[Robert DeLong]

Hydrogen sulfide is often produced from the microbial breakdown of organic matter in the absence of oxygen gas, such as in swamps and sewers; this process is commonly known as anaerobic digestion which is done by sulfate-reducing microorganisms. H2S also occurs in volcanic gases, natural gas, and in some sources of well water. The human body produces small amounts of H2S and uses it as a signaling molecule.

Are those holding tanks getting the water from wells?

[Paperpusher]

Yes, that tank was filled by well water and was being repaired due to leaks. maybe from corrosion.

[silent majority rising]

It appears from the video that the tank was empty. Which would have provided a large collection tank for the H2S. I can see the problem. Unfortunately, this is more common than you think in repair work on petroleum storage tanks. When they are emptied, there are always residual gases that can be a problem.

[farming pharmer]

The human body produces small amounts of H2S and uses it as a signaling molecule.

Lol, signaling others in close proximity to run away...