The standard applies to any system of mechanical cold generation (including heat pump), in which a refrigerant evaporates and condenses in a closed circuit, with the exception of: a. systems working with water as a refrigerant; b. systems that use a gas as refrigerant whose critical temperature is below 0°C (e.g. air, nitrogen); c. installations for railway and motor vehicles, aircraft, ships and underground companies, if regulations aimed at safe operation already exis for these installations.
NEN 3380-1971 history
1971NEN 3380-1971 Safety requirements for refrigeration plants