The correct answer is A) Lighting-off from hot brick work. Lighting off a boiler burner from hot brickwork presents the greatest danger of boiler flareback. This is because the hot brickwork can ignite unburned fuel, causing a sudden, uncontrolled flare-up in the boiler. Other methods, such as using a torch (B), lighting from an adjacent burner (C), or using an igniter (D), provide a more controlled and safer ignition source, reducing the risk of flareback. The Coast Guard regulations emphasize the importance of following proper boiler light-off procedures to ensure the safety of the vessel and its crew.