What signifies the ignition point in a flashover?

The ignition point in a flashover is characterized by the moment when the materials in a room reach their ignition temperature and begin to combust almost simultaneously. At this juncture, the entire room can become engulfed in flames, leading to a rapid spread of fire. This phenomenon occurs when the accumulated heat from a fire is sufficient to cause all available combustible materials to ignite, resulting in a dramatic transition from a smoldering fire to a fully developed fire.

While indicators such as the presence of smoke or flammable liquids may signal the potential for a flashover, they do not define the actual ignition point. Smoke can occur well before a flashover, and flammable liquids may be present without causing an immediate fire reaction. Firefighters entering the premises could be in a situation where a flashover is imminent, but their presence is not an indicator of the ignition point itself.

Therefore, the defining moment captured in the question is indeed when materials in a room explode into flames, marking the shift into a more catastrophic phase of fire development.