A report issued by a British health agency says that hundreds of teachers in the U.K. have died from asbestos-related diseases and that thousands more may be at risk because of the widespread use of asbestos in British schools. The report by the Government’s Health and Safety Executive says that 272 teachers died from asbestos cancers such as mesothelioma between 1980 and 2005.

According to the report, about 90% of the 25,000 schools in Great Britain contain asbestos. Teachers who work in these schools are at risk of asbestos exposure because pinning notices to ceilings or banging doors shut can cause fibers to be sprinkled into the air. Researchers say that each pin placed into school ceilings causes 6,000 asbestos fibers to be released into the air.

“A lot of people have been exposed without knowing it,” said Mary Bousted, General Secretary for the Association of Teachers and Lecturers. “I have been merrily putting pins into asbestos boards for years. If the doors bang or ceiling tiles become dislodged, as they do in many of our older schools, the danger level becomes critical.”

Exposure to asbestos can lead to mesothelioma, a deadly form of cancer that can attack the lining of the heart, lungs or abdomen. In addition to teachers, workers involved in manufacturing, construction, shipyards and other industries may also be at risk of receiving a mesothelioma diagnosis from coming into contact with asbestos-containing products in the workplace.