COPING WITH LOSS OF AIR SUPPLY IN CHEMICAL PROTECTIVE SUITS
BY ALAN VEASEY
As any haz-mat trainer will tell you, an important competency for hazardous materials technicians is the ability to work safely in a Level A ensemble of personal protective equipment (PPE). The definitive component of the Level A ensemble is the totally encapsulating chemical protective (TECP) suit, which completely encloses the wearer. Responders working in TECP suits typically use self-contained breathing apparatus (SCBA) for breathing air supply. TECP suits are fitted with exhaust valves that release exhaled air from inside the suit but do not allow outside air to enter. Thus, the Level A ensemble is designed to provide for the wearer a safe microenvironment within a chemically contaminated area.
PROTECTIVE EQUIPMENT HAZARDS
The protective equipment itself, however, may also pose hazards to the wearer. Haz-mat trainers have long recognized the importance of teaching responders to cope with these hazards, such as PPE-induced heat stress and impairment of vision, dexterity, and mobility.
In addition, personnel using Level A PPE may also lose their air supply while in a chemically contaminated area as a result of equipment failure or a total depletion of the air supply during an entry. Loss of air supply constitutes a major, life-threatening emergency, since it is possible to suffocate inside the suit. Opening the suit to obtain breathing air in such a situation would result in a chemical exposure that also may constitute a major threat to life or health.
At the first haz-mat response class I attended, we were instructed to resist any urge to open the TECP suit following the loss of air supply while in a contaminated area. As an alternative, we were instructed to disconnect the SCBA face piece and use air within the TECP suit as an escape air supply. This tactic is based on the belief that the “suit air” offers several minutes of escape breathing time–enough time to permit the wearer to reach a safe area. Over the intervening years since that initial haz-mat course, I have encountered the same instruction several times, both verbally and in print.1
DOUBTS BEGAN TO SURFACE
I began to experience nagging doubts about the effectiveness of suit air as an emergency air supply after reviewing information published by U.S. Department of Energy (DOE) safety and health training personnel. The DOE contends that workers in air-supplied suits can begin to experience symptoms of oxygen deficiency in as little as 40 seconds following loss of air supply.2 It is worth noting that air-supplied suits completely enclose the wearer much as TECP suits. However, breathable air is constantly fed into an air-supplied suit through an airline, and the encapsulated worker does not wear a respirator inside the suit, as with a Level A ensemble.
Given the serious nature of the chemical hazards requiring Level A protection, any feasible alternative seems preferable to opening the TECP suit in a contaminated area in response to the loss of the air supply. However, given the information from the DOE, I became concerned that the assertion that suit air can afford several minutes of escape breathing time might cause some trainees to underestimate the seriousness of this type of emergency. Moreover, I became concerned that we might unknowingly be misinforming trainees, or giving them a false impression, about the amount of escape breathing time this procedure would provide in such an emergency.
Obviously, resolving my concerns would require an estimate of the amount of escape time afforded the TECP suit wearer by breathing the air within the suit. Making such an estimate would involve several variables, such as the volume of air inside the suit, the oxygen content of that air, the difficulty of the escape route, and the level of physical fitness of the responder. To partially address my concerns, I designed a simple research project intended to provide an estimate of one of these variables–the oxygen content of air inside a TECP suit during use.
RESEARCH PROCEDURES AND EQUIPMENT
Research for this project was conducted using a typical Level A ensemble of personal protective equipment. Equipment used included commonly used limited-use TECP suits and 30-minute-rated SCBAs. To ensure gas-tight integrity, only new suits that had passed the manufacturer`s pressure test were used.
A probe or pass-through fitting was installed in place of one of the two exhaust valves built into the TECP suits. The probe was fitted with two tygon tubes, allowing air within the suit to be sampled without compromising suit integrity. The tubes were tightly capped when not in use.
Trainees and instructors using Level A PPE during field exercises at the UAB Center for Labor Education and Research (CLEAR) participated in the project. They made simulated hot zone entries and performed various hazardous-materials spill control and leak repair operations. Care was taken to avoid leakage of air under positive pressure from SCBA face pieces into the suit. Toward that end, all participants were clean-shaven and passed a negative pressure fit check as part of the equipment-donning procedure.
Oxygen concentration was measured with a multigas monitor. Participants wore the multigas monitor inside the TECP suits to record the oxygen content at one-minute intervals throughout the entries. For comparison, samples of suit air were collected through the tygon tubes at intervals of approximately two minutes, 10 minutes, and 20 minutes after the suits had been closed. These samples were pumped into sample bags for laboratory analysis to determine oxygen and carbon dioxide content. As each sample was collected, an oxygen meter was used to take a direct, simultaneous measurement of oxygen concentration.
Data collected during three Level A entries are shown in Table 1. Oxygen concentrations determined through laboratory analysis of comparison samples and simultaneous measurements with the oxygen meter were consistent with data recorded by the multigas monitor for the two-, 10-, and 20-minute intervals.
Figure 1 shows oxygen concentrations within TECP suits as a function of time following suit closure. The data plotted are average oxygen concentrations for each one-minute entry interval, as recorded by the multigas monitor. This plot indicates a rapid reduction in oxygen concentration within the TECP suits during the first few minutes following suit closure. After the rapid initial drop, oxygen concentrations continued to fall throughout the remainder of the entries but at significantly reduced rates.
You must consider several factors in assessing whether the air inside a TECP suit should offer enough escape breathing time to allow an entrant to reach a safe location following loss of air supply. This project focused on only one of those factors–oxygen content of air within TECP suits during use.
Symptoms of oxygen deficiency are well-documented to begin at an atmospheric oxygen concentration of approximately 16 percent.3,4 The effects become progressively more severe with further reduction in oxygen content5, as shown in Table 2.
As the results of this project indicate, the oxygen concentration of TECP suit air drops below 18 percent during the first few minutes after the suit has been closed. Results also indicate that up to and beyond 20 minutes following closure of a TECP suit, the air within the suit contains sufficient oxygen to support respiration without significant symptoms of oxygen deficiency. However, once the air within the suit begins to be used as an emergency air supply, the oxygen content would be rapidly reduced as a result of the 20- to 25-percent oxygen depletion associated with the respiratory process,6,7,8 significantly calling into question the amount of escape time available before the onset of symptoms of oxygen deficiency for a person using that air as an emergency supply.
A number of specific factors would determine whether a person breathing suit air would be able to reach a safe area. These factors include the following:
1. The volume of air inside the suit.
2. The amount of time elapsing between the closing of the suit and the occurrence of the loss of the air supply.
3. The length and difficulty of the escape route.
4. The individual`s level of physical fitness and emotional stability.
5. Individual variation susceptibility to the effects of oxygen deficiency.
FACTORS ARE INTERRLATED
The way in which these factors are interrelated can probably best be illustrated through a couple of hypothetical examples.
Example 1: Assume that a physically fit responder loses air supply early in a Level A entry and that the pathway to the decontamination area is short and over level terrain. In this case, the responder may well be able to breath suit air without significant symptoms of oxygen deficiency while completing the escape.
Example 2: Now, assume that a less-fit responder loses air supply late in an entry and that the escape pathway is long and difficult. The responder could experience sufficient effects of oxygen deficiency to make self-rescue impossible.
Given the potentially complex and unpredictable interactions between the factors involved, this seems a dangerous topic for generalization.
Loss of air supply in a TECP suit can constitute a major, life-threatening emergency. For this reason, hazardous materials emergency response training should include procedures for coping with it.
Responders` standard operating procedures should also address this issue. For example, monitoring entrants` closed-suit times and rigorously maintaining SCBA can prevent loss of air supply from occurring in the first place.
If a loss of air supply should occur, immediately opening the TECP suit is not a reasonable response in many hazardous-materials situations, such as those involving highly toxic or corrosive substances. However, in some instances, the hazard posed by oxygen deficiency in TECP suits may be greater than that posed by the chemicals in the environment.
Trainees in hazardous-materials programs should be informed of this hazard, and they should be taught how to recognize the symptoms of oxygen deficiency. Those who use Level A equipment must be trained in standard procedures that address the hazard of oxygen deficiency and the chemical hazards they may face when coping with the loss of air supply.
Such training could be accomplished by instructing trainees to react to this type of emergency by immediately moving toward a designated safe area while breathing air from inside the suit while remaining on guard for symptoms of oxygen deficiency. In addition, trainees could be instructed to open the suit enough to admit outside air should the effects of oxygen deficiency begin to impair their ability to complete the escape. By that time, they may have at least reached a less-contaminated–if not a clean–area. Obviously, this can be done only if TECP suits that can be opened by the wearer are used in the Level A ensembles.
Given the results of this project, the assertion that several minutes of escape breathing air should remain within a TECP suit, thus allowing the wearer to reach an area of safety should the air supply be lost, may be incorrect in some instances. Given that, it seems appropriate that haz-mat trainers reevaluate traditional instruction pertaining to dealing with the loss of air supply in a TECP suit. n
This project would not have been possible without the contributions of the following UAB personnel: Lisa C. Craft, Roderick D. Moore, Dr. R. Kent Oestenstad, and Kenneth W. Oldfield.
1. Noll, G.G.; M.S. Hildebrand; and J.G. Yvorra. Hazardous Materials, Managing the Incident. 2nd ed. (Stillwater, Okla.: Fire Protection Publications, 1995), 312.
2. “Potential Oxygen Deficiency While Wearing Air-Supplied Suits.” Safety & Health Note, U.S. Department of Energy, Issue No. 96-1, 1996.
3. Sullivan, J.B. and G.R. Krieger. Hazardous Materials Toxicology. (Baltimore: Williams and Wilkins, 1992), 292.
4. “Respirator Decision Logic,” National Institute for Occupational Safety and Health (NIOSH/DHHS Pub. No. 87-108), Washington, D.C., U.S. Government Printing Office, 1987, 21.
5. “Practices for Respiratory Protection” (Pub. #Z88.2), American National Standards Institute, Inc., New York, 1992, 22.
6. Memmler, R.L.; B.J. Cohen; and D.L. Wood. The Human Body in Health and Disease, 7th ed. (Philadelphia: J.B. Lippincott Co., 1992), 260-262.
7. Vander, A.J., J.H. Sherman; and D.S. Luciano. Human Physiology, The Mechanisms of Body Function, 2nd ed. (New York: McGraw-Hill, 1975), 296.
8. Hammer, W. Occupational Safety Management and Engineering, 3rd ed. (Englewood Cliffs, N.J.: Prentice-Hall, 1985, 395).
ALAN VEASEY is curriculum coordinator for the Workplace and Environmental Safety and Health Program operated by the Center for Labor Education and Research at the University of Alabama at Birmingham (UAB/CLEAR). He has a master of arts degree in education and a master of public health degree in occupational health and safety. UAB/CLEAR provides training for hazardous materials emergency response, hazardous waste site remediation, confined space entry and rescue, and various other worker health and safety topics. UAB/CLEAR receives financial support from the National Institute of Environmental Health Sciences (NIEHS).