A refrigerant is a flammable gas and, in contact with an ignition source (electrical sparks, flame, static electricity), could ignite or burn and cause a fire. Lower (LFL) and upper (UFL) flammability limits determine the substance’s ability to produce a flame under a specific condition. These limits specify the concentration range in which the substance is flammable in the air. Below the LFL, the concentrations are too lean to burn or explode, above the UFL the concentrations are too rich or lack the oxygen to burn or explode. The risk of fire from a refrigerant is low when properly handled, used, and stored. Users, manufacturers, installers, and all other persons who come in contact with flammable refrigerants need to respect the safety rules.
Flammable refrigerants have low global warming potential, zero ozone depletion potential, are widely available, and inexpensive. Although flammable, they are widely used in refrigerating and air conditioning equipment due to their energy and cost efficiency, and high quality.
Typical flammable refrigerants used with light commercial and household appliances are R290 and R600a or R1234yf used in car air conditioning system, minibars, and truck refrigerators.
Key flammable properties of refrigerants:
|Refrigerant ||R600a ||R290 ||R1234yf |
|Lower flammability limit ||1.5% by vol. |
|2.1% by vol. |
|6.5% by vol. |
|Upper flammability limit || |
8.5% by vol.
9.5% by vol.
|Auto ignition temperature ||460°C ||470°C ||405°C |
ASHRAE 34 or ISO 817 classify refrigerants to safety groups based on their flammability and toxicity:
| ||Safety Group |
|Higher flammability ||A3 ||B3 |
|Flammable ||A2 ||B2 |
|Lower flammability ||A2L ||B2L |
|No flame production ||A1 ||B1 |
| ||Lower toxicity ||Higher toxicity |
The main difference between A2 and A2L, respectively B2 and B2L, is the refrigerant’s ability to produce a flame. Refrigerants in the *L group will burn, but their burning velocity is below 10cm/s which is lower than A2 or A3. They are difficult to ignite and self-extinguish.
All flammable refrigerants require system design and operations to follow the safety precautions. They can be used in new installations only and cannot be considered as drop-in alternative to existing HFCs systems. Electrical equipment has to comply with the IEC/EN 60079-15 standard, must be spark-free, or protected by an enclosure.
To prevent fire hazards caused by flammable refrigerants, relevant standards have been adopted to limit the charge size. They vary between regions and states and must be consulted to assure a legal requirement. If a higher charge is required, a risk analysis must be performed to identify and analyze all potential risks and prove the safety of the product. Charge quantity and ignition sources in place of application installation must be taken into consideration.
Safety standards such as ISO5149 or EN378 set requirements for the design, manufacture, installation, and operation of systems using flammable refrigerants with the aim of minimizing the risk of explosions.
Secop compressors for flammable refrigerants are marked with a yellow warning label even if they contain no refrigerant when leaving the factory.
Charging refrigerants should be done carefully and accurately. It can be done by weight or volume. In case of flammable refrigerants, it is recommended to use the weighing method as the charge quantity is low. The type of refrigerant and its quantity is stated by the refrigerator manufacturer on the label, datasheet, catalog, or other documentation. The optimal charge quantity is detected during testing under normal running condition and standard environment.
Currently valid European legislation EN60335-2-89 limits the maximum amount of refrigerant, allowed in a product to reduce flammability hazards and risk of toxicity to 150g. With this quantity it is possible to cover most plug-in commercial applications – merchandisers and food retail. Remote systems do not fall under the scope of this standard but follow EN378 with different criteria, no charge limits yet with other defined safety regulations.
HC charge increase
International Electrotechnical Commission (IEC) with its latest revision of the global safety standard IEC60335-2-89 from 2019 allows a higher charge of flammable refrigerants in self-contained commercial refrigeration appliances. Movement towards an ecological solution coupled with demands on higher charges prompted the charge increase allowance. The standard is voluntary and will come into force only when adopted and integrated by the regional bodies.
The revision covers all safety classes but with a different limit which changed to 13*LFL. For the single circuits, charge limits increased from 150 g to 500 g for refrigerants in safety class A3 (R290, R600a) and from 150 g to 1200 g for safety class A2 and A2L (R1234yf, R454C, R455A). The standard covers appliances such as display and storage cabinets, coolers and freezers, top-counter and under-counter units, blast chillers and blast freezers as well as commercial ice machines. All other appliances such as vending machines, ice cream makers, laboratory equipment, and household refrigeration comply with their own standards.
The new revision also defines additional safety requirements and measures when higher charges are used so as to not create more risk for the user. This includes hermetical sealing of the cooling circuit, protection of refrigerant containing parts against accessibility, application construction preventing excessive vibration, and appliance marking with the minimum floor area in which it is permitted to be installed.
Installation and service
Installation, service, and repair of systems with flammable refrigerants is to be conducted by properly trained personnel. This includes knowledge of tools, transportation of compressor and refrigerants, and the relevant regulations and safety precautions.
During service, possibility of refrigerant release or leak is present. Any potential sources of ignition should be eliminated, and the space should be properly vented by air or using a ventilation fan. Area should be marked with a warning symbol and monitored with a leak detector designed for a specific refrigerant to ensure the refrigerant concentration does not exceed the limits. Fire extinguishers must be available in the room. Personal protective equipment (PPE), gloves, goggles, and cloths are always needed.
Conversions of existing system from HCFC and HFC to R600a and R290 is not allowed, since the system is not approved for operation with flammable refrigerants and electrical safety has also not been tested according to current standards.