Hydrogen sulfide set off town's alarms just before explosion. What is it?

Author of the article: Dave Waddell • Windsor Star
Publishing date:Aug 27, 2021 • 

Wreckage is shown from an explosion in Wheatley, a Chatham-Kent town of about 3,000 that's been hit recently with toxic-gas leaks. Photo taken on Friday Aug. 27, 2021, about 15 hours after the blast. Dax Melmer/Postmedia

WHEATLEY – The gas that set off detectors in this Chatham-area town shortly before a massive explosion rocked its main street is familiar to most Canadians for its rotten-egg smell, associated with leaking natural gas.

Hydrogen sulfide is used by natural gas companies specifically for its noxious aroma as a safety measure, but is dangerous on its own for its flammable and explosive properties.

“It’s very nasty stuff,” Western University chemistry professor Jamie Noel said. “It’s pretty common, but for people it’s deadly. It only takes 1000 parts per million to kill you instantly.

“It’s also very combustible. It explodes at about 41/2 per cent per volume in air.”

Chatham-Kent officials confirmed gas detectors in the demolished buildings – put in place by government officials after two recent toxic-gas leaks – recorded the presence of hydrogen sulfide prior to the explosion.

“We’re talking the most probable cause is an abandoned (gas) well,” said Chatham-Kent’s top administrator, Don Shropshire. “This area has hundreds of abandoned wells from Niagara to Windsor.”


In Southwestern Ontario, hydrogen sulfide is commonly associated with such wells. Traces can also give well water that sulphur taste.

PHOTOS: A town and its residents reel after massive explosion

Hydrogen sulfide is soluble in water, most organic liquids and oil, but when agitated or in increasing temperatures solubility decreases and higher concentrations can build up.

Discovered by Swedish chemist Carl Wilhelm Scheele in 1771 and commonly nicknamed swamp gas, hydrogen sulfide forms as the result of the bacterial action of breaking down decaying materials. That process also gives the colourless gas its rotten egg smell.

“It takes less than one part per million to smell it,” said Noel. “That’s its warning system. The warning doesn’t last long because it eventually destroys your sense of smell.”

Its health impacts are many and range from eye irritation and respiratory issues in lower dosages to death from higher exposures. The gas is found in the oil and gas, manufacturing, pulp and paper, agriculture, food processing, mining and sewage treatment industries.

Hydrogen Sulfide will spontaneously ignite at 270 C (518 F).

In addition to gas wells, hydrogen sulfide occurs naturally in sewers, volcanoes, hot springs and manure pits.

It collects in low-lying areas because it’s heavier than air.

Noel said the gas is relatively stable, but it’s capable of moving through fissures and cracks in the ground.

“It’ll collect in pockets and, when enough pressure builds up, it’ll burp to the surface,” Noel said. “It’s dangerous when enough of it accumulates.

“The other concern about it is the gas is also corrosive to metal underground.”

Seven people were hospitalized after the explosion, though none of the injuries are life-threatening. The downtown gas detectors went off at about 4:30 p.m. and municipal officials and emergency crews starting clearing out residents – the explosion happened at about 6 p.m.

Officials have said that 90-minute warning almost certainly saved lives.

dwaddell@postmedia.com