ABC of Safety in the Biological Sciences
Cryostats are refrigerated chambers, kept at sub-zero temperatures which contain a microtome. They are used for cutting thin sections (5-10 microns in thickness) of fresh, frozen material. This material, under normal conditions, has not been subject to fixation so must be considered a potential hazard.
Before cutting a frozen section, from any fresh tissue, it is essential to obtain as much information as possible about the source of the material. Otherwise the specimen should be treated with all the caution afforded the most infective material.
There is also significant risk when the cryostat is cleaned. Whilst the tissue fragments remain at sub-zero temperatures within the cryostat chamber, there is little danger of infection. Once the tissue fragments reach room temperature however, organisms become viable. Consequently loose tissue fragments should be collected and placed into fixative or disinfecting agent before defrosting commences. After defrosting all tissue contaminated surfaces need to be disinfected with 70% ethanol and cleaned thoroughly before the unit is used again.