Work rooms where the spatial and instrumental equipment enables safe handling of open radioactive substances. Pursuant to IAEO recommendations, isotope laboratories are classified in three types according to the activity which they are allowed to handle: A, B and C. In this context, measurement of activity is a multiple of the free limit in accordance with the Radiological Protection Ordinance. Laboratory type C thus corresponds to a handling quantity of up to 102 times, laboratory type B up to 105 times and laboratory type A beyond 105 times the free limit. In type C laboratories, fume cupboards are to be installed when there is a risk of impermissible ambient air contamination. In general, exhaust air filtering is not required. In type B and A laboratories, provision is to be made for glove boxes or other working cells, in addition to fume cupboards, for the handling of open radioactive substances. Exhaust air filtering is required. Details are contained in DIN 25 425.