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Explosibility and Combustibility Parameters
Related Information: Chemical Sampling - Explosibility, Combustible Material
Physical Measurements Team
Industrial Hygiene Chemistry Division
OSHA Salt Lake Technical Center
Salt Lake City Utah 84115-1802
The following is a description of a series of tests that are performed to the determine the explosibility and combustibility parameters of a material. Not all tests in this method are appropriate for each sample. The analyst must determine which tests are required for every sample.
1. Percent Through 40 Mesh
An aliquot of the "as received" material is sieved through a 40 mesh (425 µm) US Standard Testing Sieve. The percent which goes through the sieve is determined as:
1) Weigh a dust aliquot; sieve through 40 mesh.2. Percent Moisture Content
Percent moisture content is determined as follows:
This test method must be modified when the materials being tested would be degraded at 75ºC.
1) Weigh crucibles and aliquots of material which passed through a 40 mesh sieve.3. Percent Combustible Material
Percent combustible material is determined as follows:
1) Weigh crucibles and aliquots of material which passed through a 40 mesh sieve.4. Percent Combustible Dust
Percent combustible dust is the product of the percent of material which went through a 40 mesh sieve and the percent combustible material. This is calculated as follows:
Be aware of the distinction between combustible material and combustible dust.
5. Minimum Explosive Concentration
Minimum explosive concentration is a test for the lower limit of explosibility and is done in the 20-L chamber. Some analytical details include:
1) Test material which has been sieved through 40 mesh.6. Maximum Normalized Rate of Pressure rise (dP/dt)
Maximum normalized rate of pressure rise (dP/dt) provides a value which may be compared with a dust classification scheme and gives a relative comparison of severity using the following equation:
maximum normalized (Dp/dt)=(dP/dt)maxV1/3