The Forensic Engineer as Expert Witness

Many forensic engineering assignments start as consulting work: a manufacturer calls after a product failure, an insurer wants to know the cause of a building collapse, a law firm needs someone to look at whether a structure was built to code. At that stage the engineer is a consultant, and their communications are often protected by attorney-client or legal professional privilege. They can explore bad news, draft speculative theories, and give the client candid assessments of risk, all without those drafts ending up in the hands of the opposing side.

The situation changes when the retaining party decides to designate the engineer as a testifying expert. At that moment, and usually at the moment of disclosure, which procedural rules require by a set deadline, the work product transitions from privileged to discoverable. In US federal litigation, Rule 26 requires disclosure of expert reports and, in many cases, draft reports and communications with counsel. UK CPR Part 35.10 requires the report to state the substance of all instructions, written or oral. The expert is now a witness, not just an adviser.

Once designated as a testifying expert, the engineer cannot take instructions from the retaining party about what conclusion to reach. They can receive factual information, be shown relevant documents, and have inaccuracies in a draft corrected. They cannot be coached toward a conclusion. The distinction is one courts police through cross-examination and, occasionally, through sanction when the line is crossed.

The case that crystallised expert witness duties in English law was The Ikarian Reefer [1993] 2 Lloyd's Rep 68, a shipping insurance dispute in which Cresswell J criticised the conduct of expert witnesses on both sides. His statement of duties became the reference point for generations of expert witness guidance:

• Expert opinion must be independent, uninfluenced by litigation pressures and not shaped by what the retaining party wants to hear.
• The expert must not omit material facts that cut against their conclusion.
• Where the expert is uncertain or where a question lies outside their expertise, they must say so.
• If, after seeing the opposing expert's report, their view changes, they must communicate that promptly rather than waiting for trial.

These duties were codified in CPR Part 35 and its Practice Directions, which require the expert to include a declaration that they understand their duty to the court and have complied with it. Similar formulations appear in Australian Uniform Civil Procedure Rules, the Federal Court of Australia's Expert Evidence Practice Note (GPN-EXPT, which replaced the earlier CM 7 in 2016), and in the rules of major international arbitration institutions (ICC, LCIA, ICSID).

An expert witness engagement should be accepted with care. Before taking instructions, the engineer should confirm their expertise covers the technical issues, check for conflicts of interest, and ensure the scope is clear enough that the engagement can be completed and reported without crossing into advocacy. A written retainer letter or engagement letter that captures the scope, the questions to be answered, and the basis on which instructions can be communicated is good practice in all jurisdictions.

1. Acceptance and conflict check
   Confirm expertise, check for prior engagement with any party or key witness, confirm the scope is within the engineer's knowledge area, and issue a retainer letter with the scope of work clearly described.
2. Evidence inspection and testing
   In multi-party litigation, opposing experts often inspect together at a joint examination. Destructive testing requires advance notice and often consent from all parties. Document all steps photographically and maintain chain of custody for any physical evidence removed.
3. Analysis and opinion formation
   Form the opinion independently. Draft notes and working papers belong to the expert, not the retaining party, but under some rules (US FRCP 26) they may be discoverable. Avoid written speculation that will need to be retracted.
4. Expert report
   The report must comply with the applicable procedural rules: in England and Wales CPR Part 35 and Practice Direction 35 require a statement of the expert's qualifications, the substance of instructions, details of literature or material relied on, a summary of conclusions, and a signed declaration of the duty to the court.
5. Joint statement / without-prejudice discussion
   Most jurisdictions require or encourage opposing experts to meet, either in person or by correspondence, to identify agreed issues and narrow disputed ones. The joint statement is produced without prejudice to the positions in the individual reports but is disclosed to the court.

One practical tension at the report-writing stage: the retaining party's lawyers may want the expert to soften a conclusion, emphasise a qualification, or add caveats that make the opinion appear less certain. The expert can and should explain their views to counsel and incorporate factual corrections. They cannot change their genuine technical conclusion because it is inconvenient. An expert who does faces cross-examination on the original draft, which in many jurisdictions will be disclosed, and the credibility damage that follows.

Under the adversarial model, each side appoints its own expert, opposing conclusions follow, and the court allocates significant time to resolving which qualified engineer to accept. Courts in many jurisdictions have introduced reforms to reduce this cost and delay. The most direct is the single joint expert (SJE).

Under UK CPR Part 35.7, the court can direct parties to use a single joint expert rather than each appointing their own. The SJE is jointly instructed, answers questions from all parties, and owes the same duty to the court as any other expert. Neither side can coach them or communicate with them without copying the other. The advantage is cost and neutrality. The disadvantage, from a party's perspective, is the loss of confidential expert advice before the SJE is appointed.

SJEs are common in lower-value personal injury and property cases in England and Wales, but rarer in high-value technical disputes where the parties need their own independent investigations and where the cost of a shared expert is less compelling. International arbitration almost never uses SJEs; the parties' own technical evidence is the norm, and the tribunal decides between them.

Concurrent evidence (colloquially called hot-tubbing, a term from Australian practice) is a procedure in which opposing experts give evidence simultaneously. They typically sit together in the witness box or at a table facing the judge. The judge leads the discussion, moving through the issues in the joint statement. Each expert can respond to what the other says, rather than waiting for cross-examination to expose the disagreements.

The procedure originated in Australian courts, with one of the earliest recorded uses by Rogers J in an insurance case in 1985 and early adoption in the Australian Competition Tribunal (then called the Trade Practices Tribunal). The Land and Environment Court of New South Wales became a leading proponent under Chief Judge McClellan, and the Federal Court of Australia subsequently formalised the approach in its practice notes. The procedure is now used in the Technology and Construction Court in England. It has also been used in international arbitration and in some US federal proceedings, though it is not yet mainstream in American courts.

For the forensic engineer, hot-tubbing demands a different preparation: rather than preparing for a lawyer's cross-examination, the expert needs to know the opposing report well enough to engage in real-time technical debate. Being corrected on a technical point in front of the judge is more damaging than during cross-examination, because the context makes the error visible to all.

Conflict-of-interest problems for forensic engineers take several forms. A prior engagement for the opposing party, even years earlier, can generate sufficient bias concern to require disclosure or recusal. A financial stake in the outcome (owning shares in a party, or depending on a single law firm for most of one's instructions) creates appearance problems. A close professional relationship with a key witness on one side can imply alignment. None of these is automatically disqualifying, but all require disclosure at the outset.

Scope creep is a different category of problem. A forensic engineer retained to examine a steel bridge connection may find, during the investigation, evidence suggesting that design calculations were also deficient. Commenting on the design calculations may be outside their retainer, or outside their competence if they are a structural materials expert rather than a bridge designer. The right response is to flag the issue to the retaining party and, if it is relevant to the litigation, to ensure a suitably qualified expert is engaged for that aspect. Overreaching expertise in a report invites cross-examination challenges and can taint the admissible conclusions.