When Judgement Replaces the Test

If a fire test is not a truth, then what happens when there is no test at all?

This is the territory of Assessment in Lieu of Test. Or, more accurately, where it should be.

At its best, an assessment is a disciplined piece of engineering. It takes available test evidence, understands its limitations, and carefully considers whether performance can be inferred in a different configuration. It is explicit about assumptions, transparent about uncertainty, and proportionate in its conclusions.

At its worst, it is something else entirely.

There is a growing tendency to present assessments as if they were equivalent to test evidence. Statements are made that a construction “will achieve” a given level of performance, without the supporting evidence actually demonstrating that outcome. The language becomes definitive. The justification, less so.

This is not what assessment is.

Standards such as BS 6336 remind us that even direct test results must be treated with care. Once we move beyond those conditions, the level of interpretation increases, and with it, the responsibility on the assessor.

Assessment is not an exercise in optimism. It is an exercise in constraint.

The starting point is always the same: what does the evidence actually show? From there, the question becomes whether the differences introduced are material. Geometry, fixings, interfaces, tolerances, workmanship. Each has the potential to alter performance, sometimes significantly.

The difficulty is that these changes are rarely binary. They sit in the space between “clearly acceptable” and “clearly not”. This is where judgement is required. And where it is most often tested.

In practice, commercial pressure does not sit comfortably with uncertainty. Programmes need answers. Designs need to progress. Contractors need confirmation. The temptation is to resolve that uncertainty with confidence.

That is where assessments begin to drift.

The emergence of so-called “letters of comfort” is a symptom of this. Conclusions are presented without a transparent chain of reasoning, or without clear linkage back to relevant test evidence. The form resembles an engineering assessment. The substance does not.

This is not simply a matter of technical disagreement. It is a matter of professional conduct.

A credible assessment should do three things. It should clearly set out the evidence base. It should explain the reasoning that links that evidence to the proposed application. And it should state the limits of that reasoning.

If those elements are absent, what remains is not an assessment. It is an assertion.

There is a place for Assessment in Lieu of Test. In many cases, it is essential. But its legitimacy depends entirely on how it is carried out.

The industry does not need fewer assessments. It needs better ones.

And perhaps a simple test can be applied. If the conclusion cannot be traced, step by step, back to evidence and reasoned judgement, then it is not an assessment in lieu of test.

It is something else.

This insight reflects on the use of engineering assessment in place of fire testing. It is intended to highlight issues of interpretation, judgement, and professional responsibility, rather than to provide prescriptive guidance.