Which of the following materials is prohibited for use in building construction due to fire risks?

Combustible materials in fire-rated assemblies are prohibited for use in building construction due to fire risks because they can compromise the integrity of the fire-rated assembly. Fire-rated assemblies are designed to resist the spread of fire, and the inclusion of combustible materials can significantly reduce their effectiveness in preventing fire from traveling through walls, ceilings, or floors. This could endanger the safety of occupants and first responders, as well as increase property damage during a fire event.

Fire-resistant materials are specifically designed to withstand high temperatures without burning, making them suitable for construction. Non-combustible materials, by their very nature, do not ignite or contribute to fire spread, and insulating materials can vary broadly but are used in ways that often comply with safety regulations, so they typically do not present the same risk as combustible materials in fire-rated assemblies. Thus, the correct answer highlights a critical consideration in fire safety and building standards.