What is the primary effect of applying water streams into a structure from the outside?

When applying water streams into a structure from the outside, one of the primary effects is to reduce temperatures in many parts of the structure. This temperature reduction can help prevent the fire from spreading and reduce the heat exposure to firefighters and building occupants. The cooling effect of water can help lower the overall thermal load inside the building, which is crucial in managing the fire and protecting structural integrity.

By lowering temperatures, this action creates safer conditions for both suppression efforts and possible rescues. It can also help prevent flashover, a rapid spread of fire throughout the entire area, by reducing heat levels in the atmosphere and on surfaces.

The other options, while relevant to fire behavior and suppression tactics, do not capture this primary effect as directly as the action of cooling. For instance, redirecting the flow path may be a consequence of how water is applied, but it is not the primary effect of those initial exterior water streams. Similarly, lowering of the smoke layer and pushing fire into uninvolved parts of the structure can occur depending on how water is applied, but they are not the primary intent or benefit of applying water from the outside. Thus, reducing temperatures stands out as the key focus of this firefighting tactic.