Cold Chain Chain-of-Custody Log

Because power state explains and predicts temperature, and assigns responsibility. A logger shows the cargo warmed; the power log shows it warmed during a 40-minute unpowered gap at a specific handoff — that's the difference between an unexplained excursion and a root-caused one with a custodian's name on it. Unpowered gaps are the single most common cold-chain failure mode, and they're invisible in temperature data alone until the damage is already done.

At transitions, not in steady transport: depot-to-terminal unplug/plug gaps, airport tarmac holds without active cooling, dock doors open during slow loading/unloading, and pre-cooling skipped before stuffing a warm product into a reefer. The sea or main-flight leg, powered and stable, is statistically safest. The custody log targets exactly these handoff points because that's where evidence and prevention both live.

Cold-chain cargo claims hinge on proving where integrity was lost and that the claimant did their part (pre-cooling, correct setpoint, proper handoffs). A signed handoff log with temperatures and power states is contemporaneous evidence that pinpoints the failure custodian and demonstrates your own compliance — far stronger than a logger download alone, which proves something went wrong but not who owned the moment it did. Underwriters and surveyors specifically ask for the custody chain.

Verify and record three things at each transfer: the displayed/measured temperature, the power source the unit is now on, and the setpoint itself (unchanged from spec). Setpoint drift — a unit accidentally reset, or a reefer running on the wrong program — is a quiet failure that a temperature spot-check might miss for hours. Logging the power state and verifying the setpoint at every signed handoff catches both the gap failures and the configuration failures.