Firefighting and Chlorine

by Harold F. Maybeck

Original Publication 1997, Revised 2006
Holderness Fire Department, Holderness, NH

Liquid chlorine is the disinfectant used in the swimming pool at the Plymouth State University Field House.


Chlorine is a poisonous, yellowish-green gas with a sharp, irritating odor and is nearly two and a half times as dense as air. Chlorine has a molecular weight of 71. The critical temperature of chlorine is 146°C so that it is easily liquefied by cooling and compression at all ordinary temperatures and is moderately soluble in water, reacting chemically with water. Chlorine boils at -34.4°C (-29.°F) and freezes at -101.6°C (-150.9°F). Chlorine attacks the mucous membranes of the nasal passages and lungs, producing effects similar to those of a bad cold even when inhaled in very dilute form. It is very poisonous and inhalation of the gas may cause serious damage to the lungs and even death. Chlorine is an element with the chemical symbol Cl.


One of the principle commercial uses of chlorine is as a bleach and almost one-third of all chlorine made in normal times is consumed by the pulp and paper industry for bleaching purposes. Another third of the chlorine manufactured is used in the preparation of chlorinated compounds of carbon. A principal one of these is trichlorethylene, being an excellent solvent of oils, fats, and waxes it is used extensively by "dry cleaners" and as a means of degreasing metals prior to plating or painting. Chlorine is employed, in relatively small quantities, for sterilizing municipal water supplies, sewage, and swimming pools. In these uses, the chlorine is fed directly into the water and either the free chlorine or the hypochlorous acid that forms upon the contact with water attacks the microorganisms. A few parts per million of the element in drinking-water is all that is required to kill all pathogenic organisms.



Chlorine is TOXIC and it may be fatal if inhaled or absorbed through the skin. A fire at a chlorine source will produce irritating, corrosive and/or toxic gases. Contact with chlorine gas or liquefied chlorine may cause burns and severe injury. Contact with escaping chlorine gas may cause frostbite. Runoff from fire control efforts may cause pollution.


Chlorine will not burn but it will support combustion. Since chlorine gas is about two and a half times heavier than air, the vapors from liquefied chlorine will sink to ground level and spread along the ground. Pure chlorine is a strong oxidizer and may react vigorously or even explosively with many materials including fuels. Chlorine frequently reacts violently with moist air and/or water and may ignite combustibles such as wood, paper, oil, clothing, etc. Chlorine gas containers are under great pressure, while liquid chlorine containers are under considerably less pressure. Even so, containers may explode when heated and cylinders may rocket when ruptured.


Call CHEMTREC 1-800-424-9300

Set up an initial isolation zone from the spill or leak for at least 300 to 600 feet in ALL directions.

Remove all persons and animals in a "crosswind" direction to outside the initial isolation zone.

Keep all unauthorized personnel away. This includes all administrative and faculty personnel of Plymouth State University unless they are part of the University Emergency Management Team.

All personnel are to stay upwind of the spill/leak.

Since chlorine gas will spread along the will collect in low or confined areas, such as basements, ground depressions, underground access points under manhole covers, etc. Therefore, all personnel are to stay out of these low areas.

Closed spaces (even on the same level as the spill/leak) are to be well ventilated before entering. Just opening doors and windows is not sufficient. If ANY odor of chlorine is present, the ventilation must be forced by use of large volume fans. Note: since chlorine gas in air is NOT flammable or explosive, the use of Fire Department smoke ejector electric fans is permissible.


Positive pressure self-contained breathing apparatus (SCBA) is a MUST. Use of older "demand type" SCBA units should NOT be allowed.

Structural firefighting protective clothing is NOT effective in chlorine spill/leak situations. It should be worn in FIRE situations only.

Chemical protective clothing should be worn. It must be remembered that chemical protective clothing provides NO thermal protection.


If chlorine is evident in a downwind direction at the edge of the initial isolation circle, then the isolation zone must be extended out on the downwind side for at least an additional 1000 feet (.2miles). The width of this extended isolation zone beyond the initial isolation circle should be equal to the length of the zone, i.e.. 1000 feet.

Evacuation areas may be altered due to varying weather conditions. Very light winds may shorten evacuation areas, while strong winds may preclude increasing the evacuation area. Incident Command should be cautious of wind direction and wind speed changes occurring during the operation. While higher wind speeds will help to disperse the chlorine gas into the atmosphere more rapidly, it will also extend the isolation area farther downwind during the early stages of the operation. Precipitation in any form, drizzle, rain, snow, etc., may suppress the expansion of the chlorine cloud into the atmosphere, but it will keep the cloud more dense in the initial area.


On small fires ...Water only; no dry chemical, CO2, or Halon. Note difference from fighting Ammonia fires. Contain fire and let burn. If fire must be fought, water spray or fog is recommended.

On large fires ... water spray, fog, or regular foam.


Move undamaged containers from the fire area if it can be done without risk.

Fires involving tanks.

Fight fires from a maximum distance using unmanned hoses or monitors.

Cool containers with flooding quantities of water until well after the fire is out.

DO NOT direct water at source of leak or safety devices. ICING MAY OCCUR.

Withdraw immediately in case of rising sound from venting safety devices or discoloration of tank.



Fully encapsulating vapor protective clothing should be worn for spills and leaks with no fire.

Do not touch or walk through spilled material.

Stop leak if you can do so without risk.

If possible, turn leaking containers so that gas escapes rather than liquid.

Prevent entry into waterways, sewers, basements or confined areas.

DO NOT direct water at spill or source leak.

Use water spray to reduce vapors or divert vapor cloud drift.

Isolate area until gas has dispersed.


Skin or eye contact with gaseous or liquid chlorine and/or the ingestion of gaseous chlorine into the respiratory system creates a very serious condition. First Aid and medical treatment at the scene should only be performed by qualified EMS personnel.

Move victim to fresh air.

Apply artificial respiration if victim is not breathing. Do not use mouth-to-mouth method if victim has inhaled or ingested chlorine gas. Use a pocket mask equipped with a one-way valve.

Administer oxygen if breathing is difficult.

Remove contaminated shoes and clothing.

In case of contact with liquefied ammonia, thaw frosted parts with lukewarm water.


Ensure that medical personnel are aware of the material involved, and they take precautions to protect themselves.

References used:

DOT North American Emergency Response Guidebook - 2004
OSHA 29 CFR 1910.120
FEMA NFA-ICS-SM, "The Incident Command System"
Transportation Skills Program, "Empties-Leakers and Emergency Responses"
Fundamentals of Chemistry, Brady/Holum

Other articles by this author:

Copyright ©1997- Harold F. Maybeck. All Rights Reserved.