Conductivity of asbestos-sampling cassette cowls

August 28, 1991
Michael A. Sirbola
Air Monitoring Equipment, Inc.
[Recipient address omitted]

Dear Michael,

I have tried over the course of the past year to find time to make a simple determination that would answer the question you posed about the resistivity of the cowl. I appreciate your patience with me. I still have not absolutely determined a suitable response to your question. I have raised considerable questions of my own about what is going on in the cassette. The situation is far from simple. The intent of the requirement for the cassette cowl to be conductive was to eliminate electric fields in the interior and give charges a path out of the cassette.

Therefore, we require that the resistivity of the cowl be sufficient that the material be considered a conductor. The standards do not specify a particular resistivity, nor do they require the cowl to be black. Both 29 CFR 1910.1001 and [29 CFR 1926.1101] simply require that the cowl be "conductive". This is the aspect of the standard that is enforceable.

We will continue to study the issue in greater detail. Should you require further assistance, feel free to call.
Sincerely,
Daniel T. Crane, Supervisory Physical Scientist
[Directorate of Science, Technology, and Medicine
Salt Lake Technical Center]
(Correction 6/2/2005)

[The requester’s July 9, 1990 letter reproduced on the OSHA page is omitted here.]