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.

August 16, 1996

Mr. Michael V. Marchlik S. Cohen and Associates 143 Pershing Avenue Ridgewood, NJ 07450

Dear Mr. Marchlik:

This is in response to your March 29 letter requesting an interpretation of the process safety management (PSM) of highly hazardous chemicals standard, 29 CFR 1910.119. Please accept our apology for the delay in responding. Your workplace scenario and question and our reply follow.

Scenario: A facility operation intends to store flammable liquids, acetone and methanol, in 2500 gallon stainless steel tanks (more than 10,000 pounds of flammable solvent). The flammable liquids are stored under a nitrogen atmosphere and are kept below their normal boiling point without benefit of chilling or refrigeration. The atmospheric storage tanks are located in a covered area, approximately 140 feet from the pilot plant building. The storage tanks are constructed of 304 stainless steel and are designed to withstand a pressure of 14 psi at 200 degrees Fahrenheit. The storage tank relief valves are set at 14 psig and the conservation vents are set at 0.4 psig.

The solvent storage tanks are interconnected to several pilot plant solvent manifold panels. At the manifold panel, each solvent line has double valves and a totalizer.

The solvent is transferred from the manifold to a separate empty intermediate holding vessel (day tank) using temporary flex hose connections. The connection is only made during transfer from the manifold to the day tank. The delivery quantity is monitored with a totalizer and controlled by the dead man valve. At no time does the quantity of flammable materials exceed 10,000 pounds in any of the day tanks. The capacity of the largest day tank is 750 gallons. The flammable liquids are kept below their normal boiling point without benefit of chilling or refrigeration.

After collecting the desired solvent quantity in the day tank, the operator discontinues the flow from the solvent manifold to the day tank by releasing the deadman valve. The temporary hose from the solvent manifold to the day tank is then disconnected.

The day tank containing the desired quantity of solvent is then connected to the process vessel for material transfer. The distinct two-stage operation ensures that the day tank serves as a storage vessel without any tie-in to the process there will never be direct transfer of solvent from the manifold to the process.

Question: Would the flammable solvent storage and associated transfer as described above meet the exemption of atmospheric storage of flammable liquids under paragraph 1910.119(a)(1)(ii)(B)?

Reply: Since acetone and methanol are stored in tanks which are subject to a nitrogen inerting pressure of 14 pounds per square inch gauge (psig) or 96.6 kilo pascal (Kpa), the atmospheric tank exception under paragraph 1910.119(a)(1)(ii)(B) would not apply to the preceding scenario. The PSM Standard covers the process(es) you describe. Also, acetone and methanol storage and transfer must meet the flammable liquids requirements under 1910.106.

We appreciate your interest in employee safety and health. If we can be of further assistance, please contact Mr. Ronald Davies of my staff, telephone # (202) 219-8031, extension 110.


John B. Miles, Jr., Director Directorate of Compliance Programs