Police are investigating a potential gas leak after a townhouse in the Sydney suburb of Whalan exploded on Saturday, injuring five and killing one.
Residents have since revealed they had been complaining about the smell of gas near the site in the days and weeks before the blast.
Detective Superintendent Darren Newman from Blacktown Police said officers will work with the gas supplier, maintenance teams and inspectors as part of their inquiries.
Belinda Jones is a forensic scientist and works as a fire investigator in Sydney.
She said just a small gas leak can cause a massive amount of destruction and be difficult to detect.
How much leaking gas would cause an explosion this big?
NSW Search and Rescue Commissioner Jeremy Fewtrell said the blast had caused "total destruction" to the townhouse.
One person died, five people were injured, four units in the complex collapsed and nearby properties were damaged in the explosion, which was heard kilometres away.
Windows in homes several streets away cracked, or blew in with the force of the explosion, and the scene was described as "confronting" for emergency service personnel.
Loading...
Ms Jones said a leak over just a few hours would be sufficient to cause that level of damage.
"The gas moves, and the gas is most flammable and explosive in its concentration mixture when it is mixed with air," she said.
"It is possible the damage seen in the Whalan explosion is likely a result of a dispersed gas throughout the structure which when ignited, caused a chain reaction in the gas which expanded rapidly.
"The resulting flame front propagates through the remaining vapour igniting it around the entire structure in milliseconds."
The source of the leak might be in a different room to the source of ignition.
"You could have a gas leak at your cooker, your oven, your heater, but the ignition source could be in another room," Ms Jones said.
"It could be under the house, totally distant. They're not together.
"The gas moves, and the gas is most flammable and explosive in its concentration mixture when it is mixed with air."
She said the level of devastation would make it difficult to isolate the point of origin of the explosion.
Would I smell gas if it was leaking in my home?
Housing Minister Rose Jackson visited the site on Monday and said she was shocked by the scale of the damage.
She said Homes NSW had received a couple of reports over the past year in relation to a gas meter at the front of the property, which were responded to on the same day.
But she said most of the damage appeared to be at the back of the home, and she was also not aware if the gas supplier had fielded other complaints.
Ms Jones said leaking gas smells like rotten eggs or sulphur.
She said it is possible that people might have a gas leak in their home without realising it.
"Because an ignition source can be remote from the site of a gas leak, the gas may be smelled where the concentration is higher," she said.
"But the explosion may occur in a different area, where the concentration of gas and air is less."
Natural gas, which is generally the type of gas provided to homes through gas pipes from the street, and usually has a smell.
But liquid petroleum gas (LPG), which is used in gas bottles, does not have much of a smell, making it harder to detect.
Ms Jones said there are other signs people can watch for, including a hissing sound around appliances and dizziness or nausea.
Dead patches of lawn around known gas lines can also indicate there is a leak.
What are the possible ignition sources?
Ms Jones said there can be various ignition sources.
"For LPG, the ignition source would be close to the ground," she said, and include hot water heaters and refrigerator switches.
"If the gas was natural gas, it could be ignited by any spark, switch or open flame in the room where the gas has accumulated."
What should I do if I smell gas?
People who suspect there is a gas leak in or near their home should notify their gas distributor.
Energy provider AGL recommends people try to identify the source of the leak through smell by investigating appliances like gas stove, or the piping near their gas meter.
If the source cannot be identified, the natural gas handle on the gas meter should be turned off.
AGL recommends power to the home to be turned off at the fuse box.
Windows should then be opened for better ventilation and a plumber or gas fitter can be called once you are safely outside the house.
Ms Jones also encouraged people to talk to their neighbours to see if they have smelled gas as well, and encourage them to notify the distributor.
"People should be concerned and try to identify the leak, and shut down the power and all the potential ignition sources," she said.
"If they smell gas in their street, talk to your neighbours.
"Get everyone you know who goes past smelling it to call it in – then you are more likely to get action from the provider."
Posted, updated
