London Underground Railway (Silica) 63. Mr. O'Halloran asked the Secretary of State for Transport in which London underground lines, over what lengths of tunnel in them, at which stations and in what proportion of train cabs, silica has been found to be at or to exceed the threshold limit value. Mr. William Rodgers Sample of airborne dust concentrations have been taken at 11 stations and also in trains running on the Central, Northern, Baker-loo and Victoria lines. Separate sampling was not carried out in the tunnels between stations. In some cases, namely at Highgate, Kennington, Tooting Broadway, Leicester Square, Bank, Victoria and Baker Street Stations, quartz concentrations were in excess of the threshold limit value for quartz-0ยท1 mg/m3. However, the quartz contained in the samples is of a type which may prove to be not biologically active and samples are presently being evaluated at the pneumoconiosis unit of the Medical Research Council. In trains, levels at or above the threshold limit value were found in guards' cabs on the Northern line and in guard's and motormen's cabs on the Bakerloo line. Mr. O'Halloran asked the Secretary of State for Transport what action he is taking or intends to take to ensure that London Underground staff and passengers are not exposed to medically dangerous levels of silica. Mr. Patrick Jenkin asked the Secretary of State for Transport what action is being taken following the recent report that parts of the London Transport Underground system contain three times the recommended level of silica. Mr. William Rodgers It is unlikely that present levels pose any risk to health. Nevertheless, London Transport is taking action to reduce the amount of respirable silica in the Underground. As quartz in train brake-blocks is the principal source, a low-quartz brakeblock is now being fitted to trains and quartz-free block is undergoing trials. New designs of rolling stocks, such as that on the Victoria line, incorporate a proportion of rheostatic braking which reduces the use of brake-blocks. At the same time, tests are being made by the pneumoconiosis unit of the Medical Research Council to establish whether the particular form of quartz dust found in the underground is biologically active or not.