Reportedly measured at 150 ppm. The odor alone must have been overwhelming.
No, at that concentration there was instant loss of sense of smell and death in the next breath. It really is that dangerous.
What makes H2S, other than its toxicity, is it is heavier than air. When there is a release, particularly at a wellsite, the concentration can be more than any human can tolerate and doesn’t dissipate without a steady wind. Wellsites generally have a burn tower that runs from a separator after the usable gases come out of the wellhead and burns off at an elevated position. Resulting gas is Sulfur Dioxide, which is just as toxic as H2S but much lighter than air.