Chances are it may have been a storm water sewer (drain). In what are commonly referred to as sewers (carrying away human waste & such), typically (though not always) have toxic atmospheres. Most of these sewers often have very high levels of methane & hydrogen sulfide from decaying materials in levels that would be almost immediately dangerous to health & life. Even storm drains can have these atmospheres from decaying leaves & such & they can have a very similar smell (rotten egg from hydrogen sulfide). This guy was very lucky that it did not kill him. In our little town we had 3 deaths in 1 day, about 15yrs ago) from a small underground chamber where a worker entered to check some gauges without first checking the atmosphere. He was overcome by the poisonous gases & found unresponsive by a police officer who went in to rescue the worker, the officer was then overcome & his partner after that trying to rescue his buddy. Unfortunately it was too late for those three. The rescuers ended up also being victims. One should never enter a confined space like that without proper training & equipment for confined spaces. No ring is worth someone's life. At work, I am a confined space atmospheric tester & also a confined space rescuer.
