Refrigerant R744 (Carbon Dioxide) Combustibility / Decomposition

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Refrigerant R744 is nonflammable. It is instead a fire retardant due to its suppression of oxygen in the air.
Refrigerant R744 dissolves in water, where it forms carbonic acid. Carbonic acid is a weak acid and can have a corrosive effect on certain materials.
Refrigerant R744 is chemically stable and inert, but it can react violently with certain materials, such as ammonia.