White Paper | Process Safety
Enhancing Process Safety Through a Holistic Approach to Safe Operating Limits
Set operating limits only at the design boundary — or pull them straight from the PHA — and operators are left without the practical, actionable thresholds they need to act before damage occurs.
Authors: Jeffrey Miller, P.E. · Dalton Carey | Focus: SOL development · PHA / LOPA alignment · Corporate guidance | AIChE Global Congress on Process Safety
What’s Covered Here
Why PHAs alone can’t define safe operating limits
Repeatable solutions for PHAs that fall short
Common vulnerabilities in PHAs & LOPAs
Benefits of a holistic SOL + PHA approach
Overview
Limits that operators can actually use
Industrial operations live with constant tension between maximizing throughput and protecting the process. When an abnormal event develops, an operator has to make a time-sensitive call: keep troubleshooting, or shut down. Safe Operating Limits (SOLs) exist to make that decision in advance — yet many facilities struggle to define limits that are both protective and practical. Without robust limits, response comes down to individual judgment: some operators shut down too early and force costly interruptions, while others push too far and increase the risk of a serious incident.
This paper examines why so many SOL programs fall short. The most common failure is treating the Process Hazard Analysis (PHA) as the sole input. PHAs are qualitative risk-assessment tools — they identify hazards, but were never designed to define enforceable operating boundaries. Relying on them alone produces limits that are misaligned with operating reality: too conservative in some cases, insufficiently protective in others.
Using a real-world case study spanning three refineries, the paper presents a holistic SOL strategy that supplements the PHA with engineering validation and corporate guidance at the unit and equipment level. The result is a repeatable workflow that delivers consistent, actionable limits — even where PHA quality varies from site to site — and that reduces risk while improving day-to-day decisions in the field.
52%
of identified SOLs were found outside the PHA (140 of 270)
25–50%
estimated share of C&E trips & interlocks actually credited as IPLs in PHAs
0%
PST pass rate at one unit — every credited instrument was too slow
What You’ll Take Away
Inside the full paper
The full white paper walks through the challenges facilities face in defining effective SOLs, practical and repeatable ways to handle PHAs that fall short of expectations, the common vulnerabilities that persist in PHAs and LOPAs, and the enhancements that strengthen SOL programs even where strong PHA inputs already exist. It closes with the key benefits of integrating SOL and PHA development into a single holistic approach — whether a facility is just beginning its SOL journey or optimizing an established program.
Read the full white paper
The complete analysis, case-study data, and the step-by-step SOL workflow.
