When should a second engine be inserted into 5" relay operation?

In the context of mobile pump operations, the decision to insert a second engine into a 5-inch relay operation is largely determined by the hydraulic conditions of the system. Introducing a second engine becomes essential when either the water pressure is low or the hose lay exceeds 1200 feet.

When the hose length increases significantly, the friction loss in the hose also increases, which can lead to inadequate water pressure at the pump discharge or at the end of the lay where water is needed. By utilizing a second engine, the overall system can maintain higher pressure and flow rates, compensating for these losses and ensuring that adequate water supply reaches the necessary locations, especially in firefighting scenarios where every drop counts. Therefore, it is crucial to monitor both the pressure and the length of the hose lay in deciding whether to deploy additional resources for optimal performance.

Other options, such as the specific distance of 800 feet or only during drills, do not account for the varying conditions encountered in real incidents and thus do not provide the necessary guidelines for when to add a second engine. Furthermore, the choice of needing a second engine at all times isn't practical, as operational needs can vary based on the specifics of the situation.