Technical Blog
“This Far, and No Further”: Why Safe Operating Limits Matter More Than You Think
In facilities with robust control systems, reliable alarms, and experienced operators, it’s easy to assume you already have everything in place to run safely and efficiently. So, when the topic of Safe Operating Limits (SOLs) comes up, the reaction is often, “Why add one more layer? We already have alarms, trip systems, and operating procedures.”
But here’s the hard truth: SOLs are not just another control measure. They serve a fundamentally different purpose—they define the line in the sand. And more importantly, they give your operators explicit permission to not cross that line—to act decisively and shut the unit down when necessary, without fear of consequences or second-guessing.
Operators Are Trained to Keep Running—Until They Shouldn’t
Operators are highly skilled and deeply familiar with the units they run. They’re rewarded for keeping the plant online, maximizing throughput, and avoiding costly downtime. That mindset is essential for productivity—but can be dangerous during a serious process deviation.
Just ask the Chemical Safety Board (CSB). Investigations like the BP-Husky Toledo Refinery fire or the Texas City refinery explosion show how process deviations—not mechanical failures or maintenance errors—can spiral into catastrophic events. In both cases, operators were faced with abnormal conditions and chose to push through, relying on experience and intuition rather than clearly defined shutdown criteria.
The Missing Link: Explicit Authority to Shut Down
In the aftermath of an incident, one question always comes up:
“Why didn’t you shut it down?”
The answers are hauntingly consistent:
- “It didn’t seem like things were that bad.”
- “The procedures didn’t say to shut down yet.”
- “I was just trying to keep the process running.”
This is precisely where Safe Operating Limits come into play. SOLs are not just technical thresholds; they are management’s declaration of the point beyond which we no longer want to run. They are the operating procedure equivalents of a trip system—clear, enforceable, and non-negotiable.
When defined and implemented correctly, SOLs:
- Remove ambiguity from the shutdown decision
- Empower operators with clear STOP WORK authority over their process
- Protect operators from judgment after the fact
- Prevent second-guessing under pressure
- Provide regulatory alignment with process safety standards (like API 584, CCPS Guidelines)
Not Redundant—Essential
Yes, you may already have alarms, corrective actions, and procedures. But ask yourself:
- Are they structured to stop the process before a catastrophe unfolds?
- Do they empower operators to act without hesitation?
- Can they answer the “Why didn’t you shut down?” question confidently in hindsight?
If the answer is no—or even “maybe”—then it’s worth rethinking the idea that Safe Operating Limits are just a redundant layer. They’re not just nice-to-have – they’re essential.
The Bottom Line
Implementing Safe Operating Limits isn’t about piling on more documentation or adding red tape. It’s about making a bold, management-level decision: “At this point, we’d rather shut down than continue running unsafely.” That’s not just good process safety—it’s good leadership.
Because in the moments that matter most, hesitation can be fatal. Safe Operating Limits eliminate that hesitation by making the path clear.
Meet the Author
Eric Nussberger – Senior Process Safety Engineer
Eric is a senior process safety engineer with over 25 years of experience in process design and troubleshooting, project conception and development, and advanced process control. He specializes in Safe Operating Limits (SOL) development, hazard reviews, and control system optimization.
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