 NORTH HILLS (CBSLA) — A family is in mourning after a mother and grandmother who worked as a mail carrier died during the heat wave that hit Southern California over the weekend. Postal Service for 28 years died on the job Friday, as a massive heat wave hit Los Angeles. Frank was pronounced dead at the scene on the 4800 block of Calderon Road after paramedics attempted to revive her, the Los Angeles Daily News reported. UPDATE: Federal investigators launch probe into Woodland Hills mail carrier’s death on 117-degree day 
 
 Temperatures soared to 117 degrees in the Woodland Hills area on Friday, surpassing the record of 106 degrees for that day, July 6, that was set in 1976. (The National Weather Service has kept records there since 1949, according to Keily Delerme, a NWS meteorologist.) But Winter could not say Monday whether the heat was a factor in Frank’s death. The corner’s office told PEOPLE that an official autopsy had been completed but that her cause of death was “deferred pending additional tests.” Results from those can take between four a six weeks. “We want to express our thoughts and prayers for the employee’s family at this difficult time,” said Evelina Ramirez, a spokesperson with the U.S. Our thoughts and prayers are with the employee’s family at this time.” 
 
 The spokesperson added that while mail trucks aren’t equipped with air conditioning units, “the safety of employees is always a priority.” Workers are reminded every day to stay hydrated, wear appropriate clothing and hats, carry sufficient amounts of water and ice and to stay in the shade as much as possible. “I can not believe it because I don’t think that it should have happened,” her sister Lynn Calkins explained to KTLA, adding that Frank had suffered a heat stroke last year during the hot summer months. Calkins places part of the blame on the Postal Service 
 
 “They need to start caring about their people a little bit more,” she said. Co-worker Joni Hogan Salvatore, who started working at the Woodland Hills Post Office before Frank, called her colleague “amazing” and “a very hard worker.” 
 
 “None of us are 20 (years old) anymore; it’s a hard job,” Salvatore said. “The most important thing is to make sure they have water and ice for their entire route,” Ramirez said.
– A 63-year-old postal carrier was found dead in her mail truck Friday amid a record-breaking heat wave in the Los Angeles area, CBS LA reports. Peggy Frank was found unresponsive in the Woodland Hills area, where temperatures had reached 117 degrees that afternoon, by a neighbor. Paramedics called to the scene could not revive her. Frank, who had worked for the US Postal Service for 28 years, was close to retirement. Friday was her first day back on the job after months off due to a broken ankle, KTLA reports. An autopsy has been completed, but her cause of death has been "deferred pending additional tests" and may not be determined for weeks, the coroner's office tells People. Frank's family believes the heat may have played a role in her death, and a colleague tells the Los Angeles Daily News that in such high temperatures, it can be as much as 15 degrees hotter inside the mail trucks, which do not have air conditioning. "They make us lock them and seal them for safety of the mail, but it’s horrible in there," she says. But a USPS rep, while expressing sympathy for Frank's family, says that mail is delivered in "all kinds of weather, including high temperatures" and that "the Postal Service strives to ensure that [carriers] have the tools and training to do so safely," including by reminding them to keep hydrated, have water and ice available for their entire route, stay in the shade when possible, and wear appropriate clothing.