By Guido Casati, International pbi
Scientists at The Air Space Technology Department of Politechnic of Milan University pioneered a new approach in April 2000 using illumined dust particles to precisely measure the ‘footprint’ of air flow throughout the SAS air sampling process.
Their method supplements previous research performed in smoke studies documenting the excellent performance of SAS in critical control environments.
Enclosed in a darkroom, they projected a light beam from a 575 Watt lamp with an iris diaphragm to regulate the amplitude of the light cone and a shaper to regulate the contour of the cone. Testing the air flow of the SAS 180, Duo SAS 360 and HiVac air samplers, they evaluated each sampler with both 55 mm contact plates and 90 mm petri dishes.
Mounted on a floor tripod, each air sampler was tested 20 cm from the light source at a fixed volume of 250 liters in an ambient temperature of 20 degrees Centigrade.
The SAS 180 and SAS Duo 360 systems showed that averages of the turbulence at air inlet were ten to fifteen centimeters and at air outlet were insignificant. The unidirectional flow was retained with the SAS 180 and SAS 360. The HiVac model exhibited an air cone of 15-30 cm due to its side venting.
To achieve unilinear air flow, the SAS Air Sampler aspirates air at a fixed speed through a solid stainless steel sampling head with 219 precision drilled holes positioned over the agar at a prescribed distance. Upon impaction, air flows over the agar’s dome shape and exits through an exhaust screen. Accuracy is preserved by the consistency of the holes drilled into rugged AISI 304 stainless steel, and the solid state electronics calibrated to NIST traceability.
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