Final answer:
A flashover is a hostile fire event that occurs when all surfaces and contents of a space simultaneously reach ignition temperature, leading to a sudden spread of fire.
Step-by-step explanation:
The phenomenon of a sudden hostile fire event that occurs when all the surfaces and contents of a space reach their ignition temperature is known as C) Flashover. This critical stage in a fire signifies a transition to a fully developed fire, which can be particularly dangerous because it leads to the rapid spread of flames throughout the space, presenting a severe risk to both occupants and firefighters. Understanding the conditions that lead to a flashover is crucial for fire prevention strategies and enhancing fire safety measures. During a flashover, the entire room becomes engulfed in flames, making it extremely dangerous for anyone inside. This phenomenon is a critical moment in the development of a fire and can result in widespread damage and loss of life.