By Vance Bennett
O2. Element 8 on the periodic table. We all need it. We can’t live without it. That’s the good. But is too much of it a bad thing? That depends.
There are three attributes of oxygen that you often hear in hazmat training.
1. Liquid oxygen (LOX) can cause streets to blow up.
2. Oxygen in high concentrations can be a dangerous product.
3. Las Vegas casinos routinely add oxygen to the atmosphere in to get guests to gamble more.
Number 3? What? If you own a casino all you have to do is pump in more oxygen and watch the money roll in. Add oxygen to your casino’s atmosphere and people will be more active, stay awake longer and gamble more. And you will sit back and count your dough.
Only one problem; it’s not true.
This legend came from a novel by author Mario Puzo a few decades ago (he also wrote The Godfather). A character in the book said casinos add oxygen to the air in the building to keep their customers active and alert. It’s pure fiction.
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I’m sure it’s possible to increase the oxygen concentration in a building. Is it practical? If you do a little math you’ll find out it would take one railcar of liquid oxygen per day per casino to get the oxygen concentration to increase by 2 percentage points. Not a very realistic scenario.
What about the bad?
Liquid oxygen can cause streets to blow up. If you’re responding to a LOX spill if you drive across the affected area the tires on your apparatus can catch fire. If you drop a tool on the affected area the street will immediately burst into flames. Those are just a few examples of the sorts of mayhem that may occur if LOX gets loose.
I’ve heard this assertion in a variety of forums. If you think about it, there is a certain logic to this claim. LOX is pure oxygen. Streets are often paved with various forms of hydrocarbons. Oxygen plus hydrocarbons plus a source of ignition can result in a big bang. Is this true in the real world?
It turns out someone has tried to make it happen. Were they successful?
No.
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The Department of Emergency Services of the Utah Valley University researchers tried everything they could think of to make a LOX spill cause any sort of destruction and havoc. They published their results in a professional journal. Here is the abstract from that paper:
The objective of this research was to verify and qualify what has been traditionally taught as fact during first responder’s hazardous materials training regarding response precautions to and the likely behaviors of liquid oxygen (LOx) during a release. Subject matter experts disagreed that these precautions were well-founded in precedent or science. Findings showed that impact pressure causes a reaction in LOx and asphalt under specific conditions. These conditions are not realistic during an emergency response. No reactions were observed by combining LOx with common saturated and unsaturated hydrocarbons and alcohols. No reactions were observed driving fire apparatus through a LOx pool on asphalt. No reactions were observed by combining LOx and combustible materials. No reactions were observed when spark ignition was used as a source for combustion. Pilot ignition sources were introduced directly into a LOx pool on asphalt without a significant reaction. Immediate and violent reactions were observed when pilot ignition or arc ignition was used to initiate combustion when combustible materials were in an ultra-high gaseous or liquid oxygen environment. Without flaming or arc ignition sources, no reactions were observed.
Although high oxygen won’t make streets blow up it can still pose serious problems. The question is, how high is too high?
There are official rules on acceptable level levels for oxygen concentration. They are in two OSHA regulations: Respiratory Protection and Permit-Required Confined Spaces.
Also Read: 4 Best Practices for Confined Space Air Monitoring
According to these regulations the lower limit is 19.5% and the upper limit is 23.5%. If a confined space’s oxygen concentration surpasses 23.5%, the space is too oxygen-rich and could result in the ignition of combustible gases. On the other hand, low oxygen levels impair judgment and coordination. Extremely low levels of oxygen cause nausea, vomiting, and loss of consciousness.
Those aren’t the only hazards of confined spaces. According to OSHA, “…documented confined space incidents in which victims were burned, ground-up by auger type conveyors, or crushed or battered by rotating or moving parts inside mixers.” Wow.
But I digress.
The OSHA confined space regulation defines Hazardous atmosphere as “…an atmosphere that may expose employees to the risk of death, incapacitation, impairment of ability to self-rescue (that is, escape unaided from a permit space), injury, or acute illness from one or more of the following causes:
….
(3) Atmospheric oxygen concentration below 19.5 percent or above 23.5 percent;”
Note: OSHA doesn’t say 19.5-23.5% is a safe level. It says above or below those limits is hazardous. That may sound like splitting hairs, but it’s an important distinction.
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When a government agency writes regulations, the lawyers require them to use hard numbers not subjective requirements. When OSHA drafted the confined space regulation it was faced with a difficult decision — what numbers does it use?
The 19.5% level was established because concentrations below that level can cause adverse physiological effects. That’s well known and is supported by studies going back decades. That was an easy decision. But what about the upper limit?
High oxygen levels can have several adverse effects. One major effect is toxicity. However, the levels at which oxygen can become toxic are far above the levels at which flammable hazards are greatly increased. Increased flammability becomes a problem well before detrimental health effects occur. High oxygen is a problem but how high should the limit be?
When OSHA was considering what the upper limit should be, it found no consensus on which concentration to use. They had promulgated a previous regulation that used 23.5% as the upper limit. The National Institute for Occupational Safety and Health recommended 25% as the upper limit. The American National Standards Institute is a private, non-profit organization that administers and coordinates voluntary standards. Their standard recommended 23.5% as the upper limit for oxygen in breathing air. Ultimately, OSHA decided to set the upper limit at 23.5%.
As previously stated, anything outside of those limits is hazardous according to OSHA. But, they don’t say that any concentration between these limits is safe. When monitoring a potentially hazardous atmosphere it’s important to bear this in mind. It’s also important to keep in mind that any atmospheric oxygen concentration other than 20.8% is cause for concern.
The limit on low oxygen concentration is primarily based on the health effects of low oxygen. However, there is more to the story. When oxygen levels are too low that typically means another gas is displacing it. In these instances it’s important to know what gas is displacing oxygen and what that gas may do.
A typical 4-gas meter will measure oxygen. They will display the oxygen concentration in percent, but they only display the level one digit to the right of the decimal. One percent of an atmosphere is 10,000 parts per million. A 20.8% concentration of oxygen is 20,800 ppm. How many gases/vapors can kill you at a concentration level below 800 ppm? Quite a few. Some examples:
| Substance | LC50 |
|---|---|
| Arsine | 120 |
| Bromine | 175 |
| Chlorine | 450 |
| Hydrogen Sulfide | 450 |
If your oxygen meter gives you a reading of anything but 20.8%, that is a red flag. If you run into that, you better ask why?
A low level of oxygen can be a big problem, but life can get seriously ugly if you have too much oxygen.
Studies have shown that excess oxygen in a healthcare environment can lead to disastrous outcomes. (Yes, I know that studies have shown that 67% of all statistics are made up on the spot.) I could list all of the documentation but it would be easier if you search for something like “oxygen fed fire incidents” on the internet. You’ll find dozens of papers discussing these types of incidents.
Oxygen-fed fires have occurred in the medical field for decades, often in the operating room. The first recorded fire in an operating room occurred in 1850 resulting from the use of an oxidizing anesthetic agent. They have often resulted in fatalities. In some cases, multiple deaths. Here are a few sobering statistics:
- There are 550 to 650 surgical fires each year in the United States.
- A home oxygen therapy fire death occurs every 4 days.
- Fire departments respond to an estimated average of 182 home fires per year involving home oxygen equipment.
- 17% of anesthetic malpractice claims related to burns from surgical fires.
These types of incidents increased significantly in the past few years. Why? Covid. According to one study, “It appears that some hospitals may not have been fully prepared for the elevated risk of oxygen-related fire in intensive care units due to the high demand for oxygen therapy in severely ill Covid-19 patients.” Over 200 people have died in such fires during the pandemic.
In hazmat response it’s essential to find out what’s in the atmosphere in the hot zone. We have sophisticated equipment that makes it possible to do that. The most important consideration in using that equipment is to assess what it’s telling us. That starts with what the meter tells us about the oxygen concentration.
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.
