Elevator overspeed incidents are among the elevator malfunctions that appear in our forensic casework. The sudden and unexpected acceleration of an elevator beyond the accepted contract speed, followed by an abrupt stop, can result in serious injuries for passengers.
In this article, Elevator & Escalator Expert Dennis Olson explains the purpose and function of an overspeed governor and the maintenance policies and procedures which should be followed to ensure safety.
Elevator Overspeed Incidents – Expert Article
Overspeed incidents are often caused by the failure of the elevator controls system to accurately regulate the acceleration of the elevator creating what the industry identifies as an “overspeed” condition.
ASME A17.1 Safety Code for Elevators provides the definition of a Governor:
“A continuously operating speed monitoring and detection device which, at predetermined speeds, provides signals to the controller and imparts a retarding force to activate the car or counterweight safety.”
The purpose of the governor is to measure and regulate speed in a manner that prevents the elevator from exceeding a predetermined upper speed limit.
In the event the governor detects an overspeed condition, it is designed to respond by bringing the system to a halt. This can be achieved with or without activation of the mechanical safeties, depending on the elevator settings and specific conditions. After the governor initiates the stopping procedure, the elevator remains immobilized until it is re-set.
Should an elevator exceed 115% of the rated contract speed, an emergency stopping of the elevator will occur by activation of the governor overspeed switch. Activation of the governor switch will remove electrical power to the elevator hoist machine. The resulting loss of power will cause the elevator brake to set, resulting in an immediate hard and abrupt stopping of the elevator.
Should the elevator exceed 120% of the rated contract speed, an emergency stopping of the elevator will occur by activation of the safety devices mounted under the elevator car platform. The safety device shall be capable of stopping and sustaining the entire car with its rated load. Activation of the safeties will also result in an immediate hard and abrupt stopping of the elevator.
Elevator Maintenance Standard of Care
The ASME A17.1 Safety Code for Elevators and Escalators is a standard for elevator design, maintenance and operation which is widely accepted throughout the elevator industry and the building management industry. To meet the intent of the Code, the most widely recognized industry practice is for the elevator company to maintain a logbook containing the required information in the elevator machine room. The purpose of the maintenance log is to provide a written record of work performed on the elevator that mechanics and inspectors can reference when performing maintenance or responding to service calls.
Elevators require regular and systematic maintenance at predetermined periodic timeframes, in addition to unplanned/as-needed adjustment and/or repair when a specific issue is reported. Factors considered when developing a maintenance plan for elevators / escalators and other forms of vertical transportation equipment are identified in ASME A17.1.
The maintenance procedures and intervals shall be based on:
- equipment age, condition, and accumulated wear
- design and inherent quality
- environmental conditions
- improved technology
- the manufacturer’s recommendations for any SIL rated devices or circuits
In a forensic investigation, review and understanding of the information provided in the maintenance log and maintenance records may provide critical information about the condition of the elevator and the maintenance that was performed leading up to the incident.
ELEVATOR SAFETY INVESTIGATIONS
The Elevator and Escalator experts at Robson Forensic have the necessary training, education and experience to investigate a broad range of mishaps involving elevators, escalators and other forms of vertical transportation equipment encompassed under the A17.1 and associated Safety Codes. Our elevator and escalator experts are industry veterans who have worked for companies involved in the design, manufacture, installation, modernization, service/repair and maintenance of elevators, escalators and various other forms of vertical transportation equipment. They understand how this specialized equipment is designed to function and can reliably identify the factors related to the failure of system components that may or may not have contributed to the injury or loss in your case.
For more information, submit an inquiry or contact the author of this article.
Elevator & Escalator Expert
Mr. Olson is an elevator/escalator expert with more than 35 years of experience in the design, construction, modernization, maintenance and service of elevators and escalators. Mr. Olson is a QEI-1 Certified Elevator Inspector through the National Association of Elevator Safety Authorities and former Elevator Constructor / Mechanic certified through the International Union Elevator Constructors.