4.4 Fire Safety in Thermal Processes

Thermal processing equipment (Reflow Ovens, Wave Soldering, Curing Ovens) essentially operates as a controlled fire inside a manufacturing enclosure. The boundary between a functional soldering profile and a catastrophic facility fire is defined strictly by thermal regulation and fuel management. Treat flux residue not as "dirt," but as accumulated fuel waiting for an ignition source.

Fuel Management (Flux Residue)

Vaporized flux condenses on cooler surfaces within the oven tunnel and exhaust ducting. This condensate is highly flammable.

• If Process is Reflow Soldering -> Then implement a preventive maintenance (PM) schedule to scrape/clean tunnel entrance and exit zones.
  • Threshold: Residue depth must never exceed 2 mm.
• If Process is Wave Soldering -> Then remove dross and spent flux daily.
  • Risk: Titanium fingers and solder pots operate at > 250˚C. Accumulated paper/flux debris near the pot is an immediate ignition hazard.
• If Exhaust Velocity drops < 5 m/s -> Then inspect ductwork for blockage.
  • Physics: Low flow allows volatile organic compounds (VOCs) to pool, creating an explosive atmosphere inside the oven.

Pro-Tip: Use thermal imaging cameras during maintenance cycles to identify "hot spots" in the electrical cabinet or heating elements that indicate failing insulation or loose connections before they arc.

Thermal Runaway Protection

Software controls can hang or fail. Relying solely on the PLC to control temperature is negligence.

• If Primary Control Loop fails (Solid State Relay shorts ON) -> Then a dedicated Hardware Over-Temperature Switch must cut main power.
  • Constraint: This switch must be independent of the PLC logic and physically break the contactor coil circuit.
• If Conveyor stops (Jam/Motor failure) -> Then Heaters must auto-shutoff.
  • Reason: Stationary PCBs under active heaters will char and ignite within seconds.

Suppression Systems

Water sprinklers destroy electronics and can cause steam explosions in molten solder.

• Inside the Machine: Use CO2 or Clean Agent extinguishers. These suppress fire by displacing oxygen without leaving conductive residue that destroys the machine's electronics.
• Surrounding Area: Standard building sprinklers are the final defense for the structure, not the machine.

Final Checklist