What should be done after turning on the emergency lights during firefighting duties?

After turning on the emergency lights during firefighting duties, closing the flight deck door is an essential step. This action helps to ensure that the cockpit remains secure and that the flight crew is not exposed to any unnecessary risks from smoke or flames that might enter the flight deck.

Keeping the flight deck door closed also helps to maintain the safety and operational integrity of the aircraft's systems, as it limits the exposure to possible hazards and ensures that crew members can focus on managing the situation without external distractions.

The sequence following the activation of emergency lights is crucial in maintaining control and ensuring safety during an emergency situation. While there may be occasions when other actions could be necessary—such as checking all emergency exits for safety or maintaining illumination—the priority during firefighting duties is to secure the environment that the flight crew operates in.