Advanced high pressure hyperbaric techniques in tunnelling.

Work in compressed air and diving are both occupational activities that have been around since the mid-19th century, and those undertaking their work under elevated pressure. Meeting the demand to go to "higher pressure for longer" in tunneling has lagged in diving, but both activities have found it necessary to adopt mixed gas breathing and saturation exposure techniques. This paper explains how work in hyperbaric conditions at high pressure is undertaken in tunneling and is illustrated by the hyperbaric activity likely to be involved in constructing a large-diameter road tunnel below a body of water such as an estuary. It also explores the practical differences between work in compressed air and diving.