Thermal attenuation by white smoke is indicated to be 88.5%, 95.8%, and 98.6% respectively at distances from ground zero 2,500, 4,500 and 6,500 ft. These figures were based on an assumed wind velocity of 2 to 3 mi/hr at the time of test. The calculated temperature rise in an assumed 100-ft layer of fairly dense, carbon smoke at ground zero is shown to be from about 3,800°C at the top of the cloud layer to about 170°C at ground surface. For a thin smoke, the expected temperature increase would be between 400°C at the top of the cloud and200°C at the ground. The temperature rise in similar cloud layers at 2,000 f from ground zero would be expected-to range from 300°C at the tope of a fairly dense cloud to 0.1°C at the ground, and from 35°¢ to 13°C for a thin smoke. CRLR - 159 ~ “ LABORATORY EVALUATION OF THE PORTABLE PARTICULATE SAMPLER, E31. Luther M, Hardin and Michael J. CONFIDENTIAL Schumchyk, 20 April 1953. ef The Portable Air Sampler, E31, was set up inside a cubical test chamber 1 m on a side, into which and from which a radioactive sodium iodide (1431) aerosol was introduced and exhausted at constant rates, so that the air within the chamber was maintained at about atmospheric pressure and was completely changed every 10 mip. The aerosol radioactivity levels varied between 1 x 107° a ” and 500 x 10°Y had a median diameter of 0.6 py. fan-induced air turbulence. yc/ec, and the aerosol particulate matter Tests were made in both static air and Twenty-minute samples were collected by individual sampling tubes of the instrument, at rates of 1 liter/min and 0.5 liter/min, in quiet air and in turbulent air. At the conclusion of the test, the perpendicularly mounted sampling filters were counted for radioactivity. The results indicated an accuracy of + 10% in the determination of aerosol activity-concentrations when the particles were less than 5u in diameter, and with simulated wind speeds up to 6 mi/hr. Less reliable resuits were obtained at flow rates of 0.5 liter /min through the filter ‘ 4 activity concentrations as low as 10~° are used. yc/cec when 20-min sampling periods "> oe" Nena ase 2 i than at 1 liter/min. Activity-concentration values at the lower rate of flow deviate from the standard filter-sample values by as much as + 20%. Finally, it was established that the 31 sampler can be used to determine 26 21