Why was Door Lock Monitoring Added to the Code?

In our last post, we explored the two main requirements of door lock monitoring. Today, we’ll focus on the practical safety considerations and provide links to some of the accidents that led to door lock monitoring being implemented.

Elevators are designed to move only when their doors are closed. However, like any complex piece of equipment with many moving parts, elevators experience wear and tear over time. This includes the door locks and gate switches, which, if worn or damaged, may incorrectly report their status—open when they are closed or vice versa. Additionally, actions taken by mechanics during troubleshooting or repair, if not properly undone, can cause gate switches or door locks to give false readings.

This is where door lock monitoring (DLM) adds an extra layer of safety.
DLM improves elevator safety by double-checking all sensors against each other and comparing them to the door’s open and closed limits. It ensures that an elevator cannot move if the doors are open and verifies that the door locks and gate switches are functioning correctly, allowing the system to accurately detect whether the doors are open or closed.

By doing so, DLM helps prevent horrific accidents.

Without door lock monitoring, an elevator could begin moving with its doors open, because the controller mistakenly believes the doors are closed. This can result in severe injury or death if a passenger becomes trapped between the car and the floor as the elevator moves unexpectedly.

Although rare, accidents caused by elevators moving with open doors occurred in the absence of Door Lock Monitoring, often making the news due to the resulting fatalities:

Thankfully, as Door Lock Monitoring is implemented in additional jurisdictions, these accidents can be prevented from occurring in the future.

As more states adopt this critical safety feature, Argus is looking forward to partnering with OEMs and independent contractors to ensure these accidents become a thing of the past.