumption. According to the type of waste water and to increase efficiency, part of the treated water is recirculated to the top of the filter bed.

Where land is available, low-cost filling materials of appropriate size (e.g., crushed stone, clinker and limestone) are used, and on account of the weight of the bed the percolating filter is generally constructed as a 1 m high concrete tank usually sunk in the ground. If there is not enough land, more costly lightweight packing materials such as high-rate plastic honeycomb media, with up to 250 square metres of surface area/cubic metre of media, are stacked in percolating towers up to 10 m high.

The waste water is distributed over the filter bed by a mobile or fixed sparging mechanism and collected in the floor to be eventually recirculated to the top and to be passed into a sedimentation tank where the sludge formed can settle. Openings at the bottom of the percolating filter allow for air circulation through the filter bed. Pollutants removal efficiencies of 30 to 90% are achieved. In many cases several filters are arranged in series. This technique, which requires little energy and is easy to operate, has found widespread use and is recommended for cases where land is available, for instance, in developing countries.


A set of flat plastic discs mounted parallel on a horizontal rotating shaft are partially immersed in the waste water contained in a tank. Due to the rotation the biological felt that covers the discs is brought into contact with the effluents and atmospheric oxygen. The biological sludge coming off the biodiscs remains in suspension in the waste water, and the system acts as activated sludge and sedimentation tank at the same time. Biodiscs are suitable for small to medium-sized industrial factories and communities, take up little space, are easy to operate, require little energy and yield efficiencies of up to 90%.

Anaerobic processes

Anaerobic processes are carried out by two groups of micro-organisms—hydrolytic bacteria, which decompose complex substances (polysaccharides, proteins, lipids, etc.) to acetic acid, hydrogen, carbon dioxide and water; and methanogenic bacteria, which convert these substances to a biomass (that can be removed from the treated sewage by sedimentation) and to biogas containing 65 to 70% methane, the remainder being carbon dioxide, and having a high heat value.

These two groups of micro-organisms, which are very sensitive to toxic contaminants, act simultaneously in the absence of air at an almost neutral pH value, some requiring a temperature of 20 to 38oC (mesophilic bacteria) and other, more delicate ones, 60 to 65oC (thermophilic bacteria). The process is carried out in stirred, closed concrete or steel digesters, where the required temperature is held by thermostats. Typical is the contact process, where the digester is followed by a sedimentation tank to separate the sludge, which is partially recirculated to the digester, from the treated water.

Anaerobic processes need neither oxygen nor power for oxygen supply and yield biogas, which can be used as a fuel (low operating costs). On the other hand, they are less efficient than aerobic processes (residual BOD5: 100 to 1,500 mg/l), are slower and more difficult to control, but enable faecal and pathogenic micro-organisms to be destroyed. They are used for treating strong wastes, such as sedimentation sludge from sewage, sludge in excess from activated sludge or percolating-filter treatments and industrial effluents with a BOD5 up to 30,000 mg/l (e.g., from distilleries, breweries, sugar refineries, abattoirs and paper mills).

Tertiary Processes

The more complex and more expensive tertiary processes make use of chemical reactions or specific chemicophysical or physical techniques to remove water-soluble non-biodegradable pollutants, both organic (e.g., dyes and phenols) and inorganic (e.g., copper, mercury, nickel, phosphates, fluorides, nitrates and cyanides), especially from industrial waste water, because they cannot be removed by other treatments. Tertiary treatment also enables a high degree of water purification to be obtained, and the water thus treated may be used as drinking water or for manufacturing processes (steam generation, cooling systems, process water for particular purposes). The most important tertiary processes are as follows.


Precipitation is carried out in reactors made of an appropriate material and equipped with agitators where chemical reagents are added at a controlled temperature and pH value to convert the pollutant to an insoluble product. The precipitate obtained in the form of sludge is separated by conventional techniques from the treated water. In waste water from the fertilizer industry, for instance, phosphates and fluorides are rendered insoluble by reaction with lime at ambient temperature and at an alkaline pH; chromium (tanning industry), nickel and copper (electroplating shops) are precipitated as hydroxides at an alkaline pH after having been reduced with m-disulphite at a pH of 3 or lower.

Chemical oxidation

The organic pollutant is oxidized with reagents in reactors similar to those used for precipitation. The reaction is generally continued until water and carbon dioxide are obtained as final products. Cyanides, for instance, are destroyed at ambient temperature by adding sodium hypochlorite and calcium hypochlorite at alkaline pH, whereas azo- and anthraquinone-dyes are decomposed by hydrogen peroxide and ferrous sulphate at pH 4.5. Coloured effluents from the chemical industry containing 5 to 10% non-biodegradable organic substance are oxidized at 200 to 300°C at high pressure in reactors made of special materials by blowing air and oxygen into the liquid (wet oxidation); catalysts are sometimes used. Pathogens left in urban sewage after treatment are oxidized by chlorination or ozonisation to render the water drinkable.


Some pollutants (e.g., phenols in waste water from coking plants, dyes in water for industrial or drinking purposes and surfactants) are effectively removed by absorption on activated carbon powder or granules which are highly porous and have a large specific surface area (of 1000 m2/g or more). The activated carbon powder is added in metered quantities to the waste water in stirred tanks, and 30 to 60 minutes later the spent powder is removed as a sludge. Granulated activated carbon is used in towers arranged in series through which the polluted water is passed. The spent carbon is regenerated in these towers, that is, the absorbed pollutant is removed either by chemical treatment (e.g., phenols are washed out with soda) or by thermal oxidation (e.g., dyes).

Ion exchange

Certain natural substances (e.g., zeolites) or artificial compounds (e.g., Permutit and resins) exchange, in a stoichiometric and reversible manner, the ions bound to them with those contained, even strongly diluted, in the waste water. Copper, chromium, nickel, nitrates and ammonia, for instance, are removed from waste water by percolation through columns packed with resins. When the resins are spent, they are reactivated by washing with regenerating solutions. Metals are thus recovered in a concentrated solution. This treatment, though costly, is efficient and advisable in cases where a high degree of purity is required (e.g., for waste water contaminated by toxic metals).

Reverse osmosis

In special cases it is possible to extract water of high purity, suitable for drinking, from diluted waste water by passing it through semi-permeable membranes. On the waste water side of the membrane the pollutants (chlorides, sulphates, phosphates, dyes, certain metals) are left as concentrated solutions which have to be disposed of or treated for recovery. The diluted waste water is subjected to pressures up to 50 bars in special plant containing synthetic membranes made of cellulose acetate or other polymers. The operating cost of this process is low, and separation efficiencies of greater than 95% may be obtained.

Sludge Treatment

Rendering pollutants insoluble during waste water treatment results in the production of considerable amounts of sludge (20 to 30% of the removed chemical oxygen demand (COD) which is strongly diluted (90 to 99% water)). The disposal of this sludge in a manner acceptable to the environment presupposes treatments with a cost of up to 50% of those required for waste water purification. The types of treatment depend on the destination of the sludge, depending in turn on its characteristics and on local situations. Sludge may be destined for:

  • fertilization or dumping at sea if it is substantially free from toxic substances and contains nitrogen and phosphorus compounds (sludge from biological treatment), using fixed outfalls, lorries or barges
  • sanitary landfill into pits dug in the ground, alternating layers of sludge and soil. Impermeabilisation of peats is required if the sludge contains toxic substances that may be washed out by atmospheric precipitations. The pits should be remote from water-bearing strata. Non-stabilized organic sludge is usually mixed with 10 to 15% lime to retard putrefaction.
  • incineration in rotary or fluidized-bed furnaces if the sludge is rich in organic substances and free from volatile metals; if necessary, fuel is added, and the smoke emitted is purified.


The sludge is dewatered before its disposal to reduce both its volume and the cost of its treatment, and it is frequently stabilized to prevent its putrefaction and to render harmless any toxic substances it may contain.


Dewatering includes previous thickening in thickeners, similar to sedimentation tanks, where the sludge is left for 12 to 24 hours and loses part of the water which collects on the surface, while the thickened sludge is discharged below. The thickened sludge is dewatered, for example, by centrifugal separation or by filtration (under vacuum or pressure) with conventional equipment, or by exposure to the air in layers of 30 cm thick in sludge-drying beds consisting of rectangular concrete lagoons, approximately 50 cm deep, with a sloped bottom covered with a layer of sand to facilitate water drainage. Sludge containing colloidal substances should be previously destabilized by coagulation and flocculation, according to already described techniques.


Stabilization includes digestion and detoxification. Digestion is a long-term treatment of the sludge during which it loses 30 to 50% of its organic matter, accompanied by an increase in its mineral salt content. This sludge is no longer putrescible, any pathogens are destroyed and the filtrability is improved. Digestion may be of the aerobic type when the sludge is aerated during 8 to 15 days at ambient temperature in concrete tanks, the process being similar to activated-sludge treatment. It may be of the anaerobic type if the sludge is digested in plants similar to those used for the anaerobic waste treatment, at 35 to 40°C during 30 to 40 days, with the production of biogas. Digestion can be of the thermal type when the sludge is treated with hot air at 200 to 250°C and at a pressure of more than 100 bars during 15 to 30 minutes (wet combustion), or when it is treated, in the absence of air, at 180°C and at autogenous pressure, for 30 to 45 minutes.

Detoxification renders harmless sludge containing metals (e.g., chromium, nickel and lead), which are solidified by treatment with sodium silicate and autothermically converted into the corresponding insoluble silicates.



Monday, 28 March 2011 19:58

Street Cleaning

Adapted from 3rd edition, Encyclopaedia of Occupational Health and Safety.

Prevention of dirt-borne disease, prevention of damage to vehicles by harmful objects and the joy of viewing a neat, attractive city are all benefits derived from clean streets. Herded animals or animal-drawn vehicles, which in earlier times caused unsanitary conditions, have generally ceased to be a problem; however, the expansion in world population with the resultant upsurge in waste generated, the increase in the number and size of factories, the growth in the number of vehicles and newspapers and the introduction of disposable containers and products have all contributed to the amount of street refuse and added to the street-cleaning problem.

Organization and Processes

Municipal authorities recognizing the threat to health posed by dirty streets have sought to minimise the danger by organizing street cleaning sections in the public works departments. In these sections, a superintendent responsible for scheduling frequency of cleaning various districts will have forepeople responsible for specific cleaning operations.

Normally, business districts will be swept daily while arterial roads and residential areas will be swept weekly. Frequency will depend upon rain or snowfall, topography and the education of the populace toward prevention of litter.

The superintendent will also decide the most effective means of achieving clean streets. These could be hand sweeping by one worker or a group, hose flushing or machine sweeping or flushing. Generally a combination of methods, depending on the availability of equipment, type of dirt encountered and other factors will be used. In areas of heavy snowfall, special snow-clearing equipment may be used on occasion.

Hand sweeping is generally done in the daytime and confined to cleaning of gutters or spot cleaning of pavements or adjacent areas. The equipment used consists of brooms, scrapers and shovels. One sweeper generally patrols a specified route and cleans about 9 km of curb per shift under favourable conditions; however, this may be reduced in congested business districts.

Dirt collected by one-person sweeping is placed in a cart which he or she pushes ahead and dumps in boxes placed at intervals along his or her route; these boxes are emptied periodically into refuse trucks. In group sweeping, dirt is swept into piles along the gutters and loaded directly into trucks. Normally a group of 8 sweepers will have 2 workers assigned as loaders. Group sweeping is particularly effective for massive clean-up jobs such as after storms, parades or other special events.

Advantages of hand sweeping are: it is easily adjusted to meet changing cleaning loads; it can be used in areas inaccessible to machines; it can be conducted in heavy traffic with minimum interference with vehicle movement; it can be done in freezing weather and it can be used on pavements where surface conditions do not permit machine cleaning. Disadvantages are: the work is dangerous in traffic; it raises dust; dirt piled in gutters may be dispersed by wind or traffic if not collected promptly; and hand sweeping may be costly in labour-expensive areas.

Hose flushing is not considered an economical operation today; however, it is effective where there is a large amount of dirt or mud adhering to the pavement surfaces, where there are large numbers of parked vehicles or in market areas. It is generally done at night by a two-person crew, one of whom handles the hose nozzle and directs the stream and the other connects hose to the hydrant. Equipment consists of hoses, hose nozzles and hydrant wrenches.

Machine sweepers consist of motorized chassis mounted with brushes, conveyors, sprinklers and storage bins. They are generally used in late evening or early morning hours in business districts and during the day in residential areas. Cleaning action is confined to the gutters and adjacent areas where most dirt accumulates.

The machine is operated by one worker and can be expected to clean approximately 36 km of curb during an 8 hour shift. Factors affecting output are: number of times and distance which must be travelled to dump dirt or pick up sprinkling water; traffic density; and amount of dirt collected.

The advantages of machine sweepers are: they clean well, rapidly and raise no dust when sprinklers are used; they pick up the dirt as they clean; they can be used at night; and they are relatively economical. The disadvantages are: they cannot clean under parked cars or in off-pavement areas; they are not effective on rough, wet or muddy streets; the sprinkler cannot be used in freezing weather and dry sweeping raises dust; and they require skilled operators and maintenance personnel.

Flushing machines are essentially water tanks mounted on a motorized chassis which is fitted with a pump and nozzle to provide pressure and direct the stream of water against the pavement surface. The machine can be expected to clean about 36 km of 7 m wide pavement during an 8 hour shift.

The advantages of flushing machines are: they can be used effectively on wet or muddy pavements; they clean rapidly, well and under parked cars without raising dust; and they can operate at night or in light traffic. The disadvantages are: they require additional cleaning to be effective where street, litter or sewer conditions are not favourable; they annoy pedestrians or vehicle operators who are splashed; they cannot be used in freezing weather; and they require skilled operators and maintenance personnel.

Hazards and Their Prevention

Street cleaning is a hazardous occupation due to the fact that it is conducted in traffic and is concerned with dirt and refuse, with the possibility of infection, cuts from broken glass, tins and so on. In crowded areas, hand sweepers may be exposed to a considerable amount of carbon monoxide and to a high level of noise.

Traffic hazards are protected against by training sweepers in ways of avoiding danger, such as arranging work against the traffic flow and providing them with highly visible clothing as well as attaching red flags or other warning devices to their carts. Machine sweepers and flushers are made visible by fitting them with flashing lights, waving flags and painting them distinctively.

Street cleaners, and in particular hand sweepers, are exposed to all the vagaries of weather and occasionally may have to work in very severe conditions. Illness, infection and handling accidents can in part be prevented by the use of PPE and in part by training. Mechanical equipment such as that used for snow cleaning should be operated only by trained workers.

There should be a conveniently accessible central point providing good washing facilities (including showers where practicable), a cloakroom with arrangements for changing and drying clothes, a messroom and a first-aid room. Periodical medical examination is desirable.

Environmental Concerns of Snow Disposal

Snow removal and disposal introduces a set of environmental concerns related to the potential deposition of debris, salts, oil, metals and particulates in local waterbodies. A particular danger exists from the concentration of particulates, such as lead, that originate in atmospheric emissions from industrialized areas and automobiles. The danger of melt-water runoff to aquatic organisms and the risk of soil and groundwater contamination has been countered by the adoption of safe handling practices that protect sensitive areas from exposure. Snow disposal guidelines have been adopted in several Canadian provinces (e.g., Quebec, Ontario, Manitoba).



Monday, 28 March 2011 20:00

Municipal Recycling Industry


Recycling means different things to different people. To consumers, recycling may mean putting out bottles and cans for curbside collection. To a product maker—a manufacturer of raw materials or fabricator of goods—it means including recycled materials in the process. To recycling service providers, recycling can mean providing cost-efficient collection, sorting and shipping services. For scavengers, it means culling recyclable materials from garbage and waste cans and selling them to recycling depots. To public policy makers in all levels of government, it means establishing regulations governing collection and utilization as well as reducing the volume of waste to be disposed of and deriving revenue from the sale of the recycled materials. For recycling to work effectively and safely, these diverse groups must be educated to work together and share responsibility for its success.

The recycling industry had been growing steadily since its inception a century ago. Until the 1970s, it remained basically unchanged as a voluntary private sector effort conducted largely by scrap dealers. With the advent of incineration in the 1970s, it became desirable to separate out certain materials before putting waste into the furnaces. This concept was introduced to address the emission problems created by metals, batteries, plastics and other materials discarded in urban wastes which were causing many old incinerators to be shut down as environmental polluters. The increasing concern about the environment provided the primary impetus for the organized separation of plastics, aluminium, tin, paper and cardboard from the residential waste stream. Initially, the recycling industry was not economically viable as a self-sustaining business, but by the mid 1980s, the need for the materials and the increase in their prices led to the development of many new material recycling facilities (MRFs) to handle commingled recyclable materials across the US and Europe.

Work Force

The broad range of skills and expertise makes the range of employment for a MRF very wide. Whether it is a full-service MRF or a single sorting-line operation, the following groups of workers are generally employed:

  • Operators of heavy equipment (front end loaders, grapples, bull-dozers, etc.) work on the tipping floor, coordinating the movement of waste from the staging area of the tipping floor to the area where the materials are sorted.
  • Material sorters, the majority of the workforce, segregate and sort recyclable materials by product and/or colour. This may be done entirely by hand or with the assistance of equipment. The sorted materials are then baled or crated.
  • Forklift operators are responsible for moving finished bales from the throat of the baler to the storage area and from there to the trucks or other means of transportation.
  • Maintenance workers are becoming increasingly important as the technology advances and the machines and equipment become more complicated.


Processes and Facilities

The recycling industry has been growing very rapidly and has evolved many different processes and procedures as the technology of sorting recyclable materials has advanced. The most common types of installation include full-service MRFs, non-waste stream MRFs and simple sorting and processing systems.

Full-service MRFs

The full-service MRF receives recyclable materials mixed in the residential waste streams. Typically, the resident places the recyclables in coloured plastic bags which are then placed in the residential waste container. This allows the community to combine recyclable materials with other residential wastes, eliminating the need for separate collection vehicles and containers. A typical sequence of operations includes the following procedures:

  • The waste and recyclables bags are dropped from the collection vehicle onto the tipping/collection floor.
  • The mixture of waste and recyclables is moved either by a grapple or a front-end loader to an in-floor conveyer.
  • The conveyer moves the material into the sorting area where a rotating trommel (a cylindrical sieve) opens the bags and allows the very small particles of dirt, sand and gravel to pass through the openings to a collection container for discarding.
  • The remaining materials are semi-automatically sorted by screens or disks according to weight and bulkiness. Glass is sorted by its heavier weight, plastics by their lighter weight and paper fibre materials by their bulk.
  • Employees hand sort materials, typically from an elevated position above bunkers into which the materials can be stored. Materials are sorted according to the grade of paper, the colour of glass, the physical properties of plastic and so on.
  • Refuse and other wastes are collected and removed by tractor-trailer loads.
  • The separated materials are moved from the bunkers by forklift or by a “walking floor” (i.e., a conveyer) to a baler or a shredding and baling operation.
  • The formed bale is discharged from the baler and moved to the storage area by a forklift.
  • Collected bales are shipped either by rail or a tractor-trailer. Instead of baling, some MRFs loose load the materials into a rail car or a tractor trailer.


Non-waste stream MRF

In this system, only the recyclables are delivered to the MRF; the residential wastes go elsewhere. It involves an advanced, semi-automated sorting and processing process system in which all of the steps are the same as those described above. Because of the smaller volume, fewer employees are involved.

Simple sorting/processing system

This is a labour-intensive system in which the sorting is performed manually. Typically, a conveyer belt is used to move material from one work station to another with each sorter removing one type of material as the belt passes his station. A typical sequence for such a simple, inexpensive processing system would include these processes:

  • Mixed recyclables are received on a tipping floor and are moved by a front-end loader to the main sorting conveyor belt.
  • Glass bottles are separated manually by colour (flint, amber, green and so forth).
  • Plastic containers are sorted by grade and accumulated for baling.
  • Aluminium cans are removed manually and fed to either a compactor or baler.
  • The remaining materials are discharged into a residue pile or container for disposal.


Equipment and machinery

The machinery and equipment used in a MRF is determined by the type of process and the volumes of materials handled. In a typical semi-automated MRF, it would include:

  • bag openers
  • magnetic separators
  • screens (disks, shakers or trommel)
  • material classification equipment (mechanical or pneumatic)
  • glass crushers
  • balers and compactors
  • eddy current separators (for non-ferrous metal separation)
  • conveyer belts
  • rolling stock.


Health and safety hazards

MRF workers face a large variety of environmental and work hazards, many of which are unpredictable since the content of the waste changes continually. Prominent among them are:

  • infectious disease from biological and medical wastes
  • acute and chronic toxicity from household chemicals, solvents and other chemicals being discarded. This risk is not very great (except when industrial wastes find their way into the residential stream) since household chemicals are usually not very toxic and only relatively small amounts are present.
  • solvents and fuel and exhaust fumes (especially vehicle operators and maintenance workers)
  • exposures to heat, cold and bad weather since many MRFs are exposed to the elements
  • noise at harmful levels when heavy machines operate in confined spaces
  • physical hazards such as slips and falls, puncture wounds, lacerations and abrasions, muscular strains, sprains and repetitive motion injuries. Sorters usually stand continuously, while vehicle operators must sometimes contend with poorly designed seats and operating controls.
  • airborne dust and particles.


Table 1 lists the most common types of injury in the recycling industry.

Table 1. Most frequent injuries in the recycling industry.

Injury type

Cause of injury

Body part affected

Cuts, abrasions and lacerations

Contact with sharp materials

Hands and forearms



Lower back

Particles in eye

Airborne dust and flying objects


Repetitive motion

Manual sorting

Upper extremities



MRF workers have the potential to be exposed to whatever wastes are delivered to it, as well as the ever-changing environment in which they work. The management of the facility must constantly be aware of the content of the material being delivered, the training and supervision of the workers and their compliance with safety rules and regulations, the proper use of PPE and the maintenance of machinery and equipment. The following safety considerations deserve constant close attention:

  • lockout/tagout precautions
  • general housekeeping
  • egress maintenance
  • emergency preparedness and, when needed, access to first-aid and medical assistance
  • hearing conservation programmes
  • protection against blood-borne pathogens
  • preventive maintenance of machines and equipment
  • traffic patterns and danger to pedestrians from the rolling stock
  • confined spaces
  • fire prevention and training and equipment for fire-fighting
  • household hazardous waste management
  • availability and use of high-quality, properly-sized PPE.



Municipal recycling is a relatively new industry that is changing rapidly as it grows and its technology advances. The health and safety of its workforce depend on proper design of processes and equipment and the proper training and supervision of its workers.



" DISCLAIMER: The ILO does not take responsibility for content presented on this web portal that is presented in any language other than English, which is the language used for the initial production and peer-review of original content. Certain statistics have not been updated since the production of the 4th edition of the Encyclopaedia (1998)."


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