Allan Whitley of the Corrections Association (Canz), the union representing prison workers, told Hawke’s Bay Today staff were “fairly certain that they saw the prisoner putting sugar in the hot water”.
Corrections said it had not yet confirmed that detail, and it would form part of the investigation.
A second, unrelated incident happened in another part of the prison the same day.
A prisoner punched a staff member, who was also assessed off-site and did not suffer serious injuries.
Police had been notified of both incidents, and internal misconduct charges were under way.
Beales said there were some unplanned staff absences on Sunday, but the prison still had the right number of staff in both its units to go about its daily routines, including the unlocking of prisoners.
Whitley claimed while one of the units involved had adequate staffing, the other did not.
He said the prison was seven staff short overall on the day, and although the volatile nature of the prison environment means some incidents may not be preventable, Corrections should take “every reasonable step to try to prevent it”.
Whitley said he had contacted the prison director requesting a review of unsecured cooking equipment in high-security areas, including sandwich presses.
“If we don’t get a response, we will be doing a provisional improvement for notice to have it removed,” he said.
A Corrections spokesperson told Hawke’s Bay Today a health and safety review of unsecured kitchen appliances would be carried out by the health and safety advisor and the high security manager.
“The general manager of the prison will then make decisions on any next steps, including if any items should be removed.”
Beales said violence in prison was not tolerated, and anyone displaying such behaviour would be held to account, including “potentially facing criminal charges”.
He said prisons could be volatile environments, with the vast majority of prisoners having violent criminal histories or mental health and substance abuse issues.
“The reality is the threat of violence is something we cannot eliminate entirely, but we do everything possible to minimise this risk.
“We have invested significantly in training and tools to keep our staff safe. This includes tactical skills, such as de-escalation, through to the provision of stab-resistant body armour, on-body cameras and the expanded deployment of pepper spray.”