SALISBURY TWP., Pa. — When a Northampton County man laced up his hunting boots last week, he had no reason to believe the heated insoles tucked beneath his feet could land him in a burn unit.
But later on that day, a lithium-ion battery inside one of the inserts overheated, ignited and burned through his sock and skin. Days later, he was undergoing treatment at Lehigh Valley Health Network’s Regional Burn Center.
Incidents like this — from warming insoles to electric gloves, vapes, drones and cellphones — are no longer rare, said Dr. Daniel Lozano, LVHN’s Chief, Department of Surgery, Division of Burn.
And while lithium-powered gear has become nearly unavoidable, problems tied to cheaply manufactured consumer devices have become a significant contributor to a disturbing trend: deep, devastating burns caused not just by flames from a fire, but by electronics exploding on the body.
“This has actually been going on for a while. It’s not new, it’s just different devices,” Lozano said Thursday.
With Pennsylvania’s deer hunting season underway and ski season just beginning, he’s warning people on the dangers of these rechargeable apparel products — and that heated inserts for boots or shoes pose a particularly high risk.
“If you contain a heated lithium-ion battery — like in a shoe insert — you’re almost asking for it,” Lozano said. “You’re creating an environment that retains heat.”
Reports document real-world risk
Cases like the Lehigh Valley hunter, whose family asked for privacy, are not just anecdotal — medical reports and regulatory alerts are beginning to catch up, and recent peer-reviewed case reports echo what Lozano and other burn physicians are seeing on the ground.
A 2024 article in the Journal of Burn Care and Research detailed a “full-thickness foot burn” suffered by a 39-year-old man after a lithium-ion battery powered insole experienced what’s known as thermal runaway — a process described by Lozano as “a chain reaction where there's a rapid increase in battery temperature, leading to the release of a large amount of energy.”
According to the authors — and just like in this local case — the battery “suddenly and unexpectedly caught fire,” burning the man’s foot in a matter of seconds.
Another broader review published earlier this year described three separate cases of full-thickness burns after heated-insole devices exploded.
Last December, a Minnesota burn unit reportedly treated three patients with similar injuries, just as the winter season was getting underway.
These documented cases underscore what doctors across the country have begun to recognize: as battery-powered apparel becomes more common, “rare but catastrophic injuries” also are more likely.
Why these burns are so severe
Most people imagine severe burns as the result of house fires or boiling liquids. But burns from lithium-ion explosions look shockingly worse, Lozano said, because the temperatures involved are dramatically higher.
The depth of a burn depends on two things, he said: temperature and duration of exposure.
“Water can’t get hotter than 212 degrees before it turns to vapor,” he explained. “But grease burns can reach 300 to 400 degrees. Lithium batteries burn hundreds of degrees hotter than that, and they stay in contact longer because they’re trapped in pockets or shoes.”
A third-degree burn can happen with instantaneous contact at just 156 degrees. The devices that fail often burn far hotter. The result: almost all lithium-related burns require surgery, Lozano said.
“The good news from all this is, usually these burns are contained to a small area. So while it's devastating to that particular area, it's not a big surface area burn which can be more life-threatening,” he said.
“But it can be limb-threatening. You can lose fingers, toes, feet, just because of the fact that it's in contact with you long enough to burn down into bone and tendons, which are not reconstructible. So that's the bad part of all of this. It causes a real, real deep burn.”
The road to recovery
“If you do get burned by one of these, you want to get away from the source of the flame if possible,” Lozano said.
“It's hard to get your pants or shoes off in a quick, timely fashion, but once you do separate yourself from it, you’ve got to cool [the burned area] very quickly, cool water, you know, something to kind of stop the heating and thermal injury process in its tracks."
For many victims, a major step in recovery is a skin graft, one of the most common burn surgeries but one of the most physically demanding for both patient and surgeon.
Burn surgery is unlike any other operation, Lozano said. While most surgeries aim to reduce bleeding, burn surgeons must deliberately shave away dead tissue until they see uniform bleeding — the sign they've reached healthy skin.
Then surgeons harvest a thin layer of skin, usually from the thigh, using a dermatome — “imagine a wood planer for skin,” Lozano said — and graft it onto the burn site.
“And you kind of keep it immobile and leave it on for about five days, and then you look and see if you have good grafting,” he said. “The graft starts to get a blood supply from the wound in about three days or so. And after about a week, it's pretty attached, pretty solidly.”
But full recovery is a long process.
“It’s going to take somewhere between eight to 10 weeks before that skin is thickened, or kind of firmed up enough to tolerate normal wear and tear. So it takes a few months for it to get you back to where you were,” Lozano said.
And burns to the feet pose a unique problem: the thick, durable skin on the soles can never fully be recreated.
"It can lead to lifelong sensitivity and durability issues,” he said, that can impact work, hobbies, and even driving.
There’s also the psychological toll of dealing with these types of injuries, Lozano said.
"As you can imagine, there isn't really an injury that's much more painful than a burn injury. Not to mention the fact that to treat it would cause a more painful injury with your donor (skin graft) site. That has to heal like a burn also.
"So there’s the pain and the anticipation of pain. Sometimes burns aren't deep enough to need a skin graft, but there's daily wound care, which is a daily initiation of pain every time you do it. So the psychological aspect of anticipatory pain is ... psychologically upsetting to patients.”
Regulators sound the alarm
In July, the U.S. Consumer Product Safety Commission (CPSC) issued a public warning urging consumers to immediately stop using a heavily marketed brand of heated insoles — iHeat — sold on Amazon.
The warning came after 11 reports of fires, explosions or other thermal incidents linked to the defective insoles — eight involving burn injuries, including second- and third-degree burns.
CPSC told owners to dispose of the insoles as hazardous waste, not in regular household trash or standard recycling streams, because lithium-ion batteries pose unique risks.
Less than two months later, on Sept. 4, the CPSC added another brand — Tajarly — to its warning list. The agency said it had already received four reports linked to burn-related incidents requiring extended hospital stays.
The local man burned last week had a different brand of insoles, also purchased on Amazon.
Lozano said cheap materials, impurities, damage from overcharging and the environment itself all need to be kept in mind.
“You're keeping it in a contained environment, which may not be ideal. So my feeling is, make sure you have good shoes and socks and think about using chemical insert warmers (think brands like HotHands) that don't cause these kinds of problems.
“Because if you do have this scenario, if you do have something that malfunctions, whether it's your manufacturing or the battery's damaged, or they're overcharged, or whatever the reason may be, it's impossible to get yourself separated from that source of heat in a rapid fashion. That's why it's going to burn even worse.”
