The Challenge: No Two Doors Should Open Simultaneously


Ensuring the safety of visitors, animals, and zookeepers, is a great challenge across zoos. For this critical task, the Amersfoort Zoo (Netherlands) entrusted Fortress Safety solutions, in collaboration with our channel partner Unique Safety Products (USP), to enhance the safety of their spectacled bear enclosure.


The zoo needed a robust system that would guarantee that two doors or hatches adjacent to the same room in the bear enclosure could never be opened simultaneously – a crucial requirement for avoiding potential accidents, especially given the unpredictable nature of wild animals. The absence of such a solution in fact could lead to potentially life-threatening situations where personnel are directly in contact with bears.


Bear enclosure at Amersfoort Zoo with doors and hatches

The Solution: Trapped Key Interlocking


The bear enclosure consists of different sections: an outdoor enclosure, a separation area, and two indoor enclosures. Each section was outfitted with doors accessible to the zookeepers.


USP proposed the use of the mGard Trapped Key System from Fortress Safety. With precise design and functionality, the system operates by releasing and trapping uniquely coded keys in a predetermined sequence. This prevents the opening of two adjoining doors or hatches at once.


The use of mechanical keys eliminates most of the electrical wiring associated with other types of interlocks, making mGard cost effective and easy to install and maintain. Keys and lock covers can be engraved and customised with different colour variations.

For Door A: To enter the separation area through door A, keys from the three hatches (coloured in red, orange, and blue respectively) are necessary. Each hatch must be closed to release its key. Only when all the keys are inserted in the interlock on door A, the door can open.

With door A open, the red, orange, and blue keys remained trapped in the lock, ensuring hatches cannot be operated.


An added layer of protection came in the form of a personnel key (coloured in yellow). By taking the key inside with them, a zookeeper ensures they wouldn’t accidentally get locked inside the enclosure.


For Other Doors: Similar systems were in place for doors B, C, D, and E. For instance, door B only opens when the keys from the blue, white and green hatch are inserted. This ensures that none of these hatches can be opened at the same time as door B.

Separation area bear enclosure with mGard interlocks

Bear enclosure zoomed in area with mGard interlocks

Outcome of the Partnership


Throughout the installation process, experts from Fortress Safety worked closely with the Unique Safety Products team, offering advice and ensuring optimal operation.


The implementation of mGard mechanical interlocks with trapped keys led to:


✅ Ensured safety for personnel, reducing the risk of accidental interactions with the bears

✅ Boosted confidence in staff, knowing they were protected by a state-of-the-art safety system

✅ Further implementations across Amersfoort zoo for different animal enclosures


Facing a complex challenge, Amersfoort Zoo turned to Unique Safety Products and Fortress Safety for a solution. This partnership not only elevated the safety at the zoo but also set a benchmark for similar establishments worldwide. You can see more examples of how our products have been used in zoo applications by visiting the USP website.


To find out more about the mGard range of mechanical interlocks click on the button below or get in touch.