ATHAR NOTE · EVIDENCE & REQUIREMENTS

When an Exceedance Is Only the Beginning

A limit comparison can be important enough to trigger action and still be insufficient to explain what happened.

This note does not determine compliance. Applicable requirements and authorised interpretation remain separate from ATHAR’s public concept.

An exceedance is a comparison between a measurement and a requirement. Before drawing a larger conclusion, both sides of that comparison need to be understood.

A threshold can tell us that review is required. It cannot, by itself, tell us the cause.

Start with the comparison

Which limit applies? What averaging period, sampling method, location, operating condition or data-quality rule belongs with it? Was the measurement valid and complete for that comparison? Those are not administrative details. They define what the result can legitimately mean.

Then examine the event

Duration, spatial extent, related parameters, station health and environmental conditions may all matter. A brief isolated value and a sustained multi-station pattern are different evidence situations, even when both initially appear above the same line.

None of this is an excuse to dismiss an uncomfortable observation. It is how a reviewer avoids both false reassurance and unsupported attribution.

ATHAR principle: evidence says what was observed; requirements say what applies; analysis explores what the pattern may mean; an authorised human makes the decision.

Escalation without overclaiming

It may be responsible to escalate, investigate or take precautionary action while causation remains unresolved. Urgency and certainty are not the same thing, and professional language should keep them separate.

The line begins the review. It does not finish the reasoning.

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