A properly assembled oxy-fuel torch system is a precision instrument. A poorly assembled or maintained one is a fire and explosion hazard. Flashback — combustion traveling back up the hose toward the cylinder — is the most dangerous failure mode in oxy-fuel welding, and it is entirely preventable through correct assembly, regular maintenance, and the use of proper safety devices.

• Reverse flow check valves (also called non-return valves) must be installed at both the torch inlets and at the regulator outlets
• These devices prevent gas from flowing backward into the wrong cylinder or hose if pressures become unequal
• Flashback arrestors must also be installed — they stop the flame itself if flashback occurs. Check valves and flashback arrestors are separate devices — you need both
• Inspect check valves monthly: test by blowing air into the outlet end — if air passes through backward, replace the valve

• Open cylinder valves slowly — stand to the side, never in front of or behind the valve
• Set working pressures per the job (typically oxygen 20–40 PSI, acetylene no more than 15 PSI)
• Apply approved leak detection solution (never soapy water mixed in the field) to all connections, valves, and fittings
• Bubbles indicate a leak — tighten fittings first. If the leak persists after tightening, replace the fitting. Never use a leaking system
• Never use a flame to test for leaks