Comments by "Reecom98" (@reecom9884) on "Fire causes two huge explosions at a oil refinery in eastern Iran" video.

An oil tank has a pressure relief/vacuum relief valve with a flame arrestor. The pressure relief is needed to let gases out as you pump oil in and the vacuum relief to let fresh air in as you pump out to relief the vacuum. A flame arrestor is part of the relief/vacuum relief valve to prevent the flame from entering the oil tank if the vapors ignite due to a spark on top of the tank. It looks like a failure of the oil tank flame arrestor on top of the tank creating a blowtorch on top of the tank.
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@cuz129 Look at the video, the blowtorch from the top of the tank. You don't need N2 gas as a padding, you keep the O2 low by connection of the plant off-gas before going to the flare tower. This is a refined liquid petroleum tank.
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@cuz129 The tank padding gas in the tank would have kept the O2% below the ignition level. If the auto ignition in the tank was reached, it would have blown up instead of blow-torching of the relief valve due to external ignition.
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@cuz129 The vacuum relief allows a minimum inflow of air to prevent collapsing of the tank if the plant off gas flow isn't enough during pump out.
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