📋 Case Study
Ethylene Oxide Sterilization Facility QRA and Bow-Tie Implementation
Regulatory pushback on offsite risk due to proximity to residential area (≤500 m)
🏗️ Project Overview
New 12-ton EO storage and sterilization unit in North Carolina pharmaceutical campus
🎯 Challenge
Regulatory pushback on offsite risk due to proximity to residential area (≤500 m)
🔧 Design Approach
Full QRA using ALOHA/PHAST; implemented double-containment EO tanks, nitrogen inerting, explosion-proof ventilation, and community alert system linked to fixed gas detectors
📐 Design Diagram
AI-generated project design illustration
📐 Key Calculations
Frequency × Fatality Probability × Population Density
Result: 1.8×10⁻⁵ /yr
Below EPA’s 1×10⁻⁶ benchmark after mitigation
Vapor Cloud Ignition Probability
Leak rate × ignition source density × dispersion persistence
Result: 0.032
Drove inerting design requirement
📊 Results
IR reduced from 4.1×10⁻⁴ to 1.8×10⁻⁵ /yr; permit approval secured in 8 weeks instead of projected 6 months💡 Lessons Learned
- •QRA must include worst-case credible scenarios—not just design basis
- •Community engagement early in QRA builds regulatory trust
- •Inerting effectiveness depends on leak detection speed
✅ Key Takeaways
- 1QRA must include worst-case credible scenarios—not just design basis
- 2Community engagement early in QRA builds regulatory trust
- 3Inerting effectiveness depends on leak detection speed