Ammonia Refrigeration in Warehouses

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What is ammonia?

Pure ammonia (NH3), also known as anhydrous ammonia, is a colorless gas, with a strong and pungent odor.  Ammonia’s odor is its greatest safety asset.  Most people can smell ammonia before it reaches a hazardous level.  Ammonia’s odor threshold is sufficiently low to provide adequate warning of its presence. However, ammonia causes olfactory fatigue (loss of sense of smell) or adaptation, making it difficult to detect its presence when exposure is prolonged.

If the odor of ammonia is present, notify a person in authority immediately. 

How is ammonia used?

More than 80% of ammonia produced is used for agricultural purposes; less than two percent is used for refrigeration.  Use of ammonia is generally safe provided appropriate maintenance and operating controls are exercised.

Industrial refrigerated warehouses and food processing facilities typically use anhydrous ammonia.  The ammonia used in these systems must be 99.995 percent pure to ensure the system operates efficiently. 

Ammonia refrigeration systems are a series of interconnected vessels and piping that compress and pump ammonia to one or more rooms to cool, chill, or freeze them to specific temperatures.  The quantity of ammonia in systems varies from less than 5,000 pounds to more than 250,000 pounds.

Are ammonia releases common?

Typically, ammonia remains contained within the pipes and components of a refrigeration system.  These systems are designed and built to strict standards and codes developed to prevent accidental releases.  In addition, facilities must comply with extensive federal regulations that promote the safe operation of the system to protect employees, others who visit or conduct business at a facility, or neighbors who may live near by.  It should also be noted that it is common for the smell of ammonia to be present during some routine maintenance procedures, even when the system is not operating.

Ammonia releases have occurred that caused injuries and/or fatalities.  However, a release that results in serious injuries or fatalities is the exception, not the rule. 

Most facilities have trained operators onsite who operate and maintain the system.  Some facilities hire specialized refrigeration contractors to operate and maintain the refrigeration system.  Only trained individual should operate an ammonia refrigeration system.  Many ammonia systems, however, are not staffed around the clock, and warehouses may be closed at nights and on weekends.

What are the general hazards associated with exposure to ammonia?

Ammonia can cause a variety of health effects, ranging from irritation to severe respiratory injuries to death.  The extent of the potential injuries varies, depending on the concentration level and the length of exposure.  Above certain levels, ammonia vapor is a severe respiratory irritant. 

When liquid ammonia is released it may mix with air and behave as a dense gas.  Because of its strong and pungent odor, ammonia can be usually detected at concentrations in the range of about 5 to 50 parts per million (ppm).  Concentrations above about 100 ppm are uncomfortable to most people; concentrations in the range of 300 to 500 ppm will cause people to leave the area immediately.

Specifically, what injuries can result from exposure to ammonia?

Generally, only those individuals in the immediate area of an accidental ammonia release are exposed to hazardous concentrations, unless it is a large release.

Exposure to a low concentration of ammonia vapor can:

Exposure to higher concentrations of ammonia vapor can:

Exposure to liquid ammonia is not common at ammonia refrigeration facilities.  If it does occur, severe injury can result, including frostbite and corrosive burns.  Symptoms of mild frostbite include numbness, prickling and itching in the affected area.  Symptoms of more severe frostbite include a burning sensation and stiffness of the affected area.  The skin may become waxy white or yellow. Blistering, tissue death and gangrene may also develop in severe cases.

Available studies have not shown significant health effects in people with long-term occupational exposure to ammonia.  People with repeated exposure to ammonia may develop a tolerance (or acclimatization) to the irritating effects after a few weeks.  Tolerance means that higher levels of exposure are required to produce effects earlier seen at lower concentrations.

Inhalation of ammonia may, however, aggravate symptoms of chronic lung diseases such as asthma and emphysema.

What are the fire and explosion dangers associated with exposure?

Ammonia is generally not considered a serious fire or explosion hazard because ammonia-air mixtures are difficult to ignite and a relatively high concentration of the gas is required.  Ignition sources such as electric discharge from a forklift, an unprotected tungsten filament lamp, a spark from a motor, or the heat of a welding or cutting torch can cause the ignition of a flammable mixture of ammonia and air.

Toxic and irritating nitrogen dioxide can form during burning in air.  Containers or cylinders may rupture violently due to over-pressurization, if exposed to fire or excessive heat for a sufficient period of time.

What can be done to protect workers?

Implementing effective control measures and work practices can significantly reduce occupational exposure to ammonia:

What should be done in case of ammonia releases and emergencies?

In the event of an ammonia release:

Which regulations and guidelines apply to ammonia use and exposure?

For more information, please contact the Safety and Health Department at (202) 624-6960.