Full-Thickness Burn Resulting From an E-Sock: A Case Report

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Li-ion batteries are an alternative power source for many new technological developments. They power common devices such as smartphones and e-cigarettes, as well as various cold weather clothing items like socks and gloves. With these devices' growing popularity, there has also been a rise in battery-associated burn injuries. Recent literature has shown the dangers of corrosion injuries from ingestion and thermal and explosive burns caused by Li-ion battery-powered everyday devices.^1-6 These injuries can cause significant morbidity and mortality, and typically require surgical intervention.^2,3 Due to their ubiquitous nature and limited studies on risk profile, it is important to continue reporting adverse outcomes associated with Li-ion battery-powered devices. Thus far, the literature has cited incidences of Li-ion battery-associated burns from e-cigarettes, mobile phones, and electric scooters and bikes.^1-6 To the knowledge of the authors of the current case report, there have been no reported injuries in the literature associated with Li-ion battery-powered socks. These socks are commonly worn by skiers, snowboarders, and winter hikers. Here, the authors present the first reported case of a thermal burn caused by an Li-ion battery-powered electric sock.

This case study consists of an otherwise healthy 43-year-old male who sustained a full-thickness burn on the left lateral lower leg from an Li-ion battery-powered electric sock after 4 hours of wearing the socks while skiing. The patient denied feeling any burning sensation during usage and was wearing the socks on both feet. However, after removing the socks, he noted a contact burn to the skin in the area where the battery was positioned on the left lower extremity only.

The patient cleaned and covered the burn and presented to a local emergency department 1 day later. He was diagnosed with a partial-thickness burn and prescribed trimethoprim/sulfamethoxazole but transitioned to a 10-day course of doxycycline to be completed as infection prophylaxis after developing a full body rash. The patient cleaned the wound daily for the first 5 days with either hydrogen peroxide or rubbing alcohol and kept it uncovered.

The patient first presented to the authors' outpatient burn clinic 10 days post-injury, at which time he was noted to have a 7.5 cm² full-thickness burn to the left lateral lower leg with mild surrounding erythema. The area was debrided in the office via sharp tangential excision of eschar down to muscle fascia under local anesthesia, and a non-adhesive dressing was applied (Figure 1). The wound was clean and presented with no evidence of infection at the 1-week follow-up (Figure 2). Non-excisional debridement in the form of minor sharp debridement of any non-viable tissue and gentle scrubbing with gauze and antiseptic was performed at each subsequent visit (3, 7, 9, and 12 weeks from initial presentation to the clinic), and the patient was advised to perform daily dressing changes with mupirocin and gauze. Given the size and full-thickness nature of the burn, the patient was offered surgical wound closure but preferred to proceed with local wound care. At the 9-week follow-up, the wound had decreased from initial size of 2.5 cm × 3.0 cm to 1.0 cm × 1.5 cm. The wound had achieved 95% closure at the 12-week follow-up (Figure 3) and 100% closure at 15 weeks (Figure 4).

This is a case of a patient who presented to the authors' clinic 10 days after sustaining a 7.5 cm² burn on his leg in the setting of Li-ion battery-powered sock use while skiing. There was evidence to suggest this was a thermal contact burn, with no suspicion of chemical or flame/explosion. The burn was likely a partial-thickness burn initially and may have progressed due to the infection, poor wound care, and time. When asked why he did not feel the initial burn when it happened, the patient did not have an answer. Ultimately, the burn progressed to a full-thickness injury with surrounding cellulitis that required surgical debridement. Although slow, complete wound closure was obtained with local wound care by 15 weeks post-injury.

Previous literature has cited Li-ion battery burns caused by e-cigarettes, mobile phones, and even electric scooters and bikes. Li-ion batteries are ubiquitous to the portable electronic devices that are in use every day. Given the increasing reports of battery-incited burns in the literature, it is necessary to consider how to safely utilize these devices. To understand the risks and recommendations associated with Li-ion batteries, it is important to first understand how these batteries function.

Li-ion batteries utilize electrochemical potential, which is a metal's tendency to lose an electron. Lithium has 1 electron in its valence shell, and therefore has some of the highest electrochemical potential. This means that pure lithium is highly reactive and can react with water and oxygen upon exposure.^5,7

The Li-ion battery is composed of an anode layer coated in a metal oxide, an electrolyte layer, a separator layer, and a cathode layer typically coated in graphite. When the battery is connected to a power source, an electron from the lithium atom is transferred to the anode while the protons from the lithium atom (Li-ions) stay behind at the cathode. This process of separating negative and positive ions continues until the Li-ion battery is fully charged. As the battery discharges, Li-ions will travel through the electrolyte layer back to the anode, while electrons travel through an external circuit to create an electrical current. In the anode, the Li-ion and electron will react to create a lithium atom once again so that the whole process can be repeated. The reaction between the Li-ion and its electron is exothermic—ie, releasing energy in the form of heat—which is why many Li-ion batteries have a cooling system.

Occasionally, these batteries malfunction. Li-ion battery malfunctions stem from chemical, electrical, and/or mechanical causes. Chemical malfunction is usually the result of overuse of the battery. With normal use, the Li-ion battery creates an SEI film, which creates resistance for the Li-ions traveling back to the anode.⁷ This resistance creates heat, thereby accelerating the increase in the battery's internal temperature.⁸ The SEI layer increases each time the battery is used, meaning overuse creates a larger SEI layer and thus more resistance; consequently, this results in more heat production. Chemical malfunction also releases oxygen into the cathode layer, which can be damaged due to excessive charging and energy storage. Lithium is highly reactive and becomes oxidized when exposed to oxygen, which further increases the battery's internal temperature. The excess heat in the battery system builds and leads to thermal runaway, resulting in rapid overheating and possible explosion.^6,9 Any physical damage to the battery's internal components or external shell is known as mechanical malfunction. Deformities to the external shell expose the internal components to additional environmental hazards such as oxygen or water.⁹ Most notably, lithium-water reactions result in the formation of lithium hydroxide and flammable hydrogen gas; it is this type of malfunction that can cause the corrosive and thermal burns cited in the literature.⁷

Given the history and appearance of the burn reported in the current case study, and the previously described mechanisms of battery malfunction, it is likely that this patient's injury was caused by the common thermal runaway effect of the battery-powered sock. Assuming the patient followed the sock's wear and care guidelines, mechanical malfunction may have occurred earlier in the day while he was skiing. The warm, moist environment of a skier's foot and ankle, and the possibility that the patient may have fallen while wearing the socks, could have precipitated an exothermic reaction. It is also possible that the patient left the battery charging for too long, resulting in a breakdown of the cathode layer and a less controllable Li-ion and electron reaction. Alternatively, the patient's socks may have surpassed the advised use limit, subjecting the batteries to chemical malfunction and leading to lithium oxide formation. Any of these scenarios could have led to thermal runaway. All 3 forms of malfunction are possible given the injury observed, especially when considering that the burn was unilateral rather than bilateral. If the injury were due to a simple overheating mechanism—ie, that the socks were simply worn for too long—bilateral injuries would be expected. However, given the unilateral nature of this injury, it is much more likely that the battery in the left sock had become compromised, thus leading to the thermal runaway effect and resulting burn.

It is worth noting that, although the patient's injury was likely due to a battery malfunction, improper initial wound care may have slowed the healing time. Burns such as this should be managed with a moist wound dressing to promote optimal healing and prevent infection. The patient's use of hydrogen peroxide may have contributed to the subsequent wound conversion, requiring more aggressive debridement.

Given the nature of Li-ion batteries and their combustibility, it is worth considering if they are truly safe for use in everyday devices. Particularly in the context of winter sports, where socks will commonly retain moisture from sweat and snow while being subjected to potential mechanical damage, consideration should be given to the potential dangers of these batteries as they degrade over time and become more prone to malfunction.

This study is limited in that it is a case report describing the clinical course and outcome of a single patient. This limits the generalizability to larger patient populations.

Li-ion batteries have become ubiquitous as an alternative power source for a multitude of everyday devices, from cell phones and heated socks to electric scooters and cars. With this increasing use in Li-ion batteries, clinicians have seen a corresponding increase in the incidence of battery-associated burns. Here, the authors present what they believe to be the first report of a burn caused by an Li-ion battery-powered sock. Skiers, snowboarders, winter hikers, and others should use caution when wearing heated socks, as cold weather, snowy conditions, and sweat may increase the likelihood of Li-ion battery malfunction. Further research should be performed to better evaluate the safety profile of these Li-ion batteries over time. 

Authors: Kailah Greenberg¹; Kristina M. Chang, MS²; Matthew D. Supple, BS³; and Jeremy Goverman, MD^3,4

Affiliations: ¹Bates College, Lewiston, ME; ²Tufts University School of Medicine, Boston, MA; ³Department of Surgery, Massachusetts General Hospital, Boston, MA; ⁴Harvard Medical School, Boston, MA

Disclosure: The authors disclose no financial or other conflicts of interest.

Correspondence: Jeremy Goverman, MD; MGH Fraser Burn Center, 55 Fruit Street, Boston, MA 02114; jgoverman@MGB.org

Manuscript Accepted: July 2, 2024