Detecting Ammonia Hazards In Refrigeration

Anhydrous Ammonia (NH3) is commonly used as a coolant in large industrial refrigeration systems. While ammonia refrigeration has long been a standard in the food/beverage industry, it is also now found in pharmaceuticals production, in air-conditioning equipment for some public buildings and in electric power generation plants. Ammonia is a toxic gas, though, and the proper safety monitoring procedures and equipment must be in place at all times to avoid serious accidental injury or death.

Ammonia refrigeration is considered cost efficient, and has been credited with keeping the price of food at affordable levels in the U.S. It also plays a role in the floral industry, as well as in various types of cold storage warehouses and in ice production. Ammonia industry experts say its use in refrigeration systems is environmentally friendly, and it does not destroy ozone or contribute to the greenhouse effect linked to global warming.

When installed and maintained properly, with trained operators as well as safety equipment and procedures in place, ammonia refrigeration is generally considered safe. The accidental release of pressurized ammonia from refrigeration systems, however, is a potential toxic gas hazard that can injure workers, damage plant equipment and potentially affect the general public outside the plant environment.

Refrigeration Applications
A colorless gas, ammonia occurs naturally in the environment and is also man-made for industrial purposes such as refrigeration. In nature, bacteria, decaying plants and animals, and animal waste in the soil produce the gas. Ammonia is manufactured by mixing natural gas with steam, which is reformed over a catalyst bed to produce hydrogen and carbon dioxide. The hydrogen and nitrogen, from the air, react in a final catalyst bed to produce ammonia gas, which is cooled for tank storage.

While agriculture (fertilizer) accounts more almost 80 percent of ammonia use in the U.S., refrigeration use is less than 2 percent in mostly the food industry in the following applications:
  • Beverage Bottling
  • Meat Packing
  • Snack Foods
  • Dairies and Creameries
  • Bakeries
  • Confectionaries
  • Produce
  • Safe Exposure Levels - Ammonia
    The Occupational Safety & Health Administration (OSHA) has set a limit of 25 parts-per-million (ppm) in the workplace during an 8-hour shift and a short-term limit (15 minutes) of 35 ppm. International standards for ammonia exposure are similar to those in the U.S. The effects of ammonia exposure range from irritating smells to life-threatening situations.

    The Environmental Protection Agency (EPA) regulates ammonia under the Clean Air Act’s General Duty Clause [Section 112(r)(I)] and Risk Management Program (RMP) Rule [40 CFR 68]. Facilities with over 10,000 pounds of ammonia are required to develop a hazard assessment, a prevention program, an emergency response program and submit a risk management plan to the EPA.

    Exposure Risks - Ammonia
    Reliable ammonia detection ensures both personnel safety and product quality. The nose may detect ammonia in concentrations as low as 5 ppm. Typical exposure symptoms are irritation of the eyes, throat and respiratory organs. At a few hundred ppm, irritation of the mucous membrane of the eyes occurs. Breathing is intolerable at about 1000 ppm and vision may be impaired. The risk of fatality rapidly increases at concentrations of around 2500 ppm.

    In addition to personal injury, ammonia accidents can result in considerable equipment, materials, product and property losses. According to the EPA and Factory Mutual, ammonia releases have resulted in several catastrophic losses ranging up to several million dollars. Such losses have resulted from ammonia contamination to product, as well as explosions because ammonia is potentially combustible.

    Ammonia Monitoring System
    Ammonia is liquefied under pressure in refrigeration units. When accidentally released to the atmosphere and undetected, ammonia becomes an aerosol that is a mixture of liquid and vapor. Once in the air, the ammonia becomes a cloud that can travel through a plant and beyond into surrounding neighborhoods, posing a general public health threat.

    The General Monitors' MC600 Multi-Channel Controller is designed to provide an advanced gas monitoring system that sounds the alarm when ammonia or other toxic and combustible gases are a problem. One MC600 Controller can be hardwired to six TS400 Series Ammonia Toxic Gas, TS420 Oxygen Deficiency, S4000TH H2S or IR400 Combustible Gas detectors installed at strategic plant locations. It delivers a total solution—high performance, reliability and safety at a low cost per point.

    TS400 Ammonia Gas Detector
    The TS400 Toxic Gas Detector is a compact, fixed toxic gas detector with electrochemical cell sensors that detect a wide range of gases, including ammonia. Two-wire loop power eliminates the need and cost of a separate power supply. A built-in LCD indicator provides for status, fault and calibration cues. The TS400 also detects Cl, CO, NO, NO2, SO2, ClO2, HCl, and O3.

    Ammonia Hazard Reduction
    Along with proper equipment, maintenance, training, etc., the U.S. EPA recommends the use of ammonia gas detectors in facilities that are not manned 24-hours per day. Even if a plant is manned 24-hours per day, you may want to install fixed ammonia gas detectors near refrigeration equipment to reduce the risk of injury to workers.

    The EPA’s Chemical Accident Prevention Group has been evaluating facilities with ammonia refrigeration systems and has compiled a list of steps that plant operators can take to both reduce the likelihood and severity of ammonia accidents. These preventative measures as well as more information on ammonia refrigeration are available online from the EPA.

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