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Confined Spaces

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Confined spaces are ubiquitous throughout industry as recurring sites of both fatal and nonfatal accidents. The term confined space traditionally has been used to label particular structures, such as tanks, vessels, pits, sewers, hoppers and so on. However, a definition based on description in this manner is overly restrictive and defies ready extrapolation to structures in which accidents have occurred. Potentially any structure in which people work could be or could become a confined space. Confined spaces can be very large or they can be very small. What the term actually describes is an environment in which a broad range of hazardous conditions can occur. These condition include personal confinement, as well as structural, process, mechanical, bulk or liquid material, atmospheric, physical, chemical, biological, safety and ergonomic hazards. Many of the conditions produced by these hazards are not unique to confined spaces but are exacerbated by involvement of the boundary surfaces of the confined space.

Confined spaces are considerably more hazardous than normal workspaces. Seemingly minor alterations in conditions can immediately change the status of these workspaces from innocuous to life-threatening. These conditions may be transient and subtle, and therefore are difficult to recognize and to address. Work involving confined spaces generally occurs during construction, inspection, maintenance, modification and rehabilitation. This work is nonroutine, short in duration, nonrepetitive and unpredictable (often occurring during off-shift hours or when the unit is out of service).

Confined Space Accidents

Accidents involving confined spaces differ from accidents that occur in normal workspaces. A seemingly minor error or oversight in preparation of the space, selection or maintenance of equipment or work activity can precipitate an accident. This is because the tolerance for error in these situations is smaller than for normal workplace activity.

The occupations of victims of confined space accidents span the occupational spectrum. While most are workers, as might be expected, victims also include engineering and technical people, supervisors and managers, and emergency response personnel. Safety and industrial hygiene personnel also have been involved in confined space accidents. The only data on accidents in confined spaces are available from the United States, and these cover only fatal accidents (NIOSH 1994). Worldwide, these accidents claim about 200 victims per year in industry, agriculture and the home (Reese and Mills 1986). This is at best a guess based on incomplete data, but it appears to be applicable today. About two-thirds of the accidents resulted from hazardous atmospheric conditions in the confined space. In about 70% of these the hazardous condition existed prior to entry and the start of work. Sometimes these accidents cause multiple fatalities, some of which are the result of the original incident and a subsequent attempt at rescue. The highly stressful conditions under which the rescue attempt occurs often subject the would-be rescuers to considerably greater risk than the initial victim.

The causes and outcomes of accidents involving work external to structures that confine hazardous atmospheres are similar to those occurring inside confined spaces. Explosion or fire involving a confined atmosphere caused about half of the fatal welding and cutting accidents in the United States. About 16% of these accidents involved “empty” 205 l (45 gal UK, 55 gal US) drums or containers (OSHA 1988).

Identification of Confined Spaces

A review of fatal accidents in confined spaces indicates that the best defences against unnecessary encounters are an informed and trained workforce and a programme for hazard recognition and management. Development of skills to enable supervisors and workers to recognize potentially hazardous conditions is also essential. One contributor to this programme is an accurate, up-to-date inventory of confined spaces. This includes type of space, location, characteristics, contents, hazardous conditions and so on. Confined spaces in many circumstances defy being inventoried because their number and type are constantly changing. On the other hand, confined spaces in process operations are readily identifiable, yet remain closed and inaccessible almost all of the time. Under certain conditions, a space may be considered a confined space one day and would not be considered a confined space the next.

A benefit from identifying confined spaces is the opportunity to label them. A label can enable workers to relate the term confined space to equipment and structures at their work location. The downside to the labelling process includes: (1) the label could disappear into a landscape filled with other warning labels; (2) organizations that have many confined spaces could experience great difficulty in labelling them; (3) labelling would produce little benefit in circumstances where the population of confined spaces is dynamic; and (4) reliance on labels for identification causes dependence. Confined spaces could be overlooked.

Hazard Assessment

The most complex and difficult aspect in the confined space process is hazard assessment. Hazard assessment identifies both hazardous and potentially hazardous conditions and assesses the level and acceptability of risk. The difficulty with hazard assessment occurs because many of the hazardous conditions can produce acute or traumatic injury, are difficult to recognize and assess, and often change with changing conditions. Hazard elimination or mitigation during preparation of the space for entry, therefore, is essential for minimizing the risk during work.

Hazard assessment can provide a qualitative estimate of the level of concern attached to a particular situation at a particular moment (table 1). The breadth of concern within each category ranges from minimal to some maximum. Comparison between categories is not appropriate, since the maximum level of concern can differ considerably.

Table 1. Sample form for assessment of hazardous conditions

Hazardous condition

Real or potential consequence





Hot work


Atmospheric hazards


oxygen deficiency


oxygen enrichment








Ingestion/skin contact


Physical agents




heat/cold stress


non/ionizing radiation




Personal confinement


Mechanical hazard


Process hazard


Safety hazards














visibility/light level




hot/cold surfaces


NA = not applicable. The meanings of certain terms such as toxic substance, oxygen deficiency, oxygen enrichment, mechanical hazard, and so on, require further specification according to standards that exist in a particular jurisdiction.


Each entry in table 1 can be expanded to provide detail about hazardous conditions where concern exists. Detail also can be provided to eliminate categories from further consideration where concern is non-existent.


Fundamental to the success of hazard recognition and assessment is the Qualified Person. The Qualified Person is deemed capable by experience, education and/or specialized training, of anticipating, recognizing and evaluating exposures to hazardous substances or other unsafe conditions and specifying control measures and/or protective actions. That is, the Qualified Person is expected to know what is required in the context of a particular situation involving work within a confined space.

A hazard assessment should be performed for each of the following segments in the operating cycle of the confined space (as appropriate): the undisturbed space, pre-entry preparation, pre-work inspection work activities (McManus, manuscript) and emergency response. Fatal accidents have occurred during each of these segments. The undisturbed space refers to the status quo established between closure following one entry and the start of preparation for the next. Pre-entry preparations are actions taken to render the space safe for entry and work. Pre-work inspection is the initial entry and examination of the space to ensure that it is safe for the start of work. (This practice is required in some jurisdictions.) Work activities are the individual tasks to be performed by entrants. Emergency response is the activity in the event rescue of workers is required, or other emergency occurs. Hazards that remain at the start of work activity or are generated by it dictate the nature of possible accidents for which emergency preparedness and response are required.

Performing the hazard assessment for each segment is essential because the focus changes continuously. For example, the level of concern about a specific condition could disappear following pre-entry preparation; however, the condition could reappear or a new one could develop as a result of an activity which occurs either inside or outside the confined space. For this reason, assessing a level of concern to a hazardous condition for all time based only on an appraisal of pre-opening or even opening conditions would be inappropriate.

Instrumental and other monitoring methods are used for determining the status of some of the physical, chemical and biological agents present in and around the confined space. Monitoring could be required prior to entry, during entry or during work activity. Lockout/tagout and other procedural techniques are used to deactivate energy sources. Isolation using blanks, plugs and caps, and double block and bleed or other valve configurations prevents entry of substances through piping. Ventilation, using fans and eductors, is often necessary to provide a safe environment for working both with and without approved respiratory protection. Assessment and control of other conditions relies on the judgement of the Qualified Person.

The last part of the process is the critical one. The Qualified Person must decide whether the risks associated with entry and work are acceptable. Safety can best be assured through control. If hazardous and potentially hazardous conditions can be controlled, the decision is not difficult to make. The less the level of perceived control, the greater the need for contingencies. The only other alternative is to prohibit the entry.

Entry Control

The traditional methods for managing on-site confined space activity are the entry permit and the on-site Qualified Person. Clear lines of authority, responsibility and accountability between the Qualified Person and entrants, standby personnel, emergency responders and on-site management are required under either system.

The function of an entry document is to inform and to document. Table 2 (below) provides a formal basis for performing the hazard assessment and documenting the results. When edited to include only information relevant to a particular circumstance, this becomes the basis for the entry permit or entry certificate. The entry permit is most effective as a summary that documents actions performed and indicates by exception, the need for further precautionary measures. The entry permit should be issued by a Qualified Person who also has the authority to cancel the permit should conditions change. The issuer of the permit should be independent of the supervisory hierarchy in order to avoid potential pressure to speed the performance of work. The permit specifies procedures to be followed as well as conditions under which entry and work can proceed, and records test results and other information. The signed permit is posted at the entry or portal to the space or as specified by the company or regulatory authority. It remains posted until it is either cancelled, replaced by a new permit or the work is completed. The entry permit becomes a record upon completion of the work and must be retained for recordkeeping according to requirements of the regulatory authority.

The permit system works best where hazardous conditions are known from previous experience and control measures have been tried and proven effective. The permit system enables expert resources to be apportioned in an efficient manner. The limitations of the permit arise where previously unrecognized hazards are present. If the Qualified Person is not readily available, these can remain unaddressed.

The entry certificate provides an alternative mechanism for entry control. This requires an onsite Qualified Person who provides hands-on expertise in the recognition, assessment and evaluation, and control of hazards. An added advantage is the ability to respond to concerns on short notice and to address unanticipated hazards. Some jurisdictions require the Qualified Person to perform a personal visual inspection of the space prior to the start of work. Following evaluation of the space and implementation of control measures, the Qualified Person issues a certificate describing the status of the space and conditions under which the work can proceed (NFPA 1993). This approach is ideally suited to operations that have numerous confined spaces or where conditions or the configuration of spaces can undergo rapid change.



Table 2. A sample entry permit









Date:                                                 Assessor:

Duration:                                           Qualification:







Atmospheric Hazards

Oxygen Deficiency                       Yes  No  Controlled

Concentration:                              (Acceptable minimum:                             %)

Oxygen Enrichment                     Yes  No  Controlled

Concentration:                              (Acceptable maximum:                            %)

Chemical                                      Yes  No  Controlled

Substance Concentration            (Acceptable standard:                                )

Biological                                      Yes  No  Controlled

Substance Concentration            (Acceptable standard:                                )

Fire/Explosion                              Yes  No  Controlled

Substance Concentration            (Acceptable maximum:                     % LFL)

Ingestion/Skin Contact Hazard   Yes  No  Controlled

Physical Agents

Noise/Vibration                            Yes  No  Controlled

Level:                                          (Acceptable maximum:                        dBA)

Heat/Cold Stress                         Yes  No  Controlled

Temperature:                              (Acceptable range:                                     )

Non/Ionizing Radiation                 Yes  No  Controlled

Type Level                                   (Acceptable maximum:                              )

Laser                                            Yes  No  Controlled

Type Level                                    (Acceptable maximum:                              )

Personal Confinement
(Refer to corrective action.)         Yes  No  Controlled

Mechanical Hazard
(Refer to procedure.)                   Yes  No  Controlled

Process Hazard
(Refer to procedure.)                   Yes  No  Controlled



Safety Hazards

Structural Hazard
(Refer to corrective action.)          Yes  No  Controlled

(Refer to corrective action.)          Yes  No  Controlled

(Refer to corrective action.)          Yes  No  Controlled

(Refer to procedure.)                    Yes  No  Controlled

(Refer to corrective action.)          Yes  No  Controlled

(Refer to corrective action.)          Yes  No  Controlled

Visibility/light level                          Yes  No  Controlled

Level:                                            (Acceptable range:                                  lux)

(Refer to corrective action.)           Yes  No  Controlled

Hot/Cold Surfaces
(Refer to corrective action.)           Yes  No  Controlled

For entries in highlighted boxes, Yes or Controlled, provide additional detail and refer to protective measures. For hazards for which tests can be made, refer to testing  requirements. Provide date of most recent calibration. Acceptable maximum, minimum, range or standard depends on the jurisdiction.

4. Work Procedure


Hot Work
(Refer to protective measure.)            Yes  No  Controlled

Atmospheric Hazard

Oxygen Deficiency 

(Refer to requirement for additional testing. Record results. 
Refer to requirement for protective measures.)

Concentration:                                    Yes  No  Controlled

                                                            (Acceptable minimum:                             %)

Oxygen Enrichment                           

(Refer to requirement for additional testing. Record results.
Refer to requirement for protective measures.)                                    

Concentration:                                   Yes  No  Controlled

                                                           (Acceptable maximum:                             %)


(Refer to requirement for additional testing. Record results. Refer to requirement
for protective measures.)
Substance Concentration                  Yes  No  Controlled

                                                           (Acceptable standard:                                 )


(Refer to requirement for additional testing. Record results. Refer to requirement
for protective measures.)
Substance Concentration                 Yes  No  Controlled

                                                          (Acceptable standard:                                 )


(Refer to requirement for additional testing. Record results. Refer to requirement
for protective measures.)
Substance Concentration                 Yes  No  Controlled

                                                          (Acceptable standard:                                 )

Ingestion/Skin Contact Hazard         Yes  No  Controlled

(Refer to requirement for protective measures.)                      



Physical Agents


(Refer to requirement for protective measures. Refer to requirement for
additional testing. Record results.)
Level:                                                Yes  No  Controlled

                                                         (Acceptable maximum:                         dBA)

Heat/Cold Stress           

(Refer to requirement for protective measures. Refer to requirement for
additional testing. Record results.)
Temperature:                                    Yes  No  Controlled

                                                          (Acceptable range:                                      )

Non/Ionizing Radiation            

(Refer to requirement for protective measures. Refer to requirement for
additional testing. Record results.)
Type Level                                        Yes  No  Controlled

                                                          (Acceptable maximum:                               )

(Refer to requirement for protective measures.)            Yes  No  Controlled

Mechanical Hazard
(Refer to requirement for protective measures.)            Yes  No  Controlled

Process Hazard

(Refer to requirement for protective measures.)           Yes  No  Controlled

Safety Hazards

Structural Hazard
(Refer to requirement for protective measures.)            Yes  No  Controlled

(Refer to requirement for protective measures.)           Yes  No  Controlled

(Refer to requirement for protective measures.)            Yes  No  Controlled

(Refer to requirement for protective measures.)           Yes  No  Controlled

(Refer to requirement for protective measures.)            Yes  No  Controlled

(Refer to requirement for protective measures.)            Yes  No  Controlled

Visibility/light level
(Refer to requirement for protective measures.)            Yes  No  Controlled

(Refer to requirement for protective measures.)             Yes  No  Controlled

Hot/Cold Surfaces
(Refer to requirement for protective measures.)            Yes  No  Controlled

For entries in highlighted boxes, Yes or Possible, provide additional detail and refer to protective
measures. For hazards for which tests can be made, refer to testing requirements. Provide date of
most recent calibration.

Protective Measures

Personal protective equipment (specify)

Communications equipment and procedure (specify)

Alarm systems (specify)

Rescue Equipment (specify)

Ventilation (specify)

Lighting (specify)

Other (specify)

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Testing Requirements

Specify testing requirements and frequency


Entry Supervisor

Originating Supervisor

Authorized Entrants

Testing Personnel




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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
Accident Prevention
Audits, Inspections and Investigations
Safety Applications
Safety Policy and Leadership
Safety Programs
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

Safety Applications References

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