JACKSONVILLE, Fla. – The death toll in San Antonio has risen to 53 as federal authorities investigate who was behind the southern border’s deadliest human smuggling episode.
The driver along with two other men from Mexico remained in custody as of Wednesday.
Authorities said 67 people were packed into a semitruck found abandoned near auto salvage yards on the edge of San Antonio.
More than a dozen survivors are being treated for heat-related injuries which are as serious as brain damage and internal bleeding.
As the investigation continues, the News4JAX I-TEAM is looking at how high temperatures can go in a shipping container.
The I-TEAM teamed with instructors at the Fire Academy of the South in Jacksonville to find a trailer very similar to what these people were in near the United States-Mexico border in Texas.
In Florida on Wednesday, the temperatures reached around 90 degrees. At the time of the discovery in Texas, it was 103 degrees. Firefighters say it is quite literally a death trap.
At the Fire Academy of the South, first responders are used to training in high heat, but they have protective clothing, oxygen and water.
None of that appears to be the case for the migrant trailer smuggling nearly 70 people.
“I would think 70 people they would be sitting shoulder to shoulder,” said Jason Carpenter, the academy’s director. “Front and back. You close it up, there’s no ventilation of air.”
Most containers can only be opened from the outside, leaving people inside trapped.
The experiment started at 11:30 a.m., with Carpenter and News4JAX using an infrared thermometer.

Temperatures inside the container were between 90 and 100 degrees, depending on where the thermometer was pointed. Metal and dark surfaces produced higher temperatures.
After closing the hatchers and returning two hours and 15 minutes later, the temperature had risen significantly.
“You can feel the rush of hot air come out of it,” Carpenter said.
Inside, it feels like a convection oven. At this time, we don’t know how long the people were in there and conditions are actually cooler in Florida than they were in the desert, but the demonstration shows the danger.
The thermometer marked anywhere from 110 degrees in the front to 130 degrees in the back.
“You were just in there a short time, you can easily become dehydrated, even if you had water with you, just an hour or two,” Carpenter said.
Another trailer, which had been sealed all day, was even hotter.
The infrared marked temperatures from 130 to 145 degrees. Temperatures were higher along the roof and the metal walls.
It can take much less for someone to have heat stroke and die.
While the details are horrific to think about, Carpenter was not surprised that more than 50 people lost their lives. He said he hopes something like this never happens again.