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 http://www.osha.gov.

February 13, 1986

 
MEMORANDUM FOR: LINDA ANKU
REGIONAL ADMINISTRATOR
 
FROM: JOHN B. MILES, JR.,
DIRECTOR
DIRECTORATE OF FIELD OPERATIONS
 
SUBJECT: Applicability of 1910.106 to Chemical Plants
 

This is in response to your memo of December 23, 1985, same subject.

The art of determining sufficient pressure relief for the storage of unstable liquids is not simple nor even a direct engineering solution. As stated by API 2000 and 521, no one method of sizing the relief ports has gained widespread acceptance, therefore engineers must use their best solution and apply a liberal safety margin. It is generally recognized that only rupture discs can provide the reaction time and volume flow necessary to vent an unstable liquid. Suppression techniques applicable to the situation should also be evaluated.

The referenced Boiler and Pressure Vessel Code-1968, does not provide specific coverage of this issue, therefore only the 1910.106(b)(2)(v) requirement addresses unstable liquid storage pressure relief considerations. In this instance of ethylene oxide storage, it is thought that Union Carbide had an adequate design for pressure relief, as demonstrated at Bhopal, however the handling of the escaping toxic material through a neutralizer of adequate capacity is a primary concern and was an apparent shortcoming of the equipment at Bhopal. Suppression techniques appear to have been woefully deficient.

We recognize that this is a general response to your question. Should you require an analysis of a specific situation, further assistance can be arranged.