Refrigerant Properties and Safety

The properties of refrigerants and refrigerant safety can be categorized in several ways, including:

• Ozone Depletion Potential (ODP). Ozone in the upper atmosphere provides protection for animals and plants from the large ultraviolet component of sunlight. ODP refers to the damage a substance can cause to ozone in the stratosphere measured relative to CFC-11 which is defined with an ODP of 1.

• Global Warming Potential (GWP). GWP indicates a substance's ability to trap heat in the atmosphere over a period of time, called an integrated time horizon or ITH. The measurement is relative to CFC-11 or carbon dioxide, and an ITH of 100 years is typical for CFCs, HCFCs and HFCs.

• Both direct GWP and indirect GWP are considered in refrigerant environmental impact. Direct is from the refrigerant itself. Indirect considers the carbon dioxide and other emissions produced at the power plant that supplies electricity to the cooling system.

• Flammability considers the refrigerant/air ratio, pressure, temperature and potential sources of ignition. ASHRAE rates systems from "no flame propagation" Class 1, to the more flammable Class 2 and 3 substances.

• Personnel exposure limits are established using toxicology tests. The Threshold Limit Value (TLV) sets the amount of time most workers may be exposed to a substance during an eight hour day and 40-hour week without adverse effects. Other measures include Acceptable Exposure Limit (AEL) published by refrigerant manufacturers, and Permissible Exposure Limit (PEL) published by the federal government. Again, ASHRAE rates systems from Class A (lower toxicity) to Class B (more toxic).

Additionally, ASHRAE Standard 15 requires that for Class A1 refrigerants (that's "A" for lower toxicity, and "1" for no flame propagation), equipment rooms must be equipped with oxygen sensors to warn of oxygen levels below 19.5 percent. For other refrigerants, a vapor detector must be installed to warn of potentially harmful concentrations of refrigerant vapors.

Two other issues relate to this discussion:

1. CFCs are no longer listed by the Environmental Protection Agency as a hazardous waste. The original 1990 rule has been suspended.

2. Local building codes may not yet allow the use of HCFC-123, HFC-134a, and other alternatives because the codes have not yet been updated. At present, the major model code groups have accepted an interim proposal recognizing the alternative refrigerants. The needed official code changes are forthcoming. Check them in your area.