“Hydrocarbons are constituents of natural gas and petroleum.”

ASHRAE, Refrigerants and their Responsible Use

Hydrocarbons such as propane (e.g., R-290, R-600) are a refrigerant option where highly flammable gases can be safely used.

Hydrocarbons, such as propane and isobutane are separated from fossil fuels in oil refineries and purified on-site.

Hydrocarbons have a A3 safety classification (“lower toxicity, higher flammability”).

Switching to hydrocarbons in existing systems is not possible due to charge size limits and need to mitigate the flammability hazards. For this reason, these refrigerants are only used in newly manufactured and appropriately designed equipment