Air Samples with less than 2000 Liters
Do I have to draw 2,000 liters for my air sample?
Phase contrast microscopy requires that a sufficient volume of air be drawn through a sample to determine fiber concentration. Minnesota Department of Health (MDH) asbestos rules require that you attempt to draw a minimum of 2,000 liters of air through all sample filters of those samples required by MDH (preliminary or background samples, outside samples, negative air machine exhaust samples, and final air clearance samples).
Drawing 2,000 liters may overload my air sample. Is there an alternative?
In certain situations, samples could potentially become overloaded with material when attempting to draw 2000 liters of air through the sample. The alternative is to draw less air through the sample.
I drew less than 2,000 liters. Does this affect the analysis?
- Determine the number of fields to be counted by dividing 2,000 liters by the actual volume you have drawn and then multiply the result by 100 fields.
(2,000 liters)/(actual liters) * (100 fields) = (number of fields to count)
- Additional segments of the sample filter must be used for counting.
I counted 100 fibers before reaching the total number of fields I needed to count. What do I do now?
If you count 100 fibers before you reach the total number of fields you need to count, you can stop counting and the analysis of the sample ends.
I finished counting the total number of fields I needed to count. Does this affect the concentration calculation?
The fiber concentration must be calculated based on the number of fibers and the number of fields you actually counted.
How do I find out more information?
For more information about asbestos, contact the Asbestos Program at MDH through the internet or by telephone at (651) 201-4620.
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