PHYSIOLOGICAL EFFECT OF COMPRESSED AIR. In the application of the compressed-air process, the question of the ability of the human system to bear the increased pressure of the air becomes very important.
After entering the air-lock, as the pressure increases, the first sensation experienced is one of great heat. As the pressure is still further increased a pain is felt in the ear, arising from the abnormal pressure upon the ear-drum. The tubes extending from the back of the mouth to the bony cavities over which this membrane is stretched are so very minute that compressed air can not pass through them with a rapidity sufficient to keep up the equilibrium of pressure on both sides of the drum (for which purpose the tubes were designed by nature), and the excess of pressure on the outside causes the pain. These tubes can be distended, thus relieving the pain, (1) by the act of swallowing, or (2) by closing the nostrils with the thumb and finger, shutting the lips tightly, and inflating the cheeks, or (3) by taking enough snuff to cause sneezing. Either action facilitates the passage of the air through these tubes, and establishes the equilibrium desired. The relief is only momentary, and the act must be repeated from time to time, as the pressure in the air-lock increases. This pain is felt only while the air in the lock is being "equalized," i.e., while the air is being admitted; and is most severe the first time com pressed air is encountered, a little experience generally removing all unpleasant sensations. A drop of oil in each ear is a material help in obstinate cases. The passage through the lock, both going in and coming out, should be slow; that is to say, the compressed air should be let in and out gradually, to give the pressure time to equalize itself throughout the various parts of the body.
When the lungs and whole system are filled thoroughly with the denser air, the general effect is rather bracing and exhilarating. The increased amount of oxygen breathed in compressed air very much accelerates the organic functions of the body, and hence labor in the caisson is more exhaustive than in the open air; and on getting outside again, a reaction with a general feeling of prostration sets in. At moderate depths, however, the laborers in the caisson, after a little experience, feel no bad effects from the compressed air, either while at work or afterwards.
In passing through the air-lock on leaving the air-chamber, the workman experiences a great loss of heat owing (1) to the expansion of the atmosphere in the lock, (2) to the expansion of the free gases in the cavities of the body, and (3) to the liberation of the gases held in solution by the liquids of the body. Hence, on coming out the
men should be protected from currents of air, should drink a cup of hot strong coffee, dress warmly, and lie down for a short time.
At the Williamsburg Bridge (a 902) across the East River, New York City, the working time and wages were as follows: When placing concrete in the air chamber, the price was increased 25 cents per shift. In 1906 in New York City, the rates were 20 per cent more than the above.
The injurious effect of compressed air is much greater on men addicted to the use of intoxicating liquors than on others. Only sound, able-bodied men should be permitted to work in the caisson.
For an exhaustive account of the various aspects of this subject, see an article by Drs. Hill and Macleod in Journal of Hygiene, Vol. in, p. 401-45, a full abstract of which is published in Engineering News, Vol. LI, p. 436 40.