Health error and critical tasks in remote afterloading brachytherapy: Approaches for improved system performance

Remote afterloading btachytherapy (RAB) is a medical process used in the treatment of cancer. RAB uses a computer-controlled device to remotely insert and remove radioactive sources, close to a target (or tumour) in the body. Problems related to the dose delivered during RAB have been reported and attributed to human error (Swann-D'Emilia, Chu and Daywalt 1990). Callan et al. (1995) evaluated human error and critical tasks associated with RAB in 23 sites in the United States. Evaluation included six phases:

Phase 1: Functions and tasks. Preparation for treatment was considered to be the most difficult task, as it was responsible for the greatest cognitive strain. In addition, distractions had the greatest effect on preparation.

Phase 2: Human-system interferences. Personnel were often unfamiliar with interfaces they used infrequently. Operators were unable to see control signals or essential information from their workstations. In many cases, information on the state of the system was not given to the operator.

Phase 3: Procedures and practices. Because procedures used to move from one operation to the next, and those used to transmit information and equipment between tasks, were not well defined, essential information could be lost. Verification procedures were often absent, poorly constructed or inconsistent.

Phase 4: Training policies. The study revealed the absence of formal training programmes at most sites.

Phase 5: Organizational support structures. Communication during RAB was particularly subject to error. Quality-control procedures were inadequate.

Phase 6: Identification and classification or circumstances favouring human error. In all, 76 factors favouring human error were identified and categorized. Alternative approaches were identified and evaluated.

Ten critical tasks were subject to error:

  • patient scheduling, identification and tracking
  • applicator placement stabilization
  • large volume localization
  • dwell position localization
  • dosimetry
  • treatment set-up
  • treatment plan entry
  • source exchange
  • source calibration
  • record-keeping and routine quality assurance


Treatment was the function associated with the greatest number of errors. Thirty treatment-related errors were analysed and errors were found to occur during four or five treatment sub-tasks. The majority of errors occurred during treatment delivery. The second-highest number of errors were associated with the planning of treatment and were related to the calculation of dose. Improvements of eqiupment and documentation are under way, in collaboration with manufacturers.



The National Institute for Occupational Safety and Health (NIOSH) studied lifting and other related injuries at two grocery warehouses (referred to hereafter as “Warehouse A” and “Warehouse B”) (NIOSH 1993a; NIOSH 1995). Both warehouses have engineered standards against which order selector performance is measured; those who fall below their standard are subject to disciplinary action. The data in table 1 are expressed in percentages of order selectors only, reporting either all injuries or back injuries alone each year.

Table 1. Back and all reported workplace injuries and illnesses involving order selectors at two grocery warehouses studied by NIOSH, 1987-1992.


Warehouse A: all injuries (%)

Warehouse B: all injuries (%)

Warehouse A: back injuries only (%)

Warehouse B: back injuries only (%)































Sources: NIOSH 1993a, 1995.

At the risk of generalizing these data beyond their context, by any reckoning, the magnitude of recordable injury and illness percentages in these warehouses are quite significant and considerably higher than the aggregate data for the industry as a whole for all job classifications. While the total injuries at Warehouse A show a slight decline, they actually increase at Warehouse B. But the back injuries, with the exception of 1992 at Warehouse B, are both quite stable and significant. In general terms, these data suggest that order selectors have virtually a 3 in 10 chance of experiencing a back injury involving medical treatment and/or lost time in any given year.

The US National Association of Grocery Warehouses of America (NAGWA), an industry group, reported that back strains and sprains accounted for 30% of all injuries involving grocery warehouses and that one-third of all warehouse workers (not just order selectors) will experience one recordable injury per year; these data are consistent with the NIOSH studies. Moreover, they estimated the cost of paying for these injuries (workers’ compensation primarily) at $0.61 per hour for the 1990-1992 period (almost US$1,270 per year per worker). They also determined that manual lifting was the primary cause of back injuries in 54% of all cases studied.

In addition to a review of injury and illness statistics, NIOSH utilized a questionnaire instrument which was administered to all grocery order selectors. At Warehouse A, of the 38 full-time selectors, 50% reported at least one injury in the last 12 months, and 18% of full-time selectors reported at least one back injury in the previous 12 months. For Warehouse B, 63% of the 19 full-time selectors reported at least one recordable injury in the last 12 months, and 47% reported having at least one back injury in the same period. Seventy per cent of full-time workers at Warehouse A reported significant back pain in the previous year, as did 47% of the full-time selectors at Warehouse B. These self-reported data closely correspond with the injury and illness survey data.

In addition to reviewing injury data regarding back injuries, NIOSH applied its revised lifting equation to a sample of lifting tasks of order selectors and found that all the sampled lifting tasks exceeded the recommended weight limit by significant margins, which indicates the tasks studied were highly stressful from an ergonomic point of view. In addition, compressive forces were estimated on the L5/S1 vertebral disc; all exceeded the recommended biomechanical limits of 3.4 kN (kilonewtons), which has been identified as an upper limit for protecting most workers from the risk of low-back injury.

Finally, NIOSH, using both energy expenditure and oxygen consumption methodologies, estimated energy demand on grocery order selectors in both warehouses. Average energy demands of the order selector exceeded the established criterion of 5 kcal/minute (4 METS) for an 8-hour day, which is recognized as moderate to heavy work for a majority of healthy workers. At Warehouse A, the working metabolic rate ranged from 5.4 to 8.0 kcal/minute, and the working heart rate ranged from 104 to 131 beats per minute; at Warehouse B, it was 2.6 to 6.3 kcal/minute, and 138 to 146 beats per minute, respectively.

Order selectors’ energy demands from continuous lifting at a rate of 4.1 to 4.9 lifts per minute would probably result in fatigued muscles, especially when working shifts of 10 or more hours. This clearly illustrates the physiological cost of work in the two warehouses studied to date. In summing up its findings, NIOSH reached the following conclusion concerning the risks faced by grocery warehouse order selectors:

In summary, all order assemblers (order selectors) have an elevated risk for musculoskeletal disorders, including low back pain, because of the combination of adverse job factors all contributing to fatigue, a high metabolic load and the workers’ inability to regulate their work rate because of the work requirements. According to recognized criteria defining worker capability and accompanying risk of low back injury, the job of order assembler at this work site will place even a highly selected work force at substantial risk of developing low back injuries. Moreover, in general, we believe that the existing performance standards encourage and contribute to these excessive levels of exertion (NIOSH 1995).



Thursday, 27 October 2011 20:34

Classification Systems

3.1.     General

3.1.1. The competent authority, or a body approved or recognised by the competent authority, should establish systems and specific criteria for classifying a chemical as hazardous and should progressively extend these systems and their application. Existing criteria for classification established by other competent authorities or by international agreement may be followed, if they are consistent with the criteria and methods outllined in this code, and this is encouraged where it may assist uniformity of approach. The results of the work of the UNEP/ILO/WHO International Programme on Chemical Safety (IPCS) coordinating group for the harmonisation of classification of chemicals should be considered when appropriate. The responsibilities and role of competent authorities concerning classification systems are set out in paragraphs 2.1.8 (criteria and requirements), 2.1.9 (consolidated list) and 2.1.10 (assessment of new chemicals).

3.1.2. Suppliers should ensure that chemicals they supplied have been classified or that they have been identified and their properties assessed (see paragraphs 2.4.3 (assessment) and 2.4.4 (classification)).

3.1.3. Manufacturers or importers, unless exempted, should give to the competent authority information about chemical elements and compounds not yet included in the consolidated classification list compiled by the competent authority, prior to their use at work (see paragraph 2.1.10 (assessment of new chemicals)).

3.1.4.  The limited quantities of a new chemical required for research and development purposes may be produced by, handled in, and transported between laboratories and pilot plant before all hazards of this chemical are known in accordance with national laws and regulations. All available information found in literature or known to the employer from his or her experience with similar chemicals and applications should be fully taken into account, and adequate protection measures should be applied, as if the chemical were hazardous. The workers involved must be informed about the actual hazard information as it becomes known.

3.2.     Criteria for classification

3.2.1.     The criteria for the classification of chemicals should be based upon their intrinsic health and physical hazards, including:

  1. toxic properties, including both acute and chronic health effects in all parts of the body;
  2. chemical or physical characteristics, including flammable, explosive, oxidising and dangerously reactive properties;
  3. corrosive and irritant properties;
  4. allergenic and sensitising effects;
  5. carcinogenic effects;
  6. teratogenic and mutagenic effects;
  7. effects on the reproductive system.


3.3.     Method of classification

3.3.1.     The classification of chemicals should be based on available sources of information, e.g.:

  1. test data;
  2. information provided by the manufacturer or importer, including information on research work done;
  3. information available as a result of international transport rules, e.g., the United Nations Recommendations on the Transport of Dangerous Goods, which should be taken into account for the classification of chemicals in the case of transport, and the UNEP Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and their Disposal (1989), which should be taken into account in respect of hazardous wastes;
  4. reference books or literature;
  5. practical experience;
  6. in the case of mixtures, either on the test of the mixture or on the known hazards of their components;
  7. information provided as a result of the risk evaluation work performed by the International Agency for Reseach on Cancer (IARC), the UNEP/ILO/WHO International Programme on Chemical Safety (IPCS), the European Communities and various national and international institutions, as well as information available through systems such as the UNEP International Register of Potentially Toxic Chemicals (IRPTC).


3.3.2.  Certain classification systems in use may be limited to particular classes of chemicals only. An example is the WHO Recommended classification of pesticides by hazard and guidelines to classification, which classifies pesticides by degree of toxicity only and principally by acute risks to health. Employers and workers should understand the limitations of any such system. Such systems can be useful to complement a more generally applicable system.

3.3.3.  Mixtures of chemicals should be classified based on the hazards exhibited by the mixtures themselves. Only if mixtures have not been tested as a whole should they be classified on the basis of intrinsic hazards of their component chemicals.

Source: ILO 1993, Chapter 3.



A systematic approach to safety requires an efficient flow of information from the suppliers to the users of chemicals on potential hazards and correct safety precautions. In addressing the need for a written hazard communication programme, the ILO Code of Practice Safety in the Use of Chemicals at Work (ILO 1993) states, “The supplier should provide an employer with essential information about hazardous chemicals in the form of a chemical safety data sheet.” This chemical safety data sheet or material safety data sheet (MSDS) describes the hazards of a material and provides instructions on how the material can be safely handled, used and stored. MSDSs are produced by the manufacturer or importer of hazardous products. The manufacturer must provide distributors and other customers with MSDSs upon first purchase of a hazardous product and if the MSDS changes. Distributors of hazardous chemicals must automatically provide MSDSs to commercial customers. Under the ILO Code of Practice, workers and their representatives should have a right to an MSDS and to receive the written information in forms or languages they easily understand. Because some of the required information might be intended for specialists, further clarification may be needed from the employer. The MSDS is only one source of information on a material and, therefore, it is best used along with technical bulletins, labels, training and other communications.

The requirements for a written hazard communication programme are outlined in at least three major international directives: the US Occupational Safety and Health Administration (OSHA) Hazard Communication Standard, Canada’s Workplace Hazardous Materials Information System (WHMIS) and the European Community’s Commission Directive 91/155/EEC. In all three directives, the requirements for preparing a complete MSDS are established. Criteria for the data sheets include information about the identity of the chemical, its supplier, classification, hazards, safety precautions and the relevant emergency procedures. The following discussion details the type of required information included in the 1992 ILO Code of Practice Safety in the Use of Chemicals at Work. While the Code is not intended to replace national laws, regulations or accepted standards, its practical recommendations are intended for all those who have a responsibility for ensuring the safe use of workplace chemicals.

The following description of chemical safety data sheet content corresponds with section 5.3 of the Code:

Chemical safety data sheets for hazardous chemicals should give information about the identity of the chemical, its supplier, classification, hazards, safety precautions and the relevant emergency procedures.

The information to be included should be that established by the competent authority for the area in which the employer’s premises are located, or by a body approved or recognized by that competent authority. Details of the type of information that should be required are given below.

(a) Chemical product and company identification

The name should be the same as that used on the label of the hazardous chemical, which may be the conventional chemical name or a commonly used trade name. Additional names may be used if these help identification. The full name, address and telephone number of the supplier should be included. An emergency telephone number should also be given, for contact in the event of an emergency. This number may be that of the company itself or of a recognized advisory body, so long as either can be contacted at all times.

(b) Information on ingredients (composition)

The information should allow employers to identify clearly the risks associated with a particular chemical so that they may conduct a risk assessment, as outlined in section 6.2 (Procedures for assessment) of this code. Full details of the composition should normally be given but may not be necessary if the risks can be properly assessed. The following should be provided except where the name or concentration of an ingredient in a mixture is confidential information which can be omitted in accordance with section 2.6:

  1. a description of the main components, including their chemical nature;
  2. the identity and concentrations of components which are hazardous to safety and health
  3. the identity and maximum concentration to be found of components which are at the concentration or exceed the concentration at which they are classified as hazardous to safety and health in lists approved or recognized by the competent authority, or which are prohibited at higher concentrations by the competent authority.


(c) Hazard identification

The most important hazards, including the most significant health, physical and environmental hazards, should be stated clearly and briefly, as an emergency overview. The information should be compatible with that shown on the label.

(d) First-aid measures

First-aid and self-help measures should be carefully explained. Situations where immediate medical attention is required should be described and the necessary measures indicated. Where appropriate, the need for special arrangements for specific and immediate treatment should be emphasized.

(e) Firefighting measures

The requirements for fighting a fire involving a chemical should be included; for example:

  1. suitable extinguishing agents;
  2. extinguishing agents which must not be used for safety reasons;
  3. special protective equipment for firefighters.

Information should also be given on the properties of the chemical in the event of fire and on special exposure hazards as a result of combustion products, as well as the precautions to be taken.

(f) Accidental release measures

Information should be provided on the action to be taken in the event of an accidental release of the chemical. The information should include:

  1. health and safety precautions: removal of sources of ignition, provision of sufficient ventilation, provision of suitable personal protective equipment;
  2. environmental precautions: keeping away from drains, need to alert the emergency services, and possible need to alert the immediate neighbourhood in the event of an imminent risk;
  3. methods for making safe and cleaning up: use of suitable absorbent materials, avoiding production of gases/fumes by water or other diluent, use of suitable neutralizing agents;
  4. warnings: advise against reasonably foreseeable hazardous actions.


(g) Handling and storage

Information should be given about conditions recommended by the supplier for safe storage and handling, including:

  1. design and location of storage rooms or vessels;
  2. separation from workplaces and occupied buildings;
  3. incompatible materials;
  4. conditions of storage (e.g., temperature and humidity, avoidance of sunlight);
  5. avoidance of sources of ignition, including particular arrangements to avoid static build-up;
  6. provision of local and general ventilation;
  7. recommended methods of work and those to be avoided.


(h) Exposure controls and personal protection

Information should be given on the need for personal protective equipment during use of a chemical, and on the type of equipment that provides adequate and suitable protection. Where appropriate, a reminder should be given that the primary controls should be provided by the design and installation of any equipment used and by other engineering measures, and information provided on useful practices to minimize exposure of workers. Specific control parameters such as exposure limits or biological standards should be given, along with recommended monitoring procedures.

(i) Physical and chemical properties

A brief description should be given of the appearance of the chemical, whether it is a solid, liquid or gas, and its colour and odour. Certain characteristics and properties, if known, should be given, specifying the nature of the test to determine these in each case. The tests used should be in accordance with the national laws and criteria applying at the employer’s workplace and, in the absence of national laws or criteria, the test criteria of the exporting country should be used as guidance. The extent of the information provided should be appropriate to the use of the chemical. Examples of other useful data include:

  • viscosity
  • freezing point/freezing range
  • boiling point/boiling range
  • melting point/melting range
  • flashpoint
  • auto-ignition temperature
  • explosive properties
  • oxidizing properties
  • vapour pressure
  • molecular weight
  • specific gravity or density
  • pH
  • solubility
  • partition coefficient (water/n-octane)
  • parameters such as vapour density
  • miscibility
  • evaporation rate and conductivity.


(j) Stability and reactivity

The possibility of hazardous reactions under certain conditions should be stated. Conditions to avoid should be indicated, such as:

  1. physical conditions (e.g., temperature, pressure, light, shock, contact with moisture or air);
  2. proximity to other chemicals (e.g., acids, bases, oxidizing agents or any other specific substance which may cause a dangerous reaction).

Where hazardous decomposition products are given off, these should be specified along with the necessary precautions.

(k) Toxicological information

This section should give information on the effects on the body and on potential routes of entry into the body. Reference should be made to acute effects, both immediate and delayed, and to chronic effects from both short- and long-term exposure. Reference should also be made to health hazards as a result of possible reaction with other chemicals, including any known interactions, for example, resulting from the use of medication, tobacco and alcohol.

(l) Ecological information

The most important characteristics likely to have an effect on the environment should be described. The detailed information required will depend on the national laws and practice applying at the employer’s workplace. Typical information that should be given, where appropriate, includes the potential routes for release of the chemical which are of concern, its persistence and degradability, bioaccumulative potential and aquatic toxicity, and other data relating to ecotoxicity (e.g., effects on water treatment works).

(m) Disposal considerations

Safe methods of disposal of the chemical and of contaminated packaging, which may contain residues of hazardous chemicals, should be given. Employers should be reminded that there may be national laws and practices on the subject.

(n) Transport information

Information should be given on special precautions that employers should be aware of or take while transporting the chemical on or off their premises. Relevant information given in the United Nations Recommendations on the Transport of Dangerous Goods and in other international agreements may also be included.

(o) Regulatory information

Information required for the marking and labelling of the chemical should be given here. Specific national regulations or practices applying to the user should be referred to. Employers should be reminded to refer to the requirements of national laws and practices.

(p) Other information

Other information which may be important to workers’ health and safety should be included. Examples are training advice, recommended uses and restrictions, references, and sources of key data for compiling the chemical safety data sheet, the technical contact point and date of issue of the sheet.



In a case-control study looking at environmental and occupational factors for congenital malformations (Kurppa et al. 1986), 1,475 cases were identified from the Finnish Register of Congenital Malformations during the period between 1976 and 1982 (see table 1). A mother whose delivery immediately preceded a case, and was in the same district, served as a control for that case. Exposure to visual display units (VDUs) during the first trimester of pregnancy was assessed using face-to-face interviews conducted either at the clinic during a post-natal visit, or at home. The classification of probable or obvious VDU use was determined by occupational hygienists, blind to the pregnancy outcomes, using job titles and the responses to open-ended questions asking to describe the ordinary work day. There was no evidence of increased risk either among women who reported exposure to VDUs (OR 0.9; 95% CI 0.6 – 1.2), or among women whose job titles indicated possible exposure to VDUs (235 cases/255 controls).

A cohort of Swedish women from three occupational groups was identified through a linkage of occupational census and the Medical Birth Registry during 1980–1981 (Ericson and Källén 1986). A case-base study was conducted within that cohort: cases were 412 women hospitalized for spontaneous abortion and an additional 110 with other outcomes (such as perinatal death, congenital malformations and birthweight below 1500 g). Controls were 1,032 women of similar age who had infants without any of these characteristics, chosen from the same registry. Using crude odds ratios, there was an exposure–response relation between VDU exposure in estimated hours per week (divided into five-hour categories) and pregnancy outcomes (excluding spontaneous abortion). After controlling for smoking and stress, the effect of VDU use on all adverse pregnancy outcomes was not significant.

Focusing on one of three occupational groups identified from a previous study by Ericson a cohort study was conducted using 4,117 pregnancies among social security clerks in Sweden (Westerholm and Ericson 1986). Rates of hospitalized spontaneous abortion, low birthweight, perinatal mortality and congenital malformations in this cohort were compared to rates in the general population. The cohort was divided into five exposure groups defined by trade union and employer representatives. No excesses were found for any of the studied outcomes. The overall relative risk for spontaneous abortion, standardized for mothers’ age was 1.1 (95% CI 0.8 – 1.4).

A cohort study involving 1,820 births was conducted among women having ever worked at the Norwegian Postal Giro Centre between 1967–1984 (Bjerkedal and Egenaes 1986). The rates of stillbirth, first-week death, perinatal death, low and very low birthweight, preterm birth, multiple births and congenital malformations were estimated for pregnancies occurring during employment at the centre (990 pregnancies), and pregnancies occurring before or after employment at the centre (830 pregnancies). Rates of adverse pregnancy outcomes were also estimated for three six-year periods, (1967–1972), (1973–1978) and (1979–1984). Introduction of VDUs began in 1972, and were extensively used by 1980. The study concluded that there was no indication that introduction of VDUs in the centre had led to any increase in the rate of adverse pregnancy outcomes.

A cohort of 9,564 pregnancies was identified through logs of urine pregnancy tests from three California clinics in 1981–1982 (Goldhaber, Polen and Hiatt. 1988). Coverage by a Northern California medical plan was a requirement to be eligible for the study. Pregnancy outcomes were found for all but 391 identified pregnancies. From this cohort, 460 of 556 spontaneous abortion cases (<28 weeks), 137 of 156 congenital abnormality cases and 986 of 1,123 controls (corresponding to every fifth normal birth in the original cohort), responded to a retrospective postal questionnaire on chemical environmental exposures including pesticides and VDU use during pregnancy. Odds ratios for women with first trimester VDU use over 20 hours per week, adjusted for eleven variables including age, previous miscarriage or birth defect, smoking and alcohol, were 1.8 (95% CI 1.2 – 2.8) for spontaneous abortion and 1.4 (95% CI 0.7 – 2.9) for birth defects, when compared to working women who did not report using VDUs.

In a study conducted in 11 hospital maternity units in the Montreal area over a two-year period (1982–1984), 56,012 women were interviewed on occupational, personal and social factors after delivery (51,855) or treatment for spontaneous abortion (4,127) (McDonald et al. 1988).These women also provided information on 48,637 previous pregnancies. Adverse pregnancy outcomes (spontaneous abortion, stillbirth, congenital malformations and low birthweight) were recorded for both current and previous pregnancies. Ratios of observed to expected rates were calculated by employment group for current pregnancies and previous pregnancies. Expected rates for each employment group were based on the outcome in the whole sample, and adjusted for eight variables, including age, smoking and alcohol. No increase in risk was found among women exposed to VDUs.

A cohort study comparing rates of threatened abortion, length of gestation, birthweight, placental weight and pregnancy-induced hypertension between women who used VDUs and women who did not use VDUs was carried out among 1,475 women (Nurminen and Kurppa 1988).The cohort was defined as all non-cases from a previous case-control study of congenital malformations. Information about risk factors was collected using face-to-face interviews. The crude and adjusted rate ratios for the outcomes studied did not show statistically significant effects for working with VDUs.

A case-control study involving 344 cases of hospitalized spontaneous abortion occurring at three hospitals in Calgary, Canada, was conducted in 1984–1985 (Bryant and Love 1989). Up to two controls (314 prenatal and 333 postpartum) were chosen among women having delivered or susceptible of delivering at the study hospitals. The controls were matched to each case on the basis of age at last menstrual period, parity, and intended hospital of delivery. VDU use at home and at work, before and during pregnancy, was determined through interviews at the hospitals for postnatal controls and spontaneous abortion, and at home, work, or the study office for prenatal controls. The study controlled for socioeconomic and obstetric variables. VDU use was similar between the cases and both the prenatal controls (OR=1.14; p=0.47) and postnatal controls (OR=0.80; p=0.2).

A case-control study of 628 women with spontaneous abortion, identified through pathology specimen submissions, whose last menstrual period occurred in 1986, and 1,308 controls who had live births, was carried out in one county in California (Windham et al. 1990). The controls were randomly selected, in a two-to-one ratio, among women matched for date of last menstrual period and hospital. Activities during the first 20 weeks of pregnancy were identified through telephone interviews. The participants were also asked about VDU use at work during this period. Crude odds ratios for spontaneous abortion and VDU use less than 20 hours per week (1.2; 95% CI 0.88 – 1.6), and at least 20 hours per week (1.3; 95% CI 0.87 – 1.5), showed little change when adjusted for variables including employment group, maternal age, prior foetal loss, alcohol consumption and smoking. In a further analysis among the women in the control group, risks for low birthweight and intrauterine growth retardation were not significantly elevated.

A case-control study was conducted within a study base of 24,352 pregnancies occurring between 1982 and 1985 among 214,108 commercial and clerical employees in Denmark (Brandt and Nielsen 1990). The cases, 421 respondents among the 661 women who gave birth to children with congenital abnormalities and who were working at the time of pregnancy, were compared to 1,365 respondents among the 2,252 randomly selected pregnancies among working women. Pregnancies, and their outcomes, and employment were determined through a linkage of three databases. Information on VDU use (yes/no/hours per week), and job-related and personal factors such as stress, exposure to solvents, life-style and ergonomic factors were determined through a postal questionnaire. In this study, the use of VDUs during pregnancy was not associated with an increased risk of congenital abnormalities.

Using the same study base as in the previous study on congenital abnormalities (Brandt and Nielsen 1990) 1,371 of 2,248 women whose pregnancies ended in a hospitalized spontaneous abortion were compared to 1,699 randomly selected pregnancies (Nielsen and Brandt 1990). While the study was carried out among commercial and clerical workers, not all of the pregnancies corresponded to times when the women were gainfully employed as commercial or clerical workers. The measure of association used in the study was the ratio of the rate of VDU use among women with a spontaneous abortion to the rate of VDU use among the sample population (representing all pregnancies including those ending in spontaneous abortion). The adjusted rate ratio for any exposure to VDU and spontaneous abortion was 0.94 (95% CI 0.77 – 1.14).

A case-control study was carried out among 573 women who gave birth to children with cardiovascular malformations between 1982 and 1984 (Tikkanen and Heinonen 1991). The cases were identified through the Finnish register of congenital malformations. The control group consisted of 1,055 women, randomly selected among all hospital deliveries during the same time period. VDU use, recorded as never, regular or occasional, was assessed through an interview conducted 3 months after the delivery. No statistically significant association was found between VDU use, at work or at home, and cardiovascular malformations.

A cohort study was carried out among 730 married women who reported pregnancies between 1983 and 1986 (Schnorr et al. 1991). These women were employed as either directory assistance operators or as general telephone operators at two telephone companies in eight southeastern states in the United States. Only the directory assistance operators used VDUs at work. VDU use was determined through company records. Spontaneous abortion cases (foetal loss at 28 weeks’ of gestation or earlier) were identified through a telephone interview; birth certificates were later used to compare women’s reporting with pregnancy outcomes and when possible, physicians were consulted. Strengths of electric and magnetic fields were measured at very low and extremely low frequencies for a sample of the workstations. The VDU workstations showed higher field strengths than those not using VDUs. No excess risk was found for women who used VDUs during the first trimester of pregnancy (OR 0.93; 95% CI 0.63 – 1.38), and there was no apparent exposure–response relation when looking at time of VDU use per week.

A cohort of 1,365 Danish commercial and clerical workers who were gainfully employed at the time of pregnancy, and identified through a previous study (Brandt and Nielsen 1990; Nielsen and Brandt 1990), was used to study fecundability rates, in relation to VDU use (Brandt and Nielsen 1992). Fecundability was measured as time from stopping birth control use to time of conception, and was determined through a postal questionnaire. This study showed an increased relative risk for prolonged waiting to pregnancy for the subgroup with at least 21 weekly hours of VDU use. (RR 1.61; 95% CI 1.09 – 2.38).

A cohort of 1,699 Danish commercial and clerical workers, consisting of women employed and unemployed at the time of pregnancy, identified through the study reported on in the previous paragraph, was used to study low birthweight (434 cases), preterm birth (443 cases), small for gestational age (749 cases), and infant mortality (160 cases), in relation to VDU use patterns (Nielsen and Brandt 1992). The study failed to show any increased risk for these adverse pregnancy outcomes among women with VDU use.

In a case-control study, 150 nulliparous women with clinically diagnosed spontaneous abortion and 297 nulliparous working women attending a hospital in Reading, England for antenatal care between 1987 and 1989 were interviewed (Roman et al. 1992). The interviews were conducted face to face at the time of their first antenatal visit for the controls, and three weeks after the abortion for women with spontaneous abortion. For women who mentioned VDU use, estimates of time of exposure in hours per week, and calendar time of first exposure were assessed. Other factors such as overtime, physical activity at work, stress and physical comfort at work, age, alcohol consumption and previous miscarriage were also assessed. Women who worked with VDUs had an odds ratio for spontaneous abortion of 0.9 (95% CI 0.6 – 1.4), and there was no relation with the amount of time spent using VDUs. Adjusting for other factors such as maternal age, smoking, alcohol and previous spontaneous abortion did not alter the results.

From a study base of bank clerks and clerical workers in three companies in Finland, 191 cases of hospitalized spontaneous abortion and 394 controls (live births) were identified from Finnish medical registers for 1975 to 1985 (Lindbohm et al. 1992). Use of VDUs was defined using workers’ reports and company information. Magnetic field strengths were retrospectively assessed in a laboratory setting using a sample of the VDUs which had been used in the companies. The odds ratio for spontaneous abortion and working with VDUs was 1.1 (95% CI 0.7 – 1.6). When VDU users were separated in groups according to the field strengths for their VDU models, the odds ratio was 3.4 (95% CI 1.4 – 8.6) for workers who had used VDUs with a high magnetic field strength in the extremely low frequency bandwidth (0.9 μT), compared to those working with VDUs with field strength levels below the detection limits (0.4 μT). This odds ratio changed only slightly when adjusted for ergonomic and mental work-load factors. When comparing workers exposed to high magnetic field strengths to workers not exposed to VDUs, the odds ratio was no longer significant.

A study, looking at adverse pregnancy outcomes and fertility, was carried out among female civil servants working for the British Government tax offices (Bramwell and Davidson 1994). Of the 7,819 questionnaires mailed in the first stage of the study, 3,711 were returned. VDU use was determined through this first questionnaire. Exposure was assessed as hours per week of VDU use during pregnancy. One year later, a second questionnaire was sent out to assess the incidence of adverse pregnancy outcomes among these women; 2,022 of the original participants responded. Possible confounders included pregnancy history, ergonomic factors, job stressors, caffeine, alcohol, cigarette and tranquillizer consumption. There was no relationship between exposure as assessed one year previously and the incidence of adverse pregnancy outcomes.



Thursday, 27 October 2011 19:57

Formulae and Definitions

In general there is a square root relationship between thickness d of a static air layer and air velocity v. The exact function depends on the size and shape of the surface, but for the human body a useful approximation is:

Still air acts as an insulating layer with a conductivity (a material constant, regardless of the shape of the material) of .026 W/mK, which has a heat transfer coefficient h (units of ) (the conductive property of a slab of material) of:

(Kerslake 1972).

Radiant heat flow () between two surfaces is approximately proportional to their temperature difference:

where T is the average absolute temperature (in Kelvin) of the two surfaces, is the absorption coefficient and is the Stefan-Boltzmann constant ( ). The amount of radiation exchange is inversely related to the number of intercepting layers (n):

Clothing insulation () is defined by the following equations:

where is intrinsic insulation, is (adjacent) air insulation, is total insulation, is average skin temperature, is the average temperature of the outer surface of the clothing, is air temperature, is the dry heat flow (convective and radiant heat) per unit of skin area and is the clothing area factor. This coefficient has been underestimated in older studies, but more recent studies converge to the expression

Often I is expressed in the unit clo; one clo equals .

McCullough et al. (1985) deduced a regression equation from data on a mix of clothing ensembles, using thickness of the textile (, in mm) and percentage covered body area () as determinants. Their formula for the insulation of single clothing items () is:

The evaporative resistance R (units of s/m) can be defined as:

(or sometimes , in )

For fabric layers, the air equivalent () is the thickness of air that provides the same resistance to diffusion as the fabric does. The associated vapour and latent heat () flows are:

where D is the diffusion coefficient (), C the vapour concentration () and the heat of evaporation (2430 J/g).

(from Lotens 1993). is related to R by:


D is the diffusion coefficient for water vapour in air, .



I. Index of thermal stress (ITS)

The improved heat balance equation is:

where  is the evaporation required to maintain heat balance,  is the solar load, and metabolic heat production H is used instead of metabolic rate to account for external work. An important improvement is the recognition that not all sweat evaporates (e.g., some drips) hence required sweat rate is related to required evaporation rate by:

where nsc is the efficiency of sweating.

Used indoors, sensible heat transfer is calculated from:

For outdoor conditions with solar load,  is replaced with  and allowance made for solar load (RS ) by:

The equations used are fits to experimental data and are not strictly rational.

Maximum evaporation heat loss is:

and efficiency of sweating is given by:


nsc = 1, если


nsc = 0.29, если

The index of thermal stress (ITS) in g/h is given by:

where  is the required evaporation rate , 0.37 converts  into g/h andnsc is the efficiency of sweating (McIntyre 1980).

II. Required sweat rate

Similar to the other rational indices,  is derived from the six basic parameters (air temperature (), radiant temperature ( ), relative humidity air velocity (v), clothing insulation ( ), metabolic rate (M) and external work (W)). Effective radiation area values for posture (sitting = 0.72, standing = 0.77) are also required. From this the evaporation required is calculated from:

Equations are provided for each component (see table 8 and table 9). Mean skin temperature is calculated from a multiple linear regression equation or a value of 36°C is assumed.

From the required evaporation (Ereg) and maximum evaporation (Emax) and sweating efficiency (r), the following are calculated:

Required skin wettedness 

Required sweat rate 

III. Predicted 4-hour sweat rate (P4SR)

Steps taken to obtain the P4SR index value are summarized by McIntyre (1980) as follows:

If , increase wet bulb temperature by .

If the metabolic rate M > 63 , increase wet bulb temperature by the amount   indicated in the chart (see figure 6).

If the men are clothed, increase the wet bulb temperature by .

The modifications are additive.

The (P4SR) is determined from figure 6. The P4SR is then:

IV. Heart rate

where M is metabolic rate,  is air temperature in °C and Pa is vapour pressure in Mb.

Givoni and Goldman (1973) provide equations for predicting heart rate of persons (soldiers) in hot environments. They define an index for heart rate (IHR) from a modification of predicted equilibrium rectal temperature,

IHR is then:

where M = metabolic rate (watts), = mechanical work (watts), clo = thermal insulation of clothing,  = air temperature = total metabolic and environmental heat load (watts),  = evaporative cooling capacity for clothing and environment (watts).

The equilibrium heart rate (in beats per minute) is then given by:

for IHR 225

that is, a linear relationship (between rectal temperature and heart rate) for heart rates up to about 150 beats per minute. For IHR >225:

that is, an exponential relationship as heart rate approaches maximum, where:

= equilibrium heart rate (bpm),

65 = assumed resting heart rate in comfortable conditions (bpm), and t = time in hours.

V. Wet bulb globe temperature index (WBGT)

Wet bulb globe temperature is given by:

for conditions with solar radiation, and:

for indoor conditions with no solar radiation, where  Tnwb= temperature of a naturally ventilated wet bulb thermometer, Ta = air temperature, and  Tg = temperature of a 150 mm diameter black globe thermometer.



Thursday, 27 October 2011 19:36

Case Study: What does dose mean?

There are several ways to define a dose of ionizing radiation, each appropriate for different purposes.

Absorbed dose

Absorbed dose resembles pharmacological dose the most closely. While pharmacological dose is the quantity of substance administered to a subject per unit weight or surface, radiological absorbed dose is the amount of energy transmitted by ionizing radiation per unit mass. Absorbed dose is measured in Grays (1 Gray = 1 joule/kg).

When individuals are exposed homogeneously—for example, by external irradiation by cosmic and terrestrial rays or by internal irradiation by potassium-40 present in the body—all organs and tissues receive the same dose. Under these circumstances, it is appropriate to speak of whole-body dose. It is, however, possible for exposure to be non-homogenous, in which case some organs and tissues will receive significantly higher doses than others. In this case, it is more relevant to think in terms of organ dose. For example, inhalation of radon daughters results in exposure of essentially only the lungs, and incorporation of radioactive iodine results in irradiation of the thyroid gland. In these cases, we may speak of lung dose and thyroid dose.

However, other units of dose that take into account differences in the effects of different types of radiation and the different radiation sensitivities of tissues and organs, have also been developed.

Equivalent dose

The development of biological effects (e.g., inhibition of cell growth, cell death, azoospermia) depends not only on the absorbed dose, but also on the specific type of radiation. Alpha radiation has a greater ionizing potential than beta or gamma radiation. Equivalent dose takes this difference into account by applying radiation-specific weighting factors. The weighting factor for gamma and beta radiation (low ionizing potential), is equal to 1, while that for alpha particles (high ionizing potential) is 20 (ICRP 60). Equivalent dose is measured in Sieverts (Sv).

Effective dose

In cases involving non-homogenous irradiation (e.g., the exposure of various organs to different radionuclides), it may be useful to calculate a global dose that integrates the doses received by all organs and tissues. This requires taking into account the radiation sensitivity of each tissue and organ, calculated from the results of epidemiological studies of radiation-induced cancers. Effective dose is measured in Sieverts (Sv) (ICRP 1991). Effective dose was developed for the purposes of radiation protection (i.e., risk management) and is thus inappropriate for use in epidemiological studies of the effects of ionizing radiation.

Collective dose

Collective dose reflects the exposure of a group or population and not of an individual, and is useful for evaluating the consequences of exposure to ionizing radiation at the population or group level. It is calculated by summing the individual received doses, or by multiplying the average individual dose by the number of exposed individuals in the groups or populations in question. Collective dose is measured in man-Sieverts (man Sv).



ILO 80th Session, 2nd June 1993

ILO 80th Session, 2nd June 1993


Article 1

1. The purpose of this Convention is the prevention of major accidents involving hazardous substances and the limitation of the consequences of such accidents.…

Article 3

For the purposes of this Convention:

(a)    the term “hazardous substance” means a substance or mixture of substances which by virtue of chemical, physical or toxicological properties, either singly or in combination, constitutes a hazard;

(b)    the term “threshold quantity” means for a given hazardous substance or category of substances that quantity, prescribed in national laws and regulations by reference to specific conditions, which if exceeded identifies a major hazard installation;

(c)    the term “major hazard installation” means one which produces, processes, handles, uses, disposes of or stores, either permanently or temporarily, one or more hazardous substances or categories of substances in quantities which exceed the threshold quantity;

(d)    the term “major accident” means a sudden occurrence—such as a major emission, fire or explosion—in the course of an activity within a major hazard installation, involving one or more hazardous substances and leading to a serious danger to workers, the public or the environment, whether immediate or delayed;

(e)    the term “safety report“ means a written presentation of the technical, management and operational information covering the hazards and risks of a major hazard installation and their control and providing justification for the measures taken for the safety of the installation;

(f)    the term “near miss” means any sudden event involving one or more hazardous substances which, but for mitigating effects, actions or systems, could have escalated to a major accident.


Article 4

1. In the light of national laws and regulations, conditions and practices, and in consultation with the most representative organizations of employers and workers and with other interested parties who may be affected, each Member shall formulate, implement and periodically review a coherent national policy concerning the protection of workers, the public and the environment against the risk of major accidents.

2. This policy shall be implemented through preventive and protective measures for major hazard installations and, where practicable, shall promote the use of the best available safety technologies.

Article 5

1. The competent authority, or a body approved or recognized by the competent authority, shall, after consulting the most representative organizations of employers and workers and other interested parties who may be affected, establish a system for the identification of major hazard installations as defined in Article 3(c), based on a list of hazardous substances or of categories of hazardous substances or of both, together with their respective threshold quantities, in accordance with national laws and regulations or international standards.

2. The system mentioned in paragraph 1 above shall be regularly reviewed and updated.

Article 6

The competent authority, after consulting the representative organizations of employers and workers concerned, shall make special provision to protect confidential information transmitted or made available to it in accordance with Articles 8, 12, 13 or 14, whose disclosure would be liable to cause harm to an employer’s business, so long as this provision does not lead to serious risk to the workers, the public or the environment.


Article 7

Employers shall identify any major hazard installation within their control on the basis of the system referred to in Article 5.


Article 8

1. Employers shall notify the competent authority of any major hazard installation which they have identified:

(a)            within a fixed time-frame for an existing installation;

(b)            before it is put into operation in the case of a new installation.

2. Employers shall also notify the competent authority before any permanent closure of a major hazard installation.

Article 9

In respect of each major hazard installation employers shall establish and maintain a documented system of major hazard control which includes provision for:

(a)    the identification and analysis of hazards and the assessment of risks including consideration of possible interactions between substances;

(b)    technical measures, including design, safety systems, construction, choice of chemicals, operation, maintenance and systematic inspection of the installation;

(c)    organizational measures, including training and instruction of personnel, the provision of equipment in order to ensure their safety, staffing levels, hours of work, definition of responsibilities, and controls on outside contractors and temporary workers on the site of the installation;

(d)    emergency plans and procedures, including:

(i)        the preparation of effective site emergency plans and procedures, including
emergency medical procedures, to be applied in case of major accidents or threat
thereof, with periodic testing and evaluation of their effectiveness and revision as

(ii)        the provision of information on potential accidents and site emergency plans to
authorities and bodies responsible for the preparation of emergency plans and
procedures for the protection of the public and the environment outside the site of
the installation;

(iii)        any necessary consultation with such authorities and bodies;

(e)    measures to limit the consequences of a major accident;

(f)    consultation with workers and their representatives;

(g)    improvement of the system, including measures for gathering information and analysing accidents and near misses. The lessons so learnt shall be discussed with the workers and their representatives and shall be recorded in accordance with national law and practice.…

*  *  *



Article 15

Taking into account the information provided by the employer, the competent authority shall ensure that emergency plans and procedures containing provisions for the protection of the public and the environment outside the site of each major hazard installation are established, updated at appropriate intervals and coordinated with the relevant authorities and bodies.

Article 16

The competent authority shall ensure that:

(a)    information on safety measures and the correct behaviour to adopt in the case of a major accident is disseminated to members of the public liable to be affected by a major accident without their having to request it and that such information is updated and redisseminated at appropriate intervals;

(b)    warning is given as soon as possible in the case of a major accident;

(c)    where a major accident could have transboundary effects, the information required in (a) and (b) above is provided to the States concerned, to assist in cooperation and coordination arrangements.

Article 17

The competent authority shall establish a comprehensive siting policy arranging for the appropriate separation of proposed major hazard installations from working and residential areas and public facilities, and appropriate measures for existing installations. Such a policy shall reflect the General Principles set out in Part II of the Convention.


Article 18

1. The competent authority shall have properly qualified and trained staff with the appropriate skills, and sufficient technical and professional support, to inspect, investigate, assess, and advise on the matters dealt with in this Convention and to ensure compliance with national laws and regulations.

2. Representatives of the employer and representatives of the workers of a major hazard installation shall have the opportunity to accompany inspectors supervising the application of the measures prescribed in pursuance of this Convention, unless the inspectors consider, in the light of the general instructions of the competent authority, that this may be prejudicial to the performance of their duties.

Article 19

The competent authority shall have the right to suspend any operation which poses an imminent threat of a major accident.


Article 20

The workers and their representatives at a major hazard installation shall be consulted through appropriate cooperative mechanisms in order to ensure a safe system of work. In particular, the workers and their representatives shall:

(a)    be adequately and suitably informed of the hazards associated with the major hazard installation and their likely consequences;

(b)    be informed of any orders, instructions or recommendations made by the competent authority;

(c)    be consulted in the preparation of, and have access to, the following documents:

(i)    the safety report;

(ii)    emergency plans and procedures;

(iii)    accident reports;

(d)    be regularly instructed and trained in the practices and procedures for the prevention of major accidents and the control of developments likely to lead to a major accident and in the emergency procedures to be followed in the event of a major accident;

(e)    within the scope of their job, and without being placed at any disadvantage, take corrective action and if necessary interrupt the activity where, on the basis of their training and experience, they have reasonable justification to believe that there is an imminent danger of a major accident, and notify their supervisor or raise the alarm, as appropriate, before or as soon as possible after taking such action;

(f)    discuss with the employer any potential hazards they consider capable of generating a major accident and have the right to notify the competent authority of those hazards.

Article 21

Workers employed at the site of a major hazard installation shall:

(a)    comply with all practices and procedures relating to the prevention of major accidents and the control of developments likely to lead to a major accident within the major hazard installation;

(b)    comply with all emergency procedures should a major accident occur.


Article 22

When, in an exporting member State, the use of hazardous substances, technologies or processes is prohibited as a potential source of a major accident, the information on this prohibition and the reasons for it shall be made available by the exporting member State to any importing country.

Source: Excerpts, Convention No. 174 (ILO 1993).



Thursday, 27 October 2011 00:48

Applying Organizational Psychology

The official in the company’s EDP Department and the claims adjuster in the Occupational Injury Department were involved in intensive collaboration for a period of about six months. They had never previously had the opportunity to work together and did not know each other well. The EDP specialist is the head of his department, which forms a part of the company’s central financial administration, positioned immediately below head-office management. The occupational-injury claims adjuster is head of one of the company’s business units, the Occupational Injury Department, which is geographically located in another part of the town.

The EDP Department has the duty, on a continuous basis, to rationalize and redesign the forms used by the company, so that the registration of documents and correspondence within the company’s various business units is simplified and made as effective as possible.

The Occupational Injury Department has the task of handling the occupational-injury claims of its policyholders (circle of clients) in a scrupulous and accurate manner, so that clients feel that they are correctly treated. The EDP Department has a rationalizing function in the company, whereas the Occupational Injury Department has a client-oriented function in a specialized area of insurance business.

The occupational-injury claims adjuster has daily contacts with other officials in his own work group and also with members of other work groups within the Occupational Injury Department. These contacts are made primarily to discuss matters concerning occupational injuries that will enable the maintenance of an intra-departmental consensus on the guiding principles for claims adjustment. The Occupational Injury Department lives in a world of its own within the company, and has very few direct contacts beyond those with its own circle of clients. Contact with the rest of the company is extremely limited.

The EDP Department is a part of the company’s central financial-control system. The head of department has brief but regular contacts with all parts of the company, in fact more with these parts than with the personnel of parallel departments in central finance.

The primary reason why collaboration between the EDP official and the occupational-injury claims adjuster arose is that the EDP Department received instructions from management to so design its rationalization activities that insurance officials in the business units were able to increase their productivity, and thereby provide scope to accommodate a wider circle of clients (in part by offering new kinds of policies/insurance packages). The occupational-injury claims adjuster reacts with great hesitation to the EDP official’s proposal when the latter indicates management’s motive. The adjuster wants to achieve his own goal and fulfil his own function in the company, namely that of satisfying the needs of policy holders for the scrupulous administration of matters concerned with occupational injuries. He considers that this goal is incompatible with a further increase in productivity.

The interaction between the official from the EDP Department and the occupational-injury claims adjuster is complicated by factors concerned with their different locations within the organization, their different kinds of obligations and their differing “points of view” on activities in general. In other words, the two officials have to approach problems (in this case the problems of profitability) from different perspectives.

What we have discovered is the existence of conflicting goals and forces, which are built into an organizational design for activities, and which make up a platform for interaction between two officials.



Page 1 of 16

" 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)."


Part I. The Body
Part II. Health Care
Part III. Management & Policy
Part IV. Tools and Approaches
Part V. Psychosocial and Organizational Factors
Part VI. General Hazards
Part VII. The Environment
Part VIII. Accidents and Safety Management
Part IX. Chemicals
Part X. Industries Based on Biological Resources
Part XI. Industries Based on Natural Resources
Part XII. Chemical Industries
Part XIII. Manufacturing Industries
Part XIV. Textile and Apparel Industries
Part XV. Transport Industries
Part XVI. Construction
Part XVII. Services and Trade
Part XVIII. Guides