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HFO-1234yf flammability no excuse for HC temptation

VASA is aware of concerns in the industry over the flammability of HFO-1234yf and the temptation to switch to less expensive hydrocarbon refrigerants.

This knee-jerk reaction must be avoided, not least because using hydrocarbon refrigerants means servicing air conditioning systems with gases they were never designed for.

Here are some facts to show the difference in flammability between HFO-1234yf and hydrocarbon refrigerants:

HFO-1234yf has an ASHRAE (formerly the American Society of Heating, Refrigerating and Air Conditioning Engineers ) rating of A2L (mildly flammable) and hydrocarbon refrigerant R-290 (propane) has an ASHRAE rating of A3 (highly flammable).

The numbers speak for themselves and explain why it is difficult for HFO-1234yf to sustain and propagate a flame:

  • The minimum ignition energy required to set HFO-1234yf alight is between 5000 and 10,000 millijoules, compared with just 0.25mJ for propane.
  • HFO-1234yf has a burn velocity of 1.5 centimetres per second, compared with 46cm/s for propane.
  • The heat of combustion for HFO-1234yf is 10.7 kilojoules per gram, compared with 46.3kJ/g for propane
  • For comparison, petrol has a minimum ignition energy of 0.29mJ, a burn velocity of 34cm/s and a heat of combustion of 47kJ/g

The fact is, HFO-1234yf requires much more energy to ignite than hydrocarbon refrigerant and if it does, it burns relatively slowly, whereas hydrocarbon refrigerants are easily ignited and can be explosive.

Another concern when using hydrocarbon refrigerants is that they can degrade the rubber hoses used in air conditioning systems, potentially leading to leaks or problems with other components as bits of damaged rubber enter the refrigerant flow.

There are currently no hoses on the Australian market that are certified for carrying hydrocarbons under the conditions found in an automotive air conditioning system.

That is partly because no vehicle manufactures would entertain the idea of using hydrocarbon refrigerants!

Like hydrocarbon refrigerants, HFO-1234yf has a Dangerous Goods class of 2.1, meaning cylinders containing both types of refrigerant must carry a flammable label and workshops must adopt the same handling and transport practices with both mildly and highly flammable refrigerants – it is not ideal, but these are the rules we must work within.

Remember this: It is very unlikely that Australian workshops will be forced to retrofit R-134a systems with HFO-1234yf in order to comply with environmental regulations.

Vehicles designed for use with HFO-1234yf will come onto the market and require servicing with HFO-1234yf, while R-134a will continue to be available for servicing vehicles designed for use with R134a until eventually those vehicles become so old that they will be few and far between.

If anything, the biggest risk is that unscrupulous workshops will try servicing HFO-1234yf vehicles with R-134a in an attempt to save money, just as is happening now with hydrocarbons.

And if that happens, at least nobody will be put at risk from highly flammable gases being used where they shouldn’t.

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