Asbestos found at Bronglais Hospital in Aberystwyth
Up to 30 maintenance staff could have been exposed to asbestos at Bronglais Hospital in Aberystwyth, say health officials.
Hywel Dda Health Board said it was trying to trace former workers and was offering screening tests.
The board said asbestos had not entered public areas and patients and visitors were safe.
The Health and Safety Executive (HSE) is conducting an inquiry into the "management of asbestos".
Asbestos is a problem when fibres become airborne and are inhaled, and can lead to life-threatening illness.
The problem at Bronglais Hospital occurred between 2004 and 2009, before the health board's formation.
A health board spokesperson said: "I can give an assurance that systems and processes have been put in place across the health board to prevent this happening again.
"We would like to offer assurance that the asbestos was not in areas accessible to patients or the public.
"We are ensuring that all maintenance staff are involved in the HSE investigation and we continue to offer support and advice to those who have concerns."
The spokesperson added that measures were now in place to ensure asbestos was properly managed, and it regretted that any of our staff could have been exposed to it.