1. Field of the Invention
This invention relates generally to exit devices that secure a door in the closed position. More specifically, the present invention relates to exit devices that keep a door closed when subjected to a high-energy impact as may occur when debris is hurled by a tornado against the door.
2. Description of Related Art
An “exit device” is a lock mechanism operated from the inside of an exit door through the use of a crossbar, pushbar, pushrail or panic bar actuator. The term “pushbar” will be used herein to refer to the above types of exit device actuators and other types of actuators including paddles and various other mechanisms that move towards the exit door to actuate the latch. The exit device is designed to open the exit door, allowing exit without prior knowledge of how the lock operates, whenever a horizontal force is applied to the pushbar actuator. Exit devices are typically required by fire or building codes and are used in public buildings where many people may be gathered, to provide rapid, safe and easy egress in case of emergency.
Exit devices of this general type may be seen in U.S. Pat. Nos. 4,384,738; 5,531,492 and U.S. Design Pat. No. 279,647 all of which are assigned to Sargent Manufacturing Company, the assignee of the present patent application.
Conventional exit devices typically include a mounting rail that is mounted on the interior surface of the exit door and a pushbar actuator that is mounted so that it can move towards the mounting rail to operate the exit device. The pushbar actuator is spring biased away from the exit door. When horizontal pressure is applied to the pushbar, it moves horizontally in towards the mounting rail, compresses the bias springs and retracts a latchbolt to open the exit door.
In a tornado rated exit device, the exit device must keep the exit door closed when subjected to a high-energy impact on the exterior surface of the door. The test to provide a tornado rating involves loading a cannon with a long 2″×4″ board of the type used in construction and firing it at a speed of one hundred miles per hour (160 kilometers per hour) into the exterior side of the exit door. The exit device must keep the exit door closed, and remain operable after the impact.
Conventional exit devices are unable to pass this test because the high-energy impact on the exterior side of the door pushes the mounting rail and the exit door towards the pushbar. The impact energy is so high that the door and mounting rail rapidly move towards the pushbar actuator, while the pushbar remains stationary due to inertia. As the door and mounting rail move towards the pushbar, the biasing springs that hold the pushbar away from the exit door are compressed and the door opens.
The exit device may also fail this test if the pushbar rebounds towards the exit door during dissipation of the impact energy. In both cases, the pushbar and the mounting rail move towards each other as a result of the high-energy impact. This relative motion compresses the bias springs and retracts the latchbolt exactly as if the pushbar had been pushed towards the mounting rail to operate the exit device in the normal manner.
The prior art has addressed this problem by increasing the strength of the bias springs that hold the pushbar away from the support rail. The increased spring strength prevents the pushbar from moving towards the mounting rail during the impact. While this is effective, it means that every time the door is operated the user must apply sufficient force to compress the stronger bias springs. This higher level of required force for normal operation is an undesirable characteristic for an exit device and makes it difficult to operate for the elderly and other users.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an exit device that operates with a normal level of force and which automatically blocks operation during a high energy impact, but which thereafter releases the blocking so that the exit device operates normally.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.