Oxygen Depletion in Level A Hazmat Suits


What seems to be the greatest danger to fire and rescue personnel at the scene of a hazmat incident? Is it the unknown substance oozing from a tractor trailer? Is it the plume of smoke from a burning tanker? Is it contamination of numerous victims? Thankfully, today hazmat teams are equipped with state-of-the-art tools and technology to deal with such situations, greatly reducing the risk posed to hazmat technicians. The symbolic Level A hazmat suit has long been the standard for protection against unknown agents. Many consider the Level A suit to be the best protection available, but how safe is it? Is the environment inside the suit that much safer than outside? Ironically enough, hazardous materials might not be the biggest danger to a hazmat technician. Many hazmat technicians have wondered what would happen if they ran out of air or if they had a self-contained breathing apparatus (SCBA) malfunction. Would they have enough time to make it to a decontamination station and get out of the suit before oxygen drops to dangerous levels? This study was designed to examine the worst-case scenario.


As many know, Level A suits provide full, vapor-tight, encapsulating protection. Typically, in emergency hazmat situations, the wearer of the suit uses an SCBA to provide a fresh supply of air. When a person is using an SCBA inside a vapor-tight Level A hazmat suit, the environment within the suit changes drastically. Compressed atmospheric air is inhaled from the SCBA air tank. Within the individual’s lungs, oxygen is exchanged for carbon dioxide. When the person exhales, the carbon dioxide is exhaled into the suit. On average, the gases humans exhale are roughly four to five percent carbon dioxide and four to five percent less oxygen than was inhaled.1 As exhaled air accumulates in the suit, the concentration of oxygen within the suit decreases while the concentration of carbon dioxide increases.

This accumulation of exhaled air in the suit leads to a very hot and humid environment. The environment is so extreme that the standard operating procedures for Harrisonburg, Virginia, do not allow hazmat personnel to work in a Level A suit for more than 20 minutes at a time. At the end of 20 minutes, the individual must then leave the scene and proceed to decontamination facilities before removing the suit.

Under normal atmospheric conditions, the concentration of oxygen in the air is 20.9 percent.2 The National Institute for Occupational Safety and Health (NIOSH) defines an oxygen-deficient atmosphere as any atmosphere containing oxygen at a concentration of 19.5 percent or lower at sea level.3 An oxygen concentration lower than this value can pose serious health risks. At 16-percent oxygen concentration, individuals exhibit increased heart and breathing rates along with some impairment in judgment and coordination. At 14-percent concentration, fatigue and emotional upset can appear. Nausea and vomiting may occur at an oxygen concentration of 12 percent along with a significant decrease in judgment, coordination, and respiration. When the oxygen concentration dips below 10 percent, individuals can lose consciousness. (2)

This study focuses on the concentration of oxygen within the suit over a period of time of normal use. The air quality within the suit is especially important in the case of SCBA failure. In this case, the person in the suit would have to remove his mask and breathe the air within the suit until reaching a safe location where the suit can be removed. The Virginia State Department of Emergency Management states that a person would have up to five minutes of breathable air in the suit if an SCBA fails.

We studied the concentration of oxygen inside the suit to determine if this claim is true. Parameters measured included oxygen concentration within the suit over a 20-minute period while on air and then for a five-minute period off air. Participants’ oxygen saturation and heart rate were monitored continuously. Participants’ blood pressure was taken before and after participation in the study. All possible precautions were taken to ensure the participants’ safety. Participants were male firefighters who were also hazmat technicians and had extensive experience working in Level A hazmat suits. The Harrisonburg (VA) Rescue Squad (HRS) provided equipment to use for testing, and two emergency medical technicians (EMTs) from the HRS were present throughout the testing.


Pretest Health Evaluation

To begin, test subjects’ age, height, and weight were recorded, and their medical history was evaluated to determine their ability to participate in the study. Each test subject’s heart rate, blood pressure, and oxygen saturation were assessed to establish baseline vital signs. Virginia-certified EMTs did all the assessments. If the test subjects’ vital signs were within normal limits, they were cleared to participate in the study.

Entry into Level A Hazmat Suit

Individual test subjects were fitted with an SCBA and with the appropriate size Level A hazmat suit recommended by the manufacturer. Prior to zipping the suit closed, the test subject had a pediatric pulse oximeter adapter taped to the ring finger of the left hand, the wire threaded through a hole in the glove, and the hole in the glove was sealed using electrical tape. A gas meter was set to record oxygen concentrations and secured on the shoulder strap of the SCBA so that it could be easily read through the window of the hazmat suit. The hazmat suits were then zipped closed, and the initial time, concentration of oxygen within the suit, heart rate, and oxygen saturation of the participant were recorded.


Test subjects were led through a course to simulate working in a hazmat situation. Initially, test subjects walked through various patterns around tables and obstacles. They were then instructed to pick up and carry an oxygen tank. To test mental acuity, participants had to put together large wooden puzzles, to simulate putting together tools during a hazmat situation with the thick hazmat Level A suit gloves. In addition, test subjects had to wipe down the surface of the window of the hazmat suit to remove condensation so that the gas meter could be easily read.

Every 60 seconds, the oxygen concentration within the suit and the test subject’s pulse and oxygen saturation level were recorded for 20 minutes. After 20 minutes of activity, test subjects removed the air supply of their SCBA and continued to walk in a pattern around tables in a room with a person on each side of the individual to supervise and monitor him. During this time while participants were off air, the oxygen concentration within the suit, the test subject’s pulse, and oxygen saturation level were recorded every 30 seconds. Test subjects were allowed to continue for a maximum of five minutes off air or until the test subject wished to stop. Test subjects were allowed to stop at any point during the study.

Post-Testing Health Evaluation

After being off air for several minutes, test subjects were assisted out of the suit, and a full medical evaluation was performed. State-certified EMTs did all the assessments. The test subjects’ heart rate, blood pressure, and oxygen saturation level were assessed. If the test subjects’ vital signs were within normal limits, they were cleared to leave the study. No test subjects had any negative physiological responses to being involved in the study; no interventions were needed.


Table 1 shows the oxygen concentration in the suit for the first 20 minutes of testing while participants were on air. The initial concentration of oxygen inside the suit was the same as atmospheric conditions at an average of 20.6 percent. Given the elevation above sea level of our testing facility, this was within normal limits. Oxygen concentrations within the suit dropped 2.1 percent within the first two minutes of activity while on air. The rate of oxygen depletion then began to slow and started to plateau around minute 14, with a concentration of 16.5 percent, as seen in Figure 1. After 20 minutes on air, the average oxygen concentration within the suit was 16.3 percent. This yielded an overall drop in oxygen concentration of 4.3 percent in 20 minutes. This percentage became the baseline oxygen concentration for the next five minutes off air.

Figure 1. Average Oxygen Concentration (%) Within the Level A Hazmat Suit Over 20 Minutes While Participants Were on Air

Once participants went off air, the decrease in oxygen concentration followed a linear pattern, as seen in Figure 2. The average starting oxygen concentration was 16.3 percent, and the average ending oxygen concentration was 12.8 percent, as tabulated in Table 2. This resulted in a decrease in oxygen concentration of 3.5 percent in five minutes. Based on the linear regression of the data, oxygen concentration decreased at a rate of 0.7 percent per minute.

Figure 2. Average Oxygen Concentration (%) Within the Level A Hazmat Suit While Participants Were Off Air After 20 Minutes of Activity on Air

Each participant’s oxygen saturation level remained fairly constant while on air for the first 20 minutes of the trial. This was expected because each breath the participant took contained the same concentration of oxygen. Once participants removed their air supply, a decrease in oxygen saturation was observed, as seen in Figure 3. On average, each participant’s oxygen saturation was 96 percent after 20 minutes on air. After five minutes off air, the average oxygen saturation was 91 percent, as documented in Table 3. The data did not follow a linear pattern but did show an obvious decline in oxygen saturation over the five-minute off-air time period.

Figure 3. Average Oxygen Saturation (%) for All Participants While Off Air After 20 Minutes of Activity While on Air

Variations in data can be explained by a number of variables. The plateau seen in the oxygen concentration over 20 minutes while on air can be explained by the composition of exhaled air. As mentioned, gases exhaled are roughly four to five percent carbon dioxide and four to five percent less oxygen than was inhaled. The overall drop in oxygen concentration observed during the 20 minutes was 4.3 percent, and thus a plateau of 16.3 percent oxygen was feasible (see Table 1). This result indicates that at the end of 20 minutes, the concentration of air within the suit was the same as the concentration in each exhaled breath while participants were on air.

During the five minutes off air, participants complained that their masks fogged up and they were unable to clean them off to improve their vision. Therefore, participants were not able to walk around and experienced difficulty completing the puzzles. It was observed that there was no correlation between the difficulty of the puzzles and whether the participant was on air or off air. During the five minutes off air, participants did not exhibit any signs of decreased mental acuity. While off air, participants described the environment as very hot and humid. Many reported that they felt as if they were at a high altitude because of lower oxygen levels. Two participants also reported having headaches. Participants did state that while off air, they had to focus more on the current tasks in an effort to alleviate the anxiety of being in the oxygen-deficient environment. On exiting the suit, participants were soaked in sweat, and there was a copious amount of condensation on the SCBA and the interior of the suit.

It is important to note that the testing situation was well controlled and that tests were conducted under optimal conditions. Participants were not under significant physical or emotional stress. They were aware of their oxygen saturation, heart rate, and oxygen concentration within the suit. In a real hazmat situation, participants would have been under far more stress, thus increasing their respiratory rate and the physiological impact. They would be unaware of the gas concentrations of the suit and their physiological status. In case of an SCBA failure, the lack of this information could increase anxiety and fear, which could lead to panic. Also, if the participants were in a hazmat area in which hazardous materials were present, they would have to proceed to decontamination first before getting out of the suit. That process takes several minutes and highly depends on the setup of the scene. If all of this had to occur while off air because of an SCBA failure, a more drastic drop in oxygen concentration would be expected. The testing process used in this study required minimal physical exertion and thus did not simulate a real hazmat scene. A more strenuous test would yield more realistic results. 

After only a minute inside a Level A hazmat suit while using an SCBA, oxygen concentrations drop below safe levels to 19.2 percent. The concentration of oxygen continues to drop until it reaches the same concentration as that contained in exhaled air at 16.3 percent. After 20 minutes on air, oxygen levels are high enough within the suit for a person to maintain consciousness with a possibility of impaired judgment, but levels quickly deplete. When exposed to this oxygen-deficient environment for five minutes, a person’s oxygen saturations decrease to near hypoxic levels. If after 20 minutes on air an SCBA malfunction occurred, it would be possible to survive for an additional five minutes but likely would be dangerous. If strenuous activity were required during the five minutes, oxygen concentrations would drop to levels that could cause loss of consciousness and potentially death. Given the results of this study, all hazmat technicians should be warned of the dangers associated with oxygen deprivation and the environment within the Level A hazmat suit. Also, special care should be taken to ensure all SCBA equipment is maintained and in proper working order.

This study was conducted in conjunction with the Faculty of the Undergraduate College of Integrated Science and Technology, James Madison University, Virginia; the Harrisonburg (VA) Fire Department; and the HRS.


1. Parks, M. “Breath-Holding and its Break Point,” Experimental Physiology . 2006.

2. WorkSafe BC. No Warning with Deadly Lack of Oxygen in Air. WorkSafe Bulletin. 2006.

3. NIOSH Respirator Selection Logic 2004. National Institute for Occupational Safety and Health Centers, Centers for Disease Control and Prevention, October 2004.

TIFFANY JENKINS graduated from James Madison University with a bachelor’s degree from the College of Integrated Science and Technology with a concentration in biotechnology. For 41⁄2 years, she volunteered as an EMT with the Harrisonburg (VA) Rescue Squad until relocating to North Carolina. She is pursuing a master’s degree in physician assistant studies at Wake Forest University School of Medicine.

JOSH SMITH graduated from James Madison University with a bachelor’s degree from the College of Integrated Science and Technology with a concentration in biotechnology. For the past three years, he has been involved as an EMT with the Harrisonburg (VA) Rescue Squad. He serves on the Board of Directors as well as a volunteer responding to emergency calls.

BEN ZIMMERMAN is a 14-year veteran of the fire service and a lieutenant in the Harrisonburg Fire Department, where he is also the hazmat training coordinator. He is a Virginia Department of Emergency Management-certified hazmat specialist.

RON RAAB is a professor in the College of Integrated Science and Technology at James Madison University, where he teaches courses in biotechnology and awareness and understanding hazardous materials as well as weapons of mass destruction. He serves as a regional hazmat responder and educator for the City of Harrisonburg and Rockingham County Fire Departments in Virginia. In addition, he is a volunteer firefighter.

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