The royal commission into the Rudd government’s home insulation scheme continues, and comments of some authorities have shown just how rushed the plan was.

Dr Troy Delbridge, a science and engineering expert, has been giving evidence from his time as a technical advisor for the program.

Dr Delbridge has described the shoddy planning for the scheme, which was aimed at reducing power bills through cheap insulation.

The program was rushed, under pressure and forged ahead intending to pass the buck on safety issues, he said.

Delbridge told the hearing that when he inquired about the detailed costings for the scheme, others said they had been “drawn up on the back of a napkin by a senior Labor Party politician and the head of the bulk insulation industry association”.

“It was one of the prime minister's inner circle, whether it was himself, I'm not sure,” he said, when asked about the Labor figure.

The Commonwealth’s home insulation program (HIP) saw the deaths of four young workers and hundreds of house fires before it was halted in 2010.

Dr Delbridge told commissioners that the architects of the HIP knew of the significant risks in introducing the scheme so quickly, but says they intended to push the blame over to the installers if anything happened.

He says he was fired for raising his concerns.

“I was a squeaky wheel,” Dr Delbridge told the commission.

He says a senior Environment Department official told him safety was not a priority.

“Mr [William] Kimber was prepared to accept that there could be injuries, serious injuries,” Dr Delbridge said.

“The program policy was that was acceptable.”

“And that's what I had concerns with - for the HIP program not to be regulating, not to get involved in the safety aspect,” he said.

Delbridge said he was threatened by Kimber, the senior bureaucrat, and told: “Shut up or you are no longer on the program”.

He says he was sacked within an hour of voicing his concerns to the department director.

But Mr Kimber has blamed higher-ups too.

He told the commission hearing that he implored his superiors, including Environment Department assistant secretary Kevin Keeffe, to look at the safety issues soon after he started working on it.

“I made representations that … the business model selected and the speed of implementation meant that the risks could not be controlled and that we should have a review, or at least a time-out,” he said.

After the first of four deaths, Mr Kimber says he tried to push for a suspension of the use of foil layers, which were responsible for the electrocutions.

“I made representations to that effect, including before the death happened, and the practice continued,” he said.

“The risks that we had been concerned about had come to fruition,” he said of the department’s response.

“The risk in the program was at such a level that it was likely there were going to be further occurrences.”

Mr Kimber could not provide details of emails he claims to have sent during the time, and was reminded of his duty to provide accurate and reliable evidence.

Dr Delbridge will continue his evidence this week, while former prime minister Kevin Rudd and his environment minister Peter Garrett will appear before the commission later this month.