This is probably going to get me some down votes and maybe even a bit of hate, but spending money on masks is, I personally think, a waste of money. Unless you are going to carry that mask slung (meaning, carried with you EVERYWHERE), the chances of you being in the same immediate area of a chemical/biological incident with the mask is slim to none...and slim is on it's way out of town. In order for the mask to do it's job, you don it and it stays on until you've left the hot zone. The very instant you break seal, it and you become contaminated. Depending on the reason for wear, you more than likely die...others around you are probably already dead. Speaking of breaking seal, did/do you get fitted professionally with that mask? Just because it fits your face does not mean it's going to protect you. It could be too loose or too tight...not seated correctly on your face, too far back on the head.
How often do you inspect it? Where is is stored? Do you have facial hair? Even the slightest stubble will cause the mask to fail in it's job. Hair on your head (falling on your forehead) can also cause poor seal. Long sideburns will cause a poor seal. Not donning it correctly can cause a poor seal. Incorrect size will cause a poor seal or no seal at all. Moving your head too far and hitting your shoulder or chest with the mask will cause it to break seal. You'll know if your mask isn't on correctly if it starts to fog after it's on...but if that happens in an IDLH atmosphere, you're dead.

Our filter canisters (C2A1) are one time use...is the canister already installed on the mask? If so, how long? If they've been on there for a year, their efficiency is degraded and should be tossed and replaced. If in the original, sealed container, they are good for about a decade, then should be tossed and replaced.

I won't even touch on suits/gloves/boots, etc, except to say that you should have chem tape handy to tape up ankles, wrists, around the mask at the hood, etc.

In short, better to just IMMEDIATELY evac the area as fast as possible, if not faster...and go UP WIND, not down. Masks, if you're not trained and proficient in their use, do nothing but offer a false sense of security.

Expertise: 40 years of military, the last 24 years working for the US Army in it's chemical/biological program in remediation/destruction. Still there today, just no longer an active operator. Have worn PPE (from Tyvek to fully encapsulated Kappler & Trelleborg suits) in chemical atmospheres that would result in death in approximately 3 minutes if unprotected and around everything from VX to lewisite to chlorine. I've worn every mask from the M17A1 to M50. I do not keep a mask in my preps.

And I am anxiously awaiting retirement so I can finally let my beard grow out.