The Commission for Energy Regulation (CER) has said it will carry out an investigation after non-odourised gas was introduced into the local gas network in Galway and Mayo.

Gas Networks Ireland has said it hopes to restore full access to the gas supply in Mayo and Galway by Sunday afternoon, after the odourless gas was added due to a technical fault at the Shell facility in Bellanboy.

In a statement released this evening, the CER said that "the first priority is to restore odourised gas to the affected areas".

"The CER is actively involved in the Gas Emergency Response Team under the Natural Gas Emergency Plan.

"The membership includes Gas Networks Ireland (GNI), the Department of Communications, Climate Change and Environment (DCCAE) and the other relevant network operators," added the statement.

Network Safety Manager Owen Wilson said GNI is working to establish how odourless gas entered the supply chain. 

The odour was not added due to a technical fault at the Shell facility at Bellanaboy. With no smell, it is impossible to detect a gas leak.

Gas Networks Ireland has said that customers in Galway city, Oranmore, Salthill, and Claregalway, are now safe to resume using their natural gas supply.

Supplies are expected to be restored to homes around Galway city this evening, with customers in Castlebar, Ballina, Westport, Claremorris, Ballinrobe and Crossmolina to be reconnected as soon as it is safe to do so. 

Large flames emanating from the Corrib Gas Terminal have been visible for miles this afternoon, as Shell technicians burn off the odourless gas.

It is been pumped back to the plant at Bellanaboy and a process known as flaring is continuing to clear it from the network.

Shell says its contacting people in the immediate vicinity of the terminal to inform them about what's happening but many locals are angry at a lack of notification from the company.

Mr Wilson said the risk to customers is "very very low" and is "absolutely" happy with how quickly customers were told to switch off their supply.

Speaking on RTÉ's Morning Ireland, he said GNI is making good progress to return the supply to full safety levels.

It emerged last night that odourless gas from the Corrib field had been delivered onto the network and customers in Galway and Mayo were told to switch off their supplies.

The affected gas is being piped back to the Shell terminal in north Mayo, where it is being burned off.

The company said this is a standard safety mechanism but some locals are concerned at the noise and flames associated with the process, which is expected to continue throughout the day.

Inspectors from the Environmental Protection Agency are monitoring the situation.

Gas Networks Ireland said it could take up to three days before normal supplies are restored.

Michael Ring, Minister for Rural Affairs has said the issue needs to be investigated immediately by the State agencies to reassure people and businesses.

Speaking on RTÉ’s News at One, he said he knows it was a glitch but that it is a very dangerous substance and people want an assurance that it does not happen again.

"We need to know what went wrong. We need it investigated. We need the State agencies now to investigate and to tell us what happened and to reassure the public and the business sectors that this won’t happen again," he said.