The low GWP alternative to R410A was introduced in certain models of air conditioner in Australia last year, is available in the Far East and was introduced in some Daikin splits in Europe at the end of last year. In global moves towards lower GWP refrigerants, R32 is considered a key future replacement for R410A in air conditioners.
Although being a more environmentally friendly alternative, R32’s A2L “mildly flammable” classification and potential hazards as recorded in the chemical’s material safety data sheets (MSDS) has brought opposition from some quarters in Australia.
In an effort to explain and answers questions about R32, the Australian Airconditioning and Refrigeration Equipment Manufacturers’ Association of Australia (AREMA) and the Consumer Electronics Supplier Association (CESA) have prepared a technical fact sheet on the refrigerant.
“Research conducted to prepare the document confirms that R32 is not an extremely flammable, highly toxic gas that causes cancer, as some industry representatives have suggested,” claims AREMA.
Far from being extremely flammable and highly toxic, the new document, R32 – Common Questions, maintains that R32 is not explosive, is extremely difficult to ignite and is the least toxic of all the Class A (non toxic) refrigerants listed in ISO 817.
In Australia, some confusion has been created by the contents of R32’s material safety data sheet which describes R32 as extremely flammable. The AREMA/CESA document explains that the MSDS is published in accordance with the Globally Harmonised System of Classification and Labelling of Chemicals (GHS) which uses a simplistic approach to classifying flammable gases and does not take into consideration the percentage concentration of gas required to create a flammable mixture in air, how easy the gas is to ignite or how it behaves once ignited.
On the subject of toxicity, AREMA argues that all refrigerant gasses classified in ISO 817 can initiate some form of adverse health effect if the concentration is high enough but insists that, compared to all other common refrigerants, R32 requires the highest concentration level to cause any adverse health effect.
With an Acute Toxicity Exposure Limit (ATEL) of 220,000ppm, R32 has the highest ATEL of the 99 refrigerants designated in Table 5 of ISO 817, which includes R22, R410A, R134a, R290 (propane) and R600a (isobutane).
Byproducts of combustion
Concerns over the production of toxic byproducts when burnt are also dispelled. It points out that all fluorinated refrigerants will decompose and produce toxic byproducts such as hydrogen fluoride (HF) and carbon dioxide when burnt. Tests are said to have shown that R32 is no more likely to produce HF than other currently used HCFC/HFC refrigerants.
Analysis of R32 exposed to a variable temperature heater revealed that hydrogen fluoride started to be produced when the temperature was in the range of 570°C to 590°C. Other commonly used refrigerants R410A, R407C, R404A, R134A, and R22 also start to decompose at around the same temperature.
Further tests of R32 demonstrated that a 5% in air mixture exposed to a red hot wire produced less HF (5ppm) than an equivalent mixture of R22 (70ppm).
The source of claims that R32 is carcinogenic are less easy to pin down but are thought to relate to a California law.
“We believe this concern is based on the Honeywell MSDS for R32 and R410A which contain the statement: ‘Warning – This product contains a chemical known to the State of California to cause cancer – Dichloromethane’,” explains the AREMA/CESA document.
“It is important to note that the warning is in relation to a chemical called dichloromethane (methylene chloride) and not difluoromethane (the chemical name for R32). Dichloromethane is a raw material used in the production of R32. After production, trace levels of less than 0.003% may still be present in the final product.”
The AREMA/CESA document points out that under California law, a compound must display the “cancer warning” unless a person exposed to the substance at the expected level for 70 years is estimated to have a 1 in 100,000 chance or less of getting cancer due to the exposure. “As a result, it says, “many common items such as foods, cosmetics, supplements, cups and eating utensils, clothing, tools, sporting goods, electronic appliances and gases carry this warning if the substance is intended to be available in California.”
Now accepted as a classification in the International Standard ISO 817:2014, R32’s A2L mildly flammable classification is reserved for flammable gases with a burning velocity of less than 10cm/s. This means that the flame front does not propagate readily in a horizontal direction and effectively means that an A2L refrigerant is not explosive if ignited.
And ignition, tests have shown, is hard to achieve. R32’s flammability limit is between 14% volume (300g/m³) and 29% volume (620g/m³). AREMA points out that a 14% concentration of any foreign gas in air is the accepted oxygen deprivation safety limit and, in addition, is well above the acute toxicity exposure limit for existing refrigerants like R22 (5.9%) and R134a (5%).
As well, in order to ignite, a flammable gas mixture must have a velocity lower than 3 to 4 times its burning velocity. In the case of a heavier than air R32 leaking from a wall-mounted split, the refrigerant will exceed 4 times its burning velocity due to gravity within 40cm. In addition, the new document maintains that measurements and computational fluid dynamic modelling has shown that even a rapid R32 leak of 1kg in one minute will not present a flammable mixture outside of the wall unit due to dilution and the falling velocity of the refrigerant.
Unlike common flammable gases such as propane, R32 cannot be ignited by static electricity and tests are said to have shown that sparks from light switches or contactors in residential appliances do not have sufficient energy to ignite the refrigerant.
“Therefore,” says AREMA/CESA, “the most likely source of ignition in a residential application is an open flame such as a candle, combustion heater or gas cook top.”
Consequently, if an accidental release of R32 refrigerant occurs from a cylinder or piping, the velocity will be too high to ignite near the release point and the concentration will be too low where the velocity becomes low enough.
“So, ignition of R32 is difficult even if it is attempted intentionally,” says the document.
A copy of the report is available for download here.
R32 – the Australian view – November 12 , 2013
With Daikin well advanced in the development of air conditioning units running on R32 and others not far behind, the introduction of split air conditioners with this low GWP “mildly flammable” refrigerant seems inevitable. While information from the Far East is sparse, there is another country preparing for R32 units – Australia. Read more…