Final answer:
The bilge blower should be run for at least four minutes before starting a boat's engine to ensure the removal of flammable fumes and prevent explosions.
Step-by-step explanation:
Before starting your engine on a boat, it is important to run the blower in the bilge to remove any potentially explosive fumes or gases that may have accumulated. According to the United States Coast Guard (USCG) boating safety guidelines, you should run the blower for at least four minutes before starting the engine.
This period allows for adequate ventilation and ensures that the concentration of any flammable substances is reduced to a safe level, minimizing the risk of an explosion or fire.