When evaluating chemical gas masks, the most critical factor is the filter type and protection class. You must ensure the mask supports multi-gas cartridges (e.g., ABEK levels) that protect against organic vapors, inorganic gases, acid gases, and ammonia. The facepiece material should be made of medical-grade silicone or high-quality EPDM to ensure skin compatibility and a superior hermetic seal. Additionally, look for wide-angle polycarbonate lenses that are anti-fog and scratch-resistant to maintain clear visibility in hazardous environments.