ABSTRACT
Specific times for each of the three stages of decanting were measured after saturation exposures to compressed air at working pressures between 1.3 and 2.8 bar gauge at four contracts using different site design and equipment between 1963 and 1990.
Times were derived from 200 pressure recorder charts in the first study, by direct timing to 0.25 min blocks at the second study for 446 shifts over 13 months, and by precise timing to within 1 s at two minor contracts in 1989 over 25 and 118 shifts.
The men studied worked in compressed air for nominal 8-h shifts at all pressure levels and included men with and without previous compressed air and decanting experience. The study contracts employed 163, 130, 8 and 15 shift men respectively. All decompressions after decanting conformed to the decompression tables of the 1958 regulations in 1962/3 and to the Blackpool Tables from 1966. The results show that the decanting procedure fails to conform to the advisory statutory limitations of 5 min from working pressure to working pressure and significant delay to over 7 min occurred in 6-28% of procedures with the higher rates at working pressures over 2 bar g.
Analysis of the stage times contributing to the overall delay indicates specific areas that require alteration. Improvement during the progression of one contract is presented in detail.
Feasibility and practicality have been cited as reasons for prolonging times but only recompression delay is inevitable, the frequency can be reduced by improved pre-employment lock testing and equipment control.
The long-term effects of delay in decanting are not apparent. Further study of this group of men, small by comparison to other compressed air workers, is required.
