ABSTRACT
Strait crossing by means of a tunnel boring machine is becoming more frequent and will continue in the future. The normally automatic tunnelling progress needs occasional human intervention in the pressure-exposed part of the shield even at pressures beyond those considered acceptable for breathing air. It is important to establish that with due attention to the physiological and human exposure requirements, this work can be done safely, and it may be less expensive than doing it by other methods. The need is likely to be for short (< 2 h) interventions by specialists, but could involve multiple shifts of an entire team. In addition to the usual considerations of working with a tunnel boring machine, the high-pressure work situation involves many other factors like selection and management of breathing gases and breathing equipment, later re-use of pressure chambers, effects of gases on human performance, selection of decompression patterns, fire and oxygen safety, mobilisation time and integration with normal work shifts and training at several levels. Many of the risk factors and redundancies necessary for diving are not applicable here. Decompression procedures are better if designed for the operational situation, not the reverse. Partial saturation profiles not commonly used in diving for economic reasons may work well in the tunnel situation.
