By Vance Bennett
If you’re wearing a Level-A PPE and your self-contained breathing apparatus fails, you can breathe the air remaining in your suit. How long will that air last?
Standard texts and training programs recommend leaving the hot zone immediately if the air supply fails. None provide any specifics about how long the air supply will last.
Here’s some background on how we got here.
When a hazmat team makes an entry into the hot zone, they must decide what level of protection and what type of respiratory protection to use. How much flexibility do they have in making that decision? As it turns out, not much.
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Hazmat response is governed by legal mandates. Response procedures? There’s a regulation that lays it out. How many people do you need for an entry? There’s a regulation that tells you. Are you required to have a safety officer? There’s a regulation that clearly answers that question.
When a regulation uses the word “shall”, there is no wiggle room; what follows “shall” must be done. When you see “should”, you have more latitude to choose.
The relevant regulation, commonly called Hazwoper, is 29CFR 1910.120(q)(3)(iv).
“Employees engaged in emergency response and exposed to hazardous substances presenting an inhalation hazard or potential inhalation hazard shall wear positive pressure self-contained breathing apparatus….”
“Shall wear….” The only thing to decide is, do we use Level-A or Level-B? Both require an SCBA. Either way, you shall wear an SCBA in an emergency response.
In the fire service, SCBA is one of the most commonly used pieces of gear. Many responders use them almost daily. Yes, they do fail, but rarely. If they do fail to do their job it’s a problem. If they fail while a responder is in the hot zone at a hazmat incident it can be catastrophic. This is especially true if the person is wearing a fully-encapsulating chemical-protective suit. A problem in that circumstance can be life-threatening.
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One of the most frightening types of breathing apparatus failure is a free flowing SCBA. This can be caused by operator error or the failure of some key components. In this situation the air from the SCBA cylinder will flow uncontrolled into the encapsulating suit.
Regardless of the type of SCBA failure, this situation will require the responder to leave the hot zone immediately.
Fully encapsulated chemical protective suits are designed to be worn in an atmosphere containing a gas or vapor that is immediately dangerous to life and health. They are intended to prevent outside air from getting into the suit.
At the same time, they are equipped with valves that will prevent the internal pressure in the suit from increasing to an unsafe level. The valves allow suit air to escape if the in-suit pressure becomes excessive. They are tested to ensure they are gas tight. If the bottle becomes empty or if the SCBA ceases to function properly the suit will have a supply of breathable air.
Is there enough oxygen in that air to allow a responder to safely exit the hot zone and go through the required decontamination?
We started off discussing how hazmat response has several legal mandates. There seems to be a regulation that addresses every eventuality. But not this one. Responders are on their own in deciding how to deal with being in a Level-A suit when the SCBA stops working.
Fortunately, researchers at the University of Alabama looked at this situation and ran tests to see just how much time you have before the air in the suit becomes unsafe to breathe. Here is what they did.
Several participants donned Level-A PPE. All of them passed a fit test prior to donning the PPE. The suits were new and had passed the manufacturer’s recommended pressure test. The entire ensemble weighed approximately 31 pounds.
The participants made simulated hot zone entries and performed various standard operations. The oxygen level in their suits was sampled at intervals of 2 minutes 10 seconds. They used two different monitoring instruments and a gas analyzer to measure the oxygen concentration in the suits. All the instruments were calibrated as required by the manufacturers.
What did they find? Within 2 minutes of suit closure, the oxygen level had fallen to 19.5%. After 5 minutes, the oxygen level fell to 18.5%. At 10 minutes, the oxygen level was 17.5%. The oxygen level continued to fall until it leveled off. Here is what it looked like with oxygen percentage being the vertical axis and minutes elapsed being the horizontal axis.
Within 2 minutes the oxygen concentration was at 19.5%, the legal minimum for confined space entry. However, 19.5% isn’t a safe level. It’s the minimum level.
OSHA’s confined space standard lists several factors that make an atmosphere hazardous. One is “…atmospheric oxygen concentration below 19.5 percent….” There are two primary reasons why an oxygen level of 19.5% is a big red flag.
ONE
What made the oxygen go away? The concentration of gasses in the atmosphere is a zero-sum game. If one gets bigger another gets smaller. If the oxygen concentration has gone down from a normal level that means the concentration of other gasses has increased. There are common gasses such as carbon monoxide and hydrogen sulfide that are lethal at less than a 1% concentration. If the oxygen concentration has fallen from 20.8% to 19.5% the atmosphere can easily contain a gas that can kill you.
TWO
Air taken into the lungs ends up in tiny structures called alveoli. Oxygen and carbon dioxide move across the alveoli membranes into and out of the blood stream. The amount of oxygen that passes into the hemoglobin in the blood is determined by the partial pressure of oxygen in the atmosphere. As the oxygen concentration decreases, that partial pressure also decreases. When the oxygen concentration drops to 19.5%, it approaches the level at which the partial pressure cannot move oxygen into the bloodstream. At that point, the margin of safety between sufficient oxygen and oxygen deficient begins to narrow considerably.
So, how long will suit air last? At 2 minutes you will see a big red flag (19.5% oxygen). A few minutes later you will approach a level where your pulse and breathing rate increases. You will begin to have impaired thinking and reduced coordination, but you won’t be aware of it.
If your SCBA fails you will have only a few minutes to exit the hot zone and go through decon.
About the Author
Vance Bennett is retired from California Specialized Training Institute, the training branch of the Governor’s Office of Emergency Services. During his 30 years at CSTI he was an Emergency Management coordinator and instructor in the Hazardous Materials Section. He was the course manager for several CSTI courses including Hazmat Incident Commander, First Responder Operations and CSTI Instructor Certification. As the CSTI representative to the FIRESCOPE Hazardous Materials Subcommittee, he helped develop hazmat team typing and equipment standards for California hazmat teams. Vance was also a regular presenter at the Hazmat Continuing Challenge Workshop.
Prior to coming to work for CSTI, he was on active duty in the U. S. Coast Guard specializing in marine safety and pollution response. During that time he was involved in responses to hazmat incidents and oil spills including the EXXON Valdez and American Trader spills. He served in a variety of USCG units including the Pacific Strike Team before retiring in 2009.
