how dangerous is hydrogen sulfide (cat exhaust?)

You can smell it at levels as low as 2 parts-per-billion (ppb).

The safe exposure limit at places like rubbish dumps and slurry pits is

15parts-per-*million* - that's 15,000 ppb.

The lethal limit is somewhere around 200ppm, so there's quite a way between smelling it and dying from it.

The page below details a monitoring experiment which showed ambient levels were about 2ppb and cars added another 1-2ppb to that. So there's quite a way to go to the 200,000ppb required to kill somebody.

It doesn't smell very nice though, you're right.

I take it by the spelling you're posting from the US?

You could take it up with your petrol companies who are still apparently producing high sulphur petrol.

In message , snipped-for-privacy@yahoo.com writes

Hydrogen sulphide is extremely toxic, but it is also noticeable at extremely low concentrations. You can smell it at as little as 0.008 parts per million, but it won't start to do you any harm until it's over

20ppm.

One peculiarity is that at potentially lethal concentrations, the first thing it kills off is your sense of smell. Lots of people have been killed by H2S poisoning, but almost always in confined spaces; sewers, silage tanks, holds of ships, etc.

The risk from hydrogen sulphide in exhaust emissions is similar to the level of risk from eggy farts.

ppm

0.008-0.2 Olfactory threshold -?rotten eggs? smell detectable 20 Sense of smell to gas lost Concentrations tolerated for some hours without harm 20-50 Eye irritation 50 Prolonged exposure may cause pharyngitis and bronchitis 60 Prolonged exposure may cause conjunctivitis and eye pain 150+ Irritation of upper respiratory tract Sense of smell lost 250 Pulmonary oedema with risk of death 500 Very dangerous, evacuation should occur well below this level 1000 Loss of consciousness occurs 1000-2000 Acute intoxication: symptoms include rapid breathing, distress, nausea and vomiting. May be rapidly followed by loss of consciousness, coma and cessation of breathing. 2000+ Immediate loss of consciousness and high probability of death

In message , "Dave Plowman (News)" writes

Technically, he's correct. IUPAC standardised on the 'f' spelling for sulphur and derivatives. Bastards.

Oddly enough my Pug 406 sometimes puts out the rotten egg smell but as I nearly always buy my petrol from Sainsbury I presume their quality control isn't quite as good as it could be?