Life-threatening heat gripping US has first responders on high alert

Race organizers canceled the New York City triathlon this weekend as the city remained under a heat emergency; power officials were confident the grid would hold.
2:33 | 07/19/19

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Transcript for Life-threatening heat gripping US has first responders on high alert
So many of you dealing with the brutal heat and it's turned deadly now. And 34 starts, more than 200 million Americans under alert right now. Look at the numbers tomorrow. The heat index. Feel like 111 in D.C. 110 in Philadelphia. 108 in New York City. The midwest, already seeing numbers that high. Tonight, the fompler pro football player who died of heat stroke and a power station exploding leading thousands without power. And several subway lines shut down here in New York City. Gio Benitez leading us off. Reporter: Tonight, the heat and the high alert. Who is most at risk? Anyone is at risk. Reporter: There is a reason parents need watch their kids. You are talking about children, and the body temperature rising three or five times faster than us. Correct. They cannot regulate the temperature like you or I can. Reporter: Not far away. Elderly residents forced to evacuate when they lost power. Describe what it's like in the apartment? It's 95 degrees. Reporter: In Chicago -- The heat will be so intense today, it could be light thetenning. Reporter: A heat index of 105 pushing the limits of infrastructure. The high temperatures can cause pavement blow outs or roads to buckle. Reporter: Former offensive lineman Nick Petris dying after working outside all day. He was just 32. New York City San keling the triathlon. And worryinged about the black out. We expect id to rival all time weekend peeks. Reporter: New York City's mayor is asking the residents to turn the them stat up to 78 degrees to help save power. Today, we are looking at index of 104. The number can go to 113 over the weekend. We just learned in New York City, several subway lines have shut down. We don't know if that is heat related. There are major concerns over infrastructure. Thank you. The real concern in New York after the black out days ago.

This transcript has been automatically generated and may not be 100% accurate.

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