I agree with this point and have always assumed the material to be
"potentially a biohazard" and treated as such. As to cleaning out a
cryostat: I have always fumigated the cryostat with formaldehyde vapour
overnight before anyone touches anything inside the cryostat. After the
formaldehyde fumigation, we neutralise the area with ammonia fumes.  Then
the microtome is striped down and cleaned, along with the inside of the
cryostat.

Evelyn Kaplan
Sultan Qaboos University
Oman