Also known as: ガスマスク, 防毒面具
A full-face Mask that protects the wearer from toxic gases and airborne pollutants by covering their nose, mouth, and eyes.
They protect the wearer by forming a sealed cover over the nose and mouth and filters the air that they breath in to prevent inhaling toxic gases or pollutants. The mask also protects the eyes from exposure to toxic gases or pollutants that may cause irritation, temporary blindness, or even permanent eye damage.
If the mask doesn't cover the eyes, then it's a Respirator, not a Gas Mask.