A feeble breeze kicked up the black dust in the scruffy encampment of homeless men and women beneath I-95 at Oregon Avenue Thursday afternoon. In the shade of the highway's concrete awning, they relaxed, uncomplaining, on grimy mattresses and folding chairs, during the most blistering hours of the day. But when Project H.O.M.E outreach worker Sam Santiago arrived in his familiar red van, bearing bottles of chilled water, the group rose eagerly to greet him.

"It's hot," said Joe Schlacter, accepting an armload of bottles beaded with condensation. "But not as hot as Vietnam." The 66-year-old veteran, who has weathered years of homelessness, said he found it easier to cope with winter's extreme cold than this kind of oppressive heat.

In winter, Schlacter said, he and his friends light fires in a barrel to keep warm. "But there's no air-conditioning under here."

"And at night, there's mosquitoes," added Chrissy Pasquarello, sweat sticking her T-shirt to her chest and darkening her overalls.

Pasquarello, 38, who has been homeless on and off for 10 years, spent last fall and winter in an apartment with Schlacter, but they moved out in March.

"Bed bugs," she said.

Santiago crossed over to a blue tent about 50 yards away.

"Frank?" he said, poking his head through an opening. "Would you like some water?"

Inside, huddled in the airless enclosure, a 63-year-old man with wild, charcoal-gray hair reached up to accept two bottles.

"I'm used to the heat," he said. "I was a roofer by trade." Diagnosed with paranoid schizophrenia, he has been homeless, he said, for some time and living in the tent - vacated by a previous tenant - for five months.

Thursday, three news crews from radio, television, and newspapers accompanied the city's teams doing outreach to help the homeless in the heat. "But the problem isn't just when it's hot. It's 365 days a year, 24/7," said Santiago, a retired Philadelphia police officer who has worked for Project H.O.M.E for 12 years.

Making the rounds of the city during his 7 a.m.-to-3 p.m. shift, he handed out more than 50 bottles of cold water to men and women, most of them familiar faces, and most with enough sense to get out of direct sunlight.

Driving along Spring Garden Street past Sixth Street, Santiago spotted a man sprawled on the sidewalk.

Speaking to him in Spanish, Santiago asked whether he could help. Did he need water? Was he ill? Drunk? Could he offer him a ride home?

The man, Rene Benitez, groggily sat up and gratefully drank the bottle of water that Santiago gave him. Asked his name, Benitez slurred his words, so Santiago checked the hospital identification bracelet still on the man's wrist. He had had a fight with his wife, he told Santiago, then, accepting a second bottle of water but no other help, started to put on the sweatshirt he'd been using as a pillow.

"Better not put that on," Santiago advised. "It's hot." Then he watched the man drape the sweatshirt around his neck and shuffle off toward Broad Street.

For the second day, the city had all-time high temperatures - 99 degrees Thursday, breaking the record of 98 set in 1933. Weather like that can be fatal, particularly to vulnerable populations like the homeless and the elderly.

The danger has a stealthy quality, says George Luber, associate director of climate change at the Centers for Disease Control and Prevention. "It's an almost imperceptible shift from heat exhaustion to heat stroke."

Among the factors that put people at risk, Luber said, are exercise, diabetes, heart disease, and substance abuse. The mentally ill face a dual threat. "Many of their medicines inhibit thermal regulation, and their illness may also impair their ability to perceive a risk and act upon it."

Learning from recent heat waves, Luber said, cities have become more vigilant.

"Philadelphia is a top example of a well-functioning response system," he said. "Following the 1993 heat wave, it became a model for the rest of the country."

On Wednesday, several dozen outreach workers were dispatched to find vulnerable people on the city's streets. Marcella Maguire, director of homeless services for the Department of Behavioral Health, said 10 people were taken to shelters, emergency rooms, and other facilities.

The region's senior centers extend their hours during extremely hot days, some until as late as 8 p.m. during the week, and open on the weekends.

Normally, the center on South Broad Street draws 200 members a day, but attendance was up 25 percent due to the heat warning this week.

Visitors receive educational talks about how to prepare for and deal with the heat. The center also provides fans to some who are going home to unventilated rooms.

Martin Krasner, treasurer of the center's advisory council, has air-conditioning at his Northeast home, but it reaches only his living and dining rooms. He uses a window fan to try to cool his bedroom.

"It doesn't do anything, Krasner, 76, said. "When it's hot and you put a fan on, all you get is hot air being blown in your face."

During hot summer nights, Krasner, who has a heart condition, sleeps on the sofa in his living room. Then, around 2 or 3 a.m., when temperatures outside are milder, he returns to his bedroom.

"It's hot, much too hot at this time of the year. Even in July and August, but we learn to live with it," Krasner said. "But it's June, and we don't want it so early."

For some enterprising Philadelphians, the day provided an opportunity to make the best of a bad situation.

"Beat the heat, beat the heat," sang Alex Napper, a damp cloth over his head, as cars passed by his North Philadelphia home near Sixth and Jefferson Streets. "Ice-cold water. One dollar. Uno peso."

Napper, 42 and in between jobs, sold 30 bottles in roughly the same number of minutes, mostly two at a time.

"That's the best thing you can drink on a day like today," said Napper, a self-described summer baby.

And his water is better than store-bought water, he said. He deep-freezes it the night before - his trademark.

While Napper worked the curb, his wife, Sarita Broadnax, the block captain, camped out under a canopy, dousing herself with water from a garden hose. Their year-old granddaughter sat in her walker near a deflated pool that had been tragically punctured by a tree branch.

A relative was en route with a repair kit.

The family's three-story home has air-conditioning, but Broadnax said they use it sparingly because it's expensive.

"We're just staying in the water," she said. "It feels good."

If you see a person in need of support and housing, call the Philadelphia Homeless Outreach Hotline at 215-232-1984.