CO2 is an odorless, colorless, electrically non-conductive, non-corrosive, and non-deteriorating inert suppression agent. It is approximately 50% heavier than air, and is normally present in the atmosphere at about 0.03% by volume. CO2 is instrumental in controlling respiration and other vital responses in animals and humans, but it WILL NOT support life.
Usage Limitations and Personnel Safety Recommendations
CO2 is a standard commercial product commonly used for carbonating beverages, fast-freezing food products, purging pipes and tanks, medical purposes, and a multitude of additional tasks. It is also used for firefighting purposes: i.e. hose reels, portable hand extinguishers, and engineered fixed pipe systems. CO2 is available in most large cities and seaports throughout the world.
CO2 extinguishes fire by reducing the oxygen content of the protected space and/or local flame front to a point where it will not support combustion. Oxygen reduction below 16% by volume will extinguish most fires. Surface or “flash” type fires (oils, paints, etc.) are quickly extinguished. Deep-seated or “smoldering” type fires (paper, baled cotton, clothing, etc.) are extinguished by the prolonged action of a high concentration of CO2. Retaining the agent within the protected space reduces the fire’s ability to re-ignite. In addition, CO2 has a cooling effect on the surrounding atmosphere that has been found to be a benefit to fire extinguishment.
Storage and Pressure
When used as a fire-fighting agent, CO2 is stored under pressure in a liquid/vapor state. There are two forms of CO2 storage: Low Pressure, using a refrigerated storage tank, and High Pressure, using spun-steel cylinders of smaller capacities. Systems utilize high-pressure storage cylinders containing CO2 at an internal pressure of 850 psig (5861 kPa) when stored at an ambient temperature of 70ºF (21ºC).
The temperature of liquid CO2 is approximately –110ºF. (-78.8ºC.) as it is discharged from a nozzle. Direct contact with the liquid agent being discharged from the nozzle(s) will have a freezing effect on objects within the hazard and can cause frostbite and/or freezing if contact is made with the skin. The liquid phase of the agent vaporizes quite rapidly when coming into contact with the atmosphere, thus limiting this hazard to the immediate vicinity of the nozzle.
The discharge of CO2 resembles a cloud as liquid agent vaporizes. The low temperature of the agent chilling the moisture in the atmosphere causes this cloud effect, or fogging. The fine “snow” accompanying the discharged liquid is remnant particles of “dry ice”.
The high pressure/velocity discharge from the system nozzles(s) can cause noise loud enough to be startling, but is ordinarily insufficient to cause traumatic injury.
Cleanup.CO2 vaporizes completely after discharge; whereas the cost of clean-up and peripheral damage associated with water sprinkler systems, foam systems, and dry chemical agents can exceed the cost of the actual fire damage itself. Therefore, the cleanup costs and downtime associated with a CO2 system discharge are negligible. CO2 is an inert gas and most materials or equipment are totally unaffected by exposure to the agent. It is stable, even at high temperatures, and does not decompose when subjected to open flame or extreme temperatures; therefore, CO2 does not cause metals to deteriorate or corrode.
Use and Limitations
CO2 systems can be used on Class “A” fires involving wood, paper, cloth, or any product that leaves a carbon ash when it burns. Class “B” fires involving flammable liquids or vapors, and Class “C” fires involving live electrical equipment can be protected with CO2.
Areas of Use
CO2 is particularly useful for extinguishing fires in specific hazard areas or equipment where:
- An inert, electrically non-conductive medium is essential or desirable.
- The cleanup or down-time of another medium would be detrimental or costly.
- Other mediums might contaminate solvents, coolants, or other products associated with the hazard being protected.
- Some of the hazard types and equipment that can be satisfactorily protected with CO2 include:
- Battery Rooms
- Flammable Liquid Storage
- Engine Test Cells
- Printing Presses
- Solvent Recovery Equipment
- Record Storage
- Wet Benches
- Electric Generators
- Coating Machines
- Underfloor Areas
- Fur Storage Vaults
- Dust Collectors
- Wave Solder Machines
- Spray Booths
- Dip Tanks & Drain Boards
- Switchgear Equipment
- Transformer Vaults
- Hydraulic Pump Units
Areas of Non-Use
CO2 should NOT be used on fires involving the following materials:
- Chemicals that contain their own oxygen supply such as: cellulose nitrate (old movie film) and gunpowder, which are capable of rapid oxidation in the absence of air.
- Reactive metals such as: Lithium, Sodium, Potassium, Magnesium, Titanium, Uranium, or Plutonium.
- Metal Hydrides such as: Sodium Hydride, Lithium Hydride, Calcium Hydride, Lithium Aluminum Hydride, and Sodium Borohydride.
While CO2 will not extinguish fires involving these products, it will not react dangerously with them or increase their burning rate. A CO2 system designed for Total Flooding will provide protection of adjacent combustibles when used in these situations. Local Application systems with their attendant high velocity and directed discharge should NOT be used for these applications.
CAUTION: Where CO2 may be discharged into potentially explosive atmospheres. Electrostatic charging of non-grounded conductors may occur during the discharge of liquefied gases. These conductors may discharge to another object causing an electric spark of sufficient energy to initiate an explosion.
Extinguishing concentrations of CO2 create a health hazard to area personnel. High concentrations of CO2 will cause suffocation. In addition, fogging during and after discharge can limit visibility in protected areas. CO2 does not contain oxygen in any form or quantity and WILL NOT sustain life.
The following human reactions to CO2 have been documented
- At concentrations of 3 to 4% by volume in the atmosphere, the breathing rate increases and headaches may occur.
- At concentrations exceeding 9% by volume, personnel can lose consciousness within minutes. This is generally preceded by disorientation, visual disturbance, ringing in the ears, tremors, etc.
- At concentrations greater than 20% by volume, death is likely.
The above effects are important to note as inexperienced personnel may fail to think clearly and take proper action if suddenly exposed to relatively low concentrations of CO2.
Any person overcome by CO2 should be moved immediately to a location where plenty of fresh air is available and artificial respiration applied, as in a case of drowning. DO NOT use CO2 as a stimulant. Call a physician or take the patient to a hospital for examination. Persons rendered unconscious by exposure to CO2 can usually be revived without any permanent ill effects when promptly removed from a CO2 atmosphere.
Direct contact with liquid CO2 or the dry ice particles associated with the agent discharge will cause severe frostbite burns to the skin. CO2 vaporizes quite rapidly; therefore, the hazard is generally limited to the immediate vicinity of the discharge nozzle(s).
CO2 can drift into, and settle in adjacent spaces unless specific precautions are taken to prevent leakage from the protected space, and/or leakage into nearby areas. Such leakage can accumulate into dangerous concentration levels if left unattended. Consideration must be given to warning all personnel in the area of possible agent migration. A means of ventilating the CO2 from enclosed areas, pits, etc., shall be considered when designing a CO2 suppression system.
Consult NFPA 12 for additional personnel safety guidelines.
Typically, flooded hazards and low-lying areas must be well ventilated before personnel are allowed to re-enter the protected space(s). Under some circumstances, it may be necessary to provide self-contained breathing apparatus (SCBA) to all persons responsible for investigating the event. When all traces of the fire have been extinguished and the possibility of re-ignition eliminated, thoroughly ventilate the hazard to ensure that only fresh air is remaining in the protected space. When there is a question as to the presence of CO2 after a discharge, DO NOT ENTER. Rely on the fire department or other responsible authorities to determine when it is safe to re-enter. 1.4.3 SAFETY RECOMMENDATIONS
Safeguards MUST be provided to ensure the safety of personnel occupying areas in which the atmosphere could be made hazardous from the discharge of CO2.
The following list taken from NFPA 12 contains safety recommendations that we urge the installer to follow with each installation.
- Provide open aisle ways and exit routes. Keep them clear and well marked at all times.
- Provide emergency lighting and directional signs to ensure quick and safe evacuation.
- Provide audible/visual alarms inside and outside all protected areas that operate immediately upon the detection of a fire condition. Delay the CO2 discharge and the actuation of door closing devices for a sufficient time period to allow evacuation of the affected area(s).
- Provide ONLY outward swinging, self-closing doors at all exit points from the hazard area(s). Where such doors could be latched or secured, provide “panic” hardware.
- Provide continuous alarms at the entrances to all protected spaces that will operate until the atmosphere has been returned to normal and the control panel has been reset.
- Provide warning and instructional signs at all entrances to, and inside of, each protected space. These signs should inform persons inside, or entering into the protected space, that a CO2 system is protecting the area. These signs may also contain additional information or instructions pertinent to the conditions of the specific hazard.
- Provide for the prompt discovery and rescue of any person(s) trapped or rendered unconscious in all protected areas. This is accomplished by having all affected areas searched by trained personnel equipped with the proper breathing and rescue equipment. Only personnel trained in its use and in rescue techniques including artificial respiration should perform this task.
- Provide instructions and drills for all personnel within, or in the near vicinity of the protected area. This instruction should include all maintenance and construction personnel who may be brought into the area. This training will ensure that the area personnel will respond correctly, should the CO2 system operate.
- Provide a means of prompt ventilation of the protected area(s). Forced ventilation will often be necessary. Care must be taken to ensure that the CO2 atmosphere is dissipated and not merely moved to another location.
- CO2 is much heavier than air and can collect in pits, cellars, and other areas that lie below the floor level of the protected space. Care must be taken when entering these areas after a discharge.
- Provide all other steps and safeguards that a careful study of each CO2 system application indicates are necessary to prevent injury or death.