OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at https://www.osha.gov.

October 20, 1988

Bill Lybrand
So. Carolina Department of Labor
P.O. Box 11329
Columbia, SC 29211

Dear Mr. Lybrand:

In response to your concerns about analytical services necessary to support the new OSHA Grain Handling Standard I am supplying you with the following information:

Fugitive Grain Dust is defined in the new standard as "combustible dust particles, emitted from the stock handling system, of such size as will pass through a U.S. Standard 40 mesh sieve (425 microns or less)". The standard specifies that fugitive grain dust accumulations of 1/8 inch will trigger the employer to initiate actions to remove these accumulations.

This definition greatly simplifies the analytical work necessary to characterize the dust found in a grain handling facility. To determine the percentage of fugitive dust in a sample obtained from one of these facilities where dust levels exceed 1/8 of an inch, a laboratory would need to perform the following analyses:


Percent Fugitive Dusts (Lab Tests)

1- The sample will be passed through a Standard 40 mesh sieve. The laboratory would need to make a weight determination to measure the percentage of the material that passes through the sieve.

2- An aliquot of the material that passed through the 40 mesh sieve would then need to be ignited in a furnace at 600oC. The combustible fraction of the sample is determined by measuring the difference in weight of the sample aliquot before and after ignition.

These two parameters are then combined mathematically and a value, in percent, is reported as "% Combustible Dust". These analyses are all that are necessary to meet the requirements for the characterization of a sample found in a grain handling facility as "Fugitive Grain Dust" as defined by the standard.

Additional tests may be conducted. They include suspending some of the dust in a 20-liter explosibility test chamber and igniting it with a strong chemical ignitor. By monitoring the pressure developed in the chamber we are able to determine if the sample exploded. This is not a requirement of the standard, but it is done to provide additional supportive documentation about the explosive nature of the samples.

To answer your question about the containers we recommend for sampling I have enclosed one of the containers that we are currently using for sampling grain dust. This container will hold 8 oz. (~ 250 ml) of material. This will be enough sample to perform the following tests:

1- % 40 mesh - Percent that passes through a 40 mesh sieve (ie particles less than 425 microns in size)


2- % Combustible Dust - Percent Combustible Dust

3- Kst - Normalized Rate of Pressure Rise - This is a parameter associated with explosions that indicates that the dust exploded. (This test is performed only if specifically requested for special purposes.)

I have also included three bottles of sieved dust for reference in regard to particle size. This material was obtained from a pooled grain dust that we have at the laboratory. This material may be useful as a training aid for your staff so they can recognize the size of dust the standard addresses. They are composed of the following sized grain dusts:

1- Coarse dust greater than 40 mesh (425 micron).

2- Dust that is less than 40 mesh but greater than 200 mesh (425 micron and 75 micron). Dust this fine or finer is what we need to meet the criteria of the Grain Handling Standard.

3- Fine dust less than 200 mesh ( 75 microns).

Finally, I have included pages from the 1988 Fisher Scientific supply catalog for sieves, containers and furnaces to give you an idea of their cost. This equipment is readily available from any number of scientific supply distributors besides Fisher so you may check with some other suppliers to get the best price. The 20-liter explosibility testing chamber used for the supplemental tests is not available as an off the shelf item, but can be obtained through speciality suppliers.

I trust that I have provided you with the information that you requested. If I can be of further assistance please feel free to contact me at the laboratory, my phone number is (801 487-0073).


Steven L. Edwards
Supervisory Chemist