high-performing materials. An example are FKM o-rings used as an upgrade to the original neoprene seals on Corvair pushrod tubes that deteriorated under the high heat produced by the engine, allowing oil leakage. FKM tubing or lined hoses are commonly recommended in automotive and other transportation fuel applications when high concentrations of biodiesel are required. Studies indicate that types B and F (FKM- GBL-S and FKM-GF-S) are more resistant to acidic biodiesel. (This is because biodiesel fuel is unstable and oxidizing.) FKM O-rings have been used safely for some time in SCUBA diving by divers using gas blends referred to as nitrox. FKMs are used because they have a lower probability of catching fire, even with the increased percentages of oxygen found in nitrox. They are also less susceptible to decay under increased oxygen conditions. While these materials have a wide range of applications, their cost is prohibitive when compared to other types of elastomers, meaning that their adoption must be justified by the need for outstanding performance (as in the aerospace sector) and is inadvisable for low-cost products. FKM/butyl gloves are highly impermeable to many strong organic solvents that would destroy or permeate commonly used gloves (such as those made with nitriles). Precautions At high temperatures or in a fire, fluoroelastomers decompose and may release hydrogen fluoride. Any residue must be handled using protective equipment. See also Magnesium/Teflon/Viton FFKM, perfluoro-elastomers FEPM, tetrafluoro ethylene/propylene elastomers References Overview of different types and their applications. External links Properties of Elastomers - Chemical Resitancelist (PDF; 0,6 MB) Designing with Fluoroelastomers (PDF; 0,8 MB) Organofluorides Elastomers Materials science Fluoropolymers