Licensed Professional Engineers

FORENSIC CLUES # 31- "Overhead Door Safety Requirements - Understanding UL 325" by John L. Ryan


A newsletter dedicated to keeping attorneys informed of the technical side of product liability cases.

Issue 31: Vol. 1 May/June 2009

"Overhead Door Safety Requirements—Understanding UL 325"

By John L. Ryan and L.D. Ryan

Overhead Door


Over 20,000 adults and children were injured last year due to overhead doors. These injuries range from simple pinched fingers to amputation from unspooled cables and injuries and death from being crushed by closing doors. Most overhead door accidents are due to the malfunctioning of a safety device and/or failure to have failsafe devices or backup devices. This issue of Forensic Clues deals with what the requirements are of the standards that cover overhead doors.

What Happens?

Overhead door accidents that are serious usually involve getting crushed by a closing or falling door. Broken cables can send a door crashing, but this doesn’t occur frequently. Most overhead door safety devices do not safeguard this hazard, although designs exist that can prevent a free falling door from reaching the ground. Another injury occurs when loops of cable spool out when a reversing edge or other safety device malfunctions, and the door hits an obstacle. When the door is raised, these loops of cable cinch down, and have resulted in amputated limbs. Usually serious overhead door accidents involve a person getting crushed by a closing door. This will not occur with a properly safeguarded door.


OSHA doesn’t say much specifically in regard to overhead doors. The requirements for guarding all machines, 29 CFR 1910.212, calls for protecting a machine operator from the point of operation. This may or may not apply to overhead doors, depending on the interpretation of the standard. This section also calls for guarding devices to conform to applicable standards.


The American Society of Mechanical Engineers publishes ASME B15.1, Mechanical Power Transmission Apparatus. This calls for safeguarding of motion hazards. Section 3.2.2 states “A motion hazards safeguarding device shall provide protection to people by preventing and/or stopping normal motion of the mechanical power transmission source of hazard if people enter the hazardous area., and by providing the means to stop the system in the event of involvement with the hazard.” Overhead door crushing hazards are a motion hazard. The ASME standard calls for safeguarding methods that will prevent a closing overhead door from impacting a person, or stop the door if there is ‘involvement’ with the hazard.



Safety Engineering Resources invention to stop free falling doors

 UL 325

UL 325 is Underwriters Laboratories 325 Standard—Door, Drapery, Gate, Louver, and Window Operators and Systems. This standard is a voluntary standard, although OSHA does call for hazardous machinery to meet applicable standards. Much of UL 325 discusses specific electrical connector requirements of overhead door operators. UL 325 also discusses entrapment protection. UL 325 offers specific safeguarding requirements for different door and gate installations.

 Classes of Doors and Gates

Gate and door installations are broken down into four different classes, I, II, III, and IV. Class I is residential Vehicular Gate Operator, for use in a home of one to four single family dwelling. Class II is Commercial/General Access Vehicular Gate Operator, for commercial buildings like five family + buildings, hotels, stores, and other buildings open to general public. Class III is referred to as Industrial/Limited Access Vehicular Gate Operator. This class includes gates and doors for industrial locations such as a factory, loading dock, or other area that is not open to the general public. Class IV is designated Restricted Access Vehicular Gate Operator. This is for use in guarded locations not servicing the general public, where access is controlled by security personnel. An example of a Class IV installation is airports. UL 325 entrapment protection measures call for a primary and secondary method of safeguarding. The standard states the same type of device cannot meet both the primary and secondary criteria. This is often the crucial mistake that occurs in overhead door accidents—the safety system is not redundant, and/or isn’t failsafe.

Safety Devices in UL 325

UL 325 calls for specific safety devices. Type A is an inherent entrapment protection system. The criteria for an inherent entrapment protection system is that the system shall sense an obstruction and stop the motion of the door or gate, and initiate reversal of the door/gate within two seconds. The door will require a manual override before any automatic actuation device like a timer can be used after the reversing function occurred. Inherent entrapment protection also calls for stopping the door or gate when additional obstructions are detected. The door will require a “renewed, intended input” before any door opening or closing actuating device that is not in line of site of the door can be used. Non-contact sensors are Type B1 and are typically photoelectric sensors. These are the beam sensors seen on most residential installations. Contact sensors are Type B2 and are typically mounted on the leading edge of the gate or door, and sense when an obstruction is encountered. An inherentadjustable Clutch, Type C, is specified for swing gates only, This is a slip clutch that will stop motion of the gate when a certain force is encountered by the gate. When the gate hits an obstacle, the amount of force at the clutch increases as the gate tries to move. At a pre-determined force, the clutch will slip, stopping the gate. UL 325 calls for the gate to stop with an increase in load of 10%.

Continuous pressure actuation device, Type D, is another safeguarding measure referenced in UL 325. These are open/close controls that require constant pressure to open or close the door, and stop motion of the door when pressure is released from the control.

The last safety device referenced in the entrapment protection provisions of Section 31.1 of UL 325 is an inherent audio alarm, Type E.

An inherent entrapment protection system relies on sensors such as contact and non-contact sensors to determine when an obstruction is encountered.

Class I and II

Class I and Class II are grouped together. The entrapment protection provisions of UL 325 for these classes call for a primary protection method of an inherent entrapment protection system for doors. Secondary protection for doors can be a non-contact sensor, a contact sensor, or a continuous pressure control. For Class I and II swing gates, primary safeguards can be inherent entrapment protection system or inherent adjustable clutch or pressure relief device. Secondary safeguards for gates of these classes can be any of the listed safety devices except for an audible alarm.

Class III

Class III primary protection options for doors include inherent entrapment protection system, non-contact sensor or a contact sensor. Secondary protection provisions include inherent entrapment protection, non-contact sensors, contact sensors, continuous pressure actuation device or inherent audio alarm. Class III gates must have as primary safeguard an inherent entrapment protection system, non-contact sensor, contact sensor, or an inherent adjustable clutch. Secondary Class III gate safeguards include any of the listed safety devices.

Class IV

Class IV door operators must have as primary safeguards an inherent entrapment protection system, non-contact sensor, contact sensor, or continuous pressure actuation device. Secondary safeguards include all listed safeguards except the clutch. For Class IV gates, primary protection devices must be an inherent entrapment protection system, non-contact sensor, contact sensor, an inherent adjustable clutch, or a continuous pressure actuation device. Secondary safeguards for Class IV gates can be any of the listed safety devices.

Sensor Malfunction

UL 325 also calls for monitoring for correct operation of non-contact and contact sensors when they are used as the primary method of safeguarding. If a fault is detected in the sensor or wiring, the controls that open and shut the door must only engage the opening/closing mechanism when constant pressure is applied. This is to help prevent accidents that occur when a sensor quits working.


If a contact or non-contact sensor is used as the sensor for an inherent entrapment protection system, the same sensor cannot fulfill the secondary requirements of UL 325.

There are other provisions in UL 325, many regarding residential garage doors. Contact us at (479) 549-4860 for questions on whether a specific door or gate meets UL 325.

Please call us to discuss any questions you have about unsafe products. (479) 549-4860

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