exida Case Studies

Case Study

Functional Safety Lifecycle Gaps Closed at Greenfield Fertilizer Facility

exida® helps a chemical producer close gaps in functional safety design and implementation before hazards are introduced to the process.


Iowa Fertilizer Company, Wever, IA USA


Identifying gaps in IEC 61511/ISA 84 implementation and effecting resolution rapidly


Perform a gap assessment against IEC 61511/ISA 84 requirements and systematically work through the lifecycle to close the gaps. Establish procedures and processes to support IFCo into the Operation and Maintenance phase of the functional safety lifecycle.


Iowa Fertilizer was able to start up the facility with the confidence that the functional safety lifecycle is compliant with IEC 61511/ISA 84 requirements to Stage 3 FSA and that process risk is effectively managed across the facility.

The Iowa Fertilizer Company (IFCo) facility in Weaver, IA is a world-scale greenfield fertilizer plant with a capacity of up to 3 million metric tons of nitrogen fertilizers.  Contracted by a global producer of fertilizers and industrial chemicals, a project management team and multiple engineering design firms were to deliver a turnkey facility. Prior to start-up the operations team conducted a thorough review of the project design documentation and contacted exida for assistance in addressing potential gaps with the HAZOP and LOPA records. The gaps raised concern about the adequacy of the Safety Instrumented System (SIS) including the potential for previously unidentified risk, insufficiently mitigated risk, and incomplete implementation of the functional safety lifecycle. The owner’s intent was for the facility to be ANSI/ISA 84 (IEC 61511) compliant. As the project documentation was reviewed, it became apparent that contractors had a very different expectation on how to achieve compliance. A key lesson learned is the importance of beginning with a Functional Safety Management Plan to guide all contractors and technology providers on the owner’s expectations for implementation of the Functional Safety Management Lifecycle.

exida provided IFCo with assistance in identifying and closing gaps in all phases of the Functional Safety Lifecycle. These include:

  • Hazards and Risk Assessment and Allocation of Safety Function to Protection Layers: When IFCo operations team completed a compliance phase HAZOP, they identified safety and/or environmental consequences that were not addressed in the technology providers project phase HAZOPs, and observed inconsistencies in the SIL targeting methodology between the vendors.  exida® was contracted to facilitate a LOPA with the operations team using a consistent methodology. Significant outcomes include:
    • 108 interlocks identified by vendors as SIFs were re-classified as critical process interlocks (CPI). These were primarily located in packaged equipment control systems that were not designed to meet SIS standards. Risk reduction credit applied in the LOPA is that of a BPCS protection layer. CPIs will be managed in operating and maintenance phases as Independent Protection Layers (IPL) to ensure they remain effective, independent and auditable.
    • SIL 3 SIFs were eliminated by providing alternate IPLs to reduce scenario risk.
    • 20 SIFs were eliminated by providing alternate IPLs to reduce scenario risk.
    • SIL 1 and SIL 2 SIF count was reduced by nearly 75%, reducing the lifecycle cost significantly.
    • LOPAs considered all initiating events together allowing an accurate assessment of SIF demand  
  • Safety Requirements Specification (SRS): exida® developed a complete SRS document for the safety logic solver. An SRS was prepared for each SIF incorporating information from vendor packages.
  • Design and Engineering: Where preliminary verification identified non-compliance in the original design and equipment selection, exida® performed optional analysis to evaluate alternate equipment and redundancy requirements.
  • Verification: exida® performed preliminary and final design verification.
  • Functional Safety Assessment (FSA): exida® performed a functional safety lifecycle gap assessment to identify any gaps that needed to be closed prior to beginning of operations. A stage 3 FSA was completed once the gaps confirming full compliance with IEC61511/ISA 84 through the installation, commissioning and validation phase, had been addressed.
  • Maintenance and Testing Procedures: exida® developed proof test procedures for each SIF.
  • Validation: exida® reviewed results of initial proof tests and witnessed a sampling of tests as they were conducted.
  • Management and Assessment: exida® prepared an equipment library in SILStat™ to enable IFCo to track key operational information and analyze the data as required by IEC 61511 /ISA 84.

This project is the subject of the paper “Functional Safety Management Planning” jointly authored by exida and Iowa Fertilizer and presented at the 2017 Mary Kay O’Connor Process Safety Symposium.