Flammable storage tanks are potential bombs and should be treated as such. Same as "unloaded" weapons: you have to take positive measures to ensure they are. We read about people being killed or injured by weapons and flammable storage tanks on a regular basis and continue to ignore sound safety procedures. I will continue to be a "safety net" when caution is to be strictly followed. I knew a couple of younger guys that were in the business of cleaning flammable tanker trucks and trailers. They had been in business for several successful years when it caught up with them. They had spent the morning cleaning a tanker trailer before breaking for lunch. They returned and started a planned repair when it exploded. Their remains were so jumbled that it was difficult to determine who was who. Never heard the final analysis as to what went wrong, but just another event to learn from.
By the way, radiator shops in my area will not clean fuel tanks. OSHA Snake's head is too deadly for them.