Underground construction: working in high-pressure compressed air

Working in compressed air is a well recognised technique for tunnelling in soft, wet ground. This paper describes techniques for working in pressures of up to 15 bar, significantly above normal statutory limits. For health and safety reasons, working at such pressures requires the use of mixed-gas breathing mixtures and saturation exposure techniques. It requires a much greater knowledge of hyperbaric physiology than traditional compressed air work because of the toxic effects of oxygen and the narcotic effect of nitrogen at such pressures. The risks and mitigation measures for high-pressure work are explained.