What occurs when pure oxygen is mixed with burning material?

When pure oxygen is mixed with burning material, the resulting reaction significantly enhances the combustion process. This is because oxygen is a critical oxidizing agent that supports and accelerates the burning of fuels. When introduced into a fire, particularly in high concentrations, it provides a much richer environment for combustion to occur, leading to a rapid increase in flame intensity and heat production. As a result, a fire will flare up and become uncontrollable, as the rate of combustion increases exponentially with the presence of additional oxygen.

In contrast, other scenarios such as a reduction in flames or the material cooling down do not occur in this context. A controlled burn typically refers to a situation where the combustion is managed and intentionally maintained, which is not the case with an uncontrolled flare-up caused by an increase in oxygen levels.