Compressed Air Work And Diving 1909

30 COMPRESSED AIR WORK. knapsack containing the caustic soda. A rubber mask covers the face, and the oxygen is breathed from a reducing valve from the cylinder which communicates with the mask by a flexible pipe. It is then exhaled, and by means of another pipe and a simple system of valves circulates through the knapsack where the CO2 is absorbed by the caustic soda. It is then breathed over again by the wearer, together with a small fresh supply of oxygen. When this apparatus has to be used with a helmet and diving dress for work below water, and the clepth is greater than 17 ft., the oxygen shoulcl be mixed with air, since oxygen at high pressure acts as a poison. For a clepth of 70 ft. 60 per cent, air woulcl be required.* This apparatus was the one used by Messrs Siebe, Gorman & Co.’s famous di ver Lambert, in his historie clive through the workings of the Severn Tunnel.t During the construction of the tunnel the water on one occasion suddenly broke in, and the workers quickly retreating forgot in their haste to shiit a valve. After pumping had been tried without any effeet upon the height of the water, it was decided to try and shut the sluice by means of a diver in the ordinary dress. The work to be done by the diver was as follows : to go behind an iron door in a head wall and shut clown a Hap valve on an 18-in. pipe, come back through the door, lift up two tram rails, and then shut the door, then screw clown a 12-in. sluice valve on another pipe on the near side of the door. The distance to be walked was 1,000 yds. under a head of water of 30 ft., and this * See Dr Haldane’s leeture before the North Staffordshirc Institute of Mining and Mechanical Éngineers, published in Wate>-, 151b April 1908. t “ History of the Severn Tunnel,” Walker.