sidejob this is just my opinion but I came to the conclusion that these mask although they do work pretty well only prolong the inevitable. You have to come out of it sometime to attend to nature's calls. These masks especially with the hood will cause the wearer to sweat unbelievable profuse. The loss of the body's water at such a rate will soon result in severe dehydration, not to mention heat protestration in warm climates.
During my time in the first Gulf War MANY of us found that we were more fixed on getting out of buildings of bunkers during a Scud mission attack.
These mask again in my opinion are quit suitable for short term (read a few hours in warm climate to perhaps a day in cold climate) use against tear gas or other non-persistent chemical attacks .
If the terms of life were to be forced to live inside of an M-17 and a MOPP suit...........I am not sure I would want to live in those conditions. I point you to Revelations......where is points out those who pass on first will be the fortunate ones.
Not trying to be a gloom and doomer.... these chemical suits and mask are NOT fun to wear and are VERY taxing on the body over time. To be effective, the masks must be worn with the entire MOPP suit. The activate charcoal liner imprenated into the MOPP suit eventually reaches its max. ability to absorb chemicals and or become saturated with sweat and body excrements and MUST be changed out every few days or more frequently depending upon condition.
Been there......done that......got the T-shirt, sweat pants, sneakers, and baseball cap.

Not saying it is impossible to do but just not worth it in my opinion.