Entrapment protection

Prevent Entrapment and Unintended Restart When Entering Guarded Machinery

Why preventing entrapment in machine spaces is critical

Entrapment of operators or technicians inside guarded machine zones is a major safety hazard in industrial environments. During maintenance, troubleshooting or cleaning, personnel may enter areas that are normally protected by safety guards. Without a dedicated entrapment-prevention solution, there is a risk that the machine could be restarted while someone remains inside the hazard zone. This can lead to severe injury or fatal accidents. A mechanical entrapment-prevention system is therefore an essential component of any compliant safety architecture.

What is an entrapment-prevention system?

An entrapment-prevention system is a fully mechanical safety mechanism that ensures an operator cannot be locked inside a hazardous area. It works using a mechanical trapped key interlock sequence with a mandatory personal safety key. When entering the safeguarded area, the operator removes the safety key and keeps it on their person. As long as this key is not returned, the access door cannot be fully closed and the machine cannot be re-energised. This provides guaranteed protection against unintended restart.

Where is entrapment protection used?

Entrapment-prevention systems are used in:

• Fully automated production lines
• Robot cells with perimeter guarding
• Conveyor systems and bulk-handling equipment
• Hazardous process zones in food, chemical and pharmaceutical plants

Wherever a safety door allows access to an area with restricted visibility, a mechanical entrapment-prevention system is the most reliable solution.

How does a mechanical entrapment system work?

A mechanical entrapment solution operates through a trapped key interlock system. When energy is isolated, a key is released from the isolator or safety switch. This same key becomes the personal safety key and must remain with the operator while inside the hazard zone. Without this key, the door cannot be closed and the machine cannot restart, making unintended energisation mechanically impossible.

Mechanical entrapment protection with ALPHA and BRAVO modules

To prevent unintended restart when entering guarded zones, the ALPHA and BRAVO modules from Unique Safety Products provide a fully mechanical interlock solution.

The ALPHA module is available for both hinged and sliding doors. The personal safety key prevents complete door closure until it is returned. As long as the key is removed, safety interlock switches cannot re-engage, ensuring that the machine remains de-energised.

The BRAVO module is designed specifically for safety light curtains. It mechanically blocks the light beam via a shutter plate. The light curtain is physically prevented from clearing until the operator returns, inserts the key, and resets the mechanism.

Both systems are:

• Fully mechanical with no wiring required
• Manufactured from 316 stainless steel for demanding industrial and hygienic environments
• Suitable for retrofit installation on existing hinged or sliding doors and light curtains
• Extremely simple to install and configure

Why choose a mechanical solution?

Unlike electronic solutions, a purely mechanical entrapment system provides maximum reliability in harsh conditions such as moisture, dust or explosive atmospheres (ATEX). Without wiring, sensors or software, the system is tamper-resistant, maintenance-free and highly suited for retrofitting existing machines.

Key advantages

• Prevents restart as long as the operator is inside the hazard zone
• No wiring or electrical components required
• Maintenance-free and mechanically robust
• Suitable for ATEX zones and hygienic environments

Example application: preventing entrapment in a robot cell

In a robot cell with multiple access points, a key-operated isolator is combined with a BRAVO entrapment device. After isolation, the operator removes the key and carries it inside the cell. This key must be returned before the cell can be reclosed and re-energised. This simple but highly effective mechanical sequence prevents unintended restart and improves safety without adding complexity.

Technical support from our machine-safety specialists

Our experts can help you select the correct entrapment-prevention system for your machinery. Whether you require a solution for a single access door or a multi-zone installation, we design a complete trapped key sequence to eliminate entrapment and unintended restart risks. Let us advise you based on your risk assessment and machine layout.