Queen Latifah had been scheduled to perform on Independence Mall as part of semiquincentennial celebrations in Philadelphia, but organizers canceled the event because of the extreme temperatures.
The effects of the heat were evident elsewhere in the region, including in Muhlenberg Township, Berks County, where a large crowd gathered to watch Union Pacific's historic Big Boy locomotive pass through on its way to Philadelphia.
Emergency crews declared a mass casualty incident after dangerous heat and the large crowd - thousands of people - overwhelmed resources. More than 100 people were treated for heat-related illnesses, with patients ranging from infants to elderly adults, according to police Chief Randall Hoover.
Temperatures exceeded 100 degrees as the train was delayed. Officials said 35 people were hospitalized, including a patient who suffered cardiac arrest and was revived at the scene.
Around the same time, firefighters in Wilmington battled a four-alarm fire under triple-digit temperatures.
"The fact that they contained it as quick as they did is really good," Wilmington resident Jayden Gonzalez said.
Officials brought the fire under control in about an hour, but one firefighter was taken to a hospital for heat exhaustion. First responders took breaks, drank water and cooled off near a large fan as they worked in the extreme conditions.
"The burnout on interior crews is usually 5-10 minutes on heat-related stuff like this, so we try to keep a quick rotation, get everybody in and out just so no one gets burned out really quickly," said Deputy Chief Tim Strusowski of the Five Points Fire Company.
Everyone escaped safely from the fire, but six homes were destroyed, and 20 people were displaced, according to the Delaware State fire marshal's office who continue to investigate the cause. Nearby residents also lost power during the emergency response.
"This is not a day for the power to be off," resident Betty Houston said.
Houston said her husband has heart problems. They were leaving their home temporarily for his safety.
"We will go to the library or the VA or something. We gotta get him some place cool," Houston said.
The extreme heat comes as Fourth of July celebrations are planned throughout the region. With the Pops on Independence concert featuring Idina Menzel scheduled for Friday night on Independence Mall, officials are urging attendees to take precautions and protect themselves from the heat.