Industrial Door Safeguarding
Help your customers reduce accidents

By Jac Whitmire and Tim Castello

Itseems as though every time you turn on the news or read a newspaper, seemingly frivolous legal claims jump from the headlines. These claims can cost enormous sums of money for the defendants, who are often major corporations with “deep pockets.” Unfortunately, the publicity that some of these cases has generated has proven to be inspirational to a select few that look for any opportunity to stake their claim to the big money.

However, small businesses can also be exposed to the frustrations of frivolous claims. As professionals in the industrial door industry, there are steps that can be taken to help your customers substantially reduce the risk of actual or staged injuries created by motorized commercial doors.

Safety Strategies

Of course, the best safety practice for motorized commercial doors is to create the requirement for constant contact on the close button. In theory, this allows an individual to monitor the opening to ensure that personnel and equipment are protected. However, in practice, this is frequently not the case. The employee may be tired, distracted or even oblivious to potential hazards.

In some instances, employees will find ways to override the system so they may move on to the next task. In any event, the system no longer performs as intended, creating the possibility of injury or a costly accident. It also goes without saying that some customers order motor operators simply for the fact that they want the increased efficiency of allowing a momentary contact close.

Keeping this in mind, there are many fine products on the market today that provide efficient, reliable safeguarding. There are options to fit every application —as well as every budget. Some of these devices are very simple to wire into the motor operator, while others may be a bit more technical. The key is finding the correct solution for your customer. The ultimate goal, of course, is to assist your customer in reducing injuries (real or staged), as well as damage to equipment, product or to the door system itself. Here are some of the methods through which this can be achieved.

Electric sensing edges typically consist of two electric contact elements that are separated by a small gap or normally open (N.O.). When compressed, the edge essentially “shorts,” creating a signal to the motor operator to stop and/or reverse. In some cases, the motor operator will need a normally closed (N.C.) input, in which case the sensing edge is wired through a relay.

Sensing edges can also be designed as a 4-wire or 2-wire with a resistor, “fail-safe” system. In this case, the motor operator must be constructed to send voltage through the edge and identify a voltage return or an external fail-safe controller must be used. As long as voltage is coming back through the system, the motor operator performs properly. In the event of a break in the wiring or any malfunction to the sensing edge, the motor operator or controller will not detect the voltage return and will hold the door in the failto- safe, or open, position until the safety issue is addressed.

The sensing edge also doubles as weather seal, as it replaces the stock bulb or loop seal on the door and comes in a wide variety of shapes and sizes to fit virtually any door or application. While it’s necessary that contact be made with an obstruction before an electric sensing edge can activate, the electric sensing edge is typically padded to help reduce the possibility of injury or damage.

Another type of electric sensing edge is an optical edge. This consists of an infrared transmitting and receiving device inserted into a bottom astragal. Installation is critical with the optical edge because the transmitting and receiving devices require a small round tube incorporated in the bottom astragal to remain round and relatively straight. The motor operator’s down limit needs to be set to not overcompress the edge.

There are also optical noncontact edges which are inserted into a flexible holder and work outside and 3 inches below the bottom astragal. When the light beam is blocked a N.O or N.C. output signal is sent to the sensing edge circuit in the motor operator. Optical edges contain fail-safe controllers that monitor eye blockage, wiring breakage or power loss. The optical sensing edge also doubles as weather seal and replaces the stock bulb or loop seal on the bottom of the door. The noncontact optical sensing edge works in conjunction with the stock bulb or loop seal on the bottom of the door.

Pneumatic sensing devices come in a wide range of styles and prices. Typically they’re the lowest priced of all possible sensing methods and require a stronger impact to activate than an electric sensing edge. Generally, a pneumatic device consists of a simple latex bladder with an affixed metal contact. As air is forced into the switch, the bladder expands and forces the affixed metal contact to touch another metal contact that is wired to the motor operator. As in the electric edge, this causes a N.O. circuit to “short” and send an output signal to the motor operator.

Many pneumatic switches have a third wire for a quick transition to N.C. if needed. Although pneumatic switches frequently utilize gum rubber hose that slides into the doors bottom astragal, more conventionally designed sensing edges can be made pneumatic instead of electric, offering additional padding and a higher quality finished look.

Air Wave sensing devices work by detecting the change in volume of compressed air inside an extrusion or gum rubber hose. While air wave switches utilize air pressure to activate a switch, the similarity to pneumatic ends here.

Although standard pneumatics generally do not offer any sensitivity adjustments, this is one of the strong points that air wave has to offer. By simply turning a screw, the change of pressure required to activate the switch can be adjusted from a fairly light tap to a stronger impact. The sensitivity adjustment —and recognizing the change in air volume as opposed to pressure—allows the air wave sensing edge to work at very long lengths of 60 feet or more.

The basic construction consists of a silicone diaphragm that provides for greater resistance to ozone corrosion, leading to a much longer life. Air wave switches can also easily convert between N.O. and N.C., and may also be used with gum rubber hose or specialized extrusions. Typically, they are also very costeffective and can be ordered with a waterproof enclosure.

Consisting of an infrared beam of light with a transmitting and receiving device, photo eyes are standard accessories to residential garage door openers and are fairly typical in industrial applications as well. They may be thru-beam, which consists of an emitting and receiving eye, or retro-reflective, which utilizes a reflector to return the light to the sending unit.

In most applications, they are stationary and mounted to the door track or on a post. In order to properly function, the obstruction must break the beam. Raised forks on a forklift or stationary pallets may be higher or lower than the beam can detect. Also, an individual standing in the door opening may not be in position to interfere with the beam. Alignment is fairly critical, so typically they are unforgiving if impacted. In recent years, however, improvements have been made incorporating flexible brackets or door-mounted applications. Traveling with the door, these products will detect any obstruction along the door’s path. Commonly used in the high-speed door market, these are now readily available for the sectional or rolling door market as well (see optical sensing edges).

Loop detectors work by applying current to wires, wound in the form of a coil (usually imbedded in concrete or pavement), creating a magnetic field around the wire. When the magnetic field is interrupted by a conductive object, the loop detector module monitors the change. While these are effective for detecting vehicles or material handling equipment, they do not offer human protection. They are generally very reliable and function well if installed properly. However, it’s also necessary to saw-cut into the floor in order to lay the wire loop, which is not always acceptable to your customer.

Utilizing the same type of technology commonly found in police radar guns, microwave detection works by sending a microwave signal out in a sharp clear (adjustable) pattern. When the microwaves strike a moving object, the detector analyzes the reflection, frequency and amount of time it takes for the signal to return. The device can determine both speed and angle of the motion.

Commonly seen on commercial pedestrian doors in department stores, these devices have proven their reliability and flexibility. Tremendous advancements in this technology have resulted in the development of some great industrial door products. Some of these devices have the ability to activate a door opening if a forklift is detected, but not a human, for instance.

Some can discriminate between traffic moving toward a door or away from the door, or be set to activate only when perpendicular motion is detected, not when parallel motion is detected. Other units will not allow a door to close as long as it detects that anything is in the sensing area, whether moving or not. Many units are fully customizable, work at heights up to 23 feet and are programmed via a remote when the door technician is standing on the ground.

It’s important to analyze traffic patterns, the environment around the opening, and the type and size of obstructions going through the door opening to provide the most wellsuited safety device for the application. It’s also very important to visually inspect and test all safety devices in accordance with the manufacturer’s written instructions.

The bottom line is that there are several great options available to the professional door dealer to assist the end user with providing the highest degree of safety and sensing possible. While no single system is ever completely failure-proof, by becoming more knowledgeable about these products it’s possible to help your customer create a safer, more efficient workplace. You can help your customers understand a few extra dollars up front may help avoid the loss of many more dollars in the future.

Share this article: Email, Slashdot, Digg, Del.icio.us, Yahoo!MyWeb, Windows Live Favorites, Furl
Add this article feed to: RSS, My Yahoo, Newsgator, Bloglines

Read Comments [0]