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|Title: 10/25/1995 - The (PSM) for Highly hazardous chemicals Standard and its applicability to the specific scenarios outlined.|
|Record Type: Interpretation||Standard Number: 1910.119; 1910.1200|
October 25, 1995
Sam Mannan, Ph.D, PE, CSP
Process Safety and Risk Assessment
RMT/Jones & Neuse, Inc.
912 Capital of Texas
Austin, Texas 78746-6163
Dear Dr. Mannan:
This is in response to your letter of July 24, addressed to Mr. Michael A. Marshall of the Office of Construction and Engineering, regarding the Process Safety Management (PSM) for Highly hazardous chemicals Standard, 29 CFR 1910.119 and its applicability to the specific scenarios that you have outlined. Your letter was forwarded to our office for response.
Following are the scenarios outlined in your letter and our response to each inquiry, respectively.
Scenario 1: Does simple blending or mixing (without a chemical reaction) of a flammable mixture (quantity less than 10,000 pounds) in proximity of multiple storage containers of flammable liquid with an aggregate in excess of 10,000 pounds require coverage under PSM?
Response: According to the information that you have provided, 1910.119 would apply to this scenario. Paragraph (a)(1)(ii) of the referenced Standard states that this Section is applicable to, "A process which involves a flammable liquid or gas (as defined in 1910.1200 of this part) on site in one location, in a quantity of 10,000 pounds or more. Please note that a "process" according to 1910.119, "means any activity involving a highly hazardous chemical including any use, storage, manufacturing handling, or the on-site movement of such activities. For purposes of this definition, any group of vessels which are interconnected an separate vessels which are located such that a highly hazardous chemical could be involved in a potential release shall be considered a single process."|
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2(b): Please define blending, mixing and agitation if they are viewed differently with regard to PSM.
Response 2(b): Blending, Mixing and Agitation are not viewed differently with regard to PSM. That is, the method of achieving a desirable product or intermediate, etc., is not a condition of the Standard's applicability, according to 1910.119(a). As you may be aware, during the process of gas-liquid mixing in agitators, the materials involved in an air-gas mixture are capable of forming an explosive mixture (due to the simple process of evaporation), and due care must be exercised to eliminate possible sources of ignition. In addition, hazards of possible combustion could be expected during liquid-liquid mixing. Currently, OSHA reviewed an accident involving a blender. No chemical reaction was intended in this process. This particular blend, however, resulted in a major explosion including a number of fatalities. In this event, a leaking line resulted in the formation of a reaction between the water and the water reactive chemicals in the blender. This process was designed as a simple blending process, but due to the inadvertent leak, a massive explosion occurred. Therefore, the applicability of PSM is determined by the scope of 1910.119 which is under paragraph (a) and not by the method utilized to mix or blend chemicals.|
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John B. Miles, Jr., Director
Directorate of Compliance Programs
The official, public domain, OSHA version of this document is available at http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=21989&p_text_version=FALSE