Most boats have a gasoline or diesel-fueled internal combustion engine.
Many also include gas-burning appliances for cooking or heating. Having one or more sources of fuel on board presents a potential danger, especially if you are unaware of leaks or vapor accumulation. Many boaters have some serious misconceptions about fuel fumes in the bilge or engine compartment. One is that the engine blower will eliminate dangerous fuel vapors prior to starting a gasoline engine. In fact, any sort of fuel leak can create new fumes as quickly as the blower fan can clear them out, so the risk of explosion is always present, whether the blower is running or not.