Air Sampling Theory

Air Sampling Theory The typical use of Sensidyne air sampler is to pull air through cassettes and collect particles or impurities that are in workers ambient breathing air. The sampler is worn on the worker's belt and the cassette is positioned and secured to the worker's collar to get an accurate sample of the air quality in the workers breathing zone. The cassette holder holds the cassette.  The cassette is usually a 37 or 25 mm diameter plastic case the size of a golf ball and it holds the collection media.  The media is usually a paper thin disc filter.  After the sample period, the recorded flow rate multiplied by the flow time gives total air volume passed through the media.  For example, 1 liter per minute x 60 minutes = 60 liters. The dirty media is sent to a lab along with the data of total volume of air passed through the media. The lab will determine the concentration of the particles or concentration of the toxic material that is in the worker's breathing air. Of course, the lab utilizes the most sophisticated accurate devices available to measure the contaminants on the filter media.  It is also essential that we provide the lab with the most accurate quantitative determination of volume of air passed through the filter media.  To do this we carefully record the elapsed time the air sampler has run and verify that the sampler has run at a Constant Flow rate for the duration of the test.  There evolves the term constant flow pump.  Gilian Air Samplers are manufactured to maintain a constant flow within at least +/- 5% of the original flow rate, throughout the duration of the test period.  Should the flow vary outside the +/- 5% range, the sampler will shut down and lock  the timer, displaying the amount of elapsed time the sampler ran at prescribed flow rates. Cassettes and filter media are used for particle collection. The determination of which filter material and which size filter and cassettes is dependant on the target substance. National Institute of Occupational Health and Safety (NIOHS) has set forth a compilation of test procedures which spell out the parameters and the instructions for the tests for the different substances. Sorbent Tubes are used for collection of gases and vapors. Tube holders hold the tubes that contain an absorbent material filled tube. Common tubes are approximately 6 mm diameter glass tube about 70mm long.  The most common sorbent tubes are filled with charcoal or other type material.  The air is passed through the tube and the material in the tubecollects the target substance.  Tubes are used for collection of gases and vapors, where cassettes and filter paper are used for particles, fibers and dusts. The tube holder securely holds the tube, protects the tube from breakage, and provides a collar clip for attaching the tube to the workers collar.