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What is a Carbon Dioxide (CO2) Fire Suppression System?

co2 fire suppression system cylinders

What is a CO2 fire suppression system?

Because of its ability to quickly displace oxygen, carbon dioxide (CO2) gas has long been used as a fire suppressor in a variety of safety and industrial applications. While some suppression agents like water reduce the heat of fire, a CO2 fire suppression system displaces the oxygen to suppress the fire. 

How does a CO2 fire suppression system work?

The most common type of CO2 fire suppression system is used to protect sensitive electronics in a room where a water sprinkler system would damage the equipment if used. The room to be protected is sealed so that when the doors are closed no air can get in our out of the room.

High pressure cylinders of CO2 gas are stored near the space. These cylinders are connected via manifolds to air ducts into the sealed room in such a way as to "flood" the room with CO2 in the event of a fire.

When the CO2 fire suppression system detects smoke it releases the CO2 gas into the room. At the same time an alarm is sounded to warn any occupants to leave the room immediately. CO2 levels above 5% are an asphyxiant and can quickly render occupants unconscious. 

Where are CO2 fire suppression systems used?

A variety of applications choose a CO2 fire suppression system over other options. Since carbon dioxide is an inert gas, it does not react with metals or plastics. This makes it a superior solution to water which oxidizes to cause rust.

For example, computer data centers or "server farms" use CO2 fire suppression systems to protect the sensitive electronics. Once the fire is extinguished the effected components in the fire can quickly be replaced and the system can be restarted.

Marine engine rooms utilize CO2 instead of water as a suppression agent for two reasons: water would damage the electrical mechanical components of the engine, and nobody wants to put water into a vessel at sea. Currently, CO2 fire suppression systems are required by the U.S. Navy and Coast Guard and commercial ships.

A large marine engine room system may require as much as 20,000 lbs. of carbon dioxide per system.

CO2 fire suppression systems are commonly used by the U.S. Navy, server farms, commercial shipping, voltage transformers, rolling mill processes, flammable liquid storage areas, and for industrial generator and turbine protection.

Industrial turbines utilize CO2 fire suppression for the same main reason as marine engines. Unlike water, CO2 is non-corrosive. Other common uses include gas turbine enclosures, power generation stations, voltage transformers, rolling mill processes and flammable liquid storage areas.

Fire Systems, Inc. uses CO2 systems primarily in rooms that hold printing presses or chemical rooms according to Geoff Zimbelman at Fire Systems, Inc.

"CO2 flooding systems require 34% CO2 concentration to extinguish a normal fire, while some chemical fires require 65-70%."

Why use CO2 as a fire suppression agent?

There is no clean-up or residue associated with a CO2 system – unlike with foaming agents or water. CO2 has been proven as a gaseous fire suppression agent as far back as the beginning of the 1960's.

The biggest advantage of CO2 as a suppression agent is that because it is an inert gas it will not adversely effect equipment. Carbon dioxide does no damage. It does not create any clean-up after a test or fire. While you will have to mitigate the damage done by the initial fire you will not have water or foam damage to re-mediate like you would with other suppression methods.

Additionally, CO2 is effective on a wide range of flammable and combustible materials, and is approved for suppression of Class A, B and C hazards. 

What NFPA code is the standard for CO2 extinguishing systems?

If you utilize CO2 as your suppression agent then you'll be required to meet NFPA 12 standards.

NFPA 12 details the requirements for testing a CO2 suppression system including the points in the room, timing requirements, and the necessary concentration thresholds. Typically, industrial suppression systems utilize banks of high pressure CO2 cylinders to release CO2 in a 100% concentration to displace the oxygen as quickly as possible.

These standards require full discharge tests and evacuation plans in order to ensure that the air be tested for normal levels before personnel can return to work.

See this video example of a co2 fire suppression system discharging to see what happens during testing. Another great example of CO2 fire suppression testing can be seen here

Hazards of CO2 in Fire Suppression

The challenge facing designers and operators of CO2 Fire Suppression Systems is that they must also be safe for people working nearby. Fire-prevention systems which result in the oxygen content being less than 19.5% are not permitted for occupied spaces by federal regulation (OSHA) in the United States. They must also be safe for first-respondents after the fire has occurred.

To protect human life in an emergency, facilities that use CO2 as a fire suppressor are required by regulatory agencies to follow the National Fire Protection Association (NFPA) standards for design, installation and testing of CO2 systems. These standards include requirements for full discharge tests and an evacuation plan for personnel. Once the fire emergency is over, the standard requires the air be tested for normal CO2 levels before personnel can return to work.

NFPA 12 lays out very clear standards for how a fire suppression system must be tested including the speed at which specified concentration levels of CO2 are achieved and how long those levels are maintained.

For reference, according to ASHRAE, the recommended CO2 level in buildings should be no more than 700 parts per million (ppm) above outdoor air. Since outdoor air is approximately 400ppm, indoor CO2 levels should be no more than 1,100ppm. If the levels are higher than average, proper ventilation is required to suffice to ensure safety.

Another main concern after a fire suppression system test has been activated, is that responders should understand how long they must wait to enter into an enclosed area. To test this, after installation, a "dry run" is performed where the carbon dioxide levels are tested over time at several locations, simultaneously. 

By measuring the CO2 levels both vertically and horizontally over time, the installer can draw a 3-dimensional map of the affected area, and can furthermore determine when it is safe to re-enter the space. Additionally, this data may be required by insurance carriers and regulated by local and national agencies. This means an individual will have to complete three tests one at each height in the discharge space OR purchase three devices to measure the different heights during a single test for efficacy.

What are the requirements for a CO2 fire suppression system?

The average CO2 fire suppression system protecting an enclosed room starts at 34% CO2 concentrations. CO2 fire suppression system requirements state that systems should protect areas of high voltage and begin concentration levels of 50% CO2.

CO2 Fire Suppression System Products

CO2 Fire Suppression System

Our CO2 Sampling Data Logger remains the most trusted 100% CO2 data logger in the field because it exceeds the NFPA requirements for specific codes and tests. Furthermore, it was designed to simultaneously measure multiple gas concentrations using fast and accurate sampling methods while also data logging.

To implement this NFPA set testing, CO2Meter.com has worked with several industry professionals to provide devices like the CM-1000 in order to test and verify CO2 levels. In addition, we have worked with worldwide fire protection and industrial companies like TYCO-SimplexGrinnell, ORR Protection, and Mitsubishi Hitachi Power to design a device that meets all the standards for CO2 fire suppression laid out in NFPA 12.

Some permitting/regulatory agencies may require an oxygen depletion test as well which will validate the absence of oxygen in the space. These tests are often requested as back-up data to the initial CO2 test or as testing when other inert gases like Argon or Nitrogen are used as a suppressant. In these cases we recommend our 0-25% Oxygen Sampling Data Logger.

Additionally, some fire inspectors are starting to require the addition of a fixed CO2 monitor where the high-pressure CO2 cylinders or low-pressure bulk storage tanks are housed. Storing the massive amount of gases required to operate a suppression system leaves the end user susceptible to potential CO2 leakage. While neither the NFPA nor the International Fire Code have yet to expand CO2 monitoring requirements beyond beverage delivery systems both organizations are considering language that would expand the monitoring requirement to all stored gases.

In these cases where a fixed monitor is required we recommend our Remote CO2 Storage Safety Three Alarm Monitor or our Remote Oxygen Depletion Safety Alarm.

For more information on fire suppression testing and CO2 safety devices contact us.


“Standard on Carbon Dioxide Extinguishing Systems, NFPA 12-2018,” American National Standards Institute, February 2, 2018

NFPA 2001: Standard on clean agent fire extinguishing systems," National Fire Protection Association, Quincy, MA, Annex C, 2008

ISO 14520-1: Gaseous fire extinguishing systems - physical properties and system design – part 1: general requirements," International Standards Organization, Geneva, Switzerland, Annex E, 2006

“A Modified Hold Time Model for Total Flooding Fire Suppression” Fire Safety Journal, Vol. 45 (1), 12-20, 2010.

“Hypoxic Air for Fire Prevention,” Wikipedia.

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