Ammonia has been in continuous use as a refrigerant longer than any other. It is in fact among the first refrigerants to be commonly used and remains one of the most widely used today. Ammonia has its drawbacks though, the largest being its high toxicity. CO2, on the other hand, is a viable alternative to ammonia. It requires minimal safety regulations compared to other A2L, B2L toxic or A3 flammable rated refrigerants and reduces or eliminates hazardous materials requirements and liability costs.