I purchased several of those mask from Centerfiresystems.com that have the side mounted filter. These are a bit better than some of the others they sell which obviously would not work at all.
The ones I got fit tightly about the face and most likely could offer some protection from maybe tear gas or a lot of smoke? They would offer eye protection so at least one might be able to see to load and fire weapons in defense.
These are the Finnish masks Centerfire sells. They would offer protection to ones face against fire and smoke. And, guard the eyes from flying glass and bullet spatter.
Something is at least better than nothing.