Isobel Miller, governor of Hydebank, Belfast, said it was impossible to safeguard the lives of vulnerable prisoners completely, despite a spate of suicides.

She was speaking at the Belfast inquest of Roseanne Irvine (34), found hanged by her pyjama cord in her Maghaberry cell in March 2004.

"If you take every precaution, they go under the blankets, females can secrete cord, they can take somebody else's shoe lace. They still can have a method of hanging themselves, they can strangle themselves," she said.

She said the only option was to put at-risk prisoners in a special cell with no ligature points and hard-to-rip materials, but said even 24-hour camera surveillance had failed in the past.

Irvine was awaiting trial accused of burning down her homeless hostel, the culmination of a decade-long battle with personality disorder, depression, alcoholism and self-harm.

She was moved to a safe cell two days before her death after threatening to hang herself - but was returned to the landing the following day. Irvine was seen pulling tufts out of her hair and told staff she had taken an overdose hours before her death.

"We have to look after their dignity - 99.9% of the time they will be fine but there is a time when we have to make a decision to move them and you feel they are getting better," she said.

"They give the appearance of being much better because they have made up their mind that they are going to commit suicide and unfortunately nobody can legislate for that."

The coroner's court also heard that changes have been made at the prison following the death. Health provision in prisons is to become the responsibility of the Department of Health.

The hearing continues.