What does the term 'seal intact' refer to during preflight checks?

The term 'seal intact' during preflight checks specifically relates to the condition of safety equipment like Protective Breathing Equipment (PBE). Ensuring that the seal is intact means verifying that the PBE is properly sealed and ready for use in the event of an emergency. A damaged or compromised seal could render the equipment ineffective, which is critical when dealing with situations requiring breathing protection due to smoke or toxic fumes.

By focusing on the integrity of safety equipment, crew members ensure that all necessary tools for emergency situations are available and functioning correctly. This is essential for the safety of both crew and passengers. The other choices, while important, pertain to different aspects of preflight checks that are not directly linked to the term 'seal intact'.