One of the major requirements of an illuminated exit sign is it has to keep glowing ... It’s what’s powering the green glow of emergency exit lights. Tritium decays when one of its neutrons ...

The Mexico City International Airport acknowledged in a statement Friday that a man had opened an emergency exit and walked out on a wing of a plane that was parked and waiting for takeoff Thursday.

There will be a pre-flight warning telling passengers not to open the emergency exits mid-flight, per JoongAng Daily. It follows an earlier measure to sit uniformed workers in exit rows.