This week, county health officials issued a public-health alert and advised residents to take precautions to protect family members and pets. They warned residents to carry bottled water, check on the elderly and not leave children or pets unattended in closed cars. The California Independent System Operator, which runs the state power grid, warned of power shortages if the heat wave and power demand persists. While Mayor Antonio Villaraigosa urged residents to save energy, the city broke the August power-use record as air conditioners thrummed across the city. “We’re calling on all our resources to generate and purchase enough power to meet demand,” the mayor said. Throughout the Valley, about 4,100 residents and businesses lost power, officials said. Thursday’s demand of 6039 megawatts broke a DWP record for the month of August. The all-time high was set in July 2006, at 6165 megawatts. To beat the heat, the workers at Swiss Cleaners stepped out from clothes racks and clouds of steam at least once an hour for ice-water breaks. “We work a little bit, then go outside for relief,” store manager Martin Aguilar said. “We can’t work inside all the time.” Staff Writers Rick Coca and Ramona Shelburne contributed to this report. [email protected] (818) 713-3730160Want local news?Sign up for the Localist and stay informed Something went wrong. Please try again.subscribeCongratulations! You’re all set! The National Weather Service posted an excessive-heat warning for inland valleys and mountains. An excessive-heat watch remains in effect today for Los Angeles and Ventura counties. “We’re going to suffer this all weekend long through the Labor Day holiday,” said Stuart Seto of the National Weather Service in Oxnard. On Thursday, the mercury hit highs of 109 in Woodland Hills, 109 in Newhall, 106 in Northridge and Van Nuys, 105 in Lancaster, 103 in Burbank and 91 in downtown Los Angeles. In Ventura County, temperatures reached 110 in Simi Valley, 109 in Ojai and 96 in Thousand Oaks. Some trace rainfall, courtesy of remnants from Hurricane Dean, fell in mountains north of Los Angeles and San Diego. Meanwhile, Angelenos suffered afternoon humidity levels close to 50 percent. CHATSWORTH – When temperatures shot up to 109 degrees Thursday, Luz Lopez and her co-workers headed outside for relief. Inside Swiss Cleaners, the wall thermometer hit the max of 120. “Mucho calor, mucho agua,” said Lopez, 37, one of four workers at the Chatsworth cleaners. Very hot, and lots of water. A muggy heat wave sapped Southern California, creating record power demand and blackouts in the San Fernando Valley and canceling at least one junior varsity football game – at Birmingham High School.