A large number of tests are currently available for assessing the fire resistance of functional fluids and lubricants. Since it is extremely difficult to simulate fire conditions for fluids in laboratory tests, the main use for the different methods is a comparative assessment of the various fluids.
The fluids in commercial use, where fire resistance is a critical feature, can be divided into those which depend on water for their performance and non-aqueous fluids, where the fire resistance depends on the chemical composition. Ideally a fire resistance test should be capable of assessing the behaviour of all candidate fluids on an equal basis, but because the two groups of fluids behave in totally different ways comparison in most tests is not valid.
Although some tests suffer from indifferent precision or are unable to satisfactorily discriminate one type of fluid from another (within the same group), many rank the fluids in approximately the same order and therefore do not provide any additional information.
The introduction of two new spray ignition tests which enable all the different fluids to be compared under similar conditions is a major step forward. These tests, however, cannot simulate a condition where the water content of aqueous fluids can volatilise and leave behind a flammable residue. As a result, for the minimum assessment of the behaviour of both groups of fluid it is advisable to obtain both spray ignition test performance and performance in a ‘hot surface’ test.