Whenever you use a gas mask, you will probably need several filters to change after every use. Not only do filters have a shelf life, but they also don’t last as long while in use as you might imagine. Most need to be replaced after just several hours of use depending on the environment and gas concentrations. Even if breathing in “uninfected air,” they last less than 24 hours. What does this mean?
First, it’s not hard to imagine the need for several filters per person depending on exposure times. Second, it’s important to keep track of the expiration date for any filters on hand. At $40-$50 a pop, the cost of replacement filters can add up quickly. I would suggest purchasing a mask that accepts 40mm NATO threaded filter canisters. These tend to be the most readily available and popular. You can buy a nato gas mask on https://www.gasmaskpro.com/gas-masks/small-israeli-gas-mask
This filter canister was developed for the Israel Defense Force (IDF) to provide protection against all known NBC agents in the form of vapors and aerosols. It is designed for military and civil defense use. It is specially designed for comfort and extended use at a minimal physiological load, having low breathing resistance and low weight.
Its design assures optimal performance complying with all IDF specifications as well as the performance requirements of the American Army C2 filter canister. The filter is supplied with a standard Nato thread 40MM and is thus compatible with almost all military and industrial respirators. These filters are supplied sealed with leak-proof plastic caps, assuring a shelf life of 25 years.