Summary

In Hong Kong, the use of compressed air in the construction of underground tunnels for its Mass Transit Railway started in 1975 and ended in 1985. From 1982 to 1984, 1916 men had an initial medical examination before employment in compressed air work in one of the tunnelling projects. 367 men were declared unfit for employment resulting in an unfit rate of 19-2 per cent. The major disqualifying conditions were lung and cardiovascular diseases. Chest X-ray was found to be the most useful procedure since it revealed 55 per cent of the total disqualifying conditions. Of the 1549 men declared fit for employment, 130 (8-4 per cent) were later declared unfit to continue, mainly because of their susceptibility to attacks of bends. The overall bends rate was low (0-57 per cent) and only 3 cases of dysbaric osteonecrosis could be definitely attributed to the present employ-ment. Our experience suggested that strict medical criteria for medic-al examination and surveillance was important in the prevention of decompression sickness and dysbaric osteonecrosis