The pornography, which included images of sex on a train, was accessed at 7.45am on Friday, May 1.

Disability, Child, Youth and Family Services chief executive Mark Byrne said the dismissal sent a clear message to staff.

"Pornography access during work hours is not acceptable and should not be happening in the workplace," Mr Byrne said.

While there was no suggestion that any crime had been committed, downloading of images of this kind was clearly inappropriate for staff in a youth detention facility, he said.

An investigation was launched in May to determine who had access to the computer and identify the staff member responsible.

The staff member, whose identity has not been released, has 21 days from September 28 to appeal against the dismissal ruling.

The person was sacked under the provisions of the State Services Act.

Since May, internet filters have been installed on the centre's computers.

Mr Byrne acknowledged that filters can be breached, but said spot audits and filter alerts were being used to detect inappropriate internet access.

The chairman of a 2007 Upper House select committee inquiry into Ashley and Youth Detention, Rowallan MLC Greg Hall, said there were ongoing concerns about internet and computer security at the centre.

"It was woefully inadequate - regarding internet connections and porn," he said.

The committee recommended tighter screening, recruitment and induction of staff members for the centre.

"We wanted to see appropriate induction to make sure the wrong sort of people are not working at the centre," he said.

He was worried that staff screening and internet security were still a concern.