Western Pennsylvanians took to the pools, the senior centers and to basements and dens as the region endured a second day of brutal heat that put experts on watch for any signs of strain on the power grid.

On that last one, so far, so good. Instead of overloading the grid, sweltering Northeasterners overloaded local swimming facilities. Sandcastle Waterpark in West Homestead found itself unable to handle the load and turned away hundreds on Monday as sweaty patrons used the last day of the July Fourth holiday weekend to find some wet relief.

"These are the days that were made for a waterpark," explained Jeff Filicko, a park spokesman who said Sandcastle was able to handle the load on Tuesday.

Another day of temperatures in the 90s is in store today, with the high expected to reach 94 degrees.

Alexander Grattan, 9, of Dormont, passed his deep water test at the local pool Monday just in time to take advantage of a day made for water.

His mother, Mary Alice, 40, said at home the air conditioning is cranked up high.

Another Dormont resident, Carole Faloon, 57, spends about 25 hours every week at the pool to beat the heat.

"It's how we beat it every day," she said.

How the heat started beating Ms. Faloon and her neighbors is a story of an errant jet stream, the endlessly flowing column of cold air that crosses the northern part of the continent and the Atlantic, flowing eastward.

"It's just part of the meanderings of the jet stream and the atmospheric slot machine," said Bill Syrett, manager of the weather center at Pennsylvania State University in Centre County.

The stream shifted north, making room for a hot, humid air mass from the south and giving the state some of its hottest weather since summer 1988. Tuesday, central Pennsylvania flirted with its high temperature record of 95 degrees, set in '88.

UPMC spokesman Marc Lukasiak said that doctors saw people with a range of symptoms for heat exhaustion in the emergency room Tuesday.

"They're basically seeing sporadic cases of people with symptoms ranging from light-headedness and dizziness to unconsciousness and they need to be cooled off," he said.

UPMC's emergency rooms were not able to provide an exact figure for people coming in with heat-related illness, but there was a marked increase Tuesday, Mr. Lukasiak said. UPMC Presbyterian's emergency room treated the same number of patients for heat-related illness Tuesday as it normally does in a week this time of year.

The Pennsylvania Department of Environmental Protection, meanwhile, issued an air quality alert across the state, indicating the air quality in the state's west would verge on the unhealthy for people with existing health conditions, and generally unhealthy for everyone in the Philadelphia area.

And while this heat spell should taper off a bit after Thursday, it's difficult to predict what the next summers or winters will bring. This particular heat spell cannot be pinned on global warming, Mr. Syrett said.

The heat will contribute to what is quickly becoming the warmest year ever across the globe, said Michael Mann, a professor at Penn State's Department of Meteorology and also director of the Penn State Earth System Science Center. The past few days could offer a glimpse into the future, he said.

"Whether or not we can link it to climate change per se ... we do know that it gives us the flavor of what's in store."

Landscapers are cutting less and watering more in the face of intense temperatures.

Rose Worthy, owner of Diamond Cut Landscaping in Penn Hills, is having her crew cut lawns once every two weeks instead of the usual weekly service.

"When you cut the grass in extreme heat like this ... that gives it a tendency to burn."

She recommends watering grass in the early morning, around 6 a.m. when the ground is cooler. Ms. Worthy also uses a fertilizer with time-release moisture beads to keep the soil damp in the heat.

At Saint Vincent College, the fields the Steelers will use for practice this summer are being carefully monitored and cared for.

During these periods of sweltering heat, Larry Hendrick, director of facility management at Saint Vincent, is on the lookout for damaged grass on the Steelers' practice fields.

"If we notice [the fields] getting a little dry or black in the evenings or on the weekends, I call their head field guy and let them know that we are going to water."

A programmable control, similar to a timer for lights, is mostly controlled by the Steelers grounds crew so the fields used for practice are watered as the weather heats up, Mr. Hendrick said.

Landscapers aren't the only ones trying to beat the heat. Library-goers will also be affected by the high temps. And though they might be the place to stay warm in the winter, some local libraries will not keep visitors cool in the summer.

Carnegie Library of Pittsburgh closed four locations on Tuesday because none of the historic buildings has air conditioning. The libraries in Lawrenceville, Mount Washington, South Side and West End closed at 1 p.m. and are expected to re-open today.

With nothing between them and a steamy sweat save air conditioning, millions powered up the cooling units in homes and offices. But while sweltering Pennsylvanians were glancing at the thermostat, officials in Valley Forge were watching the numbers tick upward on the meter that gauges electricity consumption.

"The work week always means more people using more power during business hours," said Paula DuPont-Kidd, a spokeswoman for PJM Interconnection, a body that governs the transmission of electricity across the District of Columbia and 13 states, including Pennsylvania.

Ms. DuPont-Kidd said the demand was large but not likely to match the record demand of Aug. 2, 2006, when the 51 million people in the PJM region sucked up 144,644 megawatts at the day's peak.

"Right now we're forecasting about 139,000 megawatts at peak," she said.

That is so far. A continuing crush of hot weather could swell demand.

What trouble did arise Tuesday was not the much-ballyhooed total blackout, akin to what struck New York in 1965 and 1977. Rather, it was the usual street-by-street misery as the random power transformer overloaded. The large, gunmetal gray cylinders that hug poles throughout the region sometimes blow their tops when a surge of demand tests them, said Joe Vallarian of Duquesne Light.

"Our guys are carrying extra transformers on their trucks," Mr. Vallarian said. When they replace them, they install higher capacity transformers. Electrical demand is only likely to go up, he noted.

"We have more electronic things in our homes than we did 5 or 10 years ago," he said. Air conditioning, of course, has been around nearly a century. But power-hungry big screen televisions, added to the mix, sometimes test the transformers.

That they don't test Pittsburgh's overall supply is a perverse benefit of the region's biggest economic disaster: the disappearance of its steel industry. Mills used massive amounts of power to the point that, after the deindustrialization 25 years ago, Duquesne Light had 50 percent more power generating capacity than it has today, said Lester Lave, a professor of economics and engineering at Carnegie Mellon University and an authority on the power supply grid.

That gap has closed somewhat almost a generation later, but the region still sits with a sufficient oversupply that a backup generating station on Brunot's Island has only been fired up twice in recent memory.

But Dr. Lave adds this caveat: "We're all interconnected."

For instance, in 2003, a set of fallen power transmission lines in Ohio sent shock waves across the grid as other areas tried to make up the loss, blacking out customers from Dayton, Ohio, to Toronto and on to New York City.

"If the system goes down," said Dr. Lave, "it goes down."

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