Firefighting and Anhydrous Ammonia

by Harold F. Maybeck

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


Anhydrous ammonia is the refrigerant gas used at The Holderness School Ice-Rink.

ABOUT AMMONIA

Ammonia is a colorless gas and it has a characteristic, pungent, choking odor. Ammonia has a molecular weight of 17, which makes it about half as dense as air. Ammonia is exceedingly soluble in water (one volume of water will dissolve 1000 volumes of ammonia gas at Standard Temperature and Pressure). Ammonia boils at -33.4°C (-28°F) and freezes at -77.7°C (-108°F). Ammonia can be detected by the human nose with very small amounts present in the atmosphere. Amounts as small as about 50 parts per million in air can be detected simply by sniffing. Ammonia sharply irritates the eyes and air passages to the lungs. At high concentrations it makes the lungs fill with fluid, which can QUICKLY cause death unless prompt medical aid is given. The chemical formula for ammonia is NH3. The word "anhydrous" means "devoid of, or without water". Therefore Anhydrous Ammonia is merely "pure ammonia" with no added water.

USES OF AMMONIA

One of the principle commercial uses of ammonia is as a refrigerant. When a gas is liquefied, heat is given off; when a liquid evaporates, heat is absorbed. In the process of the manufacture of the ice for The Holderness School Ice-Rink, ammonia is compressed by pumps and becomes hot; it is then cooled by water, which flows over the ammonia pipes. When cool, the compressed ammonia liquefies. When pressure is released, the liquid ammonia evaporates; in doing so it takes up heat. The evaporation takes place in the pipes surrounded by a solution of low freezing point containing calcium chloride or common salt. This cooled solution is then piped to the skating rink where it freezes the rink water surrounding the pipes. When the ammonia evaporates it is usually reduced to a temperature of below -33.4°C (-28°F).

POTENTIAL HAZARDS

HEALTH

Ammonia may be fatal if inhaled. The vapors are extremely irritating and corrosive. Contact with ammonia gas or liquefied ammonia may cause burns to the skin, and in the case of escaping ammonia gas, severe frostbite or freezing of the skin and flesh. A fire at an ammonia source will produce irritating corrosive and toxic gases. Runoff from fire control efforts may cause ground and groundwater pollution.

FIRE OR EXPLOSION

Ammonia will not ignite in air. It will burn in pure oxygen. Ammonia gas, while only about half as dense as air is still heavy enough so that it will sink to ground level instead of remaining suspended in the air. Therefore, it will spread mostly along, or near to, the ground, rather than blowing like a full cloud. Containers of anhydrous ammonia are under great pressure. Anhydrous ammonia containers may explode when heated and cylinders may rocket when ruptured.

PUBLIC SAFETY

Call CHEMTREC 1-800-424-9300

Set up an initial isolation zone from the spill or leak for at least 300 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 personnel of The Holderness School unless they are part of the institutions Emergency Management Team.

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

Since ammonia gas will spread along the ground...it 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 ammonia is present, the ventilation must be forced by use of large volume fans. Note: since ammonia in air is NOT flammable or explosive, the use of Fire Department smoke ejector electric fans is permissible.

PROTECTIVE CLOTHING

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 ammonia 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.

EVACUATION

If ammonia 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 1000feet (.2miles). The width of this extended isolation zone beyond the initial isolation circle should be equal to the length of the zone, ie. 1000feet.

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 ammonia 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 ammonia cloud into the atmosphere, but it will keep the cloud more dense in the initial area.

FIRE

On small fires dry chemical or CO2 may be used. Note difference from fighting Chlorine fires.

On large fires ... water spray, fog, or regular foam. DO NOT GET WATER INSIDE THE AMMONIA CONTAINERS.

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.

ALWAYS STAY AWAY FROM ENDS OF TANKS.

SPILL OR LEAK

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.

FIRST AID

Skin or eye contact with gaseous or liquid ammonia and/or the ingestion of gaseous ammonia 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 ammonia 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.

Remember - THE EFFECTS OF CONTACT OR INHALATION MAY BE DELAYED.

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:

  • Rapid River Water Temperature Fluctuations - A Cursory Examination of the Dramatic Decline in Water Temperature on the Pemigewasset River at the Plymouth, NH River Stage Station on August 30-31, 2004
  • Subsidence Inversions - A brief discussion of atmospheric temperature inversions and their recognition and application in lighter-than-air flight.
  • Z-Time - Why do we refer to GMT, GCT, UTC, etc, as Z-time?
  • Firefighting & Chlorine - Firefighter's Guide to Chlorine
Copyright ©1997- Harold F. Maybeck. All Rights Reserved.

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