The spray flammability characteristics of several hydraulic fluids, and mineral oil, methanol, ethanol, and n-heptane, sprayed vertically upward in the open through a pressure-jet hollow cone nozzle and stabilized by a propane-air ring burner, have been evaluated using the Factory Mutual Research Corporation (FMRC) Fire Products Collector. A spray flammability parameter (SFP) has been defined, which combines the combustion intensity of spray fires in terms of chemical heat release rate with the fluid volatility described by the critical heat flux for ignition. An SFP value has een identified at or below which a range of hydraulic fluids cannot be stabilized as spray flames using a standard flame stabilization test. Mineral oil, some hydraulic fluids, and highly volatile fluids such as n-heptane, methanol and ethanol, have high SFP values and are easy to stabilize as spray flames. SFP appears to be useful in discriminating between flammable and less flammable fluids.
Experimentally, it was found that the burning of multi-component fluids, such as water-in-oil emulsion and polyglycol-in-water on a wick (porous ceramic disc), does not simulate burning of such fluids in an atomized spray. Thus, a spray fire test appears to be a much better method for characterizing the flammability of all types of hydraulic fluids.