Functional Safety - Examples in everyday life - Elevator System
- Anunay Krishnamurthy
- Nov 28
- 3 min read
In everyday life, we rely on countless machines in our office, shopping centers, and even the machines in our homes. When these machines malfunction, they can lead to safety hazards. That’s why they are designed with functional safety in mind: to ensure that if something goes wrong, the machine either fails safely or continues operating in a safe state.
Here are a few examples of functional safety we encounter every day:
Functional Safety of an Elevator system
Elevators are one of the most common places where we experience functional safety without even noticing it. They are used in offices, malls, and residential complexes. We trust them every day to move us safely between floors.
When we step into an elevator and press a button, it feels straightforward. But behind the scenes, a lot is happening to make sure the ride is safe:
The buttons are connected to a central control system (computer/ control unit) that interprets the selected floor.
The system checks that the elevator doors are fully closed and locked before it allows the elevator to move.
A motor is then commanded to move the elevator up or down to the correct floor.
Once the elevator reaches the destination, the system ensures it has stopped correctly before opening the doors.
All of this coordination between door sensors, motion control, braking systems, and software checks is part of the elevator’s functional safety design. It ensures that even if something goes wrong, the elevator will enter a safe state rather than putting passengers at risk.
What can go wrong and how functional safety helps
Even though elevators feel simple to use, several things can go wrong if the underlying systems fail. Functional safety mechanisms are built in to prevent these issues from putting passengers at risk. Below are 3 examples.
Doors closing when people are entering
Elevator doors are driven by a motor and often operate on a timer. After staying open for a certain period, they begin to close automatically.
To prevent the doors from closing on someone, proximity sensors are installed along the door. If these sensors fail, the elevator may not detect a person entering, which creates a safety hazard.
The proximity sensors need to be plausibilized for errors. This probably requires the uses of redundant sensors. The elevator system will stop operation if there is a fault in the sensor and will continue to remain so until the issue is fixed.
Very high speed of the elevator during descent
Elevators are designed to descend at a controlled speed. If the elevator begins moving too fast for example, due to a mechanical or control-system fault, it becomes a serious safety issue.
To avoid this, the control system uses a speed governor. If it detects the elevator exceeding safe speed limits, it automatically activates redundant emergency brakes, clamping the elevator car in place and preventing further movement.
Power failure of the Electrical/ Electronic system when the elevator is moving
If the main electronics suddenly lose power, the elevator must still be able to stop safely.
Elevators include a fail-safe braking system: the emergency brake is normally kept open only when power is supplied. If power is lost, the brake automatically clamps shut, stopping the elevator safely and preventing uncontrolled movement.
These are just a few examples. Elevators include many more mechanisms on the sensors, controllers, mechanical redundancies, and fail-safe designs, all working together to achieve functional safety and protect passengers even when things go wrong.
Safety Standards for design of Elevators
Below are some of the safety standards used when designing elevators
ISO 22201: 2017 - Lifts (elevators), escalators and moving walks - Programmable electronic systems in safety-related applications - This standard is based on IEC 61508 and adapted for elevator applications
A17.3 - Safety Code for Existing Elevators and Escalators - This is a standard followed in North America
EN 81-20:2020 - Safety rules for the construction and installation of lifts - Lifts for the transport of persons and goods - This standard is commonly followed in the European Union.
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