Which of the following does NOT affect the burning rates of solid fuels?

The factor that does not affect the burning rates of solid fuels is structural integrity. When considering burning rates, three primary factors are critical: moisture content, surface area, and oxygen availability.

Moisture content influences how readily a material ignites and burns. Higher moisture levels require more energy to evaporate the water before combustion can occur, slowing down the burning rate.

Surface area plays a significant role as well. A larger surface area enables more extensive contact with oxygen, facilitating faster combustion. Thus, finely divided fuels tend to burn quicker compared to larger chunks due to this increased surface contact.

Oxygen availability is crucial in combustion as well; without adequate oxygen, combustion cannot sustain itself properly. A higher concentration of oxygen typically leads to faster burning rates, while a lack of oxygen can inhibit combustion.

On the other hand, structural integrity refers to the physical state or condition of the solid fuel and does not directly relate to the combustion process. It might impact how the fuel is stored or used but does not influence the fundamental burning rate itself.