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RE: I factor & API 650 Appendix E

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The I factor for API 650 (10th edition with amendment 1 dated March 2000) appears to use the same seismic importance factors as the 1997 UBC, 1.0 for "standard' and 1.25 for "hazardous" classification. This distinction is that API 650 suggests using 1.0 unless the release of the contents would "be considered dangerous to the general public" and the 1997 UBC would require a hazardous  classification merely based on the quantity of the flammable liquids stored, irrespective of location.
If the UBC applies to your location, I think you would have to use a 1.25 importance factor. Even though UBC 1634.4 allows the use of nationally recognized standards for the seismic design of tanks (e.g. AWWA, API), you are still bound by the occupancy categories of UBC 1629.2.
-----Original Message-----
From: Robert M. Hanson [mailto:Bob(--nospam--at)]
Sent: Monday, January 20, 2003 3:43 PM
To: seaint list
Subject: I factor & API 650 Appendix E



I would like to get an opinion or comment on standard practice in application of I factor when using API 650 code. I found the paper (1978) where the method was first presented to API as a proposed practice as an appendix P to API 650. The paper refers to the I at that time in reference to the Uniform Building Code which had a I of 1.5 for essential facilities only. This is a gasoline storage tank. To me being downwind of a leaky tank is a public health hazard and we should be using a I of 1.25.


Robert M. Hanson, SE

Kappa Engineers

(310) 233-3800 x109