Ensure safety with IDEM trapped key interlocks

Are safety features at the top of your list of priorities? Of course they are. When you’re controlling access to hazardous machinery in industrial settings and following health and safety regulations, you’ll typically need trapped key interlocks.

We recommend IDEM’s Skorpion trapped key interlock range. It’s particularly used for mechanical coded key safeguarding and interlocking for hazardous machinery and applications. It’s available in stainless steel 316 or die cast.

What is trapped key interlocking and where is it used? 

A trapped key interlocking system traps and releases keys and locks in a predetermined order to ensure a safe sequence of operations. This means increased operator safety and greater safety in the industrial process. 

Trapped key interlocks are widely used to ensure safe access to potentially live or dangerous plant or equipment in an industrial setting.

Here is an example of a trapped key interlock.

- You use a key to isolate a power source, such as a circuit breaker or supply valve.

- This isolation key is then released. You insert it into an access lock to gain access through a gate or door to a high risk area. The isolation key remains trapped until the gate or door is closed. 

- A personnel or safety key can now be released from the access lock. This ensures that the gate or door cannot be closed and the initial key not released until this personnel or safety key is returned (assuming that no duplicate keys are available). 

Benefits of IDEM’s Skorpion trapped key interlock

Safe accessibility 

Safeguarding is the biggest and most obvious benefit of a trapped key interlock. 

By using the interlock you have control over your system and can prevent processes from happening when they shouldn’t. Using the interlock is quick and it’s reliable as you must always go through the correct sequence.

Security and safeguarding 

The trapped key system guards against risk and reduces human error. It prevents shortcuts as the procedure has to be followed for the system to work. For the machine to restart, the isolator key must always be returned to its original position within the lock. There is no way to enable the machine to re-start.

Security is ensured as all keys are coded in the factory, and it is virtually impossible to override the system!

Ultimately, because the process is complex and uncompromising, people are less likely to make errors or put others in the way of harm.

The material

What makes the IDEM trapped interlock system different is the material used: stainless steel. This makes IDEM’s trapped interlock system highly robust with a long and reliable service life.

Suitable for use in different environments

Trapped key interlocks are compatible with many different environments. 

In cleaning environments, for example, this stainless steel trapped key interlock is suitable for CIP and SIP cleaning processes so you can pressure hose and use detergents at high temperatures.

Saving space and resources

No expensive and time-consuming electrical wiring is needed to take up more space. This also makes this trapped key interlock useful in harsh environments and for challenging applications.

The nitty gritty: what does the IDEM trapped key interlock entail?

There are three elements to a trapped key interlock system: isolation, key exchange and interlocking. 

Product news
IDEM trapped key system in use, illustrating when keys can be released


First, isolate machine power before you access machinery that could be dangerous or hazardous. To do this, you release the coded mechanical keys in a pre-determined sequence, starting with the first key in the system.

Simply turn the isolator key in the isolation switch box (there are different types of isolation switch boxes to choose from) and the power is cut off. 
The isolator key can now be used in the key exchange block or in a single component like a bolt lock. You cannot restore power without putting the isolator key back into the isolator switch box. 

Key exchange

All keys used to control your application can be locked into the key exchange block and are mounted on the guards of the application. 

IDEM key exchanges are available in combinations of 1 key trapped and up to 9 keys which can be released.

Once you have isolated the machine, removing power from the hazard, you can use the isolator key to release these other trapped keys from the exchange block and so gain access to areas. 

To restore power to the machinery or hazard, the keys must be returned and re-inserted into the key exchange block. The isolation key can then be released and re-inserted into the isolation switch block. 


You use this interlocking system when, for example, locking bolts into place. OEM provides two types of IDEM interlocking systems, single and dual key (PLe/Cat4 to ISO13849-1). 

When the single key is ‘trapped’, you can retract the bolt by hand. When the key is taken out, the bolt is extended and locked back into position – like a normal key system. You then place the key into the isolator switch box or, if you have a multi-key system, the exchange system.

Dual key interlocking works differently. You can only retract the bolt when the second key is inserted and trapped into the bolt interlock. If you trap the second key and release the first key, the bolt stays retracted. 

This means, for example, that the person can take the first key to the guarded area knowing the bolt is safely retracted. The first key must be replaced and turned in the interlock in order for the second key to be released and the bolt extended. Now, you can put the second key back into the isolator switch or key exchange system and power can be started up again. 

Application details

The trapped key components you require will depend on the system you are controlling. 

If your application has more than one source of power or more than one circuit breaking element that needs actuating, you will need a key exchange box. This is as all keys must be transferred and locked in before the access key can release and transfer to the guard lock.

An exchange box will also work if you have more than one guard, by using an equivalent number of access keys. If you require a number of operations to be carried out in a definite sequence, the transferable key is locked in and exchanged for a different key at each stage.


We would be pleased to discuss your requirements with you. Email [email protected] or call 0116 284 9900 to talk to our specialist sensors and safety team.

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