How do multipurpose dry chemical agents prevent rekindling of Class A fuel?

Multipurpose dry chemical agents are effective in preventing rekindling of Class A fuels primarily by forming a crust over the fuel. This crust acts as a barrier that limits the access of oxygen, which is essential for combustion. By sealing off the fuel surface, it minimizes the chances of flames reestablishing themselves after the initial fire has been extinguished.

This method of suppression is particularly important in situations where smoldering materials could reignite, as the physical barrier not only isolates the fuel but also helps to insulate it from heat and air. Additional fire prevention techniques, such as cooling the materials or absorbing moisture, may mitigate risk but are not the primary function of the crust formed by these agents. The crust's role is vital in maintaining a safe, extinguished state of the fuel.