Small tanker, probably with empty tanks and the fumes ignited.
An empty oil tank is much more dangerous than a full one. When you weld, cut, or grind on an empty vessel which had flamables inside, you first fill it with water to displace the potential fumes. If you can’t fill it with water, you fill it with an inert gas which prevents oxygen fom being available. Any fire needs three things. Heat, fuel source, and oxygen. Remove any one of those three and there is no fire risk.
Yes. Forgot to flood the tanks with Nitrogen to reduce explosion risk
My exact first thought. I’m an electrician in oil and gas industry, and I empty tanks are extremely dangerous. Then some guy is using a grinder? I mean geez, how dumb can one be?