Study on the practical use of flammable and slightly flammable refrigerants

Date: 08 March 2022
Climate challenges, transition to 2050 objectives, regulations like F-gas are diving the RACHP sector to use lower Global Warming Potential refrigerants.

However, some low GWP refrigerants lead to other potential risks such as flammability.

Refrigerant classification includes several degrees of flammability and the implementation of these refrigerants into refrigeration systems needs to be carefully addressed.

Thus, partnering with ADEME, AFCE asked COSTIC to carry out a study attached about the practical use of these flammable refrigerants.


Regulatory requirements, in particular via EU Regulation 517/2014 on greenhouse gases (known as the F-Gas regulation), aim to progressively reduce the quantity of refrigerants that have an impact on the greenhouse effect. Under these conditions, the programmed reduction or prohibition of certain equipment and fluids, and the strengthening of leakage controls, encourage the replacement of these fluids by other "more neutral" fluids to the environment. However, some fluids with a low environmental impact do present other risks, such as flammability. The classification has been updated to include a new flammability subclass "2L" for flammable fluids that burn very slowly. 

To integrate this new category, the NF EN 378 standard on safety and environmental requirements for refrigeration and environmental requirements for refrigeration systems and heat pumps has evolved. This evolution has made it possible to add the new flammability class "2L" and all the implications for design, load calculation and operation. 

This study aims at characterizing these flammable fluids during the different phases of the life phases of an installation.

Flammable fluids: definition and characteristics

A refrigerant is a substance (or a mixture of substances) that ensures the transfer of energy in a thermodynamic system. According to the ISO 817 standard (2014), a refrigerant is classified based on 2 criteria: its toxicity (A or B) and its flammability (1 to 3).

The flammability of a fluid is defined by its capacity to propagate a flame from an ignition source.

Combustion is an exothermic chemical reaction between an oxidizer (air, oxygen) and a fuel. A body is said to be flammable when it burns with the production of flames. 

Figure 1. Characteristics related to the flammability of fluids

Flammability Class  Lower flammability limit (kg/m³)  Combustion heat (MJ/kg)  Flame propagation speed (cm/s)  Associated risks
Non flammable 
No flame propagation 
Slightly flammable 
≥ 0,1 kg/m³  ≤ 19 MJ/kg  ≤ 10 cm/s  Thermal effect  
No overpressure effect 
≥ 0,1 kg/m³  ≤ 19 MJ/kg  Limitless  Thermal effect  
Possible overpressure effect 
Highly flammable 
< 0,1 kg/m³  > 19 MJ/kg  Thermal and overpressure effect (explosion) 

Figure 2. Terminology



Lower flammability limit (LFL) (kg/m³)

It is the minimum concentration of refrigerant capable of propagating a flame in a homogenous mixture of refrigerant and air (can also be expressed as % volume in air)

Combustion heat (MJ/kg)

Amount of heat released by the combustion of a unit mass of fluid

Flame propagation speed (cm/s)

Speed at which the flame progresses in relation to the oxidizer (fresh air)

Ignition temperature (or flash point) (°C)

Temperature at which a fluid ignites in the presence of a flame

Minimum ignition energy (MJ)

Minimum energy required to ignite a flammable “air/gas” mixture. Any ignition source with an energy level below this value will not cause ignition

Auto-ignition point (°C)

Temperature at which a fluid ignites spontaneously without any heat input

The three criteria: lower flammability limit, heat of combustion and burning rate, characterise the different classes of flammable fluids.

Figure 3: Risk level of flammable refrigerants

Risk level of flammable refrigerants

The regulatory and normative context

The regulatory and para-regulatory texts that are applicable to flammable fluids can be different and complementary depending on the type of building or the flammability class of the fluid. The next table summarizes some essential texts according to the field of application and the type of building. These texts deal particularly with the specificities of design (calculation of fluid load, safety measures), installation and operation.

Depending on the fluids, other texts or standards are also to be considered, such as:

  • The F-Gas regulation (European regulation N°517/2014 of April 16, 2014): tightness control for certain fluids (pure HFC or in mixture);

  • The ATEX directives (directive 1999/92/EC of 16 December 1999 and directive 2014/34/EC of 26 February 2014) and the NF EN 60079-10-1 standard: characteristics of equipment according to the zone, determination of the extent of the leakage zone, protective devices for workers, equipment and protective systems intended for use in explosive atmospheres.

  • The PED Directive (Directive 2014/68/EU of 15 May 2014), the Order of 20 November 2017, the Professional Technical Specification for the in-service monitoring of pressurized refrigeration systems of 23 July 2020: group of fluids and associated requirements, in-service monitoring.

 All the afore-mentioned texts are further described in this chapter.

Comfort application  Commercial and industrial refrigeration application 
Residential  Other buildings (tertiary-industrial)  HRB  Housed groups (plug in)  Furniture sales, storage  Others (cold rooms, industrial refrigeration systems...) 
Reference documents for implementation, load calculation, safety devices  NF EN 378  NF EN 378  Article GH37  Guide M (French ministry of interior)  NF EN 378  NF EN 378 
Other possible documents  IEC 60335-2-40  IEC 60335-2-40 (according to the rated voltage)  IEC 60335-2-89 
Mandatory application of reference documents for implementation, load calculation, safety devices  No  No  Yes  Yes  No  No 
Possible use of flammable fluids  (A2L, A2, A3)  Yes  Yes  No  Oui sous conditions (cf. paragraphe 4.9)  Yes  Yes 

The F-Gas regulation

The European Regulation N°517/2014 of April 16, 2014 on fluorinated greenhouse gases defines 3 main actions:

  • The prevention of fluid leaks with, in particular, a reinforcement of leakage controls

  • The timetable for reducing the amount of greenhouse gases

  • Progressive bans on marketing

The fluids concerned by these requirements are hydrofluorocarbons. By definition, hydrofluorocarbons are HFC fluids and mixtures containing one of the following substances. The fluids concerned by these requirements are A2L fluids.

Read full the report

generated: 0.0066