[Edit: note that this process probably won't work for most N95 masks, as the heat will likely warp the material too much. However, it should work for cotton masks.]
If you have a pressure canner/cooker, you can sterilize used masks by steaming them at 250 F /121 C for 30 minutes.
"This article sets forth instructions for using a domestic pressure cooker for sterilization of objects such as needles, syringes, and nursing bottles in cases where an autoclave is not available. Experiments carried out at Sao Paulo University indicated that a pressure cooker is comparable in efficiency to an autoclave and can reach temperatures required to destroy bacilli. The efficiency of deep sterilization was tested by using a piece of gauze contaminated with bacillus subtilis spores. No bacillis growth occurred in items that had been sterilized for 20-30 minutes. A similar test for surface sterilization indicated that 13 minutes is sufficient for sterilizing objects such as bottles and needles. A 3-day training course covering sterilization principles was conducted for 5 community health workers. This experience suggested that pressure cooker sterilization can be easily carried out at rural health facilities or even in homes. This method is superior to boiling water because steam under pressure reaches a higher temperature. The possibility of contamination cotton-wrapped materials by handling after sterilization is also reduced."
https://www.ncbi.nlm.nih.gov/pubmed/12267939
If you have a pressure canner/cooker, you can sterilize used masks by steaming them at 250 F /121 C for 30 minutes.
"This article sets forth instructions for using a domestic pressure cooker for sterilization of objects such as needles, syringes, and nursing bottles in cases where an autoclave is not available. Experiments carried out at Sao Paulo University indicated that a pressure cooker is comparable in efficiency to an autoclave and can reach temperatures required to destroy bacilli. The efficiency of deep sterilization was tested by using a piece of gauze contaminated with bacillus subtilis spores. No bacillis growth occurred in items that had been sterilized for 20-30 minutes. A similar test for surface sterilization indicated that 13 minutes is sufficient for sterilizing objects such as bottles and needles. A 3-day training course covering sterilization principles was conducted for 5 community health workers. This experience suggested that pressure cooker sterilization can be easily carried out at rural health facilities or even in homes. This method is superior to boiling water because steam under pressure reaches a higher temperature. The possibility of contamination cotton-wrapped materials by handling after sterilization is also reduced."
https://www.ncbi.nlm.nih.gov/pubmed/12267939