Preventing unexpected machine restart in corrugated board production
How Smurfit Westrock uses ALPHA and BRAVO interlock blocking devices to protect personnel entering safeguarded machine areas.
When personnel enter a safeguarded machine area, it must remain impossible for the machine to restart unexpectedly while someone is still inside.
At the Smurfit Westrock corrugated board production facility in St. Leon-Rot, Germany, ALPHA and BRAVO interlock blocking devices are used to add a mechanical personnel-key and lockout step to existing machine safeguards.
ALPHA is used alongside interlocked access doors, while BRAVO is designed for applications protected by compatible safety light curtains. In both cases, the operator removes a personal safety key before entering the safeguarded area. As long as the key remains with the operator, the existing safeguard cannot return to its normal operating state.
This provides a simple mechanical way to help prevent an unexpected restart during machine access, without requiring additional wiring or PLC changes.
The machine safety challenge
Machine safeguards such as interlocked doors and safety light curtains are designed to stop hazardous machine functions when access to a protected area is opened or interrupted. However, an additional risk can arise in applications with full-body access, where a person can completely enter the safeguarded area.
Once the operator has passed the guard or safety light curtain, their presence inside the hazardous area may no longer be detected by the existing safeguard. This means that measures are needed to prevent the safeguard from being reset and the machine from being restarted while someone is still inside.
At the Smurfit Westrock facility in St. Leon-Rot, ALPHA and BRAVO are used as mechanical additions to the existing machine safeguarding. Instead of replacing the existing interlocks or light curtains, the devices add a forced personnel-key step before access.
The operator removes the safety key and takes it into the safeguarded area. Until that key is returned, the existing safeguard cannot return to its normal operating state. This creates a clear mechanical sequence between entering the area and restoring the machine for operation.
How to prevent unexpected restart during machine access
At the Smurfit Westrock facility in St. Leon-Rot, mechanical blocking devices are used alongside the existing machine safeguards to prevent the safeguarding from being restored while a person is still inside the safeguarded area.
The principle is simple: before entering the area, the operator removes a personnel safety key and takes it with them. Removing the key mechanically blocks the existing safeguard from returning to its normal operating state. Only after the operator has left the area and returned the key can the safeguard be restored.
Different blocking methods are used depending on the type of machine safeguard.
How to prevent unexpected restart during machine access
At the Smurfit Westrock facility in St. Leon-Rot, mechanical blocking devices are used alongside the existing machine safeguards to prevent the safeguarding from being restored while a person is still inside the safeguarded area.
The principle is simple: before entering the area, the operator removes a personnel safety key and takes it with them. Removing the key mechanically blocks the existing safeguard from returning to its normal operating state. Only after the operator has left the area and returned the key can the safeguard be restored.
Different blocking methods are used depending on the type of machine safeguard.
ALPHA: interlock blocking for access doors
ALPHA is an interlock blocking device designed for access doors that are already protected by a safety switch or sensor. When the personnel key is removed, ALPHA mechanically prevents the door from returning to the position in which the existing interlock can be reset.
This allows the existing door interlock to remain in place while adding a mechanical personnel-key step for access to the safeguarded area.
BRAVO: photoelectric blocking for safety light curtains
BRAVO is a photoelectric blocking device for applications protected by compatible safety light curtains. When the personnel key is removed, BRAVO mechanically positions a blocking element in the light curtain beam.
The light curtain therefore remains interrupted while the operator has the key, preventing the safeguarding system from being reset until the operator has left the area and returned the key.
Both ALPHA and BRAVO work mechanically alongside the existing machine safeguarding. This makes them particularly suitable for retrofit applications, as no additional wiring or changes to the machine PLC are required.
During a visit to the St. Leon-Rot facility, Santiago Hidalgo from Unique Safety Products Germany saw both solutions in use in the production environment and demonstrated their operation on site. The video in this case study was recorded during that visit and shows how ALPHA and BRAVO are used in practice.
How does it work
Alpha for doors
The Alpha interlock blocking device for hinged and sliding doors works with a safety key.
When a worker needs to enter the machine’s safety zone, they turn the key inside the Alpha, which rotates a blocking plate and prevents the door from closing.
Because the door stays open, the safety switches remain disconnected, and the machine cannot be restarted. Upon entering the safeguarded area, the worker removes the key from the Alpha and takes it with them, ensuring the blocking plate stays in position and the door remains open.
Without the key, no one can close the door or restart the machine, allowing the worker to perform tasks or maintenance without any risk of unintentional reactivation.
Bravo entrapment prevention for light curtains
The Bravo, photoelectric blocking device is designed to block light beams in a safety light curtain system.
By removing the safety key, the Bravo mechanism prevents the machine from resuming operation until the key is returned.
This simple yet robust design effectively eliminates the risk of unexpected restarts, protecting workers who are within the hazardous area.
Our partnership with Smurfit Westrock
Throughout our collaboration, Smurfit Westrock has proven to be an important and forward-thinking client, implementing these safety solutions with impressive results. Seeing the Alpha and Bravo devices in use under real production conditions was both rewarding and informative. Our team takes great pride in contributing to a safer workplace for this major player in the paper packaging sector.
We look forward to continuing our partnership with Smurfit Westrock and refining safety measures in the years to come. By combining sustainable paper production with top-tier safety protocols, the factory sets a high standard for responsible manufacturing—one that not only protects its workforce but also demonstrates a commitment to operational excellence.
