Old town gas network of pipes posing a lethal threat to construction crews in Hobart and Launceston - ABC News

Fourteen years ago, the lives of three Tasmanian construction workers changed forever.

The trio had been excavating when they unwittingly hit an old town gas main under Hobart's Evans Street in 2010.

The ruptured pipe spewed toxic gas into the air, leaving the workers with "significant, life-changing" injuries, according to Tasmania's Civil Contactors Federation.

Old town gas pipes snake throughout Hobart and the city's northern suburbs, installed from the 1850s to distribute coal gas to street lamps.

As electricity became dominant, the company that owned the network, the Hobart Gas Company, went into decline and ultimately decommissioned the pipes in the 1970s.

Since then, they've been left abandoned underground, with their exact location unknown.

And with the Hobart Gas Company now defunct, no entity is responsible for them.

Over the past half century, toxic gases have built up inside them.

The Tasmanian government warns "broken town gas pipes can contain cyanide and other harmful gases".

"When released these gases can starve the brain of oxygen leading to long term or permanent illness/injury such as memory loss, impaired spatial ability and nerve damage."

Tasmania's Civil Contractors Federation, the state's civil construction industry peak body, is alarmed by the potential dangers the network poses to unsuspecting workers.

"It's an ageing asset that's crumbling, but the gas inside the pipe contains cyanide and that can be fatal," the Federation's Jesse Brunskill said.

"It's carcinogenic, it's a volatile organic compound which can cause pretty serious effects if it's inhaled.

"The issue is, with a civil contractor who will dig in the ground, to disturb one of these pipes could have fatal consequences pretty quickly."

Mr Brunskill said one example of serious harm was the 2010 incident in Evans Street.

"The gases came into the area the guys were working on and they inhaled it, and sustained significant injuries that were ongoing and life-changing.

"Anytime a construction worker penetrates the ground in those local government areas that had old town gas there's a risk they could hit an old pipe and be exposed to the gases."

There are a long list of suburbs reticulated with old town gas mains, including most of Hobart's outer suburbs, and areas throughout Glenorchy city.

Launceston also has a decommissioned network of old gas mains.

According to Worksafe Tasmania the extent of the risk is unknown.

Not all old town gas pipes contain dangerous gases. It depends on the residue inside them at the time they were sealed.

One indicative map produced by Tas Gas, now known as Solstice Energy, at an unspecified date shows where some of the old town gas pipes are believed to be located — but warns the map was digitised from historical maps, and no responsibility can be taken for its accuracy.

The map identifies nine "encountered incidents" between 2010 and 2013. It is unclear how many relate to old town gas.

There have been two reports of emissions from old town gas mains over the past decade, according to Worksafe Tasmania.

There haven't been any injuries since 2013.

The Tasmanian branch of the Communications, Electrical and Plumbing Union (CEPU) wants action to make the underground pipes safer.

"The main concern is the lack of awareness they actually even exist in the first place," CEPU's Chris Clark said.

"Secondary to that would be the fact that we don't know where they are, and given the toxic nature of the gas that can be produced, the significant or imminent risks to worker safety should they be exposed to the gas."

The Civil Contractors Federation has been pushing the Tasmanian government for a resolution since early last year.

Jesse Brunskill said it was time for issue to be addressed.

"Ultimately we want to eliminate the risk by getting rid of the old town gas," he said.

"We'd also like to have a custodian for it, so there's an authority that has ownership, and improve the data that's available on where it's located."

Tasmania's Department of State Growth is setting up a working group to identify a way to solve the issue.

It has approached industry bodies, councils and relevant areas of government to participate.

A list of areas where old town gas was used, which includes Launceston, can be found on the Consumer, Building and Occupational Services website.

Worksafe Tasmania recommends contractors check with TasWater, TasNetworks and Dial Before You Dig Australia for records of old town gas mains before starting work.