<div class="htmlview paragraph">This paper presents the results of a study undertaken at Factory Mutual Research Corporation (FMRC) to quantify the spray flammability of hydraulic fluids. Spray flammability characteristics of several commercially available hydraulic fluids, mineral oils, methanol, ethanol, and heptane, sprayed vertically upward in the open through a pressure-jet hollow cone nozzle and stabilized by a propane-air ring burner, have been examined using FMRC Fire Products Collector.</div> <div class="htmlview paragraph">A spray flammability parameter (SFP) has been defined, which combines the chemical heat generation rate from the spray fires and the volatility of fluids in terms of a critical heat flux for ignition. The value of SFP is expected to be an indicator of burning rate (or flame propagation rate). It has been found that the fluids having SFP &gt; 20 × 10⁴ are easier to stabilize as a spray flame than the fluids having SFP ≤ 20 × 10⁴. Based on our study, SFP appears to be useful in discriminating between flammable and less flammable fluids. A new test method thus has been proposed to determine SFP values for hydraulic fluids.</div>