OSHA 1910.106 Flammable and Combustible Liquids

[don1980]

In the past, I have thought OSHA 1910.106 only applied to storage tanks and pressure vessels which function as storage tanks(operate at < 15 psig).

Someone challenged that, saying that this OSHA reg applies to all pressure vessels which function as storage tanks, regardless of the operating pressure. After re-reading the reg, I think he might be right. The reg says that pressure vessels can be used as storage tank, thus covering those vessels, and it doesn't state that vessels operating at > 15 psig are excluded.

The impact, and reason for my question, is because of the methodology used to calculate fire heat input. OSHA 1910.106 adopts the NFPA-30 heat input equation and credits. Thus, the relief device will be much large for pressure vessels that have fire-resistant insulation.

What is your interpretation of OSHA 1910.106? Is it not allowable to use the API 521 heat input methodology for a pressure vessesl operating at, say, 50 psig if that vessel contains flammable/combustible liquid and it can be described as a storage tank?

 

[stookeyfpe]

I reviewed NFPA 30-2012 edition. The standard does not specifically adopt API Standard 521 and deferes all requirements for the design and construction of pressure vessels to ASME BPV. So you would be correct in applying API 521.

Note that the emergency venting calculations in NFPA 30 are for atmospheric pressure tanks. The standard was never meant to apply to a pressure vessel operating at < 15 PSIG. I used to be a member of the NFPA 30 Technical Committee and I'm still heavily involved in the standard in my current position.

Your scenario brings up an interesting problem that I don't believe has been considered before. At a minimum, I may craft a change proposal that explicitly states that sizing of pressure relief devices for pressure vessels shall be in accordance with API 521. That would end the debate for this OSHA regulation.

 

[don1980]

stookeyfep - thanks for your comments. Regardless of the original intent of NFPA-30, I can say from experience that some companies use NFPA-30 methodology for calculating fire heat input to pressure vessels. Personally, I don't see anything wrong with that, since the calculated heat input is usually greater (more conservative) than API 521. However, by far, most companies use API 521 to calculate fire heat for pressure vessels.

I'm guessing there are very few, if any, people who interpret OSHA 1910.106 as disallowing the use of API 521 for a vessel operating at > 15 psig, if that vessel is used as a storage tank. In my experience, if it's a pressure vessel, then API 521 is used regardless of what the vessel is used for.

However, OSHA 1910.106 doesn't provide clarity. I can easily see how someone could interpret it to mean that API 521 can't be used to calculate fire heat for pressure vessels that are functioning as storage vessels, regardless of that vessel's operating pressure.

I'd sure appreciate hearing comments from others. Before you calculate the fire heat input for a pressure vessel, do any of you pause to question whether it's being used as a storage tank? Again, I'm guessing the answer is no, and I think that's perfectly OK. I don't think this interpretation of OSHA 1910.106 is correct, but I could be wrong about that. Let me know what you think. Thanks.