Public safety officials have warned people to stay hydrated and to wear hats at graduation ceremonies that were expected to be baked by hot temperatures Friday and Saturday.

The heat was expected to be especially noticeable in the eastern part of Contra Costa County, where temperatures were expected to approach 100 degrees by Sunday. On Thursday, fire and medical crews treated six people overcome by heat exhaustion at Deer Valley High's ceremony in Antioch. Two of them were hospitalized.

Liberty High in Brentwood scheduled its graduation ceremony for 6 p.m. on Friday. Freedom High in Oakley and Heritage High in Brentwood each are slated to have their ceremonies at 9 a.m. on Saturday, a half-hour earlier than originally scheduled.

"We've had contact with all three of the schools, and we've done a little bit of preplanning," said Chief Hugh Henderson of the East Contra Costa Fire Protection District. "They are doing their best, and we are as well, to get word out that people need to be hydrated and bring the shade with them in the form of hats. Wear light clothing, too. We're hoping for the best."

Stages were set up at the Deer Valley High graduation with ambulance workers and paramedics on hand to treat any issues faced by the approximately 6,000 people in attendance. But stages will not be set up at the other three ceremonies because the fire district simply lacks the manpower, Henderson said.

"If and when there are issues, we do know where those people will be taken for treatment," he said. "But as far as actually being able to set up a stage area like we did at Deer Valley, we won't be doing that."

Heritage High School is taking great pains to avoid a repeat of last year, when 17 people had to be treated for heat-related emergencies.

The school has bought 1,500 bottles of water for its 512 graduates and staff members; additional water and Gatorade will be for sale to raise money for campus clubs and classes.

In addition, the theater will be available for elderly guests to watch a live feed of the ceremony and Heritage also will be streaming the event on the Internet so those who don't want to brave the heat can view the proceedings from home.

Pop-up tents also will be scattered around the stadium in case temperatures become too much for some of the 4,800 visitors expected, and the school has designated the gym's wrestling room as a triage center if it needs to summon emergency personnel.

Heritage also has relaxed its dress code this year: Graduates will be allowed to wear sunglasses and male students can forego the traditional jacket and tie worn under their robes.

Approximately 5,700 people are expected to attend the Freedom High graduation, according to Principal Eric Faulkner. Attendance at the other two graduations is expected to reach at least 5,000 people, fire officials said.

Those treated at the Deer Valley graduation ranged in age from their 30s to 80s, Contra Costa Fire Protection District spokesman Kent Kirby said. He also said the heat can be particularly grueling for older people and for those who struggle with weight problems.

"A headache can be one of the earliest signs that your body is starting to overheat," he said. "So we want to make sure people are safe and know to seek help if they start to feel out of sorts."

Among the other symptoms of heat exhaustion are an elevated heart rate, muscle cramps, dizziness, and excessive thirst.

"The best, most preventive thing to do is drink water, room temperature," Kirby said. "The more hydrated you are, the better off you're going to be."

Contact Rick Hurd at 925945-4789 and follow him at Twitter.com/3rderh