although the use of amphibole asbestos ( crocidolite and amosite ) has been banned in most european countries because of its known effects on the lung and pleura , chrysotile asbestos remains in use in a number of widely used products , notably asbestos cement and friction linings in vehicle brakes and clutches . a ban on chrysotile throughout the european union for these remaining applications is currently under consideration , but this requires confidence in the safety of substitute materials . 
 the main substitutes for the residual uses of chrysotile are p - aramid , polyvinyl alcohol ( pva ) , and cellulose fibers , and it is these materials that are evaluated here . because it critically affects both exposure concentrations and deposition in the lung , diameter is a key determinant of the intrinsic hazard of a fiber ; the propensity of a material to release fibers into the air is also important . 
 it is generally accepted that to be pathogenic to the lung or pleura , fibers must be long , thin , and durable ; fiber chemistry may also be significant . 
 these basic principles are used in a pragmatic way to form a judgement on the relative safety of the substitute materials , taking into account what is known about their hazardous properties and also the potential for uncontrolled exposures during a lifetime of use ( including disposal ) . 
 we conclude that chrysotile asbestos is intrinsically more hazardous than p - aramid , pva , or cellulose fibers and that its continued use in asbestos - cement products and friction materials is not justifiable in the face of available technically adequate substitutes.imagesfigure 1