The Classification of Refrigerants
Refrigerants are classified in three ways: the numbering designation by which chemicals or mixtures of chemicals are known; by toxicity level; and by flammability.
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Numbering
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Refrigerants are commonly known by an R for refrigerant and a number. The number relates to the chemical formula of the refrigerant. The digit on the far right denotes the number of fluorine (F) atoms, the second number from the right the number of hydrogen (H) atoms plus one, the third digit from the right denotes the number of carbon (C) atoms minus one and the final digit denotes the number of unsaturated carbon to carbon bonds in the compound. For example, CHClF2 is called R22 and CCl2FCClF2 is called R113.
An a, b, or c is sometimes added on to the number. This refers to different isomers (structural shapes) of the same refrigerant.
Toxicity
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The letter A (attached to the flammability number) after a refrigerant means it is in the lowest toxicological class (nontoxic at concentrations lower than 400 parts per million (ppm)). The letter B means it is in a higher toxicological class (toxic at levels of less than 400 ppm).
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Flammability
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Class 1 refrigerants are nonflammable at 21 degrees Celsius and under normal atmospheric pressure. Class 2 are flammable at pressures of more than 0.10 kilogram per cubic meter (kg/m^3) and Class 3 are highly flammable, at pressures lower than 0.10 kg/m^3.
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