When a serious safety incident at a major UK heavy industrial processing facility triggered a full reassessment of plant-wide protection, Safety Systems Technology (SST) was appointed to redesign the safety-related control system across the site.
Working closely with long-standing partner SICK Sensor Intelligence, SST delivered one of the UK’s largest wide-area safety networks, using SICK Flexi Soft to daisy-chain field devices via Flexi Line and create a facility-wide integrated safety system.
Key Takeaways
- A heavy industrial facility required a verified plant-wide emergency stop capability.
- Existing safety devices were compliant individually but not architecturally integrated.
- SST redesigned the safety-related control system to achieve Performance Level e under EN ISO 13849-1.
- Stop Categories 0 and 1 were assessed per function in accordance with BS EN 60204-1.
- Each safety function was defined within a structured Safety Requirements Specification (SRS).
- Performance Level calculations and validation followed EN ISO 13849-2 principles.
- A complete, version-controlled compliance file was issued to ensure audit defensibility.
- The outcome was a facility-wide safety architecture with demonstrable compliance integrity.
Reassessing Systemic Risk
The requirement was simple to state but complex to deliver: provide a verified means of bringing the entire facility to a safe state without delay, regardless of where a hazardous event originated.
While this resembled a plant-wide emergency stop specification, it in fact required redesigning the safety-related parts of the control system across a geographically distributed production environment.
The Existing Architecture: Functional but Fragmented
The facility processes long, continuous lengths of welded steel profile. Extended conveyor systems separate machinery groupings across significant distances, and the kinetic mass of moving sections makes stopping behaviour a critical safety variable.
Historically, safety functions were implemented at equipment level. Pull-cord devices ran along conveyors, and individual machines incorporated local stop circuits. Each was compliant in isolation, but no unified safety architecture existed.
The consequences were predictable: emergency stops confined to local zones, independent reset logic, no coordinated plant-wide stop function, and limited system-level diagnostics.
Under PUWER 1998, emergency stop controls must bring dangerous movement to a safe condition as quickly as reasonably practicable. In distributed environments, compliance depends not only on device presence, but on the integrity of the architecture connecting them.
SST’s Engineering Methodology
SST’s role extended beyond hardware selection. The project required a structured safety engineering process aligned with UK regulatory expectations and EN ISO 13849-1.
Existing risk assessments were reviewed and refined to define each safety function clearly. Required Performance Levels were determined based on severity, exposure frequency and possibility of avoidance.
Stop category selection was assessed function by function. Uncontrolled stops (Category 0) and controlled stops with power maintained until standstill (Category 1), as defined in BS EN 60204-1, were applied according to hazard type and machine behaviour. On a heavy industrial line moving significant mass, stopping time and stopping distance directly influence safeguard positioning, zoning boundaries and access control measures.
This analysis defined the zoning structure and established the requirements for the safety-related control system. A programmable, network-capable safety controller was necessary to implement the defined functions while maintaining integrity across the site. Delivering this required coordinated safeguarding strategy and safety-related control system design, integrating specialist guarding design with advanced electrical engineering to create a coherent, compliant plant-wide architecture.
Technical Collaboration with SICK
SST has long worked with SICK Sensor Intelligence on machinery safety applications across demanding sectors.
For this project, SST engineers collaborated with SICK’s UK technical specialists to design an architecture capable of maintaining safe communication integrity across long industrial spans, supporting distributed I/O within coordinated safety logic, achieving Performance Level e under EN ISO 13849-1, and delivering structured diagnostics plant-wide.
The chosen platform was SICK’s Flexi Soft modular safety controller. Selected for its suitability in distributed safety networks, Flexi Soft enabled field devices to be daisy-chained via Flexi Line without compromising deterministic safety communication. The result was a facility-wide integrated system supported by jointly developed controller configuration and zoning logic.
Integrating Protective Devices Through Flexi Soft
With the architectural framework defined, SST implemented the safety functions through the Flexi Soft platform, integrating protective devices within a coordinated control structure.
Safety light curtains were connected at defined hazard zones, with blanking and muting applied selectively to prevent nuisance stops while maintaining reliable personnel detection. Mechanical and non-contact interlocks on guards, gates and doors were configured to initiate safe stops on opening, with guard locking applied where stopping time analysis required access prevention until confirmed standstill.
Laser scanners, emergency stop pushbuttons and two-hand controls were incorporated against clearly defined safety functions rather than introduced as generic protection. Protective measures were therefore implemented systematically within a unified architecture rather than layered incrementally.
From Discrete Devices to Coordinated Safety Logic
A network of local control panels created four operational zones across the facility. These were connected to a new panel in the main welding house, enabling site-wide initiation of a safe state and coordinated reset once safe conditions across all zones were verified.
The entire facility can now be brought to a safe state within response times defined by the assigned stop category for each function, regardless of hazard origin.
Safety functions operate within a single coherent control system rather than as independent subsystems. Real-time system overview via PLC and HMI provides transparency for engineering and operations teams, supporting fault diagnosis, validation confidence and ongoing compliance management.
Functional Safety Integrity
The system was specified to achieve Performance Level e under EN ISO 13849-1, reflecting the risk profile identified during assessment.
Each safety function was documented within a structured Safety Requirements Specification. Performance Level calculations were recorded as part of the project file, and validation followed EN ISO 13849-2 principles, with defined fault-condition testing to confirm correct behaviour.
Compliance is demonstrable through evidence rather than assertion.
Implementation in a Live Facility
Commissioning was sequenced to minimise disruption. Migration from legacy circuits was controlled, and each zone underwent functional testing before global integration.
Documentation and Governance
Engineering integrity depends on defensible documentation.
SST provided a complete compliance file including:
- Safety Requirements Specification
- Performance Level calculations
- Validation and test records
- As-built Flexi Soft configuration
All documentation was version-controlled, with formal change management applied during commissioning. The client retains a complete audit trail linking each safety function to its specification, calculated performance, validation evidence and installed configuration.
Outcome
If You Are Reviewing Distributed Safety
The facility transitioned from fragmented local safeguards to a verified, performance-classified safety architecture with immediate plant-wide stop capability, coordinated reset logic, structured zoning, real-time diagnostics and capacity for future expansion.
Shop floor operators now experience consistent and predictable emergency response behaviour. Engineers gained structured diagnostic visibility. Senior management gained confidence that compliance is supported by documented evidence.
If your distributed safety arrangements have evolved over time, their architectural integrity should not be assumed.
SST can undertake a structured technical review to assess compliance status, performance level validation and audit defensibility.
