Where Trapped Key Solutions Win in Safety!

History of Trapped Key Interlocking 

Trapped key interlocking has been keeping people safe from hazardous energy and environments for over 100 years. A trapped key interlock safety solution ensures that a pre-determined sequence of operations is followed each time and cannot be circumvented or short cut. The transfer of uniquely coded keys ensures that personnel remain safe throughout the process and eliminates human error.

The concept of trapped key interlocking (TKI) dates back to 1893 when French inventor Paul Bouré created engagement locking devices to ensure safe track switching operations. Two years later, Trayvou manufactured interlocking devices for the manufacturing and railway industry. In 1922, an Englishman by the name of James Harry Castell designed the first interlocking system to protect the people and assets during the electrification of London. In the United States, Ralph Levering Kirk was the first to pioneer the use of key interlocking on circuit breakers and switches in early 1930’s.

Where Trapped Key Solutions Win 

Trapped Key Interlock solutions provide a fixed mounted safety solution, customized to the user’s specific application needs, equipment, and processes.  Interlocks are designed to withstand harsh environments and heavy applications where alternative solutions such as safety switching and sensing technology may not perform consistently; and in hazardous situations, failure of a safety solution is not an option!

Trapped key interlocking systems are mounted directly to equipment, gating, and access doors and does not require field wiring or cabling around machinery, assets, or equipment. In many cases, equipment power will be isolated via a key switch mounted on a control panel or isolation unit, keeping all the electrical wiring well away from the hazardous areas. KIRK’s trapped key interlocking products are built to the highest quality, and are extremely robust, being able to withstand harsh conditions such as high temperatures, adverse weather, debris, and even wash down areas. They require little maintenance and are proven to work in challenging environments.

While trapped key interlocking was originally introduced in railway track switching applications, the technology of trapped key systems has continued to develop and is now utilized in many applications across all sectors. From machine guarding safety in industrial applications, operations and maintenance of switchgear, both HV and MV/LV, and even in logistics and warehousing preventing accidents during loading/unloading activities, trapped key interlocking solution can be found.

How a Trapped Key Solution Works

A trapped key interlocking solution consists of 3 defined actions: isolating hazardous energy, transferring or exchanging sequenced keys, and accessing the protected area or equipment.  Interlocks are designed specifically with these action in mind to ensure the comprehensive solutions operates effectively.

An isolation interlock is typically the initiating interlock and ensures the isolation of power.  Once the equipment is de-energized, the interlock key is turned, engaging the bolt, blocking the power switch, and releasing the key.  The interlock is now a physical barrier to preventing the equipment from being re-energized.

Now that power has been isolated, the released key can be taken to a transfer or exchange interlocks where there the access keys are trapped awaiting the introduction of the initiating key from the isolation interlock.  Once the initiating key has been inserted and turned in the transfer block, the access key(s) are now released, and the initiating key is trapped.

The access key(s) can now be taken to the access points and inserted into the access interlock(s). Personnel can safely enter the area with peace of mind that the power has been fully isolated and cannot be re-energized until the trapped key solution is followed in reverse.  The video below demonstrates a simple scheme for safely accessing a restricted area.


Trapped key interlocking systems have been keeping people safe at work for over 100 years. Advancements in technology, the need for real-time data, and remote management is changing the way businesses look to improve on their efficiencies and productivity. We are working to incorporate these technologies into our trapped key solutions with Smart Key Management Systems and Warehouse Insight Systems.  Trapped key safety solutions will remain relevant and often may be the best safety solution especially when it comes to harsh environments and heavy applications where the need to withstand adverse conditions is required.

For more information, contact sales@kirkkey.com