Canon LBP7210Cdn Manual page 75

CAUTION
Precautions when closing the front cover
Be careful not to catch your fingers.
IMPORTANT
If you cannot close the front cover
Make sure that the toner cartridge tray is closed.
Do not try to forcefully close the front cover, as this may damage the printer.
Do not leave the front cover open for a long time with the toner cartridges installed.
This may result in deterioration in print quality.