Before starting an inboard gasoline engine on a sports boat, why must the engine compartment bilge blower (extractor de gases) be run for at least 4 minutes?

1. To warm up the engine oil before starting
2. To check if the boat's battery is fully charged
3. To cool the cabin temperature for passenger comfort
4. To evacuate heavy, explosive gasoline fumes that settle in the lower bilge, preventing catastrophic explosions upon engine ignition