What happens to oil when it reaches its fire point?

When oil reaches its fire point, it signifies a critical temperature where the oil produces enough vapor to mix with the air and support combustion. At this point, if there is an ignition source present, the oil can flame and continue to burn. The fire point is higher than the flash point, which is the temperature at which the oil can form ignitable vapors, but it does not require a flame for combustion to occur. Thus, the ability of the oil to continue burning if ignited is a direct consequence of reaching the fire point.

The other options do not accurately represent the characteristics of oil at its fire point. Solidification typically occurs at much lower temperatures, vaporization does begin at lower temperatures but does not indicate continued combustion, and viscosity changes can happen but are not the primary concern related to the fire point.