At least eight dogs died from heat-related injuries after an AC unit that was being used to keep them cool failed during a 2-hour traffic delay. 

The dogs that died were among 18 shepherds that were being transported to a K-9 training facility from O’Hare Airport to Michigan City, Indiana on Thursday, Lake Station police said. 

During the transport, the driver became stuck in a traffic jam and the AC unit failed. The temperature rose inside the vehicle, causing the canines to go into heat-related medical distress. 

The driver wasn’t aware at first of the AC unit failure because the cargo area was separated. He only became aware of what was happening upon hearing the dogs barking. 

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The driver stopped the vehicle at the Road Ranger on Ripley Street and began removing the canines that were crated. 

Officials from the Lake Station Fire Department and EMS, as well as the Lake Station Police Department, responded to the scene. 

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Police said the response from both agencies was so "overwhelming" that civilians stopped to help where they could. 

"The scene was chaotic and took an emotional toll on all that were involved in trying to save as many canines as possible," the Lake Station Police Department wrote in a press release. "Any loss of life is tragic and thoughts and prayers are with all those that were affected by this ‘freak event.’" 

After speaking with the driver involved, police determined that the incident was not an act of animal cruelty or neglect, but a mechanical failure of the AC unit that was being used in the cargo area. 

The incident came amid a record-breaking heatwave that has walloped the United States in recent weeks. Scientists have calculated that July will be the hottest month worldwide on record. 

The Associated Press contributed to this report.