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Sour gas: Why it makes people nervous
CBC News Online | August 10, 2005

Sour gas is a term used to describe natural gas containing hydrogen sulphide, a toxic, flammable substance. Sour gas developments make people nervous, especially in Alberta, where one-third of natural gas wells contain hydrogen sulphide.

Hydrogen sulphide gives sour gas its distinctive rotten egg odour. But it�s not the smell that motivates surrounding communities to protest against sour gas wells. What they�re worried about is hydrogen sulphide�s potential for harming human and animal health.

But what is hydrogen sulphide and what kind of risk does it pose? H2S, as it is often called, is formed when organic matter decays, and is a component of unrefined fuels such as natural gas, crude oil and coal. It occurs naturally in some mineral springs and in volcanic gas.

Hydrogen sulphide is found in gas deposits across Alberta, mostly in the foothills regions, and also in Saskatchewan and British Columbia.

�Many of us are exposed to H2S on a regular basis, albeit at low levels, because we do produce it in our bodies,� Don Davies, vice-president of Ontario-based Cantox Environmental, and an authority in toxicology, told CBC News.

�Anyone with halitosis is exhaling H2S. Flatulence contains H2S �. You also find people who use sulphur hot springs are being exposed to low levels of H2S.�

But as with any substance, it�s the dose that makes it poisonous, says Davies. �If the levels get high and you�re upwards of several hundred parts per million, it�s nasty stuff and it can cause serious adverse health impacts, including death.�

If you�re unlucky enough to be exposed to low levels of hydrogen sulphide, you may find your eyes, nose and throat become irritated. And if you�re asthmatic, inhaling the gas could make it hard to breathe.

The real concern is with exposure to high concentrations of the gas – even very brief exposure. That�s why emergency authorities try to evacuate people living near sour gas wells immediately after a leak or explosion.

According to U.S. government health statistics, concentrations greater than 500 parts per million can cause you to lose consciousness and can even kill you. Children and the elderly may die after being exposed to lower concentrations.

After regaining consciousness, some people may suffer from headaches, poor attention span, memory and motor function.

Most of those killed by hydrogen sulphide poisoning are workers exposed to high levels in confined, unventilated areas. Some workers have also been killed during sour gas well explosions. In August 2005, an explosion killed one man and injured three others in southern Alberta as they tried to bring an oil well containing sour gas into service.

�In terms of any member of the public being poisoned to the point where they�ve died, I don�t know of any instance in Alberta. In fact, I don�t know of any instance in North America,� says Davies.

People living near sour gas wells are more likely to be exposed to �fugitive emissions� than they are to lethal levels of hydrogen sulphide. The difficulty in assessing this risk is that there has not been a lot of research on the effect of long-term, low-level exposure.

At least one study on the effect of �flares� designed to burn sour gas yielded disturbing results. Flaring is the petroleum industry's routine practice of burning off waste gas.

The study, by veterinarian Cheryl Waldner, looked at the flares� effect on farm animals. "We did find a consistent association between increased risk of stillbirth and exposure to flared sour gas," Waldner told CBC News.


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