The Cockburn cement plant is in trouble with the EPA for the lime dust and SO2 it is producing.
On this morning’s show I said that SO2 was not toxic to the residents in this area.
Listener Scott says:
Before making incorrect statements about chemicals on the radio I suggest you check the msds yourself mate! SO2 is toxic. Nitrogen is not. Nitrogen only kills you by displacement of oxygen. SO2 is an acute toxin, and will kill in an otherwise breathable atmosphere. Check the MSDS for IDLH yourself!
Scott is right, (MSDS) but it is still not toxic to the residents of Cockburn, and the issue simply is the concentration. It belongs to a class of toxin that, while deadly at high concentrations, is harmless at low concentrations, as it does not accumulate in your body.
Cyanide, for example, is in the same category. You could drink a solution containing 50% of a lethal dose every day for the rest of your life and it wouldn’t harm you, as it is eliminated from your body.
With SO2, the concentration required to have a toxic effect is very high:
Health Hazard
Summary
Toxic – corrosive. Exposure to 150 ppm of sulphur dioxide results in extreme irritation tolerable for minutes only. At
500 ppm, a sense of suffocation. May have fatal consequences as a result of spasm, inflammation and oedema of
the larynx and bronchi, chemical pneumonitis and pulmonary oedema. Effects are a result of irritation of the
mucous membranes of the upper respiratory gastro-intestinal tract. Chronic bronchic emphysema have been
documented. Chronic conjunctivitis may result. Dental degradation noted.
That is, you need 500ppm before you get a “sense of suffocation.” This is way, way higher than you’d ever experience even if you were living right next to the stack.
But the reason you can smell it, is that like many sulphur containing compounds, it has a very low odour threshhold (about 0.33ppm)
Incidentally, hydrogen sulphide (rotten egg gas) is even worse. You know what it smells like but you’re still alive? The reason is that it is more toxic than SO2, but with a very,very low odour threshhold (0.0047 ppm!!).
So you can smell it at tiny, tiny concentrations, that won’t effect your health.
I also said that nitrogen is toxic at high concentrations. The issue is simply asphyxiation. It’s a very common industrial gas, and there have been a number of cases where people have walked into a roomfull of nitrogen from a gas cylinder that has accidently discharged – they don’t smell anything of course – but all the nitrogen expels the oxygen from the room, and like pilots whose oxygen supply fails, they simply become drowsy, drop asleep and die – and it only has to halve the concentration of oxygen in air to have this effect!!(MSDS).
A documented case of this is here – but I haven’t come across any cases of fatalities caused by SO2 – the foul smell warns you off before you ever get to breathe enough of it.