Machine Design

Garage Door with Maladjusted Safeguards Injures Girl

A 10-year-old girl had her leg badly crushed when an automatic garage-door opener didn’t detect her presence.

A number of years ago it was not uncommon to hear of a person, usually a child, being seriously injured or killed by a garage door controlled by an automatic opener. In most cases, the person pressed the button inside the garage to close the garage door, then tried to run through the large opening before the garage door closed. The door could pin a person who wasn’t quite fast enough to the ground and injure or kill them.

On older garage doors, resisting torque would tell the motor to reverse and open the door when it met a preset threshold of resistance. I had this type of garage-door opener years ago, and I tested it monthly by trying to close it over a 1-gallon plastic bucket. As I became an empty-nester, I let this test program slide. Then, I caught my grandson trying to race the door.

I quickly installed a newer opener with an electric eye about 7 inches from the bottom of the door travel. If the beam of light is broken while the garage door is descending, the motor reverses and pulls the door back up.

The old resisting-torque safety feature was retained in the new design as well. The owner’s manual recommended I place a 1-inch-wide piece of wood in the door’s path and attempt to close the door to test whether the motor would reverse. However, the manual didn’t indicate how much resistance the opener needed to reverse the motion. The resistance offered by a 1-inch-thick board is much different from that of an arm or leg.

A few months after I installed my new door, I investigated the accident involving the 10-year-old girl. The electric eye had been mounted 22 inches above the floor, and the threshold torque for the older safety system had been raised so I could not trigger it, even when my portable scale measured 75 pounds of vertical force.

The offending door guarded the entrance to her apartment-building’s parking garage, and I wondered why the electric eye was set so much further from the ground than recommended in single-family homes. A local survey of apartment complexes and two commercial sites revealed the thinking: If the electric-eye system was 7 inches above the floor, it might miss a vehicle in the door’s path. The door owners had never considered mounting two sets of electric eyes — one 7 inches high and one 22 inches high — to protect both vehicles and people, and had opted to save the vehicles.

The owner’s manual for these commercial garage-door openers specifically discuss the safe force needed to reverse the door, and the door that crushed the girl’s leg was not within their recommended limits. It appeared the installer missed or ignored the reversing torque of the opener. He also seemed not to understand the reason for the electric-eye system.

Manufacturers of garage-door openers should add warning labels to the units to call installers’ attention to these two safety features and the reasons for them. In addition, owners manuals should clearly state both the optimal ranges for torque resistance and electric-eye height and the rationale behind those ranges.

Lanny Berke

Lanny Berke is a registered professional engineer and Certified Safety Professional involved in forensic engineering since 1972. Got a question about safety? You can reach Lanny at [email protected].

Edited by Jessica Shapiro

© 2010 Penton Media, Inc.

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