Which term refers to cracks that are smooth and extend further away from the origin due to prolonged lower heat?

The correct term for cracks that are smooth and extend further away from the origin due to prolonged lower heat is known as long crazing. This phenomenon occurs when glass experiences thermal stress over an extended period, leading to the formation of cracks that differ from those caused by sudden impacts or high-temperature changes. Long crazing typically results when a glass surface is subjected to lower temperatures that allow the cracks to develop slowly, creating a characteristic smooth appearance.

In the context of fire investigations, understanding the characteristics of these cracks can provide valuable insight into the conditions surrounding the fire incident. This knowledge helps investigators determine the source and intensity of the heat that affected the glass.

The other options do not accurately describe this specific type of cracking. Short crazing generally refers to cracks that do not extend as far or become as pronounced, while checkering of glass usually describes a different pattern of cracks that form in various designs, often due to more acute thermal stresses. The melting point of glass is an entirely different concept, referring to the temperature at which glass transitions from a solid to a liquid, rather than a descriptive term for crack patterns.