A fire-safe valve is designed so that after its soft seals are destroyed by fire, secondary metal-to-metal seating and graphite packing still limit internal and external leakage to the rates permitted by API 607 or API 6FA. The claim is proven by burning a live test valve in a certified type test.
Soft-seated valves seal with PTFE and elastomers that burn or melt near 300°C — so an ordinary ball valve caught in a plant fire becomes an open leak path feeding the flames. Fire-safe design adds a secondary metal lip behind the soft seat: when the polymer is gone, line pressure pushes the ball against that lip, and flexible graphite in the stem packing and body joints replaces the destroyed O-rings.
The certification is a destructive type test. API 607 (quarter-turn soft-seated valves) and API 6FA (API 6D pipeline valves) both envelope a pressurised valve in flame at 750–1000°C for a defined burn period, then measure leakage through the seat and to atmosphere, and finally operate the valve. Pass limits are emergency-grade — a fire-safe valve after a fire is not bubble-tight, it is survivable and operable.
Specify the certificate (API 607 latest edition, or API 6FA for pipeline valves), not just the phrase "fire-safe design", and note that certification is size- and class-family specific. VTXFLOW soft-seated ball valves for hydrocarbon service are fire-safe certified with graphite secondary sealing as standard.