Safe fill height for AST's

[plastcc]

I need help in determining a safe fill height for my #2 fuel oil tanks. They are horizontal, 20,000 - 22,000 gallon tanks built to UL-142 standards. They have a shell thickness of 1/4", an outside diameter of 120", and an outside length of 408 1/2" to 449 5/16". The heads are flat. They are not heated and are vented to atmosphere. The tanks are fitted with overfill protection valves, and monitored with a Pneumercator LDE740 level monitor. I can not find a procedure for determining the safe fill height, and I don't want to rely upon the overfill valves or the level monitor. The tank designer has passed away, and no one knows the location of his files. My state pollution prevention authority says the height is up to me to determine, as they do not have any guideline for determining the height, just a requirement to post it.

 

[saxon]

ndoukas, I've always used 90% of capacity as the max. High-High Liquid level. Secondary containment at 110% of capacity.

Hope this helps.
saxon

 

[nana6]

please refer to American Petroleum Standard API 650 for welded steel tanks for oil storage