Flammable refrigerants (A2L and A3): charge limits, standards and ATEX

International · Laws and regulations

How propane, isobutane, R32 and other flammable refrigerants may be used: LFL, m1–m3 under EN 378, the room formula, IEC 60335-2-89 (13 × LFL), ATEX and safe servicing.

Last checked: October 7, 2026

Key points

A3 refrigerants such as propane (R290) are highly flammable. A2L refrigerants such as R32 and R1234yf have lower flammability, with a burning velocity of at most 10 cm/s ^[1].
EN 378-1 limits the charge using the lower flammability limit (LFL): m1 = 4 m³ × LFL, m2 = 26 m³ × LFL, m3 = 130 m³ × LFL, multiplied by 1.5 for A2L ^[1].
For propane (LFL 0.038 kg/m³), m1 is about 150 g and m3 about 4.9 kg ^[1].
Under IEC 60335-2-89, self-contained commercial refrigerated cabinets may hold up to 13 × LFL per circuit, about 500 g of propane ^[2]^[3].
Where an explosive atmosphere can occur, the ATEX directives for equipment (2014/34/EU) and workplaces (1999/92/EC) apply ^[4]^[5].

Why flammable refrigerants are becoming more common

The low-GWP requirements of the F-gas Regulation and similar rules in other countries are phasing out high-GWP refrigerants. The most common replacements are either natural refrigerants, for example propane, isobutane and carbon dioxide, or low-GWP synthetic refrigerants, for example R32 and HFO blends. Carbon dioxide is not flammable. Most of the other replacements are A3 or A2L. Their flammability is the reason why the quantity in a room is limited and why installation and servicing require particular care.

LFL and safety classes

The lower flammability limit (LFL) is the lowest concentration of the refrigerant in air that can ignite, expressed in kg/m³. Propane has an LFL of 0.038 kg/m³ and R32 0.307 kg/m³. The lower the LFL, the smaller the quantity needed for a flammable mixture to form in a room. Class 2L has lower flammability: a flame spreads slowly, at most 10 cm/s, and more energy is needed to ignite the mixture. That is why A2L refrigerants may be used in larger quantities than A3 ^[1].

Charge limits under EN 378-1

EN 378-1 divides flammable refrigerants into three levels ^[1]:

Limit	Formula	R290 (propane)	R32 (A2L, × 1.5)
m1	4 m³ × LFL	0.15 kg	1.84 kg
m2	26 m³ × LFL	0.99 kg	12.0 kg
m3	130 m³ × LFL	4.94 kg	59.9 kg

Below m1 there are essentially no requirements linked to the size of the room. Between m1 and m3 the charge is limited by the size of the room and the installation height. A common way to calculate is the formula m_max = 2.5 × LFL^1.25 × h0 × A^0.5, where A is the floor area of the room in m² and h0 is the height at which the refrigerant can leak, for example 0.6 m for floor-standing units and 2.2 m for ceiling-mounted units. Above m3 the parts containing refrigerant must be in a machinery room, a ventilated enclosure or outdoors, depending on the location class and access category ^[1]. Always check the edition of the standard that applies to the project: the revision of EN 378 changes the method for flammable refrigerants.

The product standards IEC 60335-2-89 and 60335-2-40

Factory-made appliances are covered by product standards in the IEC 60335 series, which in Europe are published as EN 60335. IEC 60335-2-89 covers commercial refrigerated cabinets and ice and ice-cream machines with an incorporated or remote compressor. The 2019 edition raised the limit for A3 refrigerants from 150 g to 13 × LFL per refrigerant circuit, about 500 g of propane, provided that the appliance meets additional requirements on leak tightness and testing, among others. For A2L refrigerants the limit is 1.2 kg ^[2]^[3].

IEC 60335-2-40 covers air conditioners, heat pumps and dehumidifiers. It sets how much flammable refrigerant an appliance may contain in relation to the size of the room, and which measures allow a larger charge, for example leak detection, air circulation or ventilation and shut-off valves. The manufacturer's instructions on minimum floor area must always be followed during installation.

ATEX

ATEX consists of two EU directives. Directive 2014/34/EU covers equipment and protective systems intended for use in potentially explosive atmospheres ^[4]. Directive 1999/92/EC covers the employer's obligations: to assess the risk of an explosive atmosphere, divide areas into zones, select suitable equipment and document everything in an explosion protection document ^[5]. In refrigeration, ATEX becomes relevant for example in machinery rooms with propane or ammonia and during servicing where refrigerant can leak. EN 378 and the product standards are designed so that normal operation does not produce an explosive atmosphere, but the risk must be assessed for servicing and leaks.

Safe servicing of flammable systems

Assess the risk before the work and make sure there are no ignition sources nearby: open flames, sparks, hot surfaces, power tools that are not approved.
Measure the concentration with a gas detector intended for the refrigerant, before and during the work.
Ventilate the work area. Flammable refrigerants such as propane are heavier than air and collect at floor level and in pits.
Use recovery units, vacuum pumps and tools approved by the manufacturer for flammable refrigerants.
Remove the refrigerant and purge the system with nitrogen before brazing. Never braze on a system that contains flammable refrigerant.
Have a fire extinguisher at hand.
Label the system with the refrigerant and quantity, and follow the rules for storing and transporting gas cylinders.

National rules on flammable gases can require a permit or notification for larger quantities. Ask the fire and rescue service or the equivalent authority.

Calculate it yourself

HC (A3) refrigerant pipe sizing →GWP, ODP & CO2e of a refrigerant charge →HFC/HFO refrigerant pipe sizing →

Terms in this article

A2L (lower flammability refrigerant)LFL (lower flammability limit)Safety class Practical limit Location class Natural refrigerants HFO (hydrofluoroolefins)