This International Standard specifies a test method to determine the relative flammability of fluids when contacted with a hot metal surface at a fixed temperature, but it is also possible to gauge fluid ignition temperatures by adjustment of the manifold temperature. It is primarily used to assess the resistance to ignition of fire-resistant hydraulic fluids which are, by definition, difficult to ignite. It may be used with other types of more flammable fluids at lower surface temperatures, but this could significantly increase the hazards of this procedure. NOTE The procedure given in this International Standard is specified in ISO 12922:1999, Lubricants, industrial oils and related products (class L) — Family H (Hydraulic systems) — Specifications for categories HFAE, HFAS, HFB, HFC, HFDR and HFDU.