nam CRLR - 190 - PROTECTION AFFORDED BY OPERATIONAL SMOKE SCREENS AGAINST THERMAL RADIATION (UKP-58). (Operation UPSHOT-KNOTHOLE) Elmer H. Engquist, June 1993. SECRET-RESTRICTED DATA In clear atmosphere, thermal radiation normally reaches an object via a straight line from the bomb source. By introducing a smoke screen, the radiation is diffused around an object within the screen, and such radiation as reaches the object does so from many directions, thereby minimizing burns and reducing the ignition of fires. be This report sets forth the test conditions under which measurements of thermal flux were made at a station 2,166 ft from ground zero when an approximate 16 Kf nuclear device was detonated 500 ft in the air. The smoke screen for this test was developed by smoke pots in concentric rings of 200- and 300-ft diameters around the test station. Data obtained from three different types of instruments at the station showed that between 0.5 and 0.7 cal/sq em were received. Without the radiation-diffusing smoke, the incident thermal flux was approximately 78 cal/sq cm. Thus, there was indicated an attenuation of radiant energy approaching 99% under conditions of the test. Tre final report of this work appeared as CRLR-298 and wr-768. CRLR § 191 - EVALUATION OF A THERMAL ABSORBING SMOKE SCREEN (UKP-59). (Operation UPSHOT-KNOTHOLE) Elmer H. Engquist, 10 June 1953. SECRET-RESTRICTED DATA = In this experiment, the method of formation and the characteristics or a precursor shock wave were studied. The precursor was emphasized over a blast line by means of a heated-air layer resulting from the absorption of thermal radiation by a carbon-smoke screen. The effect of the carbon- smoke screen on the pressure wave is not yet completely understood, pending detailed analysis of the pressure curves. However, a generalization may be made that the distance over which the precursor was apparently formed was jess in the smoke screen than in the clear area, t ; Also, the maximum pressure in the smoke screen was two to three times greater than in the clear area, although in some cases recognition of the precursor and primary shock waves was difficult, due to marked modification of the wave form. Supplementary measurements showed that the thermal flux was significantl,;reduced by the carbon-smoke screen, the data indicating © tentatively en attenuation of thermal radiation greater than 98%. The final report of this work appeared as CRLR-283 and WT-769. 29 7 20