Fairfax Media can reveal a nurse was allegedly assaulted by a man under police guard in a separate incident only days earlier.

There have been calls for police to leave their guns in locked safes before entering the hospital, a policy unions said existed up until a few years ago.

James William Shearer, 26, was in police custody in the hospital's emergency department last week when he allegedly wrestled a gun off a police officer and shot it a number of times.

He has since been charged with attempted murder, charges his lawyer suggested were an "overreaction to circumstances".

According to witness reports, the shots narrowly missed two staff and the accused was Tasered a number of times before dropping the gun to the ground.

An officer yelled at a wardsman responding to the code black to get "me my f---ing gun", before the accused was restrained by a number of people, according to witness statements collected by the Health Services Union.

ACT Policing did not answer a series of questions relating to carrying guns in the hospital and proper protocol.

Health Services Union secretary Gerard Hayes has written to hospital chief Chris Bone urging an urgent review of ED-specific workplace health and safety policies.

He also asked for a roundtable discussion about issues including firearm protocols within the hospital.

Nursing and Midwifery Union ACT secretary Matthew Daniel said he had been trying to clarify what the policy and practice was around guns in the hospital, but had not received a clear answer.

He said members who had worked at the hospital for more than two years recalled it was previously common for police to leave their guns in a lock box provided.

"Here and in NSW in some mental health facilities guns aren't taken in, so what's the difference between an ED and mental health facility?" Mr Daniel said.

In a separate incident, only days earlier, a man in police custody is alleged to have assaulted a nurse.

It is understood the prisoner had been under police guard, and secured to the bed using soft restraints, when he allegedly threw water at an officer and nurse.

The nurse was using a towel to clean up the water when the prisoner allegedly kicked him in the stomach.

The force of the alleged blow knocked the nurse backwards and into the computer stand, before he fell to the floor.

The prisoner had to be sedated after he continued to be aggressive and abusive towards hospital staff and police.

An emergency department worker, speaking on the condition of anonymity, said code blacks were an almost daily occurrence at the hospital, and wards-people, nurses and even cleaners were forced to step in to contain the situation.

He said the de-escalation rooms were a serious concern for many staff, especially since the renovations of the hospital.

Staff said the padded rooms and lack of windows were far from a calming environment and made patients more volatile and escalated situations.

Two to six police officers usually bring patients - often violent and volatile - into the room and then leave them with support staff to deal with.

The worker said little or no support had been offered by management to staff who witnessed the events or were concerned about their colleagues' safety.

The accused was believed to have become violent as his sedation wore off.

"There was a short de-briefing some staff got to which was an absolute joke," he said.

"We're not here to cop-bash, they have a hard job to do.

"But a lot of systems fell down to create the situation that could have ended in disaster."

Australian Federal Police Association president Angela Smith said police should be commended for their bravery and "swift and measured" actions, which meant no one had been seriously injured or killed at the hospital.

"[Last week's] incident, that could have easily resulted in someone being killed, regrettably is not an isolated one," she said.

"The lengths that some people will go to, to avoid arrest, is a real concern."

An ACT Health spokesman said secure storage for firearms was provided in some areas of the hospital but police were permitted to carry guns.

"Patient and staff safety at our hospitals is extremely important, and everyone has a right to feel safe within our hospital and health services," he said.

"ACT Health works closely with unions and other staff representatives to ensure staff are supported and that their work environment is safe. As part of this, the interim director-general of ACT Health is establishing a new joint consultative committee with unions where matters such as this are able to be discussed."