The US Energy Department issued an emergency order Tuesday allowing power plants in the country's largest electricity grid to exceed their normal pollution limits, as a severe heat wave threatens to push demand to record levels across a swath of the eastern US.

The grid, known as PJM Interconnection, supplies electricity to 65 million people in 13 states, including Pennsylvania, Maryland, Ohio and Virginia, and the federal district of Washington, DC.

The order took effect Tuesday at 11.59 pm local time and runs through 11.59 pm Friday.

PJM had requested the order, telling the agency it expects demand to climb to about 159,563 megawatts Wednesday and 162,860 megawatts Thursday. One megawatt is roughly enough electricity to power 750 homes at once.

Temperatures are forecast to reach 95 °F (35 °C) across the region and surpass 100 °F in areas including Baltimore and the greater Washington, DC area.

"The forecasted demand raises a significant risk of emergency conditions that could jeopardize electric reliability and public safety," Michael Bryson, PJM's senior vice president of operations, wrote in a letter requesting the order.

The order allows designated power plants to run longer and emit more pollutants than their permits normally allow, so they can keep generating electricity through the peak heat. PJM may add more plants to the list as needed, according to the order.

The grid operator had already postponed scheduled maintenance on generators and transmission lines starting June 25 to maximize available power. Industry forecasts suggest the grid's safety buffer could shrink sharply if extreme conditions persist through the week. (Anadolu Agency)

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