Second report of the Departmental Committee appointed to inquire into the ventilation of factories and workshops. Pt. 1, Report.

  • Great Britain. Home Office. Committee on Ventilation of Factories and Workshops.
Date:
1907
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Licence: Public Domain Mark

Credit: Second report of the Departmental Committee appointed to inquire into the ventilation of factories and workshops. Pt. 1, Report. Source: Wellcome Collection.

    6/140 (page 6)
    -~ X& 6 A.—General Ventilation.*—Certain impurities can hardly be prevented from becoming generally distributed in the air of a room, and can thus only be dealt with by general ventilation of the room. In most cases this is true of the products of respiration and of combustion of gas, the water evaporated in wet processes, and the heat given off from moving or artificially heated machinery ; and in some cases of the production of dust. Intremoving these impurities or sources of inconvenience the supply of air must be sufficient for the particular purpose in view. If, for instance, heat or dust has to be removed, the ventilation | must be sufficient to effect this removal, and not merely to dilute the products of respiration. . As regards impurities from persons and lights, the legal standard proposed by this Committee in its first report was such as would prevent the proportion of CO, from respiration or combustion from ever rising beyond 12 volumes per 10,000 of air during daylight, or beyond 20 volumes at night with gas burning. If the distribution of air were perfect and constant this would imply a minimum ventilation by day of about 1,250 cubic feet of air per person and per hour. Since, however, the distribution is always more or less imperfect and liable to be interfered with by varying conditions of weather, about double this quantity of air would usually need to be supplied in order to conform to the standard. If more than about two cubic feet of gas per person and per hour were burnt in the room (or one flat-flame jet to three persons) an addition of about 1,500 cubic feet per hour for each extra flat-flame jet would probably be needed. The quantity of air required to remove excessive heat and moisture cannot well be calculated in the same way, as the loss of heat through walls and roof is usually not known, and in any case varies with the weather. The air supply must therefore be regulated with the help of thermometers. Air in which the reading by the wet bu/b thermometer exceeds about 70° begins to cause serious inconvenience with ordinary clothing, and this limit ought not to be exceeded in factories or workshops except under exceptional conditions. Experiments show that if the wet bulb reading rises beyond about 88° in fairly still air, the body temperature can no longer be prevented from rising seriously even in persons stripped to the waist and doing no work ; and with muscular work under the same conditions the body temperature may rise rapidly at a wet bulb temperature of 80°. With ordinary clothing this effect is considerably greater. At the upper limits it is not the temperature of the air, but that of the wet bulb thermometer, that matters ; and provided that the air is so dry that the wet bulb temperature does not exceed the limits specified, air temperatures up to 130° or more can be tolerated without rise of body tem- perature.f Much higher wet -bulb temperatures can of course be borne for short periods, but the body temperature soon rises seriously. In removing steam from rooms it must be borne in mind that cold air is apt to cause condensation of aqueous vapour. Thus if air saturated with moisture at 80° is mixed with even ten times its volume of air from outside at 40° condensation will nevertheless usually occur, and will always do so, whatever the dilution, if the incoming air is saturated with moisture at the outside temperature. If, however, the incoming air be warmed to a moderate extent as * A more detailed account of this subject and of the general laws of flow of air will be found in Appendix II. of the First Report of the Factory Ventilation Committee, Parliamentary Paper, [Cd. 1302], 1902. - t The following observations made recently by Dr. Haldane will illustrate this statement :—With the air temperature at 131° and the wet bulb at 88°, the body temperature remained the same after 24 hours. With the air-temperature at 89° and the wet bulb at 89° on the other hand, the body temperature rose nearly 3° in the same time, and_ with the air temperature at 94° and the wet bulb at 94° the body temperature rose 4° in two hours. The subject/who was the same in each of the experiments, was stripped to the waist, and resting. With: moderately hard work and a wet bulb temperature of 87° the temperature rose 4° in one hour. Further details will be found in a paper by Dr. Haldane on “ The effects of high air-temperature,” Jowrnal of Hygiene, 1906, p. 494.