Final answer:
The three modes of operation for door exits are manual operation, semi-automatic operation, and automatic operation, which are significant for building safety and accessibility.
Step-by-step explanation:
There are three modes of operation for door exits: manual operation, semi-automatic operation, and automatic operation. Manual operation requires someone to physically open or close the door. Semi-automatic operation allows the door to be opened manually but it will close automatically. Automatic operation means the door opens and closes in response to sensors or controls without human intervention. These modes are particularly important in ensuring safety and accessibility in buildings, especially during emergencies.