There is some H2S in that gas but probably not enough to flare it. It is dissolved in the oil and saltwater in those tanks and can become concentrated enough that if you climbed up the ladder and stuck your head in the tank (like many people do just to see some oil), it could kill you deader than a door nail. It happens all of the time, especially to teens and drunkards out looking for something to do. Could you actually smell any of the gas while on the location? If not, then it is probably not a big deal.
Sounds like there are some Darwin Award candidates around. Anywho, near as I could tell these tanks were sealed as the pic, although not the best resolution, indicates. It was a HOT July/August afternoon and we didn’t get out to look around but I opened my window to listen to the compressor/generator unit. Could BARELY hear the thing running and we couldn’t have been more than 10 - 15 feet away from it. Amazing, I says to myself! And no, no noticeable odors of any kind oddly enough — or not.