Most linear accelerator vaults are built with mazes at the vault entry to reduce the amount of shielding needed in the door to the vault. Some facilities prefer to use a mazeless entry which requires a very heavy door that is difficult or impossible to operate by hand. These doors use an electric motor to open and close the door with a battery backup system to power the door in case of power failure.

There is no rule in the Ionizing Radiation Rules that specifically addresses the use of a mazeless entry for radiation therapy linear accelerator vaults. However, Rule 315(5) states, "The enclosure shall be so constructed that persons may at all times be able to escape from within." The question of "escapability" has been raised many times and has been defined by many different entities. The Radiation Safety Section's current position is that if the local building and fire inspectors consider a room escapable, then we will concur with their decision.

Posted: July 27, 2010