The Health Department is retesting radiation levels at a school on Hobart's eastern shore.
The testing is being done as part of an investigation into a possible cancer cluster among staff at the Hazelwood school for children with special needs.
Staff have been told that despite two previous tests showing normal electromagnetic fields at the school, further tests are being carried out using improved technology.
It is believed levels at other public schools are also being measured.
At the Hazelwood school, 17 teachers and support staff have contracted cancer and related illness and there is concern the cases could be linked to the school's electricity substation or a nearby transmission tower.
The Director of Public Health, Roscoe Taylor, says he has compiled a list of 300 people who have worked at the school since 1984.
He says the next step is finding out how many of them have contracted cancer and whether the rate is higher than would normally be expected.