What effect does an atmosphere enriched with oxygen have on the upper flammable limit of flammable gases?

An atmosphere enriched with oxygen increases the upper flammable limit of flammable gases. The upper flammable limit (UFL) is the maximum concentration of a gas in the air that can support combustion. When oxygen concentration rises, the energy needed for ignition can be more readily supplied, allowing a wider range of gas concentrations to ignite.

This means that with higher oxygen levels, even those gases that normally would not ignite at lower concentrations can burn more easily and at higher concentrations. Since combustion is a chemical reaction that relies on the presence of fuel, oxygen, and an ignition source, any increase in oxygen enhances the ability for combustion to occur, thus raising the upper limit of flammability for those gases.

Conversely, reducing oxygen levels would lower the UFL, and a concentration that is too high could prevent combustion due to a lack of sufficient fuel in the necessary proportion.