Air sampling position during welding with respirators

February 3, 1999

Mr. Randy A. Milbrath
HSE Consulting and Sampling
[Recipient address omitted]

Dear Mr. Milbrath:

This is in response to your letter dated November 3, 1998, addressed to the Occupational Safety and Health Administration's (OSHA's) Directorate of Compliance Programs (DCP), regarding the proper air sampling methodology for welding operations. In your letter you have asked for a formal response regarding the correct placement of an air sampling cassette on employees performing welding operations while wearing a supplied air breathing ensemble.

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. If the employee is wearing a welding helmet and either no respirator or a negative pressure respirator, sampling should be done inside the helmet.

Since we are concerned with what an employee's potential exposure would be, sampling must always be located outside of any respiratory protective equipment. Sampling inside the ensemble that you have described would be measuring an unrepresentative atmosphere composed of a mixture of the air passing out of the respirator hood and the air outside the hood. This area would be an artificially low concentration. Therefore, sampling should be done as normally would be done for any other contaminant (i.e., in the breathing zone outside the ensemble).

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

Sincerely,

Richard E. Fairfax
Director
Directorate of Compliance Programs