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October 2010: Ammonia Refrigeration Systems

Commercial ammonia refrigeration systems are widely used throughout various industries, but are used primarily in the food industry to help prolong shelf life. All refrigeration systems operate essentially as heat pumps, removing the heat from one area and discharging it to another area. Because of its ability to absorb and discharge heat readily, ammonia is an excellent refrigerant. However, it can cause extensive property damage if not handled properly.

Anhydrous ammonia is a Group 2 refrigerant as defined by ANSI. Some selected properties of ammonia are shown below.

Refrigerant

Chemical Formula

Boiling Point

Specific Gravity

Autoignition Temp

Flammable Limits

Toxicity

°F

°C

°F

°C

Lower

Upper

R-717

NH3

-28

-33

0.59

1204

651

16

25

High

It is evident that the predominant hazard of ammonia is its toxicity; however, it can also cause significant property damage. The primary cause of property damage in industrial facilities is contamination, especially in those handling food products. Ammonia tends to change the flavor of some foods, making them less desirable or inedible. The extent of contamination usually depends on the severity of the leak (concentration of ammonia), exposure time, type of food product, and the way the food product is packaged. Those products wrapped in polyethylene are usually not as susceptible to contamination as those in cardboard boxes or other porous materials. The type of food can also play a role in the amount of damage incurred. Those products with high moisture contents like fruits and vegetables are usually more susceptible than dry products such as nuts.

In any event, the best way to limit the amount of contamination damage from an ammonia leak is to isolate the leak quickly and ventilate the affected area. The remaining ammonia can be neutralized by introducing carbon dioxide (CO2) into the area. Ammonia readily combines with CO2 to form an innocuous white powder, which can be disposed of easily. Any remaining traces of ammonia can be eliminated using one of several weak acids.

In addition to contamination, significant property damage can also occur from ammonia explosions. Although ammonia has a very narrow explosive range (16-25% by volume), explosions do occur. Though admittedly rare, the property damage from an ammonia explosion can cause significantly more property damage and business interruption than contamination alone. Explosions occur when a leak or release creates an explosive mixture and is then ignited by a heat or flame source. These incidents are most likely to occur in or around ammonia compressor (engine) rooms since there are more connections and fittings that can fail. This is also where the highest system pressures occur.

Prevention

The best way to prevent an ammonia contamination and/or explosion loss is by ensuring proper design. Ammonia compressor rooms should be of noncombustible construction and completely cut off from surrounding areas. In addition, explosion-relieving construction should be provided on exterior walls. There should be no ignition sources in the room such as space heaters or open flames. Also, all electrical equipment should be rated for use in Class I, Division II locations in accordance with the National Electrical Code (NEC). Automatic sprinkler protection is preferred; however, does not have to be provided if the room is of noncombustible construction and is kept free of combustibles (unless required by the authority having jurisdiction). There are a few exceptions to these requirements for existing machine rooms; however, they require a case by case analysis.

The integrity of the entire system should be ensured by a comprehensive preventive maintenance program based on manufacturers' guidelines. In addition, all personnel responsible for working on these systems should be well trained (especially outside contractors). Piping should be seam welded where possible and the use of threaded pipe should be kept to a minimum.

A comprehensive emergency response plan should be in place in the event of an incident involving ammonia. Site personnel should be fully trained to quickly handle spills and/or leaks so that property damage can be minimized (isolation, ventilation, and cleanup). If an on-site hazardous materials team is not an option, arrangements should be made with local emergency response organizations. To make response more effective, critical valves should be labeled and accessible. In addition, intensive training should take place at frequent intervals.

Ammonia refrigeration is an everyday hazard that doesn't always get the attention it deserves. It is absolutely vital that companies make the effort to prevent these incidents since they can have long lasting effects on the bottom line. We have only scratched the surface here, so if you would like more information on these and related issues, we recommend the following websites as a start:

www.NH3.com

www.USDA.gov

www.FDA.gov

www.industrialconsultants.com