Because a fire can take the electrical supply with it, and a pump that depends on that supply may be unavailable exactly when needed. Where no reliable secondary supply exists, codes require a diesel-driven pump for that reason rather than as a preference.

No. Fire pump engines are listed or approved for the duty, supplied with dual batteries and starting circuits, mechanical governing, a matched instrument panel and cooling taken from the pump discharge. The approval covers the assembly, so substituting an equivalent industrial engine is not permitted however capable it appears.

Enough for a defined run time set by the governing code, in a tank dedicated to the fire pump and not shared with other equipment. Fuel condition matters as much as quantity - diesel degrades in storage, and stale or contaminated fuel is a common cause of failure to run when tested.

Ventilation for combustion air and for rejecting engine heat, a code-compliant insulated exhaust route, drainage, and access for testing and service. Ventilation is the item most often underestimated, and an under-ventilated room causes the engine to overheat during the very extended run it is there to provide.

Typically weekly no-flow running and annual flow testing against the pump curve, with results recorded each time, though the exact regime follows the governing code and the authority having jurisdiction for the site. The records are part of demonstrating compliance rather than merely good practice, and they are what an inspector will ask to see first.

Batteries, fuel condition and cooling - very rarely the pump itself. Batteries are the single most common cause, which is why they are maintained on charge and replaced on a schedule rather than when they appear weak. Regular testing is what surfaces these before they matter.

Through a heat exchanger fed with water taken from the pump discharge, so cooling does not depend on any external supply that might fail at the same time as the mains. The cooling loop and its strainer are part of the routine test regime because a blocked strainer disables the engine within minutes of starting.