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.

July 19, 1978

Mr. Thomas J. Boyd
Plant Manager
Hatco Polyester Division
W.R. Grace & Co.
1605 West Elizabeth Avenue
Linden, NJ 07036

Dear Mr. Boyd:

This is in response to your letter dated May 4, 1978, to Mr. Donald A. Shay regarding the clarification of our standard 29 CFR 1910.106(b)(4)(iv)(e). This also confirms several telephone conversations on the subject matter with Mr. Peter Wasko, a member of our staff.

Since a stipulated settlement affirming a violation of 29 CFR 1910.106(b)(4)(iv)(e), with respect to processing vessels used by W.R. Grace & Co. for the thinning and blending of polyester resins, has become a final order of the Occupational Safety and Health Review Commission (Docket No. 77-2491), it is impossible to withdraw the citation issued to W.R. Grace & Co. for violation of that standard. However, we have determined that 29 CFR 1910.106(h)(4)(iv)(b) is the OSHA standard more appropriately applicable to these tanks on the basis of your representation that they are processing tanks rather than storage tanks. 29 CFR 1910.106(h)(4)(iv)(b) provides:

Where the vapor space of equipment is usually within the flammable range, the probability of explosion damage to the equipment can be limited by inerting, by providing an explosion suppression system, or by designing the equipment to contain the peak explosion pressure which may be modified by explosion relief. Where the special hazards of operation, sources of ignition, or exposures indicate a need, consideration shall be given to providing protection by one or more of the above means.

In view of this determination it is not necessary for you to seek a variance to 29 CFR 1910.106(b)(4)(iv)(e) which applies only to storage tanks. Rather you need to comply with the provisions of 1910.106(h)(4)(iv)(b) which we believe, on the basis of your representations, will adequately protect your employees. However, I would direct your attention to the last sentence of 1910.106(h)(4)(iv)(e) which may require you to take more than one of the standard's precautionary steps if such additional measures are necessitated by the circumstances of your operations.

Please do not hesitate to call me if you have further questions.


Bruce Hillenbrand
Acting Director,
Federal Compliance
and State Programs