“It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so.”
— Mark Twain.
In process safety, lack of important information can clearly be a big problem. If we haven’t properly identified our hazards or are lacking other significant information about our processes, the results can be potentially catastrophic.
But Twain’s observation is equally important. Sometimes, we think we know something, perhaps with great confidence, and it’s never really been true, is incomplete, or is no longer true because something has changed. In process safety, false certainty can be as hazardous as not knowing something in the first place.
False certainties
A tragic example occurred on Jan. 31, 2000, when Alaska Airlines Flight 261 crashed into the Pacific Ocean, killing all 88 people on board (1, 2). The cause was a failed horizontal stabilizer jackscrew. Investigators discovered that the airline had repeatedly extended the lubrication and inspection intervals for the component, confidently believing the original schedule was overly conservative. What they “knew for sure” — that longer intervals were safe — proved catastrophically incorrect. The wear rate was higher than expected, lubrication was inadequate, and the aircraft lost control.
Similar false certainties in other industries exist, and may be evident in the following phrases: “We haven’t had an incident for many years;” “That alarm is always a nuisance;” “We’ve always done it this way;” or “That hazard isn’t credible here.” These assumptions can become normalized until an incident reveals their flaws.
Challenging assumptions before they become hazards
In addition to effective process safety systems like management of change, two strategies stand out as especially important in helping us recognize when our information or understanding may be incorrect or incomplete (1):
- implementing effective feedback systems, based on the collection and review of appropriate process safety metrics, including audit results
- maintaining sensitivity to operations, based on the ability to notice and respond to small anomalies, negative trends, changes in the work environment, or other warning signs before they escalate.
On an audit, we noticed a reactor reflux temperature that had been trending slightly higher and recommended that the condenser be inspected. It was determined that many of the tubes were plugged, which over time could have led to a runaway reaction.
On other audits, we discovered (a) a safeguard that we believed operators would manually activate if needed was unlikely to be activated due to site culture, and (b) a safety system valve was observed to be locked closed even though it was required to be locked open. What we knew to be true in theory turned out not to be true in practice. Most auditors have probably had similar experiences. Unfortunately, process hazard analysis (PHA) and other teams may have experienced this as well.
Adopting a Sherlock Holmes mindset
When something feels different or warning signs appear, the best professionals don’t default to blind rule-following; they adopt a Sherlock Holmes mindset (3): stay curious, question assumptions, investigate anomalies, and maintain the ability to say, “Something might be wrong; let’s check.”
This mindset is at the heart of personal operational discipline (1). It combines deep knowledge of hazards and systems, strong commitment to doing things the right way, and constant awareness, as well as the willingness to recognize when something is different and the discipline to pause when needed to investigate further or seek more help.
In process safety, both lack of knowledge and false certainty are dangerous. Maybe what we know just ain’t so. We need to maintain awareness through sensitivity to operations and respond with curiosity and the discipline to challenge what we think we know.
Is there anything you know for sure that just might not be so? If you don’t have the mechanisms and intents in place, some things you know are true may not be.
- Klein, J. A. and Vaughen, B.K., “Process Safety: Key Concepts and Practical Approaches,” CRC Press (2017).
- National Transportation Safety Board, “Loss of Control and Impact with Pacific Ocean, Alaska Airlines Flight 261,” Aircraft Accident Report NTSB/AAR-02/01 (2002).
- Klein, J. A., “The ChE as Sherlock Holmes: Investigating Process Incidents,” CEP, 112 (10), pp. 28–34 (Oct 2016).
This article originally appeared in the Spotlight on Safety column in the July 2026 issue of CEP. Members have access online to complete issues, including a vast, searchable archive of back issues found at www.aiche.org/cep. Learn more about AIChE membership.
