A harmless but highly-pungent chemical which is added to odourless gas to make it detectable could have sparked the strong smell of gas which raised alarm in Marsa two days ago, this newspaper has learnt.

Known as mercaptan, this chemical is widely used as an additive to propane and butane gas which is used for cooking and heating. It produces a strong odour, even in extremely small quantities.

On Thursday night the Civil Protection Department cordoned a section of the Marsa industrial estate, following concerns of a gas leak from the Easygas bottling plant due to the strong odour present. However, onsite tests revealed no alarming presence of gas, possibly indicating a minor leak or none at all.

Industry sources told the Times of Malta that one possible cause for the strong smell could have been the leakage of a sludge which accumulates at the bottom of gas tanks and containers. He added that this sludge contains chemicals, including mercaptan which over time liquefy and sink to the bottom.

“Such leakage could have been caused during periodic cleansing of empty containers by unskilled workers,” the source said.

“Judging by the fact that no excessive gas presence was detected, this is the most plausible explanation for the strong smell,” the source pointed out.

“Standard procedure says that such sludge needs to be treated with certain substances which would neutralise its strong smell,” he added.

An Easygas spokesman confirmed that tests carried out by the Civil Protection Department yielded negative results.

While acknowledging there was a strong smell, he said the odour was not concentrated near their plant but at some distance away.

“Apart from the tests carried out by the Civil Protection in several parts of the plant, no leaks were detected by our equipment,” he said.

The spokesman could not answer if the smell might have been caused when the tanks were being cleaned. He pointed out that, had there been a gas leak, the alarm would have gone off and the plant would have automatically shut down as a precaution.

“This is a phenomenon whose origin seems to be unknown,” the spokesman said.

In 2012, an inquiry had found serious shortcoming in the way State energy provider Enemalta had illegally burned off hundreds of gallons of mercaptan, by failing to consult its own internal experts or the environmental authority.