H&S - COMPRESSED AIR WORK | INSIGHT
AN INTRODUCTION
ITA/BTS CAWG REPORT 10:
Latest guidance on high pressure compressed air (HPCA) in tunnelling is discussed by Dr Donald Lamont MBE C.Eng FICE, Hyperbaric and Tunnel Safety Ltd
High pressure compressed air (HPCA) work using mixed gas and saturation exposure techniques is becoming slightly more of a reality. It was used extensively and to good effect on the Tuen Mun contract in Hong Kong and is a planned contingency measure on contracts in Singapore and in the UK, where it is likely to be required for the Lower Thames Crossing tunnels. Guidance on HPCA work is given in ITA/BTS CAWG
Report 10 ‘Guidelines for Good working Practice in High Pressure Compressed Air, published in 2024. The guidance in Report 10 is both technical and
complex and, therefore, ITA/BTS CAWG published a complementary, explanatory guide to the concepts and terminology used, entitled ‘Guide to ITA/BTS CAWG Report 10 for Clients and others not familiar with High Pressure Compressed Air Works’ (Report 20).
Report 20 also provides clients with guidance on various aspects of the procurement of HPCA work.
HPCA - physical principles The physical principles behind HPCA work are the same as for low or intermediate pressure compressed air work: the application of compressed air to balance groundwater pressure (Lamont et al 2024). The major differences are in the negative physiological responses of the bodies of tunnel workers in exposure to air at high pressure. It is not the body’s response to the total pressure of the air which is the problem but the response to the partial pressure of the constituent gases (see box panel-1). Consequently non-air mixed gas breathing mixtures
are required for non-saturation and saturation high pressure exposures.
Above: TUP shuttle at factory test July 2025 | 25
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