The use of mineral oil as a hydraulic fluid in industrial plants, installations and equipment may create a problem, if exposure of the fluid to sources of iginition are possible. Many industrial processes require the use of hydraulic fluids that afford better fire safety than achievable with mineral oils. In proposals to the governments of the member states of the European Union (EU) fire-resistant fluids intended for use in underground mines must conform the “Requirements and Tests Applicable to Fire Resistant Hydraulic Fluids used for Power Transmission” (7th Luxembourg Report, adopted by the Safety and Health Commission, March 3rd 1994). The immediate stimulus for this work, which spans a period of 35 years, was the disastrous fire which occurred in 1956 at the Bois du Cazier mine at Marcinelle in Belgium, resulting in 267 fatalities.
The general classifications of hydraulic fluids are given in ISO 6743/4 (Lubricants, Industrial Oils and Related Products — Class L — Classification, Part 4: Family H, Hydraulic Systems), guidelines for use have been developed in ISO 7745 (Hydraulic Fluid Power — Fire Resistant (FR) Fluid — Guidlines for Use), but no formal standards are available to interrelate fluid classification with the relative fire risk. Two fundamental parameters are considered when selecting tests for standardisation: 1. spray ignition tests and 2. flame propagation or wick tests. This paper discusses the use of testing methods to characterize the performance of conventional fire resistant hydraulic fluids.