HVAC standards, such as EN-378, use refrigerant flammability and toxicity properties safety properties to define refrigerant classifications and practical limits for systems for different access categories. Refrigerant charge limits are defined based on the lowest charge determined from the flammability and toxicity data. A wide range of flammability properties (see below) have been investigated due to the introduction of mildly flammable refrigerants. The refrigerant safety data is generally developed by a refrigerant supplier and submitted for review by ASHRAE 34 or ISO 817 committees. Typically, ISO 5149 and EN378 use the same data sets.
International and European safety legislation and standards such as ISO 5149 and EN 378 define requirements to remain well below the lower flammable limit in case of accidental leakage. Other flammability properties determine the ease of ignition (minimum ignition energy) and the pressure rise for ignition in confined spaces.
If a refrigerant is flammable, the classification properties used are:
These are a subset of flammability properties which can also include:
Some of these properties are linked. The charts show flammability data for refrigerants R-290 (A3), R-152a (A2), R-717 (B2L), R-32 (A2L), and R-1234yf (A2L). This data supports proposed links between flammability properties and helps explain why only three properties are used for refrigerant classification:
Independent flammability testing is also carried out, for example by SAE CRPs (Co-operative Research Programs) and the Japan Society of Refrigerating and Air Conditioning Engineers as part of risk assessments for the use of flammable refrigerants.
Flammability References Journal of Loss Prevention in the Process Industries 49 (2017) 662 – 674, Flammability and explosion characteristics of mildly flammable
The refrigerant toxicity classification has 400 ppm Occupational Exposure Limit (OEL) as the divide between higher and lower toxicity refrigerants. All widely used HFCs (except HFC-245fa), HFOs and HCFOs are classed as low toxicity, with OELs in the range 400 to 1000 ppm. The hydrocarbon refrigerants are also classified as low toxicity. ASHRAE 34 also cites, in its refrigerant data and safety classification table, the toxicity category of the International Fire Code and Uniform Fire Code regulations. The toxicity category is either highly toxic (LC50 ≤200 ppm), toxic (LC50 ≤ 2000 ppm) or neither (lesser toxicity than either of these groups). All the widely used HFCs, HFOs and HCFOs are in the ‘neither’ category. Ammonia has a OEL (time weighted average TWA) of 25 ppm and a short-term exposure limit (STEL) of 35 ppm, and according to ISO817:2014 an acute toxicity exposure level of 320ppm. The acute toxicity exposure level (ATEL) of refrigerants is used to determine toxicity based practical limits, with the maximum value being set by the limit of oxygen deprivation (ODL), which is 140,000ppm (14% v/v).