Compressed Air Work And Diving 1909

CAISSON AND TUNNEL WORK. 11 such an arrangement is usually preferred by the men themselves. Rule.—Decompress to half the absolute pressure rapidly, and then at the rates given in the ttible. Table V.—In tunnel work or in caisson sinking, where the space is available, it is recommencled that a section of tunnel or large air-lock should be provided where the pressure should be constantly maintained at a little less than half the absolute pressure. With such an arrange- ment the men would be able to pass rapiclly from the working chamber or section of tunnel into the “purga- tory ” air-lock or section of tunnel, and after a clelay, proportionale to the working pressure, would pass rapiclly out. Whilst in the lock, they could occupy their time in chanQ-ino- their clothes and washing-, or in havin»' a meal, and the moving about thus occasioned would con- siderably hasten the process of desaturation. This method is a very convenient one for tunnel work, as the ordinary air-locks are kept free for ingress and egress of material, except for the few minutes during each shift actually occupied in passing in and out. In the table, in the first column, is given the working- pressure, in the seconcl the absolute working pressure 4- 2.2, which is the pressure at which the air must be maintained in the purgatory lock, and in the other columns are given the time in minutes which must be spent in the lock after different lengths of exposure. Thus, with a working pressure of 34 Ibs., the pressure in the purgatory lock or section of tunnel would be 5 = 2 2Ä-lbs. nearly of absolute pressure or 7^ Ibs. by 2.2 gauge. Any one coming out after three hours would have to spend fifty minutes in the purgatory lock as shown in the third column from the end.