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August 2004: Performance Based Hydraulic Fluid Testing

Many processes involve pressurized combustible oil in hydraulic systems. When such fluids are inadvertently released due to a break or leak in hoses and pipe systems an atomized spray can result which is easily ignited by hot surfaces. A high heat release fire can occur that is difficult for automatic sprinkler systems to control until the oil discharge is stopped.

Automatic stoppage of pumping systems with interlocks can help mitigate the fire loss potential. This can be initiated by low level oil reservoir switches, smoke or heat detectors, or sprinkler system electric waterflow alarms. Often none of these approaches seems compatible with the nature or arrangement of the hydraulic equipment - or it may pose the potential for damaging the equipment. In such cases, use of less flammable fluids may be an acceptable option to reduce the inherent hazard. These are known as "Less Hazardous Hydraulic Fluids."

For almost thirty years fluids have been tested for "listing" or "approval" as less hazardous. The testing was based on Pass/Fail criteria which consisted of two ignition tests: (1) heated and pressurized oil was sprayed on a heated steel surface to determine ignitability, and (2) heated and pressurized oil was sprayed into a propane torch which was then removed, to determine if the liquid spray would sustain combustion.

During this period, new synthetic products were being developed and the existing test criteria were becoming less valid - the results were inconclusive and lacked consistent repeatability. In addition, analysis of actual fire losses did not seem to indicate the extent of improved performance that would have been expected. This cast a cloud over the value of the testing.

In the last several years a new approach and testing protocol has been under development to move from 'pass/fail' to a graded or "performance based" system. This system uses tests for an oils heat release rate from a spray fire and the critical heat flux needed for ignition to derive a Spray Flammability Parameter (SFP) which forms the basis for a relative classification system.

The heat release rate is determined by measuring generation of carbon monoxide and dioxide when a sample fluid is heated, pressurized and sprayed through a standardized burner. Critical heat flux is derived from exposing a defined sample to an array of electric heaters in the presence of a pilot fame to determine the point at which the resulting fluid vapors ignite. The ignition time vs. radiant heat flux required for sustained ignition yields a critical heat flux value.

The Spray Flammability Parameter is categorized to allow comparison for the many fluids available:

Group 0 - Non Flammable
Group 1 - SFP up to 400,000
Group 2 - SFP from 400,000 up to 800,000
Group 3 - SFP more than 800,000 (approximates a mineral oil)

This graded selection allows an optimized choice of fluids that meet operational and equipment needs while dealing with the fire hazard. Selection of Group 0, 1, or 2 provides reasonable hazard control without the complication of shutting the oil pumping systems.