What are refrigerant safety groups?

The Refrigerant Safety Group classification consist of two alphanumeric characters (e.g. A2); the capital letter corresponds to toxicity and the digit to flammability. For toxicity, Class A toxicity signifies no toxicity at less than or equal to 400ppm, Class B toxicity signifies for which there is evidence of toxicity. For flammability, Class 1 indicates refrigerants that do not show flame propagation when tested in air at 21°C and 101 kPa, Class 2 indicates refrigerants having a lower flammability limit of more than 0.10 kg/m3 at 21°C and 101 kPa and a heat of combustion of less than 19 kJ/kg, Class 3 indicates refrigerants that are highly flammable as defined by a lower flammability limit of less than or equal to 0.10 kg/m3 at 21°C and 101 kPa or a heat of combustion greater than or equal to 19 kJ/kg.