MJC,

No 1. I have no idea or even if this information is collected anywhere. Free breathing tanks have gradually been removed or modified over the last 30 years due to emissions issues, but this sounds like a heavy fuel oil tank which might still be free vented.

Most Crude tanks above any sort of decent size are usually external floating roof.

No 2. There's no need for the " ". The roofs do actually float on the surface of the crude. And no, you can't inert them.

No 3. Not necessarily. Lightning strikes do funny things and are a common reason for starting fires in tank farms.

Not much detail in the Cuba fires yet.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

Dear Cronin Sir,

1 & 2. Crude storage tanks are floating roof with at best, secondary seals. No nitrogen shrouding.

3. Grounding systems, also called earthing connections are to be installed at quite a few locations like between the floating roof ladder and the roof, between the rail on which the ladder moves and the roof, between the tank shell and the grounding box. Miss any of these and also if you are unlucky....boom!

DHURJATI SEN
Kolkata, India

One of the references I ran down talked about floating roof tanks with geodesic dome roofs, to either keep rain off of the floating roof, or to aid in vapor recovery. The tanks at issue in the Cuba tank farm fire had domes installed, so regardless of the presence or absence of floating roof, the headspace is a risk factor.
If the space above the floating roof (or oil surface) and the dome is not kept out of the combustible / explosive region, we have one side of the boom triangle.

Reference https://cultofsea.com/tanker/flammability-composit...