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WASHINGTON (WUSA9)--The frigid temperatures in recent days prompted passengers sitting on a plane at BWI to take special notice of a few boxes that were left on the tarmac.

They watched for nearly an hour before their plane took off, as baggage handlers ignored the packages. The photos were sent to our reporter, Andrea McCarren.

If you take a close look at the labels on two boxes clearly visible to passengers seated on Southwest Airlines flight 2162, they reveal the following words:

Human blood. Avoid extreme temperatures. American Red Cross.

Photographs were snapped on Sunday afternoon, when the temperatures dipped into the 30s. Passengers watched as the baggage handlers dealt with other luggage but not the two boxes. Flight 2162 was delayed nearly an hour. The entire time, the boxes of blood sat in the cold.

"The safety of the blood supply is the highest priority of the American Red Cross," said Donna M. Morrissey,a spokeswoman for the American Red Cross. She added, "The boxes are designed to withstand extreme temperature swings for long periods of time."That, she said, despite the labeling on the two boxes in question.

Michelle Agnew,aspokeswoman for Southwest Airlines, said it moves thousands of blood shipments for the Red Cross every day and states clearly in its contract that "perishable shipments must be prepared and packed to withstand a 48-hour transit... and packed to ensure that satisfactory storage temperatures are maintained for a period of not less than 48 hours."

Based on our inquiries, Southwest Airlines and the American Red Cross investigated this incident and determined the shipment of blood was not compromised during transit.