Document e7Yw3gxp3N01k9genno1Dke2M

296 W. N. WITHERIDGE cubic feet of air 400,000,000 (specific gravity of liquid) ; pint of liquid -- (allowable concentration) (molecular weight) Thus, if the designer is given an allowable concentration for trichloroethyle" 100 p.p.m., the dilution ventilation for 100 per cent efficient distribution,' woul cubic feet pint (400,000,000) (1.5) = 45,000 (approx.) (100)(131) C. DISPERSION OF AIR CONTAMINANTS BY GENERAL VENTILATIO, One of the important disadvantages of general ventilation is that it p'ep the building or room to become a large settling chamber for any dusts, fun| mists suspended in the air, even though the concentration may be within a| able limits so far as health and safety are concerned. This has been most dr|" cally demonstrated in plants manufacturing or using highly combustible,* Although the dust concentrations at any one time were not sufficient to conf1 a nuisance or hazard, the accumulation over many months or years has resul|e. disastrous explosions of dust that had been deposited on rafters and ipaccf machinery surfaces. $* In'some cases the settling or separation of contaminants from the ai| represent condensation" of matenalI^_vaponze3"'byTTigh-temperature prtji which may accumulate on all surfaces with ever increasing danger. Seri^u] fires have occurred where the interior surfaces of the building were welli: nated or saturated with condensed vapors of flammable liquids or waxes. E. our homes, laboratory tests have shown "that some of the fish fried on the. '^j likely to condense on an upstairs window pane in a matter of seconds."7 D. AIR-SUPPLY INLETS AND EXHAUST OUTLETS The design of ventilating equipment for an industrial plant is not cqig -wit'hout-full-consideration-of-the-routes-by-which-air--will-enter-and^ working areas. In fact, the ventilation route is important not only to the.oc'c; of the building, but also to the neighbors and community at large. The denif better inside conditions may result in the transfer of contaminants from the) to the outside, in the absence of air-cleaning equipment. Although the oiv has a tremendous ultimate capacity for absorbing air contaminants, tjhdi?cj process is by no means immediate, as those who are near some industrial will verify. ' G. Nelson and H. Wright, Tomorrow's House. Simon and Schuster, New Yjirk^.S' VENTILATION 297 llllplbcation of air inlets and outlets has the following significant aspects: mk 1. Air Inlets* lit' Ms.ufficient combined or total inlet area should be planned to accommodate 5jg3*B|ed volume of make-up air during the heating or cooling season, which`^Wifeds the larger volume. This will prevent excessive inlet velocities that s'(lM^Pi^(ywer' crea^e drafts on workers, stir up dust, and interfere with local ^TtjaS'oods. The chosen inlet velocity is likely to be an engineering comproWtj|een low rates, which require large inlet areas, and high rates, which ypfeawd dilution of contaminants. MSI widespread hazardous operations are controlled by dilution or general yftBaaraf? inlets should be well distributed around the building to provide 1^ 'llprculation. SiiIf contaminants are controlled by localized dilution, or by forcefully .them into the general room-air reservoir, inlets may be purposely located .v^mphuniform air-supply distribution. "^ffilnlets should be located to take full advantage of any thermal or convec- "wtelili8 within the building. For this purpose the designer must avoid the aifflfpf inlets (and outlets) near the "neutral zone"8 of inside-outside pressure llfials, which is approximately midway between the floor and roof. ^Slnlets should be located remote from stacks or ventilators discharging injnants from the same or neighboring structures. m Air Outlets AWOutlets should be located as far as possible from air inlets to prevent diillfS^rcuiting." This advice should be followed for both natural and mechanical ^'IplpAs in the case of air inlets, if widely scattered operations are controlled lepltl dilution, outlets should be uniformly distributed around the building Ip&bove). J^JPAS in the case of air inlets, if contaminants are controlled by localized %Hpfe*ir outlets may be purposely located to short-circuit a corner of a large ^.'Sfirder to create a high rate of air change there without involving the ^Wlilihre of the entire space. This method of localized space ventilation requires S^l^r.ate of exhaust air than supply air within the area to be. controlled, so as "ll^'.cnt the spread of contaminants throughout the room (see ic). ~TMP^utlets should be placed to take full advantage of thermal effects (see The distinction between inlets and outlets is based on point of view; in this discussion, 'at of reference is the occupied space, and not the interior of air ducts. "i.'Emswiler, Trans. ASHVE, 32, 59 (1926).