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.

January 4, 1999

Mr. James T. Ferguson
National Steel and Building Company
Industrial Hygiene Department
P.O. Box 82278
San Diego, CA 92186-5278

Dear Mr. Ferguson:

This is in response to your October 14, letter addressed to Mr. Gabriel Gillotti, Director of the Occupational Safety and Health Administration's (OSHA's) San Francisco Regional Office, Office of Voluntary Programs and Outreach. Your letter has been forwarded to OSHA's National Office for response.

In your letter you have ask for an official statement regarding the correct placement of the air sampling cassette on your abrasive blasters when testing the breathing zone concentrations of abrasive blast dust. Your letter then offers several arguments why the cassette should be inside the hood. Unfortunately, this is not OSHA policy.

The correct placement for air sampling cassettes is near the breathing zone of the employee. It should be as close as possible to the nose and mouth of the employee, i.e., in a hemisphere forward of the shoulders with a radius of 6 to 9 inches. Since we are concerned with what an employee's potential exposure would be, it must also be located outside of any protective equipment.

Sampling inside the hood would indeed eliminate the abrasive particles being driven into the cassette by the force of the blasting operation. It also would be measuring an unrepresentative atmosphere composed of a mixture of the air passing out of the respirator and the air outside the hood. This would create an artificially low concentration. Both methods probably do not represent the actual level of contaminant that the employee could potentially breath in, but it is better (safer) industrial hygiene practice to err on the high side.

As you may be aware, the State of California operates its own occupational safety and health program under a plan approved by Federal OSHA. In California, the Division of Occupational Safety and Health enforces standards promulgated by the Cal/OSHA Standards Board. For information on enforcement of California's respiratory protection standard, you may wish to contact:

John Howard, Chief
California Division of Occupational Safety and Health
Department of Industrial Relations
45 Fremont Street, Room 1200
San Francisco, CA 94105
Telephone: 415-972-8500

The Cal/OSHA Standards Board also reviews applications for variances from State standards. If you wish to apply for a variance, you may contact the Standards Board at:

John MacLeod, Executive Officer
California Occupational Safety and Health Standards Board
1300 I Street, Suite 920
Sacramento, CA 95814
Telephone: 916-322-3640

I hope this answers any questions you have on OSHA's sampling policy for abrasive blasting. If you have any further questions, you may also contact OSHA's Office of Health Compliance Assistance at (202) 693-2190.


Richard E. Fairfax
Directorate of Compliance Programs