For the past 25 years, there has been extensive research evaluating hydraulic fluids using Standard 6930, Less Hazardous Hydraulic Fluids. Despite the availability of less flammable hydraulics fluids, fires have continued to occur over the years, resulting in millions of dollars in losses. The majority of these losses occurred in metalworking processes, plastics-forming processes and wood-working processes.
A new approach was needed to help better evaluate the flammability potential of hydraulic and other industrial fluids. In addition, in the past ten years there has been an introduction of many new synthetic hydraulic fluids known as polyol esters. These new synthetic hydraulics' fire resistance is more questionable than previously used hydraulic fluids.
In the fall of 2000, Factory Mutual (FM) instituted a new standard entitled Specification Test Standard for Flammability of Industrial Fluids to replace Standard 6930. The new standard can be used to evaluate a broad spectrum of industrial fluids. It assigns the fluids to one of three groupings based on their degree of flammability, instead of just assigning a pass/fail rating. The ratings are:
Group 0: Non-flammable
Group 2: Having a normalized SFP greater than 4.0, but no more than 8.0 x 104; less flammable than mineral oil fluids, but may stabilize a spray flame under certain conditions.
Group 3: Having a normalized SFP greater than 8.0 x 104; flammability approximating that of mineral oil fluids
The original Standard 6930 was intended to test only hydraulic fluids. A sample of the hydraulic fluid being tested was pressurized to 1000 psi and heated to 140° F. There were two tests performed:
– Hot Surface Ignition Test – This test was designed to mimic hydraulic fluid leaking under high pressure from a hose in an environment where hot surfaces are common. Hydraulic fluid was sprayed from a nozzle onto a steel surface heated to 1300° F.
– Flame Propagation Test – This test was designed to determine if the fluid was combustible and whether it would sustain combustion even if the torch flame was removed. The pressured hydraulic fluid was sprayed from a nozzle directly into a propane-air torch flame.
An additional test for water-in-oil emulsion fluids was included to ensure that the two elements would not separate under adverse conditions.
The new Standard 6930 can be used to test many types of industrial fluids. The new Standard has changed the two original flammability tests but it does still use the test for water-in-oil emulsion fluids when needed.
The two new flammability tests are as follows:
– First flammability test – This test is used under the new standard to determine the chemical heat release rate of the fluid. The hydraulic or industrial fluid is heated, pressurized, and sprayed vertically through a propane-air ring burner similar to one used in an oil-fire furnace.
Second flammability test – This test measures a sample's critical heat flux for ignition. A .026-gallon sample is placed in a 4-inch x 1-inch aluminum dish. The dish is placed on a platform surrounded by four electric radiant heaters which provide a radiant heat flux at the surface of the fluid in the range of 0 to 317 Btu/ft2/min. The resulting vapors produced in this test are ignited by a pilot flame located about 0.4 inches about the fluid surface. Four different values of radiant heat flux are applied to the sample, and the time of exposure required for sustained ignition of the vapor is recorded for each. Successively lower levels of heat flux are applied until it takes 15 minutes or more of exposure to ignite the vapors. The critical heat flux for ignition of the sample fluid is determined by plotting the inverse of the ignition times versus the radiant heat flux required for sustained ignition.
Since FM has issued a new standard for 6930, manufacturers of current FM approved hydraulic fluids will have one year to resubmit their fluids to be tested again so it can be determined if they meet the criteria for the new standard. If they do, they can maintain their listing in the FM Approval Guide.
The American Society for Testing and Materials (ASTM) subcommittee responsible for standards relating to hydraulic fluid flammability tested is interested in using the new FM test standard as the basis for its own test standard. In addition, FM will also work with the American Petroleum Institute to include the new specification test standard within a new hydraulic fluid flammability standard being developed by the International Organization for Standardization (ISO).