Document 2RprLwoxB8J1Q0ZE8QBZ62KOr

802 T. F. HATCH moist industries. The extent to which such direct measures can be applied var.m with the nature of the hot process but, obviously, elimination of all heat e-iamr to the environment is the most desirable action. As concern with the heat probleffl, increases, interest in direct control at the source goes up; greater efforts ai* made to isolate hot processes, and a growing tendency is seen to locate sucf equipment out of doors with only a roof shelter. j 2. Radiation Shielding Shielding against radiant heat is a primary measure for control of exposing but until recently it was not generally employed. It has the flexibility that instil tion lacks and can be designed to protect the exposed person rather than'jiT minimize escape of heat from the hot body. Reflecting shields made of aluminuni foil backed by insulating board or aluminum sheets may be employed. The stantial benefits from radiation shielding are demonstrated by the data0 in T 3. Such experimental results have led to extensive application of shielding' TABLE 3 . Reduction in Radiation by Screening (Single sheet of aluminum foil) Heat exchange by radiation (B.t.u./hr.) Test location D4 D6 D7 DIO D12 D15 D16 All A12 A14 A15 Without screening 2600 2240 1440 2450 1460 1850 3150 3525 2000 2670 1850 With ... screening 900 775 500 1010 560 775 825 1275 980 820 800 % reduction in radiatioc 65 65 65 59 62 58 74 64 ' 51 69 57 glass plants and other hot-dry industries. Absorbing shields of ordina.ry^jsKeet^ also may be used. The radiant heat is absorbed and largely converted to run. tive heat with some re-radiated at a lower temperature. Absorbing shields may, constructed of two or three sheets separated by air spaces. Insulating ..materia are even better since the radiation temperature on the shieldecTsTde wiTTbt lo than on the hot side. Water-cooled shields absorb the heat, which is carried aVi with the water. Transparent shields are required where the view of the operajti cannot be interrupted. For this purpose, chains may be employed to reduc( radiation in proportion to the area intercepted, and wire mesh screens ar" HEAT CONTROL IN THE HOT.INDUSTRIES 803 effective in the same way. Special heat-reflecting glass is available for windows in observation rooms and the like. The radiant energy impinging on employees at most work locations is not uniformly distributed.. It comes to them in concentrated amounts from certain !. directions with relatively little contribution from other quarters. The principal sources may be obvious so that shields can be interposed at the most effective |. points about the exposed persons. In other instances, it will be desirable to study | the horizontal distribution of radiation intensity about the work station to deter...mine the direction of major concern. For this purpose a directional radiometer is used,18 which yields results as illustrated in Figure 4. -2J2. iso- -276 sod Eigure 4. Variation in. distribution, pf,radiant,.,heat,..intensi>y....ar.oundawprkB8tation- ia. forming \ department.of glass factory. (After`Haines.'8) 1 ............. S. Local "Exhaust Ventilation M Canopy, hoods with-naturaL-:drafk:Ur....mechanicalT.exha.ust,Iventil'aktion are .in scommon use over furnaces and similar hot equipment. The benefits are obvious, .although it must be remembered that heat control by ventilation serves only to u G. F. Haines, Analysis and Controlof Hot Environments. Industrial Hygiene Founda-,. tion of America, Pittsburgh, Pa., April, 1950. '