49 CFR § 173.442 - Thermal limitations.
(b) The temperature of the accessible external surfaces of the loaded package will not, assuming still air in the shade at an ambient temperature of 38 °C (100 °F), exceed either -
(1) 50 °C (122 °F) in other than an exclusive use shipment; or
(2) 85 °C (185 °F) in an exclusive use shipment.
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