2.3.15 SamplingDevices The aerosol sampling devices were an electrostatic precipitator (ESP), employing a moving film coated with a drop sensitive emulsion, accompanied by millipore filter and dimethyl-terephthalate (DMT) air samplers. The millipore filter (MP) consists of a specially prepared thin (150) sheet of cellulose, of wmiform cell structure, sutmicroscopically honeycombed such that the volume of the filter is 80 per cent voids, or 5x 107 pores/sq cm. The aerosol type filter has a theoretical pore size slightly larger than 0.54, although it is claimed that 0.2 u par ticles are retained within 50 u of the surface, Tests at USNRDL on the NRL smoke penetrometer at operational face velocities (70 cm/sec) indicated 100 per cent efficiency for 0.3 4 diotylphthalate particles, The DMT filters consisted of DMT crystals packed to a thickness of 0.7 cm between two supporting screens. The DMT filters were sublimed off at USNRDL under reduced pressure and elevated temperature, leaving the captured aerosol material on microscope slides or in centrifuge tubes, ae desired, Calibration tests eas described above yielded a capture efficiency of 98 to 99 per cent. The air sampler suction units 21/designed to collect a total sample for a 6-hr period following a shot, drew 10 cfm through an effective sampling area of 64 sq cm for both the MP and IMT filters. 26