Measuring ventilation at plating-tank hoods

NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.

May 29, 1975
Mr. J. L. Wentz,
General Supervisor - Safety
Midwest Steel Division of
National Steel Corporation
[Recipient address omitted]
Dear Mr. Wentz:
Your letter of May 5, 1975 requests an interpretation of the requirements of Section [1910.124(j)(1) and (j)(2)]. The following information was secured from the Standards Division:
"Initially, during installation, provisions should have been made for a Pitot Tube traverse of the duct. At present, since some of the ducts are lined, air flow measurements can be made with a calibrated velometer, or heated thermoanemometer across the hood entry and edges of the tank. ~~Exhaust ventilation rates must meet the requirements of Table G-15."~~
[This document was edited on 06/01/99 to strike information that no longer reflects current OSHA policy.]
You are reminded that the air flows are for undisturbed locations. Higher airflows may be required to compensate for excessive cross drafts. Air sampling for a specific contaminant is one means of evaluating effectiveness of the air exhaust system.
A modified Pitot Tube does exist which consists of two tubes joined laterally (approx. 1/2" D x 1" wide). This permits straight entry into a duct. A 2" threaded sleeve welded onto the duct is the permanent entry (when not in use - a threaded cap closes the opening).
If you have additional questions pertaining to the matter above, please feel free to contact this office.
Very truly yours,
EDWARD J. LARGENT,
Associate Assistant
Regional Director for
Technical Support