The U.S. Department of Energy declares an emergency to reduce blackouts.

With 160 million people in 30 states under alert for extreme temperatures, the U.S. Department of Energy has declared an emergency as a heat wave bears down on a huge part of the nation's electrical grid.

U.S. Secretary of Energy Chris Wright issued an Energy Emergency Alert, directing officials of the biggest electrical grid, PJM Interconnections in the Mid-Atlantic region, to take action to prevent blackouts and ensure essential operations like hospitals are fully functioning during the heat wave.

"Maintaining affordable, reliable, and secure power in the PJM service territory is non-negotiable," Wright said in a statement on Tuesday.

Long Island Power Authority (LIPA) power lines along Motor Lane in Bethpage, New York. Authorities are expecting a heat wave leading into the July, 2026, holiday to put pressure on the nation's electrical grid. Newsday Llc/Newsday via Getty Images

PJM supplies power to about 65 million customers in Washington, D.C., and in all or parts of 13 states, including Delaware, Michigan, Maryland, Kentucky, New Jersey, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia and West Virginia.

Wright's emergency declaration, which went into effect at 11:59 p.m. on Tuesday and will run through 11:59 p.m. on Friday, also directs PJM to conserve energy by curtailing power to data centers that have backup generators and other non-emergency facilities that use a lot of electricity.

PJM said it is forecasting an electricity peak demand of 166,304 megawatts, or the average total electrical demand by consumers for one hour, on Thursday -- which would break a record set in 2006.

The dangerous heat wave is bringing prolonged extreme heat along the East Coast, the Midwest and the South.

A construction worker takes a water break during a heat wave in Boston, Massachusetts, July 1, 2026. Joseph Prezioso/AFP via Getty Images

Leading into the Fourth of July holiday, heat indices, or what the temperature feels like with high humidity, are forecast to soar to 100 degrees in Chicago and Detroit, 110 in New York City, 112 in Philadelphia, 113 in Washington, D.C., and 111 in Nashville, Tennessee.

"It's going to really strain the grid," Ramanan Krishnamoorti, vice president of energy and innovation at the University of Houston, told ABC News. "I think we’re going to see peak demand that is going to be a record across different geographical areas."

A woman stands in mist trying to cool off from hot weather at Dodge Fountain at Hart Plaza in Detroit, June 30, 2026. Paul Sancya/AP Photo

The New York Independent System Operator (NYISO), which operates the state's electrical grid, said it is also expecting electricity demand to approach record highs over the next few days.

The Midcontinent Independent System Operator (MISO), which covers 15 states in the Midwest and South, said it could also break its record for peak demand.

"Everything is sort of stretched to the limit," Krishnamoorti said. "I think you're going to see massive challenges in terms of demand."

Dangerous heat wave. ABC News

Making matters worse is that the heat wave is coinciding with the biggest summer holiday of the year, America's 250th birthday.

"Everybody is going to be home for the July 4th weekend, and because of that, you’re going to see, I think, a significant load on the grid," Krishnamoorti said. "Residential cooling is going to be the dominant source of where the demand is going to come, and it's going to be pretty significant through the afternoon to late evening period."

People enjoy the spray of cool water in front of a Chicago Fire Department during a hot weather day in Chicago, June 30, 2026. Nam Y. Huh/AP Photo

He said nighttime temperatures during the heat wave are expected to provide little to no relief, preventing grid operators from taking power plants offline to conduct routine maintenance.

He said some utilities may have to implement rolling blackouts in localized areas to relieve the stress on the grid.

Krishnamoorti said Independent System Operator-New England (ISO-New England) -- which provides power to Massachusetts, Connecticut, Maine, New Hampshire, Rhode Island and Vermont -- could also face challenges meeting demand because it imports some of its low-cost electricity from Canada.

“Canada is also going through a significant heat wave," Krishnamoorti said. "So, I’m not sure there will be enough supply from Canada to bring it across the border."

In a statement to ABC News, ISO-New England said it is prepared for the challenges of the heat wave.

"At a high level, we're expecting tight conditions on the system this week due to the very high temperatures, particularly tomorrow (Thursday). Weather events like these, which spread geographically across our neighboring regions, can limit our ability to assist each other, but we remain in close contact with our partners in New York and Canada about conditions in their areas," said Matthew Kakley, a spokesperson for ISO-New England.

The company said it anticipates its peak demand will be 25,850 megawatts on Thursday, which is below its record 28,000 megawatts on Aug. 2, 2006.

"We anticipate having the resources we need to meet consumer demand and required reserves, but we will be closely monitoring conditions," Kakley said. "If needed, our operators have tools at their disposal to help ensure supply and demand are in balance."