The Problem: Return air temperature readings show warm temperatures.
The Key Point: Return air temperatures are a better reflection of air temperatures within the trailer than supply air temperature readings.
The Solution: Carriers are responsible for cooling the trailer, regardless of any field heat or respiration from the product. We recently hauled a load of mixed vegetables from a shipper in Texas to a receiver in New York.
“When the load arrived, the U.S. Department of Agriculture inspection certificate showed warm pulp temperatures and condition problems with the produce. Unfortunately, no portable temperature recorder was placed on board, but the download from our reefer unit shows our driver entered the proper set point and that the unit was supplying air at the instructed temperatures.
Although the return air readings are high, we believe this is a result of the field heat coming from the product and not any failure on our part.”
Does the receiver have a carrier claim?
Based on the information provided, it appears that the reefer unit failed to maintain transit temperatures as required by the contract of carriage. Although the supply air readings appear normal, it must be remembered that reefer units are expected to cool the length of the trailer—not just supply air sufficient to cool the supply air sensors.
For this reason, the return air temperature readings tend to be more significant when warm temperatures are alleged. Here the return air readings from the reefer unit’s download indicate that the air temperatures within the trailer exceeded the temperatures the carrier was instructed to maintain by 7 to 12°F throughout the entire trip.
This temperature variance far surpasses what we would consider to be a normal variance for return air readings. And while the produce may very well have been giving off field heat and respiring at a high rate, this (even if proven) would not void the carrier’s obligation to maintain the agreed upon air temperatures during the trip.
Our Transportation Guidelines explain—
Carriers should consider all factors that may affect transit temperatures (e.g., field heat and BTUs coming from the commodity, ambient air temperatures, air flow within the conveyance, insulation, and capacity of the temperature control system) before signing for the load. If the carrier cannot warrant that transit temperatures will be maintained as instructed throughout the trip, a specific release from liability should be negotiated prior to signing for the load.
It probably goes without saying, but if the carrier is not sure it can maintain air temperatures within the trailer at the instructed temperature, it is taking on a high-risk load.
As a best practice, the time to raise concern about field heat and respiration rates is at shipping point, not at destination.