You have probably seen firefighters breathing from air tanks on their backs that look like SCUBA tanks. Did you ever think that seems dangerous? How do firefighter’s oxygen tanks not explode?
Firefighters breathe from air tanks called SCBA’s (Self Contained Breathing Apparatus). These air tanks don’t explode when exposed to heat because they are filled with compressed air, not oxygen. The air tanks have a burst disk to prevent rupture from the increased pressure due to heat.
How does an SCBA (firefighter air tank) work? Why is oxygen dangerous in a fire? Doesn’t regular, atmospheric air contain oxygen also? Keep reading and your questions will be answered.
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Is Oxygen Flammable?
We have all seen movies where an oxygen tank catches fire and explodes, but can this really happen? Is oxygen flammable? No, while oxygen can have a dramatic effect on the fire, it is not actually flammable.
Looking at the Fire Triangle, we see that in order for fire to be created and continue burning, it must always have three elements: Fuel, Heat, and Oxygen (or another oxidizer).
A flammable gas like Methane would make up the fuel, but would still need enough oxygen and enough heat in order to burn. Oxygen is not a flammable gas and in order to burn it still needs a fuel source and heat.
To learn more about the Fire Triangle, read this article, What do Firefighters Use to Put Out a Fire?
That doesn’t mean that oxygen can’t cause an explosion. If there is already a fire burning and oxygen is added, it can greatly increase the intensity of the fire and potentially cause an explosion.
This same effect can be caused by other chemicals that are also oxidizers (such as Hydrogen Peroxide and Bromine). This means that extreme care must be taken with Oxygen and fire, even if it is technically not flammable.
So, you can see why using pure oxygen in a firefighter’s air tank would be very dangerous. Even though the oxygen would be sealed in the tank, if there was any kind of leak, it would cause the fire (that already has heat and fuel) to intensify and create a very dangerous environment for the firefighters. This leak could potentially occur is from the seal on the face mask.
FUN FACT: The ability of the firefighters face mask to create a good seal is very important, even though the air tank doesn’t have pure oxygen. This seal prevents all the chemical-filled smoke and hot air out of the firefighter’s lungs. This is why firefighters can’t have beards. The facial hair can prevent the face mask from creating a good seal on the face.
Self Contained Breathing Apparatus or SCBA’s are one of the most important parts of the safety gear worn by firefighters. These portable air tanks (that are very similar to SCUBA or Self Contained Underwater Breathing Apparatus) allow the fire firefighters to breathe clean, normal temperature air.
Although the heat and smoke are dangerous to firefighter’s skin, their respiratory system is much more vulnerable to chemical-filled smoke and super-heated air.
Today more than ever, the smoke encountered by firefighters is extremely toxic and can be deadly if enough reaches a person’s lungs. Though smoke has always been dangerous, the smoke firefighters face today, is especially nasty. This is because there are so many things made with synthetic plastics that release very toxic chemicals. These chemicals can include Carbon Monoxide, Hydrogen Cyanide, Benzene, Arsenic and a variety of others.
To learn more about Carbon Monoxide, read this article, CO: How do Firefighters Check for Carbon Monoxide?
“Hydrogen cyanide (AC) is a systemic chemical asphyxiant. It interferes with the normal use of oxygen by nearly every organ of the body. Exposure to hydrogen cyanide (AC) can be rapidly fatal.”
To learn more about Hydrogen Cyanide or any of these other dangerous chemicals, see the CDC (Centers for Disease Control and Prevention) Website. Here is a page about Hydrogen Cyanide (AC): Systemic Agent.
The SCBA is essentially an Aluminum/Carbon Fiber air tank built into a backpack type harness. It has pressure regulators to reduce the high pressure it is stored under, to a pressure that you can breathe. The regulator hose connects to a full face mask that protects the face, as well as the mouth, throat, and lungs.
Most of the SCBAs I have seen have a positive pressure in the system, so when the firefighter breathes in, the pressure drops, which signals the demand valve to flow air into the mask. This helps to prevent air leaks.
SCBAs usually have a display to monitor your remaining air either on a small, strap mounted readout/computer or in your mask (or both). They also have a device called a PASS (Personal Alert Safety System) that will sound an alarm if a firefighter stops moving for a set amount of time, in order for his crew to locate and assist him when necessary.
Compressed Air Tanks Could Explode Too (Kinda)
So, if a firefighter’s air tank or SCBA doesn’t have pure oxygen inside, can it still explode? The answer is sort of.
Regular ambient, atmospheric air, the air we breathe every day, has enough oxygen for us to breathe (20.9%), which is the same as the air in the SCBA. So, the oxygen in the air pack, wouldn’t increase the fire behavior any more than the air in the building that is burning and wouldn’t cause an explosion.
However, there is another way that the air tank could, theoretically, explode (actually rupture). The compressed air that is in the air bottle, will expand or contract based on the temperature it is exposed to. If it was exposed to a hot enough environment in a fire and the pressure continued to increase, eventually it could cause the tank to rupture and be very dangerous.
The companies that manufacture the air packs are well aware of this possibility and have built-in some safety features to prevent this from happening. The bottles we use are filled to 4500 psi (pounds per square inch) and the bottles are tested to withstand at least 6000 psi. This gives some safety margin for pressure to build inside.
The bottles are also equipped with a safety valve, if the pressure inside reaches a certain preset level, a pressure relief valve or burst disk (that is designed to fail before the bottle) will vent the excess pressure and prevent the bottle itself from rupturing.
This is all somewhat of a moot point though. If a firefighter was in a room that was hot enough for long enough to cause their air bottle to rupture, they would have long since reached the temperatures that their body could handle and would be dead.
Yes, even though firefighters have special safety gear to protect them from fire, it can only do so much and there is a limit to what firefighters can be exposed to.
How Long Do Firefighter’s Oxygen Tanks Last?
Firefighters’ oxygen tanks (SCBAs) are designed to last from 30 mins to 1 hour depending on the size of the bottle. How long they will actually last can be affected by physical fitness, how hard they are working and body size. The actual working time can range from 12 mins to 2+ hours.
How Much Does a Firefighter’s Oxygen Tank Weigh? How Heavy Is an SCBA?
Though it can vary by manufacturer and air bottle size, an SCBA (Self Contained Breathing Apparatus) weighs about 25 pounds.