Mortality of gasworkers - final report of a prospective study. - Doll,R.; Vessey,M.P.; Beasley,R.W.; Buckley,A.R.; Fear,E.C.; Fisher,R.E.; Gammon,E.J.; Gunn,W.; Hughes,G.O.; Lee,K.; Norman-Smith,B. (Br J Ind Med, 1972)