Respirators are intended to be reused. Manufacturers usually provide guidelines for the appropriate procedure to sterilise masks, such as these from 3M. However...
It's been found that manufacturer's instructions are often not clear enough, and are error-prone.
We found a thorough and peer-reviewed procedure for sterilisation from Bessesen et al 2015, which minimises risk of errors in disinfecting masks.
Your Public Health Authority may also supply such a procedure, in which case please use that in preference to our links above.