Too much humidity building up in an air handling unit triggered a fire alarm at Charlottetown's Queen Elizabeth Hospital Tuesday morning.

The incident occurred in what is known as the penthouse, an area on the hospital's roof that houses various mechanical services. There were no injuries. The space is unoccupied by staff, but maintenance personnel occasionally work in the area.

An investigation revealed a malfunctioning valve probably caused the problem.

Terry Campbell, director of support services at the QEH, said people were prevented from entering the hospital for 30 to 40 minutes shortly after 7 a.m. while emergency personnel worked out what had set off the alarm and the extent of the problem.

Staff were also warned the building might have to be evacuated.

There was, however, no effect on other parts of the hospital, including the emergency department or surgeries.

"The biggest impact was somewhat of a delay in the clinics," said Campbell.

"Certainly staff were working to maintain and get caught up and hopefully clear everything up there. But nothing was cancelled in terms of services. Everyone responded appropriately and we certainly apologize to our patients and visitors for any kind of delays."

Campbell said an investigation of the air handling unit is underway and any repairs will be made.