Reversing mechanisms: protecting against entrapment
Many doors with electric tape switches will monitor for a damaged reversing edge switch and respond to failure by holding the door open in a safe position. A pneumatic switch may be able to do something similar. However, careful consideration needs to be given since the pneumatic switch can be rendered inoperable if the device develops an air leak.
By far, the most reliable configuration for addressing entrapment is a door that uses a flexible bottom edge. With such a design, the potential for a person to become entrapped is virtually eliminated due to the inherent flexibility of the bottom edge of the door. No reversing edge is needed.
High speeds drive need for safety
The popularity of high-cycle doors, which operate at speeds from 30 to 100 inches per second, is driven by the need for energy efficiency and productivity improvements in the workplace. Most high-speed doors typically include photo-eyes and warning labels as standard features to enhance safety. Other options may also be available.
A common misconception about reversing edges is that they help prevent impact. In reality, a reversing edge is only activated after an impact already has occurred. The best scenario would be to avoid the impact in the first place. To this end, manufacturers use various non-impact, door-sensing technologies, which allow a door to reverse before it reaches the object in its path.
A standard door safety package typically includes at least one photo eye, which transmits a beam of light in a straight line across the opening of the door from one side to the other. The photo eye is typically located in or on the door sideframe and is normally positioned one or two feet above the floor.
Reaching out beyond the door opening
Traditional photo-eye systems detect obstructions only within, or very near, the plane of the door opening. An area detection system, on the other hand, looks outside the plane of the doorway for people or objects that are approaching one side of the door or the other. If a person or object is detected by the system, it puts the door in a safe condition and prevents it from closing. Area detection systems generally use infrared and/or motion-sensing technology.
When considering an area detection system, factor in any cross-traffic near the door opening given that the sensor may hold the door open unnecessarily if people and/or forklifts are merely passing within relatively close proximity to the door and not intending to pass through it. The result can be significant energy loss.
Helping see the risk
Vision panels allow pedestrians and forklift operators to see through a closed doorway. Though vision panels provide greater vision capabilities, they are easily scratched and dinged, and they don’t fit every application. For example, in a cold-storage environment the vision panels can tend to frost up and quickly become ineffective. In such situations, some manufacturers offer sensor and light communication packages to alert forklift drivers to people or objects moving on the opposite side of the closed door, thus providing “virtual” visibility through the doorway.
Weighing the options
There is no one-size-fits-all solution when it comes to high-speed door safety. A good idea is to partner with established door experts who can help you make informed decisions about door safety and the best choices for the application.
