INSIGHT | H&S – COMPRESSED AIR: 30TH ANNIVERSARY WCA REGS


30TH ANNIVERSARY OF WCA REGULATIONS 1996


Dr Donald Lamont MBE C.Eng FICE, who was a member of the HSE team behind the 1996 Regulations and guidance, looks back over the regulation of compressed air work.


September sees the 30th anniversary of the coming into force of the Work in Compressed Air (WCA) Regulations in 1996. The origins of what could be considered to be a crude form of work in compressed air date back to the 1820s when Isambard Kingdom Brunel was reported to have used a four-ton diving bell to inspect the river bed above the Thames Tunnel – diving bells having been in use for around 100 years by then. He is even recorded as having taken his sister and her friend on a descent “for fun”.1 A patent for its use in caisson sinking was granted


to Admiral Sir Thomas Cochrane in 1830 but there is no evidence of the use of the patent at that time. There are reports of the use of compressed air for shaft


sinking in France from 1839 onwards. The first recorded use of compressed air in the UK was


Above: Personnel lock for mixed gas use. Image credit: TRHA.


in 1851 for bridge foundation construction at Chepstow and Rochester. Its first use in UK tunnelling was on the City and South London Underground Railway, at Stockwell. The technique developed throughout the 19th Century to the extent that, by 1900, it was frequently used in caisson construction for bridge foundations. Unfortunately, medical knowledge about decompression


theory, along with the causes of and treatment for decompression illness, lagged far behind and fatalities from compressed air exposure were relatively common. In many ways the greatest step forward in medical


Below: TUP shuttle at factory test.


treatment was the introduction of the medical lock by the UK engineer Sir Ernest Moir on the Hudson Tunnel project in the 1890s. He reported that prior to its introduction, a fatality rate of around one per month in a workforce


of around 50 men had been experienced. In 1907, Prof J S Haldane prepared the seminal report on deep-water diving (to 30 fathoms (almost 55m)) for the Admiralty. This followed on from practical trials by the Royal Navy and contained recommended decompression procedures along with recommendations for air flow in the helmets to clear carbon dioxide (CO2


). Formal regulation of and guidance on work in


compressed air in Great Britain began in 1936 with the publication of the ‘Report of the Committee on Regulations for the Guidance of Engineers and Contractors for Work carried out under Compressed Air’ by the Institution of Civil Engineers. The committee was made up of representatives of the Institution, the Federation of Civil Engineering Contractors along with leading diving hyperbaric experts – a spread of expertise still followed by the British Tunnelling Society (BTS) Compressed Air Working Group (CAWG). The report provided guidance on good working practice


of the time, along with a set of decompression tables based on the work by Haldane early in the 20th Century. Decompression was required above a threshold pressure of 22 psi (1.5 bar(g)), and a maximum exposure pressure of 50 psi (3.45 bar(g)), was set because the committee did not have faith in the effectiveness of the then current decompression procedures above that pressure. Draft regulations were first proposed in 1937 but never


brought into force. WW2 came along and regulation of work in compressed air was largely forgotten. Various unsuccessful attempts at regulation were made post-war, including a proposal for combined compressed air and diving regulations. Eventually, in 1958, the Work in Compressed Air Special


Regulations (S.I. 1958/61) came into force. They formalised the 50 psi (3.45 bar(g)), limit and contained revised decompression tables for use above a threshold of 18 psi (1.25 bar(g)). As with the 1936 report recommendations, decompression comprised an initial rapid pressure drop to half absolute pressure followed by a slow linear reduction back to atmospheric pressure. One of the first projects to be subject to these


Regulations was the Clyde Tunnels in Glasgow. Apart from the massive total of 240,259 exposures with 469 decompression sickness (DCS) events, of which two were fatal, this project became notorious for its high incidence of dysbaric osteonecrosis (DON) – 17% of a sample of 241 men surveyed radiographically towards the end of the contract had bone lesions. Within a decade of the 1958 Regulations coming into


34 | September 2026


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