I'm pretty sure it was the carbon monoxide as the guy had the pump down in the tank. Could happen I guess if you didn't know.
I remember years ago I was pumping an out of ground concrete tank out with the pump sitting on top of the tank and the fuel leaked into the tank. A chemist friend advised me to get a charcoal filter which luckily did the trick as we didn't have much water back then.
Lucky enough to have a 35,000 gallon concrete now which doubles up as a party area with pergola.
Be careful in those silos my friend.
