Tw, first thing is the cure date on the rubber. figure if you're really good to the mask and you store it in ideal conditions you can get 15 years from new out of it.
Second is I personally wouldn't buy anything that doesn't fit Nato filters except for a U.S. M17 which is the full hood one you see Army troops wearing. Positive side is that it covers your whole head, so stuff will stay off your skin. Downside is you gotta take the mask off to change filters. Designed by a freakin' committee of rocket scientists no doubt.
You need to inspect the entire mask for any nicks or tears in the rubber, make sure all the flapper valves are intact, kinda sucks to be breathing in the out door. MCU-2Ps (Like Carbon is wearing) have gone through a number of exhaust flapper valves. seems with the early ones you could get excited and suck the valve up into the exhaust port. The newer ones are black and are backed by a little screen that keeps the valve from deforming and being sucked in.
Another fun MCU stunt. They come with a polycarb faceshield that goes overtop of the soft lens of the mask. It is secured by a rubber strap at the bottom and two molded hooks at the top. Problem is the hooks sometimes have sharp corners and flashing that would wear through the mask at right about where your eyebrows are. The fix for that is to sand the corners down, unless the mask is already holed. If so, toss it.
Then you need new filters. I think the Navy keeps them for 5 years, but it's sealed in a airtight can, it's probably good for decades. (If we admitted that, the contractor would soon be out of a job, planned obsolescense, your tax dollars at work)
Get the mask, make sure a filter threads one, all the straps are in good shape. Put it on and see if it is your size. 70% of the male world can get by with a MSA medium. Tighten the straps up, block off the filter, and breathe in. If the mask doesn't suck to your face, it doesn't fit. Listen for any air leaking, find the hole if you hear it. With positive pressure(Covering exhaust valve ) The mask should hold pretty good. It will eventually vent, usually around the temples. Tighten the straps there and see if it helps. So basically, unless it were new I would not buy it sight unseen. The Israeli masks are probably ok for riot agents, dunno about real stuff.
All this is pretty useless if you have to take your mask off. Get a canteen or better yet a Camelbak with a gas mask adapter. Keep it full.
For the rest of your body a chemical suit would be ideal, but I'm thinking that Tyvek painters coveralls under rubberized raingear would be just the field expedient ticket. Rubber boots, rubber gloves, tape all openings up with duct tape(Finally a use for it!) Another thought is one of the hunters scent-lock suits under it. They use activated charcoal, as do the chem suits. Then once you are out of the area you just burn everything that cannot be easily decontaminated (your car). Anything you really like should be sealed in a big tupperware container which is easily cleaned.
For once you are out of the area, it's time to take a bath. I would personally most likely scrub down with half bleach half water. Then rinse! Bleach is great stuff, fixes most chem agents, kills bio bugs, the cleaning in itself would get any alpha or beta radiological particles off of you. Powdered bleach is great to keep on hand. Burn the clothes, walk around naked until someone feels sorry for you and gives you new ones. Better yet, have some in the tupperware.
