Industrial abseiling contractors have grave fears they have spread white asbestos through Christchurch Hospital.
The contractors were repairing the hospital's roof and says the company, Goleman, knew about the asbestos 10 days before the workers were told.
A sample of the roof tested by Chemsafety on 2 April confirmed the presence of white asbestos. But work continued on site until employees reiterated their concerns to the project manager, Fletcher, about 10 days later.
Abseiler Liam Milner says Goleman handled the problem very badly.
"Extremely poorly - they got very defensive, didn't want to take any responsibility or own up to any mistakes being made. And then just basically harassed us and tried to make it go away and keep it under covers."
The site was shut down by Fletcher on 10 April. Goleman would not comment on what measures it took over the asbestos.
Canterbury DHB chief executive David Meates said on Monday he is certain that staff and patients have not been exposed to the health hazard.
"We are absolutely confident that there has been no risk of exposure. There are some access areas that the contractors have been going out and those are the only likely areas there could have been any possible traces."
But another contractor, Neil Silcock, said workers were given swipe cards allowing them wide access to the hospital.
He said he worked on the site for about two weeks and during that time was in frequent contact with staff and patients.
Mr Silcock said he is concerned that he has unknowingly spread contaminated dust via his clothes and equipment through the hospital.