How often should canisters for the M40 Gas Mask be changed if exposed to chemical agents?

The correct choice indicates that canisters for the M40 Gas Mask should be changed after 30 days if they have been exposed to chemical agents. This timeframe is critical because chemical agents can degrade the filtration capabilities of the canister, leading to insufficient protection for the wearer. The 30-day guideline is set to ensure the effectiveness of the mask in environments where chemical exposure is a concern, thus maintaining the safety and operational readiness of personnel.

Regular changes of the canisters, as specified, minimize the risk of failure during critical situations. It's essential to adhere to these timelines, regardless of visible signs of degradation, because harmful gases or agents can compromise the filter's integrity without observable damage. By following this prescribed schedule, operators can avoid relying on canisters that may no longer provide the necessary protection, ensuring safety in potentially hazardous conditions.