A comparison of oxygen decompression tables for use in hyperbaric tunnelling

Abstract

The UK Health and Safety Executive (HSE) had a need to compare the effectiveness of a range of oxygen decompression tables for use in compressed air tunnelling and did this through the use of a mathematical model study. The results have been used to justify a more flexible approach to the statutory approval of decompression practices in the UK tunnelling industry. HSE has a long-term hyperbaric tunnelling research programme. This was used in 1996 to support the introduction of revised regulations for work in compressed air. More recently it was extensively used to inform and support the introduction of mandatory oxygen decompression in 2001. For convenience, oxygen decompression was introduced utilising a modified version of the Blackpool Tables. HSE recognised that the Blackpool Tables had been written for air-only decompression and therefore were not necessarily the most effective tables for oxygen decompression, so it undertook to conduct a comparative study of the effectiveness of a number of oxygen decompression tables and review the use of the modified Blackpool Tables in the light of that study. Using tables from another country gives an element of confidence that the tables, whilst not necessarily effective, are unlikely to be grossly unsafe. In addition, exposure data may be available and measures such as the Standardised Bends Ratio (CIRIA, 1992) can be used to make useful comparisons. The study involved the use of a physiological mathematical model. Typical results are shown in the paper along with tables ranking the performance of the modified Blackpool Tables relative to the other tables considered in the study. The effectiveness of the modified Blackpool Tables was found to be within the range of the other tables studied. No single table was best or worst overall. All were considered to be equally effective and would be acceptable for use in the UK. The study provided information, which subsequently allowed HSE to approve an application from a contractor to use German oxygen decompression tables - the first time that non-UK tables had been used on a UK contract. In assessing the effectiveness of decompression tables, the use of a range of techniques including Doppler and ultrasonic monitoring and mathematical modelling should be considered in addition to the traditional retrospective study of exposure data. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.