Sydney murders led to change in gas sales

The companies that sold and delivered carbon monoxide to a Sydney father who used the gas to kill his family made changes following the tragedy but also concede more can be done.

Fernando Manrique, 44 and his wife Maria Lutz, 43, were about to divorce when they were found dead along with their children Elisa, 11, and Martin, 10, and the family dog Tequila, in their northern Sydney home in October 2016.

They all died from carbon monoxide poisoning.

At the opening of an inquest into their deaths at Lidcombe Coroners Court, counsel assisting Adam Casselden said there was "little cause for doubt" that Mr Manrique was responsible.

He paid a friend $400 to receive a delivery of the deadly gas which, the inquest heard on Tuesday, has only a few specific industrial uses.

The gas was sourced from industrial supplier BOC.

Following the 2016 deaths the company removed carbon monoxide from its public website so only approved customers could order it, production manager Robert Brittliff told the inquest on Tuesday.

An "end-user declaration" form also became mandatory for people wishing to purchase the gas from BOC.

But once a customer follows that process the only additional check likely to stop them receiving the gas is if the delivery driver becomes suspicious it wasn't going to be used properly.

Delivery to a house may be a red flag, the inquest heard on Tuesday.

However, a customer determined to "bluff" their way through the initial declaration form would likely be able to get their hands on the gas even if they faced further questions, Mr Brittliff said.

"I'm concerned if they've already bluffed through that process once, there's not much to stop them bluffing through it again."

Trucking company Linfox says drivers are "empowered" to make decisions when they deliver products to customers.

"Linfox empower drivers to ask questions if they think something does not feel right," executive Simon Livingstone told the inquest.

"To my knowledge, drivers did ask questions in relation to this delivery, which I think is a credit to that process."

Mr Livingstone agreed it would be "helpful" for drivers to carry copies of the BOC document to query the customer about their intended use for carbon monoxide.

But he admitted highly technical scientific uses could be confusing or challenging.

Mr Brittliff said delivery drivers' judgement was an important "line of defence" and making customers' licence and declaration form available to them could be helpful.

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