What should a vessel do if there is a risk of backfire?

Engaging the ventilation system is crucial in the event of a risk of backfire because it helps to disperse any flammable vapors that may be accumulating in the engine compartment. This proactive measure lowers the risk of an explosion or fire by ensuring that any potentially dangerous fumes are ventilated out of the vessel. Proper ventilation is critical for safety, especially in enclosed spaces where flammable gases can concentrate.

Other choices may not effectively address the immediate risk of flammable vapors. Reducing speed or filling the fuel tank does not directly mitigate the potential for a backfire. Additionally, switching off all electrical devices may help in some contexts, but it does not effectively manage the air quality or vapor concentration in the engine space. The key action to take is to ensure that the area is ventilated to reduce the risk of ignition from any spark or heat source.