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Regulations (Preambles to Final Rules) - Table of Contents
• Record Type: Permit-Required Confined Spaces
• Section: 2
• Title: Section 2 - II. Hazards

II. Hazards

OSHA has determined, based upon the information presented in this section and upon the complete record developed as a result of this rulemaking, that working in permit-required confined spaces involves significant risks for employees and that this standard is necessary to alleviate or control such risks.

Incident Data and Confined Space Hazards Analysis.

The 1979 NIOSH Criteria document, "Working in Confined Spaces", cites a study by the Safety Sciences Division of WSA, Inc., San Diego, California, which was titled "Search of Fatality and Injury Records for Cases Related to Confined Spaces". The Safety Sciences study reviewed approximately 20,000 reports covering industrial accidents nationally for the period 1974-1977. Even with this limited sample, 276 confined space accidents which resulted in 234 deaths and 193 injuries were identified. Safety Sciences conducted its study to determine if regulatory action was needed to control confined space hazards, not to identify the exact causes of death and injury. OSHA, in turn, has been unable to connect the 234 fatalities and 193 injuries to specific industry segments or work activities.

More recently, OSHA examined its records of accident investigations for fatal confined space incidents. In particular, OSHA sought to identify the specific hazards and work activities involved. OSHA concluded during this review that, where multiple deaths occurred, the majority of the victims in each event died trying to rescue the original entrant from a confined space. This determination is consistent with the finding by NIOSH in its 1986 "Alert" that "rescuers" accounted for more than 60 percent of confined space fatalities. This evidence indicates that untrained or poorly trained rescuers constitute an especially important "group at risk." This group is protected from permit space hazards under the terms of this final rule.

OSHA has also gathered incident data from a number of other sources, such as the Fatal Accidents Circumstances and Epidemiology (FACE) reports produced by NIOSH and reports produced by the states. That information has been very useful to OSHA, even though in some cases there was not enough detail for OSHA to evaluate the circumstances of the incidents.

The OSHA-investigated cases which OSHA analyzed to determine the cause of death in confined spaces have been compiled in four reports prepared by OSHA's Office of Statistical Studies and Analyses. These are: "Selected Occupational Fatalities Related to Fire and/or Explosion in Confined Work Spaces as Found in Reports of OSHA Fatality/Catastrophe Investigations" (Ex. 13-10), "Selected Occupational Fatalities Related to Lockout/Tagout Problems as Found in Reports of OSHA Fatality/Catastrophe Investigations" (Ex. 13-11), "Selected Occupational Fatalities Related to Grain Handling as Found in Reports of OSHA Fatality/Catastrophe Investigations" (Ex. 13-12), and "Selected Occupational Fatalities Related to Toxic and Asphyxiating Atmospheres in Confined Work Spaces As Found in Reports of OSHA Fatality/Catastrophe Investigations" (Ex. 13-15).

These four reports focused on fatalities because OSHA found that the reporting of injuries from permit space incidents was frequently incomplete. OSHA observes that injuries are most likely to be reported when they occur as part of an incident where fatalities do occur. The Agency anticipates that this rulemaking will lead to improved data collection regarding injuries because employers and employees are being clearly alerted to OSHA's concern about permit space hazards.

OSHA analyzed the studies to determine the underlying causes of the conditions which existed when confined space related accidents occurred. From this information, OSHA has developed measures that would have prevented virtually all of the accidents in the studies and has used those measures as the basis for both the proposed standard and the final rule. OSHA notes that many of the reports did not fully document the circumstances of the accidents covered. The Agency has determined, however, that the available accident data, despite its limitations, provides the necessary basis for characterizing permit space hazards and for requiring protective measures. OSHA has continued to collect accident data during the course of this rulemaking.

OSHA has determined that a variety of confined space hazards have caused deaths and injuries. The following discussion describes the hazards identified by OSHA. Where the Agency has obtained incident data subsequent to the publication of the NPRM, the circumstances of some of those incidents are summarized as "examples". The discussion also references the portions of the NPRM where pertinent incidents were described.

1. Atmospheric Hazards.

OSHA's review of accident data indicates that most confined space deaths and injuries are caused by atmospheric hazards. OSHA has classified those hazards into three categories: toxic; asphyxiating; and flammable or explosive atmospheres, in order to account for their differing effects.

Some chemical substances present multiple atmospheric hazards, depending on their concentration. Methane, for example, is an odorless substance that is nontoxic and is harmless at some concentrations. Methane, however, can displace all or part of the atmosphere in a confined space(1); and the hazards presented by such displacement can vary greatly, depending on the degree of displacement. With only 10 percent displacement, methane produces an atmosphere which, while adequate for respiration, can explode violently. By contrast, with 90 percent displacement, methane will not burn or explode, but it will asphyxiate an unprotected worker within about 5 minutes.


Footnote(1) Methane is lighter than air when both are at the same temperature (the normal case), and the configuration of some confined spaces can trap accumulating methane at "ceiling"level. On the other hand, in the unlikely event that liquified methane is released into the atmosphere of a confined space, the methane released would be heavier than air and would displace the air from the "ground" level up.

OSHA is concerned that employees may be exposed to atmospheric hazards because the employer has not properly evaluated the work operations or the conditions within the permit space. Problems can arise, for example, where an employer has not selected the necessary atmospheric test instruments or has not ensured their proper use. Problems have arisen because most of the instruments used to test the flammability of a permit space atmosphere do not identify oxygen deficient atmospheres. In fact, because some of these instruments rely on the presence of oxygen, their readings can be inaccurate in oxygen-depleted atmospheres.

For example, instruments of the hot-platinum-filament type are designed to measure flammable gases and vapors in air. They depend on oxidation for their operation, and normal quantities of oxygen in the air are necessary for their correct operation. Any reduction in oxidation caused by lack of oxygen will result in a lower flammability reading. Such test instruments would indicate the absence of an explosion hazard simply because the atmosphere did not contain sufficient oxygen for combustion but would not indicate the oxygen deficiency that posed an asphyxiation risk.

On the other hand, a test performed only to determine the oxygen level might indicate that conditions are acceptable for entry without respiratory protection, despite the presence of 10 percent methane, an explosive level, in the atmosphere. Therefore, in the final rule, OSHA is requiring that employers test and monitor their entry spaces with instruments which will detect all aspects of hazardous atmospheres that may be encountered in the spaces.

OSHA presents the following examples regarding atmospheric hazards to illustrate how a relatively uncomplicated series of events can lead to workplace deaths and injuries. In each case, OSHA believes that death and injury would have been prevented if the procedures and safeguards required in this rule had been used. OSHA notes that the hazards confronted could only have been controlled effectively through the use of mechanical ventilation. OSHA recognizes that many confined space workplaces present situations which are more complex than those described in the following discussion.

a. Fatalities in asphyxiating atmospheres. In its analysis of these confined space incidents, OSHA uses the term "asphyxiating atmosphere" when referring to an atmosphere which contains less than 19.5 percent oxygen. Oxygen levels under 19.5 percent are inadequate for an entrant's respiratory needs when performing physical work, even if the space contains no toxic materials.

There are many potential causes of asphyxiating atmospheres. For example, the oxygen in a space may have been absorbed by materials, such as activated charcoal, or consumed by chemical reaction, such as the rusting of a vessel or container. In another situation, the original atmosphere in the space may intentionally have been wholly or partly inerted using such gases as helium, nitrogen, argon, or carbon dioxide. Victims of asphyxiation often are unaware of their predicament until they are incapable of saving themselves or even calling for help.

Three incidents involving fatalities in asphyxiating atmospheres were discussed in the preamble of the NPRM (54 FR 24083). In addition, OSHA has received information during the rulemaking (Ex. 14-159) that further documents the hazards of exposure to asphyxiating atmospheres in permit-required confined spaces.

Example #1. A worker at a Texas steel mill was assigned the task of clearing a blockage at the No. 2 degasser vessel dust collector. He entered the vessel through an access manhole and proceeded to clear the obstruction. A coworker, assigned to assist, left the area to locate an electrical receptacle. About 10 or 15 minutes later, the coworker returned and found the worker who had entered the vessel unconscious. The coworker was able to remove the unconscious man and called for assistance. Unfortunately, the worker died. An oxygen test showed a level of 10% oxygen in the vessel. (The coworker was not injured.) Example #2. A steel worker was asphyxiated when he entered a tank in the reagent storage building. There were no witnesses to the incident, but, since the tank had been used for the transport of nitrogen, it was assumed that the atmosphere within the tank was oxygen deficient.

b. Fatalities in toxic atmospheres. The term "toxic atmospheres" refers to atmospheres containing gases, vapors or fumes known to have poisonous physiological effects. The toxic effect is independent of the oxygen concentration. The most commonly encountered toxic gases are carbon monoxide and hydrogen sulfide.

Some toxic atmospheres may have severe harmful effects which may not manifest until years after exposure, while others may kill quickly. Some can produce both immediate and delayed effects. For example, while carbon disulfide at low concentrations may exhibit no immediate sign of exposure, it can cause permanent and cumulative brain damage as a result of repeated "harmless" exposures. At higher concentrations, it can kill quickly.

Two incidents involving fatalities in toxic atmospheres were discussed in the preamble of the NPRM (54 FR 24083, 24084). In addition, OSHA has received information during the rulemaking (Ex. 14-63, 14-159) that further documents the hazards of exposure to toxic atmospheres in permit-required confined spaces.

Example #1. A worker in Maryland entered a 6500 gallon tank trailer to finish cleaning the inside. He had with him a bucket containing about a gallon of a cleaning solvent (identified in the accident abstract only as "Niagara Trex 1900 Presol"). In only five to seven minutes the employee passed out and fell to the tank bottom. There was no ventilation, respirator or safety harness with lifeline provided. The outside "standby man" only checked the employee periodically (every three to five minutes). When the outside man discovered the unconscious employee, he attempted a rescue (without benefit of any protective equipment for himself) but was unsuccessful. He left the tank and called emergency personnel. The unconscious employee was rescued by emergency personnel and immediately transported to a hospital, where he was declared dead.

Example #2. An employee of a zinc refinery was working in a zinc dust condenser when he collapsed. Another employee donned a self-contained breathing apparatus (SCBA) and attempted to enter the condenser to rescue the downed employee. He was not able to fit through the portal wearing the SCBA, so he removed it, handed it to another employee and then entered the condenser. He planned to have the other employee hand the SCBA to him through the portal, re-don it and then continue with the rescue. He collapsed and fell into the condenser before he could re-don the SCBA. The first employee was declared dead at the scene; the would-be rescuer died two days later. The toxic air contaminant was later determined to be carbon monoxide.

c. Fatalities due to flammable or explosive atmospheres. OSHA considers an atmosphere to pose a serious fire or explosion hazard if a flammable gas or vapor is present at a concentration greater than 10 percent of its lower flammable limit or if a combustible dust is present at a concentration greater than or equal to its lower flammable limit. (See the definition of "hazardous atmosphere" in section 1910.146(b) and the discussion of the definition of "hazardous atmosphere", which appears in Section III, Summary and Explanation of the Standard, later in this preamble.) This category of hazardous atmospheres includes atmospheres containing gases such as methane or acetylene; vapors of solvents or fuel such as carbon disulfide, gasoline, kerosene, or toluene; or combustible dusts, such as coal or grain dusts.

An incident involving five fatalities in flammable or explosive atmospheres was discussed in the preamble of the NPRM (54 FR 24084). In addition, OSHA has received information during the rulemaking (Ex. 14-145) that further documents the hazards of exposures to flammable or explosive atmospheres in permit-required confined spaces.

Example. An employee of a trailer service company entered a 8500 gallon cargo tank to weld a leak on the interior wall of the tanker. Despite the presence of strong fumes of lacquer thinner (the material previously carried in the tanker) the welder decided to proceed with the repairs even though the written company safety policy required the use of an explosion meter at that point. When he began welding, an explosion occurred. The employee was removed from the tank and taken to a nearby hospital, where he was declared dead by the attending physician.

2. Other Hazards.

Fatalities from engulfment. "Engulfment" refers to situations where a confined space entrant is trapped or enveloped, usually by dry bulk materials. The engulfed entrant is in danger of asphyxiation, either through filling of the victim's respiratory system as the engulfing material is inhaled, or through compression of the torso by the engulfing material. In some cases, the engulfing materials may be so hot or corrosive that the victims sustain fatal chemical or thermal burns, but are never buried to the extent that they cannot breathe.

Two incidents involving fatalities from engulfment were discussed in the preamble of the NPRM (54 FR 24084). In addition, OSHA has received information during the rulemaking (Ex. 14-159) that further documents the hazards of engulfment in permit-required confined spaces.

Example. Two Ohio foundry employees entered a sand bin to clear a jam. While they were working, sand which had adhered to the sides of the bin began to break loose and fall on them. One employee quickly became buried up to his chest, just below his armpits. The other employee left the bin to obtain a rope, intending to use it to pull his coworker out of the sand. He returned to the bin, tied the rope around the partially buried employee and tried to pull him free. He was unsuccessful. During his attempted rescue, additional sand fell, completely covering and suffocating the employee who had been only partially buried.

Fatalities due to mechanical hazards. OSHA has determined that accidents have resulted in confined spaces when employers failed to isolate equipment within the space from sources of mechanical or electric energy or when the equipment was improperly guarded. In each case reviewed, death resulted from mechanical force injury, such as the crushing of the victim. OSHA has determined from its review of accidents involving mechanical hazards that the correct preventive action would have been to secure the machinery or equipment so that it would not have been inadvertently activated while employees were exposed to it. This procedure is commonly called "lockout".

When servicing or maintenance work is being performed on machinery or equipment located in a confined space, OSHA's standard on the control of hazardous energy sources (lockout/tagout), section 1910.147, also applies. When work inside a permit space does not involve servicing or maintenance of machinery or equipment in the permit space, OSHA's standards on machine guarding, in Subpart O of Part 1910, require the equipment to be guarded to protect employees from any mechanical hazards posed by the machine. In any event, this final rule on permit-required confined spaces, section 1910.146, requires employers to evaluate any mechanical hazards found in permit spaces and to take all steps necessary to protect entrants.

An incident involving a fatality due to a mechanical hazard is discussed in the preamble of the NPRM (54 FR 24085).

Fatalities due to untrained rescuers. As noted previously, OSHA has determined that a high percentage of confined space accident victims have been untrained rescuers. Indeed, in some cases, the unsuccessful rescuers have died while the initial entrants have recovered. The likelihood that good intentions and poor preparation will lead to tragedy has led the Agency to establish criteria for rescue which will protect co-workers or volunteers from accidental injury or death.

Two incidents involving untrained rescuers were discussed in the preamble to the NPRM (54 FR 24085). In addition, OSHA has obtained information (Ex. 14-145) during the rulemaking that further documents the hazards of allowing untrained rescuers to enter permit spaces.

Example. A maintenance worker entered a sewer manhole to repair a pipe and collapsed at the bottom. A coworker, who had been observing the initial entrant, entered the manhole, lost consciousness, and fell to the bottom. A supervisor looked in the manhole, saw the would-be rescuer, and entered to attempt rescue. The supervisor became dizzy, climbed from the manhole, and passed out. When he regained consciousness, the supervisor summoned rescue and emergency services. Both the initial entrant and the first would-be rescuer died of hydrogen sulfide poisoning.

Conclusion. OSHA has determined, based upon the information presented in this section of the preamble and upon the complete record developed as a result of this rulemaking, that working in permit-required confined spaces involves significant risks for employees and that this standard is necessary to alleviate or control such risks. This conclusion is further supported in the next section of this preamble, Summary and Explanation of the Standard.

[58 FR 4462, Jan. 14, 1993; 59 FR 55208, Nov. 4, 1994]

Regulations (Preambles to Final Rules) - Table of Contents

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