ABSTRACT
Over recent years in Japan, compressed-air engineering has mainly been for pneumatic caissons; in tunnelling, higher working pressures are a result of mechanisation. The authors compiled the results of five years of surveys of decompression sickness (DCS) occurrence and compared the results with previous analyses. For this comparison, the control data were chosen from among those which had been collected by the same procedures as ours (Japanese Journal of Industrial Health, Vol. 29, 1987).
It is commonly said that DCS could not be developed under conditions with working pressures less than 1.0 kg/cm2. Although we had previously encountered seven patients with DCS development under 1.0 kg/cm2, no case was observed in the present survey which involved a total of 12,503 compressed-air exposures. For those compressed-air works which were at pressures over 1.0 kg/cm2, there were: 3,623 more exposures in the period after 1986 than in the period before 1986; 5,827 more exposures were used in 1985 and earlier in the range of working pressures of 1.0-2.0 kg/cm2 and there was a considerable increase in the exposures at pressures over 2.0 kg/cm2 from 1986 onwards. This means that deep excavation works, needing higher working pressures than before, are increasingly used for today’s compressed-air works. In other words, working conditions have become more severe in recent years and, therefore, more careful safety supervision was needed. When decompression control is carried out on the basis of the current decompression table, the development rate of DCS increases in line with the rise in working pressure, as was again observed in the present study.
Comparing the onset rates of DCS during these two periods, the results from the five years (1986–90) show lower rates (for working pressures intervals of 1.0 kg/cm2) than those seen in the previous seven years. This, it is supposed, indicates that there is stricter decompression control today than previously.
