EN 378 and ISO 5149: safety classes, location classes and charge limits

The four parts of the standard

EN 378, Refrigerating systems and heat pumps – Safety and environmental requirements, applies to stationary and mobile refrigerating systems and heat pumps of all sizes, except vehicle air conditioning. The current edition is EN 378:2016, where part 1 has the A1 amendment from 2020 ^[1][2]. The standard has four parts:

1. Part 1: Basic requirements, definitions, classification and selection criteria. This is where the safety classes, location classes, access categories and charge limits are.
2. Part 2: Design, construction, testing, marking and documentation. This covers PS, pressure relief and pressure testing, among other things.
3. Part 3: Installation site and personal protection. This covers machinery rooms, ventilation, gas detection and emergency equipment.
4. Part 4: Operation, maintenance, repair and recovery.

ISO 5149, with the same four parts, is the international equivalent and is used in many countries outside Europe, for example as the basis of AS/NZS 5149 in Australia and New Zealand ^[4].

Safety classes

Each refrigerant has a safety class according to ISO 817 and EN 378-1: a letter for toxicity and a number for flammability ^[1][5].

Location class and access category

How much refrigerant a system may contain depends on where the system is located and who has access to the space ^[1].

• Access category a (general): spaces where anyone can be present, for example shops, hotels and homes. b (supervised): spaces where only a limited number of people are present and some of them know the safety procedures, for example offices and laboratories. c (authorised): spaces where only authorised persons have access, for example production areas and cold stores.
• Location class I: the system, or the parts containing refrigerant, is located in an occupied space. II: compressors and pressure vessels are in a machinery room or outdoors. III: all parts containing refrigerant are in a machinery room or outdoors. IV: the parts are in a ventilated enclosure.

Charge limits

The charge limit protects people in the room if the whole charge leaks out. For non-flammable refrigerants the limit is based on a concentration in kg/m³ that takes toxicity and oxygen deprivation into account (practical limit). The maximum charge is then essentially the limit multiplied by the volume of the smallest room into which the refrigerant can leak. For flammable refrigerants there are also limits based on the lower flammability limit (LFL): m1 = 4 m³ × LFL, m2 = 26 m³ × LFL and m3 = 130 m³ × LFL, multiplied by 1.5 for class 2L. How the limits are used depends on the location class and access category ^[1]. The article on flammable refrigerants shows examples for R290 and R32.

Machinery rooms and gas detection

If the concentration in a room can exceed the practical limit in the event of a leak, measures are required under part 3: gas detection with alarm, and sometimes mechanical ventilation or a machinery room. A machinery room must have, among other things, ventilation, a gas detector, an emergency stop outside the room and doors that open outwards. There are additional requirements for ammonia and for flammable refrigerants.

Pressure: PS, relief and testing

Part 2 requires every part of the system to have a maximum allowable pressure (PS) that is at least as high as the highest pressure the part can be exposed to in operation, at standstill and during transport, taking the ambient temperature into account. The system must be protected against excessive pressure with pressure limiters and safety valves set at no more than PS. After installation the system must be strength tested and tightness tested ^[2]. The guide to pressure testing describes how this is done.

In the EU, refrigerating systems are often pressure equipment under the Pressure Equipment Directive 2014/68/EU (PED). The category (I–IV) depends on PS, volume or pipe size and the fluid group. Flammable and toxic refrigerants are group 1, the others group 2. The category decides which conformity assessment is required before the system may be CE marked ^[6]. EN 378-2 is used to show that the requirements of the directive are met.

The revision of EN 378

CEN is revising EN 378. The draft prEN 378:2025 was out for public enquiry from 3 July to 25 September 2025. It includes, among other things, a new method for determining charge limits for flammable refrigerants, and the refrigerant table in Annex E of part 1 becomes a separate part 5. Part 4 is to be replaced by EN ISO 5149-4 without technical changes. According to AREA and IOR, the formal vote was planned for 17 July–11 September 2026 and publication for 28 February 2027. The new edition will replace the 2016 edition ^[3].