Sooysmith & Company had an experience with a work on which men were engaged in six-hour shifts, separated into two parts by half-hour intervals for lunch.

This work was excavation in open, seamy rock, carried on for several weeks under about 45 pounds pressure.

The character of the material through which the caisson is being sunk or upon which it may be resting at any time bears quite largely upon the ability of the men to stand the pressure necessary to hold back the water at that point.

If the material be so porous as to permit a considerable leakage of air through it, there will naturally result a continuous change of air in the working chamber, and a corresponding relief of the men from the deleterious effects which are nearly always produced by over-used air.
From Strasburg in 1861 Bucuoy reports that during the building of a bridge at Kehl laborers had to work in compressed air, and it was found that the respirations lost their regularity; there were sometimes intense pains in the ears, which after a while ceased.

It required a great effort to speak at 2 1/2 atmospheres, and it was impossible to whistle.