How do testing houses define fire?
Quite often users of fire-safe valves work with in-house or independent test committees to define a fire-safe test to meet their needs. Things to consider for fire-safe valve test specifications are: • Valve type (metal to metal, etc.). These may be divided into (a) seats which have continuous metal-to-metal contact in the closed position and (b) two-stage seats which rely upon some secondary means such as seat or ball overtravel, system pressure, gravity, or spring loading to establish metal-to-metal contact when fire occurs. • Stem position. This is important in evaluating the severity of a fire test and may be the most important criterion in evaluating a test as to its applicability to the chemical process industry. The thermodynamic properties of the medium, vapor pressure, expansion rate, and toxicity must be considered as well. Certainly, a valve with the stem in the vertical position handling a high-vapor-pressure monomer or solvent presents a different problem than one handling
