P2: Safety Instrumented System (SIS) Integration

Overview

The SIS Integration package provides tools for analyzing Safety Instrumented Functions (SIFs) and performing Layer of Protection Analysis (LOPA) per IEC 61508 and IEC 61511 standards.

Key Classes

SafetyInstrumentedFunction

Models a single SIF with its components and calculates PFD (Probability of Failure on Demand):

SafetyInstrumentedFunction sif = new SafetyInstrumentedFunction(
    "SIF-001",                    // SIF ID
    "HP Separator PAHH Shutdown"  // Description
);

// Set SIL target
sif.setSILTarget(2);  // SIL 1, 2, 3, or 4

// Configure architecture
sif.setArchitecture("1oo2");  // Options: "1oo1", "1oo2", "2oo2", "2oo3", "1oo3"

// Set component PFDs
sif.setSensorPFD(0.01);        // Pressure transmitter PFD
sif.setLogicSolverPFD(0.001);  // SIS logic solver PFD
sif.setFinalElementPFD(0.02);  // Shutdown valve PFD

// Set proof test interval
sif.setProofTestInterval(8760);  // Annual testing (hours)

SIL Ranges

SIL PFDavg Range RRF Range
SIL 1 0.1 - 0.01 10 - 100
SIL 2 0.01 - 0.001 100 - 1,000
SIL 3 0.001 - 0.0001 1,000 - 10,000
SIL 4 0.0001 - 0.00001 10,000 - 100,000

Calculating PFD

// Calculate PFDavg
double pfdAvg = sif.calculatePFDavg();
System.out.println("PFDavg: " + pfdAvg);

// Get achieved SIL
int achievedSIL = sif.getAchievedSIL();
System.out.println("Achieved SIL: " + achievedSIL);

// Risk Reduction Factor
double rrf = sif.calculateRRF();
System.out.println("RRF: " + rrf);

SIL Verification

SILVerificationResult result = sif.verifySIL();

System.out.println("Target SIL: " + result.getTargetSIL());
System.out.println("Achieved SIL: " + result.getAchievedSIL());
System.out.println("Verified: " + result.isVerified());

// Check for issues
if (result.getIssues().size() > 0) {
    System.out.println("Issues:");
    for (String issue : result.getIssues()) {
        System.out.println("  - " + issue);
    }
}

SISIntegratedRiskModel

Combines SIFs with other protection layers for LOPA analysis:

SISIntegratedRiskModel model = new SISIntegratedRiskModel(
    "Separator Overpressure Protection"
);

// Define initiating event
model.setInitiatingEventDescription("Loss of cooling leading to overpressure");
model.setInitiatingEventFrequency(0.1);  // per year

// Set consequence category (per risk matrix)
model.setConsequenceCategory("C4");  // Major safety/environmental
model.setTargetMitigatedFrequency(1e-5);  // Target frequency

Adding Independent Protection Layers (IPLs)

// Add non-SIS protection layers
model.addIPL("BPCS High Pressure Alarm", 10);     // RRF = 10, PFD = 0.1
model.addIPL("Operator Response", 10);             // RRF = 10
model.addIPL("PSV Relief System", 100);            // RRF = 100, PFD = 0.01

// Add Safety Instrumented Function
SafetyInstrumentedFunction sif = new SafetyInstrumentedFunction("SIF-001", "PAHH");
sif.setSILTarget(2);
sif.setArchitecture("1oo2");
sif.setSensorPFD(0.01);
sif.setLogicSolverPFD(0.001);
sif.setFinalElementPFD(0.02);
model.addSIF(sif);

Performing LOPA

LOPAResult lopa = model.performLOPA();

System.out.println("Initiating Event Frequency: " + 
    lopa.getInitiatingEventFrequency() + " /year");

System.out.println("\nProtection Layers:");
for (LOPAResult.ProtectionLayer layer : lopa.getProtectionLayers()) {
    System.out.println("  " + layer.getName() + 
        ": PFD=" + layer.getPFD() + 
        ", RRF=" + layer.getRiskReductionFactor());
}

System.out.println("\nMitigated Frequency: " + 
    lopa.getMitigatedFrequency() + " /year");
System.out.println("Target Frequency: " + 
    lopa.getTargetFrequency() + " /year");
System.out.println("LOPA Status: " + 
    (lopa.isAcceptable() ? "PASS" : "FAIL"));

// Required SIF performance
System.out.println("Required SIF RRF: " + lopa.getRequiredSIFRRF());

LOPA Calculation

The LOPA calculation follows:

Mitigated Frequency = IE × PFD_IPL1 × PFD_IPL2 × ... × PFD_SIF

Where:
- IE = Initiating Event Frequency
- PFD_IPLn = Probability of Failure on Demand for each IPL
- PFD_SIF = PFDavg for the Safety Instrumented Function

Use Cases

1. SIF Design Verification

// Define SIF requirements
SafetyInstrumentedFunction sif = new SafetyInstrumentedFunction(
    "SIF-101", 
    "Compressor High Vibration Shutdown"
);
sif.setSILTarget(2);

// Try different architectures
String[] architectures = {"1oo1", "1oo2", "2oo3"};
for (String arch : architectures) {
    sif.setArchitecture(arch);
    sif.setSensorPFD(0.02);
    sif.setLogicSolverPFD(0.001);
    sif.setFinalElementPFD(0.03);
    
    int achieved = sif.getAchievedSIL();
    System.out.println(arch + ": Achieved SIL " + achieved + 
        (achieved >= 2 ? " ✓" : " ✗"));
}

2. Complete LOPA Study

// LOPA for high-pressure scenario
SISIntegratedRiskModel model = new SISIntegratedRiskModel("HP LOPA Study");

// Scenario definition
model.setInitiatingEventDescription("Blocked outlet + heat input");
model.setInitiatingEventFrequency(0.5);  // Expected once every 2 years
model.setConsequenceCategory("C5");      // Catastrophic

// IPLs
model.addIPL("BPCS High Pressure Trip", 10);
model.addIPL("Manual Intervention", 10);
model.addIPL("PSV-101 Relief", 100);

// SIF
SafetyInstrumentedFunction sif = new SafetyInstrumentedFunction(
    "SIF-001", "PAHH with ESD Valve");
sif.setSILTarget(2);
sif.setArchitecture("1oo2");
sif.setSensorPFD(0.01);
sif.setLogicSolverPFD(0.001);
sif.setFinalElementPFD(0.015);
model.addSIF(sif);

// Run LOPA
LOPAResult result = model.performLOPA();
System.out.println("Final mitigated frequency: " + 
    result.getMitigatedFrequency() + " /year");

3. SIF Inventory Management

// Manage multiple SIFs
SISIntegratedRiskModel platform = new SISIntegratedRiskModel("Platform SIS");

// Add all platform SIFs
SafetyInstrumentedFunction[] sifs = {
    createSIF("SIF-001", "Separator PAHH", 2),
    createSIF("SIF-002", "Compressor Vibration", 1),
    createSIF("SIF-003", "Gas Detection ESD", 3),
    createSIF("SIF-004", "Fire Detection", 2)
};

for (SafetyInstrumentedFunction sif : sifs) {
    platform.addSIF(sif);
    SILVerificationResult result = sif.verifySIL();
    String status = result.isVerified() ? "✓" : "✗";
    System.out.println(status + " " + sif.getSifId() + 
        ": Target SIL " + sif.getSILTarget() + 
        ", Achieved SIL " + result.getAchievedSIL());
}

Output Format

JSON Export

String json = model.toJson();

Example output:

{
  "modelName": "HP Separator Protection LOPA",
  "initiatingEvent": {
    "description": "Blocked outlet with heat input",
    "frequency": 0.5
  },
  "consequenceCategory": "C5",
  "targetFrequency": 1.0e-6,
  "protectionLayers": [
    {"name": "BPCS High Pressure Trip", "type": "IPL", "pfd": 0.1, "rrf": 10},
    {"name": "Manual Intervention", "type": "IPL", "pfd": 0.1, "rrf": 10},
    {"name": "PSV-101 Relief", "type": "IPL", "pfd": 0.01, "rrf": 100},
    {"name": "SIF-001 PAHH ESD", "type": "SIF", "pfd": 0.0065, "rrf": 154}
  ],
  "lopaResult": {
    "mitigatedFrequency": 3.25e-7,
    "targetMet": true,
    "margin": 3.08
  },
  "sifs": [
    {
      "sifId": "SIF-001",
      "description": "PAHH with ESD Valve",
      "silTarget": 2,
      "silAchieved": 2,
      "verified": true,
      "architecture": "1oo2",
      "pfdAvg": 0.0065,
      "rrf": 154
    }
  ]
}

Best Practices

  1. Conservative IPL Selection: Only credit IPLs that are truly independent and have documented PFD values

  2. Architecture Selection: Use redundant architectures (1oo2, 2oo3) for higher SIL requirements

  3. Proof Testing: Shorter proof test intervals reduce PFD but increase operational costs

  4. Common Cause Failures: Account for CCF in redundant systems using beta factor method

  5. Documentation: Maintain complete LOPA worksheets for regulatory compliance

Standards References