You may or may not be aware aware of H2S gas but here is a reminder.
Hydrogen sulfide is a colorless, flammable, extremely hazardous gas with a "rot- ten egg" smell. It occurs naturally in crude petroleum, natural gas, and hot springs. In addition, hydrogen sulfide is naturally produced by bacterial break- down of organic materials and human and animal wastes (e.g., sewage). Industrial activities that can produce the gas include petroleum/natural gas drilling and refining, wastewater treatment, coke ovens, tanneries, and kraft paper mills. Hydrogen sulfide can also exist as a liquid compressed gas. It's heavier than air, very poisonous, corrosive, flammable, and explosive.
Where I'm from I try and avoid any gas field hunting due to this. As for rules most gas fields are signed with presence of H2S and are gated with locks to prevent access (i.e. restricted) in most gas fields. Again something you may or may not have already be aware of.