A single compliant reading does not prove a compliant interval
A storage unit holding 240 vials is checked every four hours. At 06:00 the log shows 5.1 °C and the log's history is otherwise clean; the permitted range is 2–8 °C. The 06:00 entry was written by hand by a worker who has since gone off shift. At 10:00 the data logger reads 11.4 °C. You cannot tell from the two readings whether the unit drifted gradually or failed suddenly. The vials are needed for a session starting at 14:00 and there is no spare stock. The supplier's stability guidance says product may be used if it has not exceeded 25 °C cumulative and no single excursion above 8 °C lasted more than two hours - but you have only two data points and cannot confirm duration. Replacing the stock takes five days.
1. Can you release the stock for the 14:00 session? Reason it through.
Read the worked answer
No - not on the current evidence. The guidance is conditional on duration, and duration is exactly the fact I do not have.
The tempting shortcut is the 06:00 reading: it is in range, so someone may argue the excursion cannot have been long. That is a sampling artefact, not evidence. A four-hourly check certifies the unit at four instants; it says nothing about the 239 minutes in between. The product could have been at 11 °C from 06:20 without any reading catching it.
What I gather before deciding:
- Logger data at its native interval, not the four-hourly human entries - this usually resolves duration in minutes.
- The unit's door-open and alarm history for the window.
- Whether the logger's own calibration is current (an uncalibrated logger is a third hypothesis, not a reassurance).
- Whether the manual 06:00 entry was a transcription of a display or a judgement.
If the logger genuinely has no data between 06:00 and 10:00, the excursion duration is unknown and cannot be bounded below two hours. Unknown is not the same as short. The defensible position is to hold the stock and treat the 14:00 session as a scheduling problem, not a release decision.
2. The session lead argues the 06:00 in-range reading and the supplier's 25 °C cumulative limit together mean the risk is negligible. How do you answer without simply saying no?
Read the worked answer
Separate the two limbs of the guidance, because they are being merged into a single reassurance that the guidance does not give.
The 25 °C limb is a cumulative ceiling on magnitude. A reading of 11.4 °C is well below 25 °C, so that limb may well be satisfied - I would concede this point explicitly, because conceding what is true is what makes the remaining objection credible.
The duration limb is a separate condition, and it is the one at issue. The guidance requires both conditions. Satisfying the temperature ceiling does not compensate for an unknown duration.
The 06:00 reading is one measurement of the unit, not a property of the vials. An interval is not certified by its endpoints.
Reframe toward a solution: the question is not "is 11.4 °C alarming" but "what is the shortest defensible path to a released batch". Options are a stability assessment from the supplier using the logger trace, a documented risk-acceptance with clinical sign-off if the product is judged low-risk, or rescheduling the session. Give the session lead those three routes and the evidence each needs; the disagreement then becomes about which route to take rather than about whether to ignore the rule.