Why Don’t C02 Fire Extinguishers Have a Pressure Gauge?

Have you ever noticed how some fire extinguishers have pressure gauges near the top while others don’t? I was curious as to why that was and did a little research. Here is what I found.

The basic principle behind most fire extinguishers is that they are pressurized so that when they are needed the matter inside shoots out with enough force to put a fire out. The pressure gauge at the top assures that there is still enough pressure for the extinguisher to be successful. Once the pressure has been released it must be serviced before using it again.

However, CO2 fire extinguishers are different. C02 fire extinguishers don’t have a pressure gauge because they use liquefied C02 (commonly known as dry ice) which as a chemical characteristic, always has a pressure of 830. Therefore a pressure gauge would always read 830 – making a gauge pointless.  

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If there is no gauge, how do I check my fire extinguisher?

Because CO2 fire extinguishers cannot be tested by measuring the pressure, they are weighed. This can assure the amount of CO2 inside the canister and tell the owner when it must be refilled and serviced. It is a good idea to check your fire extinguisher every year and get them serviced at least every five years.

According to the NFPA 10 table 7.3.3.1, CO2 extinguishers are required to have a cylinder pressure test every 5 years. The date of its last service should be clearly marked on your fire extinguisher. When in doubt- have it checked! It can be extremely frustrating and disappointing to feel prepared for a dangerous fire only to have the canister empty. A serviced fire extinguisher can save lives.

What is the purpose of a Pressure gauge?
Most fire extinguishers have a pressure gauge that shows the current pressure of the fire extinguisher and that it hasn’t been used or damaged and is within the proper psi range for that particular fire extinguisher. The Pressure gauge is one of several indicators of the condition of the fire extinguisher. It is divided into three parts.

1- Recharge Zone: If the arrow is pointing to the left, in the “recharge” zone, then the fire extinguisher has either been used or the pressure is leaking from the canister and needs to be fixed. This area of the pressure gauge is red.

2- Green Zone: If the pressure gauge arrow is pointing in the middle of the green zone then the fire extinguisher is properly pressured and is ready to be used if needed.

3- Overcharged Zone: If the arrow is pointing to the right, in the “Overcharged” zone then the fire extinguisher needs to be reserviced because the fire extinguisher won’t work properly under that kind of pressure.

Because each fire extinguisher is built differently and uses different extinguishing agents, they each have their ideal or proper psi pressure range. If the pressure is under or over the correct pressure zone the fire extinguisher won’t work properly.

Fire extinguishers are routinely inspected, regardless if it has been used or not, to ensure that the fire extinguisher is working properly and ready to be used.

What is a C02 fire extinguisher used for?

Carbon Dioxide fire extinguishers can be used for class B & C fires. However, they are primarily used for electrical fires (Class C) because it is not conductive with electricity like water and other elements.

How does a CO2 fire extinguisher work?

Although CO2 is stored in its solid form, once the pressure is released from the fire extinguisher and the CO2 is released into room temperature (or anything warmer than -110 degrees Fahrenheit) it immediately changes into a gas.

This neat characteristic of CO2 is called sublimation- meaning that it turns immediately from a solid to a gas.

One of the obvious reasons CO2 works to extinguish the fire is the low temperature of the dry ice combating the high temperatures of the fire resulting in an intense cooling effect. CO2 is also heavier than oxygen so when the co2 is shot at the base of the fire it will displace the necessary oxygen to keep the fire burning.

What are the benefits of a CO2 fire extinguisher?

The C02 fire extinguisher is comprised of compressed C02 gas which is considered a “clean gas”. When used, the C02 gas doesn’t leave any residue or damage any sensitive electrical equipment making it the preferred choice for fire extinguishers in computer rooms or server rooms. It is colorless and odorless and does not create a byproduct when putting out fires that could harm the environment.

C02 in its regular concentration is very common and not harmful at all to us or the environment.

The solid form of CO2 is also very dense compared to its gas form and therefore even small canister of solid CO2 can dispense a larger amount of CO2 gas to extinguish the fire.

What size of a C02 fire extinguisher do I need?

To ensure work place safety, fire extinguishers should be located throughout the workplace and clearly marked with best accessible as possible in case of a fire. Fire extinguisher sizes should be based on the location that fire extinguisher is being placed, meaning, a smaller fire extinguisher would be perfectly acceptable in a small room where there are few electrical equipment in the room and several larger fire extinguisher should be placed in a larger computer room or server farm.
 

Why do Co2 fire extinguishers have the large, plastic dispenser?

Although in its normal concentration CO2 is very safe, when it is pressurized and in its liquid form, it can burn your skin. The long plastic horn or dispenser on these fire extinguishers are to prevent skin contact. If possible, thick gloves or hand/arm protection is also encouraged.

Is a CO2 fire extinguisher the best kind?

There are 4 different types of fire extinguishers. CO2 fire extinguishers are definitely the best type to use for certain kinds of fires. There are several different kinds of fires and unfortunately, the best way to kill one fire will only fuel a different kind of fire.

How do you know which kind to use? How was the fire started.

Different Types of Fire Extinguishers

Carbon Dioxide fire extinguisher is one of six types of approved fire extinguishers that are on the market today.

They are:
1- Water Fire Extinguishers
2- Foam Fire Extinguishers
3- Dry Chemical Fire Extinguishers
4- Dry Powder Fire Extinguishers
5- Carbon Dioxide Fire Extinguishers
6- Wet Chemical Fire Extinguishers

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You can read more about these and the classification of fire they are used for by reading our article titled: “Types of Fire Extinguishers and Their Uses”