After Earthquakes or other scenarios where a large numbers of structures burned out or collapsed, numerous people sufferd from chronic respiratory diseases caused by toxic dust.
Wouldnt it be just a bit daft to survive a catastrophe just to succumb to "smokers lungs"?
A FFP 3 mask protects your respiratory system from harmful particles to airborne diseases more effective then a "surgeons mask".
A cheap, effective way to protect your health when nobody else will.
Besided that the last "flu pandemic" was a bit of a joke: A mask gives you a lot of protection in this regards, but also bear in mind that :
-virus can enter your body via your eyes and nose......so washing your hands before rubbing your eyes or picking your nose is advisable