Freezer temperature mapping (−20 °C and −80 °C)
Freezers stress the sensors as much as the space: response time, cable ingress and condensation all need managing.
Mapping a −20 °C chest freezer or a −80 °C ULT freezer follows the same logic as a refrigerator, but the practicalities change. Sensors must be rated for the range; cables through the door seal create a warm path; opening the lid to place loggers pulls in humid air that frosts everything.
Practical points
- Use loggers with external probes rated for the temperature, or internal loggers specified for it.
- Let the sensors equilibrate before the study clock starts; a warm probe takes time to settle.
- Log at short intervals around door or lid events; ULT recovery after opening can take a long time.
- For ULTs, map with and without a full load of racks if both conditions occur in use.
Excursions
Define the excursion limit and duration for the products stored, not a generic figure. A brief rise during a door opening may be acceptable for some materials and not for others; the protocol should say which.
Frequently asked questions
- How is a −80 °C freezer mapped?
- With loggers or external probes rated and calibrated at −80 °C, placed at top, middle and bottom positions and inner-door compartments, run for at least 24 hours including a door-opening test with recovery time recorded.
- How long does a ULT freezer take to recover after opening?
- It varies from minutes to over an hour depending on the unit, load and opening duration; the mapping study should measure it rather than assume it.
References
- [1]WHO Technical Supplement 8 to TRS 961 Annex 9: Temperature mapping of storage areas (2015)
General technical guidance written against the cited sources. It is not regulatory or legal advice and does not replace the applicable standard, guideline or a qualified reviewer's judgement.
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