How do you know no one has died? People die all the time. Death by hydrogen sulfide poisoning will mostly look like a stopped heart, 'natural causes', maybe a stroke. A death like that will receive no news coverage, just an ambulance siren as the corpse is relocated to a burial or cremation facility. Eventually, sure, there will be larger numbers dying - 'flocks of people' dropping dead instead of flocks of birds - and THEN they'll need some 'mass fatality legislation' (in the works), possibly millions of 'coffin liners', mass graves, that kind of thing. They might even run tests in major cities, like, say, New York, to see where a heavier-than-air gas that gets into the subways will go. (The biggest such test ever is scheduled next month, in New York City, when a gas will be released into the subways to analyze dispersion patterns.)