A classroom and science lab at Jarrell Intermediate School are off limits after elevated levels of mercury were detected following a leak, Jarrell ISD said in a letter home to parents Thursday.

The district said in the letter that they were notified Wednesday of a barometer that appeared to be leaking in the science lab at JIS. Maintenance personnel contacted the Williamson County Hazardous Materials Team after recognizing the barometer contained mercury. Mercury is a heavy metal that is liquid at room temperature and used in older barometers to measure atmospheric pressure.

The HazMat team removed the mercury and told the district the room needed to air out overnight, but Jarrell ISD said Thursday that “it was determined that there was more mercury than previously thought.” All but one classroom in the hallway with the lab checked out, with the one classroom had “slightly higher levels of mercury in the air,” the district said.

The letter stated the district would not use any of the rooms until the “All Clear” is given by the remediation firm brought in to clear out the affected rooms. The district also said the other rooms in the hallway are well under safety levels, according to the Williamson County Hazardous Materials Team.