Door interlocks

Mechanical Door Interlocks for Trapped Key Interlock Systems

What is a mechanical door interlock?

Mechanical door interlocks are physical access-control modules within a trapped key interlock system. They block access to hazardous areas and only allow doors or hatches to open once a specific coded key has been released through prior energy isolation. These interlocks operate fully mechanically, require no wiring, and provide a robust, fail-safe solution for controlled access in industrial installations.

How is a mechanical door interlock used in a trapped key system?

Within a trapped key interlock system, the door interlock receives a key released after isolating an energy source, such as electrical power or pneumatic pressure. Only after this key is inserted and turned will the actuator unlock and the door open. As long as the door remains open, the key is mechanically trapped, preventing the machine from being restarted.

DM, DMS and DMSK mechanical door interlocks

Mechanical door interlocks in the Fortress Safety mGard series are available in several variants:

• DM: heavy-duty zamac (metal alloy) construction
• DMS: full 316 stainless steel for corrosive or outdoor environments
• DMSK: hygienic 316 stainless steel, designed for food and pharmaceutical applications

These variants are suitable for demanding industrial conditions including ATEX zones, washdown processes, vibration-intensive areas and dusty environments.

Safety level and compliance

All door interlocks are TÜV-certified and suitable for high-demand safety architectures:

• PL e according to EN ISO 13849-1
• SIL 3 according to EN IEC 62061
• EN ISO 14119 compliant for coded mechanical interlocking

Retention force and mechanical durability

All models are tested to a retention force of 7,500 N and designed for long-term operation in heavy-duty industrial environments. Their mechanical construction ensures resistance to moisture, dust, vibration and extreme temperatures.

Application guidance per variant

• DM: general industrial applications with moderate corrosion exposure
• DMS: outdoor installations, washdown areas, chemical processes
• DMSK: smooth hygienic design for food/pharma (CIP/WIP washdown)

Actuator options for different door types

The door interlocks support a wide range of actuator types for various door constructions:

• DM-F: fixed actuator for hinged doors with a small opening radius
• DM-H / DM-A: handle actuators for sliding doors or large misalignment tolerance
• DM-C: compressible actuator for flexible or lightly deforming guard systems
• DM-S: self-aligning actuator for movement along hinges or rails

The head of each door interlock can be rotated in four positions (90° increments), ensuring flexible mounting across different guarding layouts.

Use in explosive atmospheres

DM, DMS and DMSK door modules are suitable for Ex zones 1, 2, 21 and 22. With no electrical parts and a robust mechanical design, they are ideal for gas- and dust-explosion environments.

Key advantages of mechanical door interlocks

• Fully mechanical operation: no wiring, PLC integration or electrical supervision
• Trapped key functionality: the key remains trapped while the door is open
• 200,000 unique key codings with optional laser engraving
• High reliability: immune to EMI, vibration, humidity and contamination
• Retrofit-friendly: straightforward installation on existing machinery

Use in partial-body access applications

Door interlocks such as DM or DMS are suitable for partial body access applications, including inspection hatches and service access. For full-body access, we recommend adding a personal safety key to prevent restart while personnel are inside the hazard zone. This accessory is available separately within the mGard system.

Installation and mounting

Mechanical door interlocks are straightforward to install thanks to standardized mounting patterns. Accessories are available for integrating the modules into guarding systems such as Troax or Axelent. The modular design allows easy expansion of existing trapped key interlock systems.

Why choose door interlocks from MachineSafety-Shop?

• Official Fortress Safety distributor with full engineering support
• Fast delivery of standard and stainless steel variants
• Complete range of components for trapped key interlock systems
• Solutions for Ex zones, hygienic applications and heavy-duty industries

Technical advice and engineering support

Our machine safety specialists can assist in selecting the correct door interlock for your trapped key architecture. Whether you are implementing a single access point or a complex multi-energy, multi-door system, we advise based on required PL/SIL levels, environmental conditions and machine functionality.