Final answer:
The temperature at which combustion is sustained after removal of the flame ignition source when a material is heated beyond its flash point is called the 'fire point'. This is where the heat from the combustion is sufficient for the reaction to continue on its own.
Step-by-step explanation:
When a material is heated to a temperature that is 10 degrees to 30 degrees higher than its flash point and an ignition flame is applied from time to time, the temperature at which combustion is sustained after removal of the flame ignition source is called the fire point. The flash point of a material is the lowest temperature at which it can vaporize to form an ignitable mixture in air. However, the fire point is a higher temperature at which the material will continue to burn after being ignited and after the ignition source is removed. This is because the energy released from the combustion process is sufficient to keep the reaction going without additional energy input.
Seeing as the flash point categories indicate the propensity of a material to ignite, the fire point is an extension of this concept where the focus is on sustained combustion. It’s important to store materials with a low flash point and fire point in a controlled environment to prevent unintended ignition, as exemplified by warning instructions to store such materials at temperatures below their flash point to avoid accidents.
Therefore, the correct answer to the student's question is C) Fire point.