What is a design feature of a demand system oxygen mask?

A demand system oxygen mask is specifically designed to deliver supplemental oxygen to the wearer when it is needed—inhaling triggers the flow of oxygen. One of the essential features of this type of mask is that it must form an airtight seal around the user's face. This seal is critical because it ensures that the oxygen can effectively bypass ambient air, providing the necessary oxygen concentration needed in low-pressure situations, such as high altitudes.

If the mask does not achieve an airtight seal, the oxygen could mix with outside air, diminishing its efficacy and potentially leading to hypoxia in the user. This design feature is particularly important in aviation, where rapid decompression can occur, necessitating immediate access to breathable oxygen. The integrity of the seal plays a vital role in the safety and reliability of the oxygen delivery system.