The gas masks kit falls into three main categories. They are used by people who work in dangerous environments where harmful gasses are present, those for medical use, and those used in hazardous environments or where there is limited oxygen such as fires or industrial chemical plants.
The main differences between the masks are largely based on the hermetic sealing of the mask to the face, the method of oxygen delivery, and the durability of the materials and design. Gas mask kit are designed to supply increased oxygen to the mouth and nose. The mask area around the face is normally light and weightless, primarily for comfort.
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There is often a secondary regulator in the mask, to ensure a safe and appropriate amount of oxygen reaches the user. Gas masks are usually extremely lightweight, small, and usually disposable. They are generally little more than shaped cones that are held in place by a piece of elastic cord.
Hazardous environment masks are sealed as completely as possible to the face much like a gas mask. Construction is typically robust and heavy. Some will incorporate a hood to help achieve a good seal. One of the most common uses for these masks is in areas that use halon fire extinguishers, where a fire can trigger an automatic gas release, excluding the oxygen from the fire.