When you buy an air conditioner from the shops, it comes with gas in it already. Usually R32, which is explicitly warned as being flammable.
Hydrocarbon refrigerant gases are also flammable.
Flammable refrigerants are becoming increasingly common in the industry and safety precautions need to be taken.
Small fridges already come with hydrocarbon refrigerant these days.
HFO refrigerants and R32 are also flammable.
Some technicians have been slipping hydrocarbon refrigerants in to systems for decades, and you wouldn’t even know it.
All systems are prone to leaking gas.
Some leak very slowly.
Others lose all their gas in one go.
Hydrocarbon gas is generally heavier than air, sinking to the floor in an unventilated room, in the event of a gas leak.
If the gas leaks, are you sure the system won't catch fire if presented with an ignition source?
Different jurisdictions have different requirements / provisions for the use of flammable refrigerants.
For jurisdictions which allow flammable refrigerant:
The system needs to be labelled as containing flammable refrigerant.
You need to follow safe working / installation practices.
Jurisdictions restricting the use of flammable refrigerants:
Queensland, Australia: Each device must be certified before charging with flammable refrigerant.
Australia (Except for Queensland): You're able to charge a system with flammable refrigerant as long as you hold a refrigerant handling licence or restricted refrigerant recoverers transitional licence.
Italy & France: Not permitted in public access buildings like hotels, shopping malls, and hospitals.
It seems common for some air conditioner installers to have their flare joins come apart on a system they installed.
Sure, you can press clamp or braze in place of a flare join, but you can't avoid not using flare joins on the outdoor unit.
Too wide or too little a flare and the refrigerant gas may push it out of the flare nut.
When tightening a flare join: Tighten it, release it, repeat this a few times. The copper from the flare tool won't initially fit the flare join properly, and can work loose. You need to mould the flare to properly suit the flare join. Anything less than 100% accuracy is set to fail.
Different refrigerant gases have different densities (Kg/m3).
Just because a cylinder says it can hold 22Kg of refrigerant doesn't mean it safely can. Some refrigerants max out at 8 or 9Kg.
Don’t rely on the weight of a reclaim cylinder as an indication of how full it is.
Shake the cylinder around to see how the liquid in it sloshes around.
If any gas escapes in to the air for whatever reason, treat it as flammable.
Flammable substances may still be present in a system where the gas has been reclaimed and vacuumed and you’re brazing pipework.
Systems usually specify a gas type and charge weight.
As an example: If an R134A car air conditioner says it takes 500g of gas, you wouldn't put 500g of Minus 30 in it. You'll likely damage the system. The system would need 230g of Minus 30.
If you put hydrocarbon in a system, the charge weight is going to be different. This is because each gas has a certain density (Kg/m3). You need to translate the charge weight to volume, and then work out what charge weight of a different substance corresponds with that volume.
For example:
R22 - R290: Multiply R22 charge weight by 0.487
R32 - HC32: Multiply the R22 charge weight by 0.518. You may need to multiply this result by 1.05 to get relatively normal cooling performance as it is suspected the manufacturers understate the R32 gas charge.
R410A - HC32: Multiply the R410A charge weight by 0.47.
R134A - Minus 30: Multiply the R134A charge weight by 0.459
Note: HC32 may be subject to change.
More conversion information is included in a calculator spreadsheet, where you can customise your gas blends.
There's only so much refrigerant gas that can leak into an unventilated space without being a safety concern. Combustion only occurs with the correct proportion of air and gas, usually between 2% and 10% of gas to air. Different refrigerant gases have different safe limits. This is called the "Practical Limit". This is based on the lower flammability limit. The upper flammability limit is about 5X higher, and anything in between these figures runs the risk of an explosion. If you need to work around it, mix in a lesser or non-flammable refrigerant, use ventilation, make suitable alterations to the system, or install gas detection alarms / interlocks.
Practical limits of different refrigerant gases (In order from highest pressure to lowest pressure):
• R170: 8g/m3
• R32: 300g/m3
• R1270: 43g/m3
• R290: 8g/m3
• R1234YF: 72g/m3
• R600A: 38g/m3
Note that when a system leaks, the highest pressure gas goes first, followed by the next highest pressure, and so on.
For some reason, the goons only want you putting no more than 1.5Kg (or less for refrigeration) of flammable gas in a system, even if the numbers indicate it's safe. R32 and R1234YF aren't counted towards this limit. For compliance, you could mix R32 and / or another non-flammable refrigerant. Or you could install a few smaller systems to service the same area.
Talking of practical limits, car air conditioners fail miserably. If you have a gas leak, the gas pools around the bottom of the cabin, and is dispersed when you open and close the doors each time you travel. That would be classed as being ventilated. If you had a gas leak, you'd soon know about it as your air conditioner won't cool as well as it should.
That VASA video from 1995 where they blew up a car, they let all the gas out and then ignited it. The only problem is that there was too much gas compared to air, preventing combustion from occurring. I think they used Acetylene gas, which is the only gas that will combust at such a high proportion of gas to air.
Flare joins:
Flare joins in unventilated indoor spaces isn't recommended.
The official method is to press clamp or braze the joins.
Then again, any refrigerant gas which leaks in an indoor space will displace oxygen.
Basic split system air conditioner installations have the flare joins in cover duct on the exterior of the building.
Ducted air conditioners:
Vents in the eaves and a mechanical whirlybird on the roof is recommended.
Not necessary if your gas mixture falls below the practical limit.
Open airflow in the roofspace will cause additional condensation to form on the refrigerant pipes and condensation drain pipe. Use additional thermal insulation.
Evaporator leaks:
Storing certain foods may corrode the evaporator coil.
Ensure the evaporator coil is sufficiently coated for protection, or replace the evaporator with a custom fabricated evaporator (such as stainless steel).
You may want to consider a gas leak detection alarm and interlock gas solenoids.
Mixing refrigerants:
You could also mix flammable and non-flammable refrigerant gases in accordance with the practical limits.
Modifications:
Parts may be discontinued, meaning repairs may require some sort of modification to the equipment in order to get it working again. Using a different gas in a system is classed as a modification. The politically correct say this isn't allowed. Common (not so common?) sense calls for safe work procedures and best work practices.
Incompatible refrigerant oils:
R22 refrigerant is one example.
Not all R22 systems contain POE oil. R407C is not compatible with Mineral Oil.
Most technicians usually change the oil. This can be a costly process.
Alternatively, you can use a small amount of R600A or R290 and fill the rest with R407C. The R600A or R290 will carry the Mineral Oil through the system to keep it lubricated.
Putting a different gas in a system than what was specified may void the manufacturer warranty. The compressor, the coils, and inverter board will likely be affected by the use of a different gas in the system.
The fan motors and indoor circuit board won't be affected by the use of a different gas. An incorrect blend of gas may result in higher evaporating temperatures on the indoor unit, resulting in mould and frequent washbag cleaning of the unit.
If you're carrying out these conversions, you need to be aware that you may have to carry the weight of the warranty, so be sure to charge for the upgrades accordingly to cover yourself in the very rare event you get a warranty claim.
If you do the job properly, the alternative gases will actually take the strain off the system, prolonging its lifespan. You will know by a measurement comparison of the power consumption. When comparing systems side by side, a higher power consumption indicates the system is working harder than it should, and that it may have an unsuitable gas blend in it. Unsuitable gas blends comprise of too much R170 and not enough R600A (especially in hot climates), or too much R32 (in Electronic Expansion Valve systems).
Sure, there's been a few incidents where people have blown themselves up. From what I gather, they all seem to have elements of gross negligence behind them.
In 2008, an explosion and fire occurred at the Icepak Cool Store in Tamahere, New Zealand. Apparently there was a refrigerant gas leak, they just kept topping up gas periodically, and they disabled the gas leak alarm system.
In 2021, a mine truck exploded. It had something to do with the metering device exploding (the weakest link in the chain). I think they just put the gas in the system until it wouldn't take any more gas - well above the recommended charge weight equivalent.
"Non-flammable" refrigerants actually ignite at a considerably higher temperature than flammable refrigerants do, and give off toxic by-products when burnt. When refrigerant gas leaks, oil may leak with it too. Oil ignites at a lower temperature than what hydrocarbon refrigerant does.