The gas mask is a device to aid and protect the user from inhaling the gas, smoke, or other poisonous fumes, have been used for years by different people and for different reasons. The gas mask has a cover for just the nose and mouth area. You can buy quality gas masks on https://www.gasmaskpro.com/
It allows the wearer to breathe easily through the filtration system without the inhaled air being contaminated by smoke, chemical, or any kind of biological agent. These impurities are filtered out at the mouth or nose vent but they can still sting your eyes.
Gas masks cover the entire ace area. They often come with a clear face-mask or an additional eyepiece to protect the eye while protecting the nose and mouth as well. However, there might arise some issues if there is a poor fit to the mask or there is a crack within the mask, which allows in the impurity other than the filtration system.
In some gas masks, the air tank is filled with high-pressure purified air. This provides consistent positive pressure on the mask. This allows for a tighter fit on the face. The pressure system is equipped to carry only 60 minutes of purified air before it runs out. They are most generally used for firefighting, rescue operations military, and diving use.