This results in both a vertical and horizontal spreading fire and the plastic container itself contributes to the fire. Even when a steel container fails due to pressure, splitting at the seams or repturing the top, the resulting fire is less severe than one with plastic containers. From a safety standpoint, the best steel containers will have a pressure relief device or will be designed to fail at a low pressure. The vapors burn, not the liquid. But, the FP is related to the rate at which a liquid vaporizes, which depends on a liquids vapor pressure.
Vaporization increases with rises in temperature.
Because the FP is generally a concern with liquids open to the atmosphere, FP is usually given in temperature at atmospheric pressure. Higher octane gasoline will have a lower FP but a higher ignition temperature. Hence, its resistance to knocking. Other ingredients will have similar effects. But, diesel does seem to vary in FP much more than gasoline.