About 40 students and staff members were exposed to a small amount of mercury at Hazel Park Middle School Academy in St. Paul on Wednesday afternoon when a small thermometer broke in a classroom.

The school was not evacuated, although students and staff members were moved from the room and the school's air handling equipment was turned off. Principal Coleman McDonough told parents in a letter sent home with students that experts with the state Department of Health, poison control experts and the Minnesota Pollution Control Agency say the level of potential exposure was not high enough to cause health concerns.

Dr. Rita Messing of the Minnesota Department of Health said, "We think it has a small potential to be a health concern, given that it was such a short exposure. Where it becomes a bigger concern is when there are repeated exposures."

However, school officials encouraged parents and students to contact their family physician if they had concerns or the school's nurse could recommend a clinic.

Why the students were using a thermometer containing mercury was unclear.

"We expect that our school uses mercury-free thermometers, and we are investigating how this thermometer came to be used in the class," McDonough wrote.

JAMES WALSH