What happens if refrigerant is exposed to a flame?
The chemistry in one paragraph
The carbon–halogen bonds that make refrigerants stable in a system break apart at flame temperatures. The fragments grab hydrogen and each other: fluorine leaves as hydrogen fluoride, chlorine (in HCFCs like R-22) as hydrogen chloride, and partial oxidation of chlorinated fragments yields phosgene (COCl₂) — the same acutely toxic gas of grim historical repute, in small but meaningful quantities. Manufacturer SDS sheets list these decomposition products for exactly this scenario; the acrid, biting smell around a torch is the warning label made literal.
Where it actually happens
| Scenario | What occurs |
|---|---|
| Brazing an un-recovered circuit | Residual gas decomposes at the joint — the classic field exposure |
| Leak near open flame / heater | Continuous HF (and HCl/phosgene) generation in the room |
| Halide-torch leak hunting (obsolete) | Deliberate decomposition — replaced by electronic detectors |
| Cutting "empty" cylinders for scrap | Residual vapour meets torch; decomposition plus pressure hazard |
| Fire in a plant room or store | Bulk decomposition; firefighters treat as toxic atmosphere |
Exposure signs and first response
HF and HCl announce themselves fast — burning eyes, nose and throat, cough, chest tightness; phosgene is more insidious, with delayed pulmonary effects hours after exposure. The response is unglamorous and standard: leave the area to fresh air, irrigate eyes with water, and seek medical attention for anything beyond momentary irritation — mentioning refrigerant decomposition products so clinicians watch for delayed effects. The SDS's first-aid section (why you keep it on hand) is written for this call.
The rules that make it a non-event
Every pathway above is procedural: recover before hot work, every time, on every class — A1's "non-flammable" does not mean flame-safe (the A1 trap); ventilate before and during torch work; hunt leaks electronically, never with flame; and keep cylinders, full or "empty", away from hot work entirely (storage rules). Decomposition injuries are among the most avoidable in the trade — the flame only meets refrigerant when a step was skipped.
Designing the hazard out of hot work: a permit-style routine
Industrial sites solved this class of hazard decades ago with hot-work permits; a lightweight version fits refrigeration service and costs minutes. Before flame: confirm the circuit is recovered to specification vacuum and isolated — 'mostly empty' is the phrase that precedes most decomposition exposures; check the workspace for refrigerant with an electronic detector, including low points and adjacent rooms sharing pipework; ventilate deliberately and position yourself upwind of the joint; move cylinders — full and 'empty' alike — out of the hot-work radius. During: torch time minimised, detector within reach, and an agreed stop signal if anyone smells the sharp acrid signature of decomposition (that smell is HF/HCl formation announcing itself — stop, ventilate, reassess). After: ventilate before re-pressurising, and log the work so the next visit knows brazing occurred. Two institutional notes complete the picture. First, the halide torch — the old leak-detection method that deliberately created decomposition colour changes — is obsolete precisely because it manufactured this exposure; electronic detection replaced it for safety, not convenience. Second, scrap-yard torch-cutting of 'empty' cylinders remains a documented injury source in India; spent cylinders belong in the return/disposal chain (formats guide), and a supplier who takes returns seriously is removing this hazard from the ecosystem, not just tidying inventory.
- Manufacturer Safety Data Sheets (Honeywell and others) — thermal-decomposition products: HF; HCl and phosgene for chlorinated fluids.
- SafeWork NSW — flammable-refrigerant and decomposition position paper.
- US EPA — refrigerant safety references — epa.gov.
This guide is general information compiled from the cited sources — not legal, safety or engineering advice. Read our full disclaimer.
Related: SDS guide · Storage safety · R-22 supply