Odourless gas which entered the network in the west of Ireland is being sucked back out of the pipes and burnt off, it has been revealed.
It may be Sunday before householders and businesses should switch back on their supplies after a technical issue allowed the natural gas into the network from Shell's Corrib gas refinery in Co Mayo.
Gas Networks Ireland, which oversees supplies, issued an alert on Thursday evening to about 10,000 customers in Galway city, Oranmore, Tuam and Headford and Ballinrobe, Claremorris, Castlebar, Westport, Crossmolina and Ballina in Mayo to cut their supplies off using a valve at the meter.
It said it recommended the action because the gas could not be detected by smell in case of the unlikely event of a leak.
Natural gas is odourless, colourless and tasteless.
A chemical containing sulphur is added to it during the refining process for safety reasons.
Shell E&P Ireland, which began refining and pumping gas from the Corrib field at the end of 2015 said it is the first time the issue has occurred at its Bellanaboy operation.
The company said a "small quantity" of the gas was in the system.
It said the advice it had was that the odourless gas would not have been supplied further south or east than Galway.
It is understood an issue with gas going out of the refinery was initially discovered by a worker at about 3am on Thursday morning.
It is thought it had been ongoing for about 12 hours.
The odourless gas being pumped back to Bellanaboy is expected to take a total of three days to clear as it is returned at a low pressure.
A spokesman Shell E&P Ireland said: "Work is ongoing to remove the un-odourised gas at the Bellanaboy Bridge Gas Terminal in a safe and controlled manner, via the on-site flare.
"All operations at the Bellanaboy Bridge Gas Terminal are operating safely."
The odourless supply was spotted early on Thursday and flaring, which involves the burning off of natural gas at the Bellanaboy refinery and can be seen up to 20 miles away, was ordered.
It is understood people who live locally were notified by text message of the flaring.
The burn off could last for another two days.
The Bellanaboy terminal had been shut down for a number of days in the week before the technical issue with the odour additive occurred.
Shell said production was down to allow for routine maintenance at the refinery.
Gas Networks Ireland said it is working with priority customers such as hospitals to keep supplies on.
"We are working with the Corrib operator to resolve this issue and remove the un-odourised gas from the network in a safe and controlled fashion," the agency said.
"Our best estimate is that this may take between 48 and 72 hours."
Inspectors from the Environmental Protection Agency (EPA) are on site at the refinery while the flaring takes place.
The agency warned of increased noise levels and visual impact from the terminal.
Gas Networks Ireland has said that he hopes to have gas supply restored after some customers in the West were told to turn off their supply.
Engineers have been out all night after a batch of odourless gas entered the network at the Corrib terminal in Mayo yesterday – making leaks harder to detect.
Safety manager Eoin Wilson said they are trying to fix the problem.
“Over the next couple of days we will be working to get customers back on gas as soon as it’s safely possible,” he said.
“The decision that we’ve taken wasn’t taken lightly. Obviously it’s going to cause some inconvenience and disruption to customers. We’re asking customers to bear with us.
“Safety is our top priority. We will be working with extra resources in the area.”
Natural gas customers in the West are being told to turn off their supply amid safety fears.
The calls comes after odourless gas entered the network in the Mayo/Galway area - making it harder to detect a leak.
For safety reasons a smell is added to domestic natural gas - as the untreated supply is odourless.
The problem arose yesterday when the operator of the Corrib gas terminal in Mayo confirmed that a quantity of odourless gas had entered the network.
The problem affects customers in Galway City, Tuam, Headford, Ballinrobe, Claremorris, Castlebar, Westport, Crossmolina and Ballina.
Customers have been told to turn off their supply at their meter box until further notice.
Gas Networks Ireland says it is working with priority customers like hospitals to ensure they are not affected.
However, last night the company said it would take between 48 and 72 hours to resolve the issue.