Providing Safety
Prevent Entrapment

Preventing entrapment

Prevent an accidental restart and entrapment in a hazardous safeguarded area.

Entrapment danger is when a person is together with a machine in a safeguarded area while the machine is being started or reset. It may sound logical, not to turn on dangerous machinery when your colleague is near it. But there is not always an unobstructed view within the safeguarded and shielded area from the start or reset device, as a result workers may go unnoticed or be overlooked.

ISO 102018-2 Robots and Robotic Devices

Methods for preventing entrapment

Safeguard a shielded area against containment

Entrapment danger prevention
Time-limited reset devices
Push button or key switch within the
installation prevents the machine from being switched on
by anyone outside the safeguarded area.
Interlocking the door switch
Lock the door switch in the open position, so that it cannot be closed by anyone outside the safeguarded area.
Audiovisual pre-reset
Signal lights and acoustic signals
indicate when a machine is switched on
is switched on and gives the operator the chance to leave the area
to leave in time.

Locking in the open position
Prevent doors from closing with interlock blocking devices.

Time-limited reset devices
Push button or key switch within the
installation prevents the machine from being switched on
on by anyone outside the safeguarded area.

The lock room

Locking in the open position
Entrapment device for light curtains
ensures that the beams of a light curtain
remain interrupted as long as an operator
is present in the safeguarded area.

Using presence detection
Therefore, it is important initially to always try to prevent entrapment. If creating an unobstructed view is not possible, this can be done by using presence detection through the use of a laser scanner, pressure mats or radar safety. However, in reality, this is often difficult to achieve due, for example, to external environmental factors or the fact that many optical safety sensors do not meet the required level of safety.

Section 5.6.3.4 from ISO 102018-2 Robots and Robotic Devices states the following:

“To ensure that no one is in the safeguarded area before starting/resetting, use the first achievable option from the following enumeration.”

  • Unobstructed view
  • Presence detection
  • Isolation & locking
  • Locking in open position
  • Time-limited reset devices
  • Audiovisual pre-reset

LOTOTO is therefore particularly used during maintenance operations, as the machine is standing still for too long for short-term inspection and cleaning work. Another disadvantage of LOTO is that it is not compulsory but a completely procedural way of safety, where mistakes can easily be made.

Interlock blocking device
Installing an interlock blocking device on access doors ensures that they can be locked in the open position when someone is in the guarded area. This blocking device ensures that the safety contacts of the installed safety switch cannot be activated and restarted. This safeguard must therefore only be capable of being unlocked by the person who is in the protected area carrying out the work. This can be done by using a safety key which the worker removes from the lock and takes with him into the safeguarded area.

It is also possible to take measures against entrapment within the protected area. To do this, you can use a time-limited reset device. This prevents the machine from being restarted or reset from outside the safeguarded zone. Upon activation, this pre-reset allows the operator to exit the protected zone via a pre-programmed delay.

Additional safety support, a warning light
In addition, it is possible to use an audiovisual pre-reset, such as a signal light with a siren. This will indicate when the machine is switched on and will allow the operator to leave the area in time. However, this solution by itself is not very effective, but can be used well as an additional tool to prevent the risk of entrapment.

With all these available solutions, entrapment in a safeguarded area should certainly be preventable. Which measures are needed for your situation depends on the risk analysis and the level of safety that needs to be achieved.

If you have any questions or would like advice from one of our safety experts, they are always at your service. We also have a range of entrapment devices for doors and light barriers available in our webshop www.machinesafety-shop.com.

Products used in this application:

Safety radar system

For walk-in and person detection in a safeguarded area.

Interlock blocking

Mechanical device against trapping people in a safeguarded area. 

Signal lights

Inform users about the status of the machine.

Lockout-Tagout

Lockout-Tagout equipment for safe maintenance of machinery.

Atom

Compact robust heavy duty safety switch.
 

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