Accepted answer
28 days is 672 hours, and phase-change shippers are qualified in hours: 96 and 120 are the common ratings. So 672 hours is 7 times a 96-hour qualification and 5.6 times a 120-hour one. Past its rated duration a phase-change pack is not partial protection — it is thermal mass that has finished changing phase, after which the payload tracks ambient. On that reading the last 552 to 576 hours are room-temperature storage in a box. The qualification also assumes a stated ambient profile, and a lane that sits on an apron in August is not the profile the figure was measured against. If you want what happened rather than what was rated, a single-use electronic logger costs less than the assay you would otherwise run afterwards and answers it with 672 hours of data instead of an argument.
Answering this needs the transit duration and the ambient temperature, and then the arithmetic is straightforward.
Once the parcel arrives, the domestic leg is the controllable part: get it into the refrigerator promptly rather than leaving it in a warm hallway for a day.
Anything shipped in solution is a different risk category, because hydrolysis and deamidation proceed in the aqueous phase and are strongly temperature-dependent.
Arrhenius kinetics predict approximately a doubling of degradation rate per ten-degree rise and are the standard basis for cold-chain design.
Nothing here is medical advice, and research-use compounds are not approved for human use.
A liquefied pack is expected. It is not evidence of a problem.
edited 2 Aug 2025 by marta_okonkwo — corrected a unit error in the worked example
The doubling-per-ten-degrees rule is the part I did not know and now use constantly. – ines_brandt 13 days ago add a comment