For nearly a decade, Viviana Gonzalez has spent her summers delivering packages for United Parcel Service under sweltering sun in Palmdale, California – in a truck without air conditioning.

A typical work day means at least 10 hours in and out of one of UPS' brown delivery vehicles, where temperatures in the back, Gonzalez said, at times surpass 150 degrees. Her only relief is a fan that blows hot air into her face.

Gonzalez has come to expect waves of nausea and weakness throughout the day.

"We're out there for hours, so you can only think about how much stress we're putting on our bodies," Gonzalez said.

Delivering packages is a solo task. Sometimes, Gonzalez calls her friends for support while she's on her delivery route, in case her health takes a turn for the worse.

Last June, a 24-year-old Palmdale UPS driver named Esteban Chavez was found unconscious in his truck while on his delivery route in Pasadena. Chavez died of sudden cardiac dysfunction, according to the medical examiner's report. Temperatures exceeded 90 degrees that day, and his family believes his heart failure was due to the heat.

Another driver, 23-year-old José Cruz Rodriguez, died from a heat-related illness, according to the Occupational Safety and Health Administration, during his UPS delivery shift in Waco, Texas, in August 2021. His family filed a wrongful death lawsuit against UPS and ultimately settled with the company.

Gonzalez often thinks of her 18-year-old son when she's out driving.

"What would've happened to him if I had died in the back of the truck?" Gonzalez said. "We are putting our lives at risk by delivering in these hot weather conditions. And we're human – we don't know what our body is going to take."

New heat safety measures at UPS

Conditions are set to change for UPS delivery drivers nationwide. UPS and the Teamsters union, which represents 340,000 UPS workers, negotiated a tentative heat safety agreement in June to install air conditioning systems in all of the company's small package delivery vehicles purchased after Jan. 1, 2024.

UPS said it will send the new vehicles to the hottest parts of the U.S. first, when possible. The company has also agreed to add new heat shields and fans in delivery vehicles.

The agreement will be finalized once UPS and the Teamsters negotiate a new contract – a process that could lead to the largest strike against a single employer in U.S. history.

Teamsters President Sean O'Brien called the heat safety agreement a "significant step towards a stronger new reality for so many workers and their families." UPS said in a statement that worker safety "remains our top priority."

Jim Mayer, a UPS spokesperson, said the company currently supplies its employees with cooling gear. But drivers have to get through this summer's heat waves – mostly without air conditioning.

"We're still going to have to live through this peak, but it's almost like a touchdown," Gonzalez said. "We're almost there."

Drivers at UPS competitors also concerned about heat risks

OSHA lists mail and package delivery as one of the primary industries where outdoor workers suffer from heat-related illnesses. The agency's work-related injury database shows at least 40 UPS drivers have been hospitalized due to heat-related illness since 2015.

It's not just a UPS concern. Drivers working similar jobs for UPS' competitors – including Amazon and FedEx – are also raising alarms about heat on the job as climate change causes temperatures to rise.

Both companies said their delivery vehicles are equipped with functioning air conditioning. But drivers Renica Turner and Demetria Forte, who deliver packages for Amazon, as well as Johnathon Ervin, the owner of an Amazon subcontractor, told NPR the air conditioning is often broken in Amazon-branded vans.

Most workers at Amazon and FedEx aren't represented by a union – and they aren't even classified as company employees, making it that much harder to demand protections.

Amazon workers join the fight

Last April, Turner was delivering Amazon packages on a 110-degree day in Victorville, California – northeast of Los Angeles – when her body started to tingle. She thought she might pass out.

Amazon said company-branded vehicles have functioning air conditioning, and those without it are immediately grounded.

But Turner said the air conditioning and fans in the van weren't working on that day. When she rolled down the windows, hot air drifted inside. She said she let the Amazon dispatcher know about her symptoms.

All she got was a 20-minute break.

"They never sent no one out to help me with the rest of the route," Turner said, referring to the 300 packages she was expected to deliver, at a rate of 25 per hour. "I had to deliver the rest of that, feeling woozy, feeling numb, and just really overwhelmed."

Turner works for an Amazon subcontractor called Battle Tested Strategies, or BTS. It's one of about 3,000 independent contractors in the e-commerce giant's delivery network – small businesses contracted by Amazon to deliver packages.

BTS owner Johnathon Ervin, who leases vans from Amazon, said Amazon regularly fails to fix broken air conditioning in the vehicles. He said it can take weeks, even months, for Amazon to repair the vans.

"It's insane that we're forced to drive these vehicles," Ervin said. "We went to Amazon, asked them to retire the vehicles, and it went on deaf ears."

Email communications reviewed by NPR show BTS has reported several cases of malfunctioning air conditioning in leased vehicles. On September 1, 2022, Ervin wrote in an email to Amazon that the air conditioning units in five vans stopped working on that day alone.

Similarly, in June 2021, emails show it took weeks for BTS to get air conditioning units fixed, as the subcontractor navigated delays from Amazon's third-party repair companies. An Amazon spokesperson said Amazon is not responsible for delays, adding that subcontractors are in charge of fixing the vans.

Turner and 83 of her colleagues unionized with Teamsters and bargained a contract with BTS in April, in large part to push for heat safety measures. It's the first union of its kind in the Amazon delivery network.

These newly-unionized drivers have been on strike since late June over Amazon's termination of its contract with BTS. Ervin and the Teamsters union allege Amazon is retaliating against the workers for unionizing; an Amazon spokesperson, however, said the company ended its contract with BTS over unrelated contract breaches.

Regarding heat safety, the spokesperson said Amazon adjusted some of its delivery routes last year so drivers can take more breaks to cool down.

The burden falls on drivers

OSHA, the federal agency that oversees workplace safety, has recommendations for how employers should handle heat – but it's still in the process of drafting heat-specific worker protections.

This means, currently, the county's biggest delivery companies have no legal obligation to provide nationwide heat protections for drivers.

Brenda Jacklitsch, a heat stress expert at the National Institute for Occupational Safety and Health, said outdoor workers can experience heat-related illnesses ranging from heat rash and heat cramps to heat stroke.

Employers, she said, can schedule the most physically intense work activities for cooler times in the day – and provide air conditioning and fans when possible.

"Even having an air-conditioned vehicle that is pre-cooled is a great way to help cool somebody down during a rest break," Jacklitsch said.

Jacklitsch added that "buddy systems" can help workers look out for one another and monitor symptoms of heat stress. This can be a challenge for drivers who deliver packages on their own.

For now, delivery drivers are doing what they can to protect themselves from extreme heat.

Forte, another driver who delivers packages for Amazon in Palmdale employed by subcontractor BTS, said Amazon's expectation of 25 to 30 package deliveries per hour puts a strain on her health when temperatures surpass 100 degrees.

Forte rotates through different vans for her delivery shifts. She tries to secure a van equipped with working air conditioning when she reports to work in the morning.

But she said some days, she's stuck without AC, in which case she pours frozen bottles of water over the van's cooling rack.

"(Customers) don't see all of that. They just see, 'Oh, yes, my package is here, great,'" Forte said. "They don't see what we go through on a daily basis."