How Process Safety Expert Witnesses Get Excluded Under Daubert — and How to Survive the Cross

Daubert is not a medicine problem. Under Kumho Tire and the 2023 amendment to Federal Rule of Evidence 702, the trial court's gatekeeping applies to every form of specialized testimony — process safety included. A 20-year study of 2,842 challenges to non-medical experts found that roughly half of those opinions were excluded or partially excluded, and the single most-cited reason was “unreliable methodology.”

The exclusion rarely happens in a written motion alone. It is built, piece by piece, in the deposition cross-examination — where opposing counsel walks a process safety expert into conceding scope, methodology, or an assumption that unravels the whole opinion. Here are the three traps, and how a prepared expert answers each one.

The three ways process safety experts lose ground

Scope: testifying outside your lane

The cross-examiner's question sounds simple:

You opine the process hazard analysis was deficient — but you've never run this exact process, have you?

Why it works: The process/scope attack. Anchor to OSHA PSM and CCPS.

A stronger answer: “I apply OSHA PSM and accepted CCPS process-safety standards, which govern the analysis, to the documented PHA and records; I cited the specific requirements.”

Methodology: the reliability attack

The cross-examiner's question sounds simple:

Your opinion relied on the incident report — you didn't independently model the reaction, did you?

Why it works: Methodology / data basis.

A stronger answer: “I analyzed the documented process data and the incident records against the standards and noted where modeling would further support the conclusion.”

Assumptions: the one premise that sinks the opinion

The cross-examiner's question sounds simple:

You assume the operators followed the procedure — but you have no proof of that, do you?

Why it works: The operator-conduct assumption. Tie to records.

A stronger answer: “I addressed both the procedure and the documented operating data and flagged where operator conduct wasn't established.”

How to prepare for the cross before you're sworn in

Every one of those traps is defeatable — but not by reading your report one more time. The experts who survive the cross have done three things:

• Rehearsed the cross-examination out loud, repeatedly, against a realistic examiner — so the scope concession, the methodology defense, and the assumption hedge are second nature.
• Mastered the record, so that when counsel asks them to recall the one line buried in thousands of pages of the PHA, process data, and PSM records, they can produce it in seconds rather than fumble.
• Stress-tested the report against FRE 702 — finding the reliability gaps before opposing counsel does.

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