Heat sterilisation dramatically reduces filter efficiency of the majority of FFP2 and KN-95 respirators

Because of the enormous demand for personal protective equipment and especially respiratory protective devices (respirators) during the initial phase of the corona pandemic shortages arose. Sterilisation of used respirators can reduce these shortages. In our study, respirator testing was carried out after only one sterilisation cycle. To determine if steam sterilisation and reuse could be safely applied for used respirators. In a cabinet an aqueous solution of NaCl (0.02% w/v) was nebulized and passed through a sample of the material of a respirator. Passing particle concentrations were measured directly from the cabinet and via the filter material of the respirator for particles ≥ 0.3 μm, ≥ 0.5 μm and ≥ 1.0 μm. only three out of ten steam sterilised respirators met the requirements of 94% filtration efficiency. The results prove that heat sterilisation cannot be generically applied for reuse of respirators safely.