Seat Heaters Still Too Hot

In October 2014, Keith and Tammie Jo Smith took a two-hour car ride from Pine Bluff, Arkansas to their home in Bastrop, Louisiana. According to a complaint filed in U.S. District Court, in Monroe Louisiana, as he exited his 2008 Chevrolet Suburban, Keith Smith put his hands on the driver’s seat and noticed that it seemed unusually hot to the touch. But, he never noticed it while driving, because an on-the-job injury had rendered Smith a paraplegic since July 1991.

That night however, when Keith undressed to bathe, his wife noticed that the skin on his left buttock appeared to be burned. When the Smiths sought medical treatment, they learned that Keith had suffered severe burns, requiring extensive medical treatment and reconstructive surgery. Keith’s paraplegia already made his skin vulnerable to break down, and even after multiple procedures, he still had to be monitored every day for redness, blisters, and other signs of skin breakdown, the complaint alleges.

Subsequent tests of the Suburban’s seat heater found that the surface temperature could get as hot as 140ºF (60ºC).

In 1947, a pair of Harvard researchers A.R. Mortiz and F.C. Henriques Jr. conducted seminal research on the effect of hot temperatures on human skin. Studies of Thermal Injury II:  The Relative Importance of Time and Surface Temperature in the Causation of Cutaneous Burns, is the source of every voluntary and many internal manufacturer standards, covering heated products – from pulse oximeters to vehicle seat heaters. Moritz and Henriques examined the relationship between time and temperature using pig skin first, then human skin, along with mathematical modeling. They found that in the humans, the lowest surface temperature responsible for cutaneous burning was 44ºC (111ºF) when exposed for six hours. As the contact temperatures increased above 44˚C, the time to damage is cut in half for each 1˚C rise in temperature up to about 51˚C (124˚F). 

Despite this well-established threshold, some automakers are still designing seat heaters to work in ranges that exceed it, are still manufacturing seat heaters that clearly get much hotter in places than their design specifications, and are still foregoing simple countermeasures that their peers have been implementing since the 1980s. These design failures have led to burn holes in clothes and seat covers, minor burns to some and severe and permanent injuries in occupants with lower body sensory deficits, such as diabetics, paraplegics, quadriplegics and individuals with neuropathy.

In February 2011, Safety Research & Strategies, with support from Dr. David Greenhalgh, a nationally recognized expert in burn surgery and burn care, and chief of burns at Shriners Hospitals for Children in northern California, and other members of the burn rehabilitation community, called upon the National Highway Traffic Safety Association, the Alliance of Automobile Manufacturers and the National Mobility Equipment Dealers Association to address this issue. (See It’s Time to Make Seat Heaters Safer) In a Safety Record Blog post, we wrote:

"With no government or industry-wide standards, manufacturers have installed a variety of seat heater systems – some that reach temperatures significantly above human tolerances or have no automatic shut-off mechanism – or both. While most drivers know when to turn a hot seat off, occupants with lower body sensory deficits don’t feel the burn. The medical literature has been documenting serious and permanent burn injuries from car seat heaters to occupants with paralysis or diabetes since 2003. Disabled motorists have been complaining about the problem to NHTSA since, at least, 2002. The industry’s response has been to bury a warning in the owner’s manual. NHTSA’s approach to seat heater defects has been: no flames, no problem. These are preventable injuries – and it’s time government and industry began preventing them."

A Lack of Substantive Action

While we heard nothing from the Alliance or the mobility dealers, NHTSA responded that it would encourage the Society of Automotive Engineers to devise a voluntary standard.

In January 2016, SAE International issued Recommended Practice J3047.

“Recommendation for Acceptable Operating Parameters of Heated Automobile Seats in Order to Mitigate Occupant Injury” was written to “promote a temperature and duration guideline that mitigates the risk of thermal injuries to the heated seat user,” and include visual cues that the seat heater is on, and warnings in owner’s manuals for users with lower body sensory deficits. The practice included an equation that included the time in hours and the threshold temperature to achieve a first degree burn, with a maximum setting at 43ºC. Like all voluntary standards, the threshold was based on the work of Moritz and Henriques, and ISO 13732, which provides temperature threshold values for burns that occur when human skin is in contact with a hot solid surface, but does not set surface temperature limit values. The practice suggested a few strategies automakers could use to ensure that seats did not exceed the threshold: using an ECU to monitor the heater system via a thermostat or temperature sensor, or set the maximum operating temperature to 43 °C, or install an auto adjustment feature that turns the heater down or off before it exceeds the time/temperature threshold.

Indeed, some manufacturers have used lower maximum temperatures and shut-off timers since the 1980s. The 1995 Volvo 850, the 1996 Mercedes-Benz E-Class, the 2006 Ford F-150, the 2007 Dodge Charger, and the 2008 Ford Mustang use shut-off strategies. The 1983 Volvo limited the seat surface temperature to 86˚F; the 2006 Saab limited the seat temperature to 104ºF.

But the automakers that have lagged their peers in adopting designs that prevent seat heaters from overheating have done little else.

Dr. Greenhalgh says his team continues to see burns – particularly affecting diabetics – from the heat output of vehicle HVAC systems, but has not treated any seat heater burn cases lately.

“It’s been quite a while since I’ve seen any activity,” he added.

But, other doctors have – recent civil complaints show that incidents continue to occur. For example, in November 2016 after a two-hour drive, a paraplegic living in Memphis, Tennessee, alleges that he sustained severe burns on his buttocks and scrotum caused by the seat heater in his 2013 Kia Sorento SX. In August 2015, Wayne Butler of Harris Heights, Texas alleges that he was severely burned in his 2008 Chevrolet Silverado during a 30-minute drive, in which the seat heating system generated temperatures over 130ºF.

In 2003, Dr. Greenhalgh and his colleagues, Drs. Pirko Maguiña and Tina L. Palmieri wrote Car Seat Heaters: A Potential Hazard for Burns, which presented the case of a 48-year-old paraplegic who sustained third-degree burns on his buttocks after driving for 20 minutes with the seat heater on. The researchers tested the seat surface temperature of a Chrysler Town and Country vehicle and found that that one of the vehicle’s four heating panels reached a localized temperature of 120°F. At this temperature third-degree burns can occur within 10 minutes.

“The car seat heaters should never reach these temperatures,” they wrote in the Journal of Burn Injury Rehabilitation. “Because there is no warning light on the dashboard to signal when the heaters are ON, patients with impaired sensation may not be aware that the car seat heater is on. In addition, the heating elements should have a control device to turn them off when they overheat. The seat heaters could be improved if they offered a temperature control instead of just an on/off button that sets to maximal heat every time. Most importantly the seat heaters on every car should be tested to prevent accidents with heaters that come defective from the factory.”

Seven years later, Dr. Kenneth Diller, a member of the SAE sub-committee that wrote the standard, and a defense expert witness who teaches biomedical engineering at the University of Texas’s Cockrell School of Engineering; chastised Greenhalgh, Maguina and Palmieri alleging they misinterpreted Moritz and Henriques research,  by stating that at 120ºF  “third-degree

burns can occur within 10 minutes.”  Diller argued that the Moritz and Henriques data showed only second-degree burns would result at that time and temperature.

“Although this article has now been in the literature for many years, it is not too late to set the record straight regarding the scientific basis of the recommendations therein. Hopefully, professionals working in the field of seat heater design will have a more accurate guide to consider in determining the criteria for the regime of safe operation.”

The trio’s reply, published in the same issue, schooled Diller on the details of the Mortiz and Henriques experiments, showing that they had accurately used that foundational research and had made no errors in their conclusions. They noted “the patient discussed in the article clearly suffered from a third-degree burn as a result of using a car seat heater. That patient, being a paraplegic, was at a higher risk than most people for a burn injury because of lack of sensation and pressure to the area, both of which increase the risk of any injury…The burns that we treat, just as we described for the person in our car seat heater report, are real. Burns often lead to lifelong scars and occasionally, deaths.”

Greenhalgh says that the attack was odd: “People write papers and disagree, but not in that way. There’s theory and then there’s the real world, and it was very surprising for someone to be so vehement in making a big issue of telling people in the burn world that burns don’t hurt people.”

One Jury Verdict, Lots of Settlements

In the last decade, attorney Daniel DeFeo, based in Kansas City Missouri, has handled more than 20 civil liability cases in which a plaintiff with lower body sensory deficits suffered serious and permanent injuries.

In the course of his casework, DeFeo has tested seat heaters from several different automakers, and found that all exceeded the recommended threshold in places, hitting temperatures of 120-150ºF in spots. He’s also identified basic design errors in the two types of seat heater designs. The wire-grid style seat heater used in older model vehicles tends to develop hot spots near the seat bite, where the seat heater wires join with vehicle’s wiring harness. Or, the wires can become fatigued and short out. Newer vehicles use a forced hot air system, in which warmed air is circulated through a network of ducts in the seat. In those designs, hot spots can develop at the exhaust ports.

In either design, if the seat’s thermostat is located away from the hot spots, it will not accurately regulate the surface temperature as required by the manufacturer’s own standards or by the medical community’s recommendations that seat temperatures not exceed 105 º F, DeFeo says.

The vast majority of seat heater cases have been settled before trial. One exception was a $500,000 verdict for the plaintiff in a California case. Erica Davis, a paraplegic who became the first woman to reach the summit of Kilimanjaro in a wheelchair and the 2012 National Paratriathlon champion, suffered severe burns from her thigh to her buttocks from a malfunctioning seat heater in 2009 Chevrolet truck. In 2013, Davis successfully sued the dealership Chase and Shellworth Chevrolet. General Motors, which assisted the dealership in its defense, issued a statement in response:

“Although it was not a party to this case, GM believes the seat heater in Ms. Davis' vehicle is safe and performed appropriately. While respecting the jury's verdict, GM does not believe the seat heater caused Ms. Davis' alleged injuries.”

That’s a typical defense, says DeFeo.

“They defend them with the fictional argument that it’s not a burn, it’s a pressure sore. It creates a question of fact,” he says. “They don’t have a credible defense. In some cases, their own specifications prove the defect in their designs.”

GM is a case in point. In deposition testimony in the Smith case, two GM experts on seat heater design have conceded that that GM’s design parameters allow a maximum temperature for its seat heaters that are within the temperature/duration range that will cause burns to occupants. One of the experts, Louis Carlin, a Senior Technical Expert in Engineering Analysis in GM’s Global Vehicle Safety division, acknowledges that it is possible that the seat surface temperature could get as high as 46ºC and it would still be within the GM design specifications. In addition, Carlin acknowledges in his deposition that a person in contact with the seat for up to 8 hours can burn at temperatures lower than 46 ºC.

Other GM employees such as Ray Bush, the former manager of the GM’s mobility program, agreed in an April 2014 deposition, upon reviewing photographs, that the wounds of one victim were “severe “burns, and  “I think if I was the engineer or the person  responsible, I certainly wouldn't want to cause injury to anyone.”

DeFeo finds it perplexing that automakers like GM have relied on owner’s manual warnings, added in the latter half of 2010, rather than add a time-out feature to their seat heaters or recommend to the customers in their mobility programs that the seat heater be disconnected.

The burns suffered by para- and quadraplegics usually occur in the area of the ischial tuberosities – boney bumps located on the back side of the ischium, three bones that form the pelvis. And because of their unique risk of developing pressure sores, para- and quadriplegics are many more times at risk of skin breakdown after a severe burn. For clients that had active lifestyles, an encounter with an over-heated seat forced them to give up leisure activities such as horseback riding, skiing and hunting.  

Terry Cole, a successful businessman, and an incomplete paraplegic (his spinal cord was bruised, rather than severed in 1976) had gone to China in 2006 for stem cell treatments, which restored his ability to grip a ball, stand, and take a few steps on his own. But in November 2007, Cole was severely burned by the seat heater in his 2007 Cadillac Escalade on a 45 mile trip from a riverboat casino in Caruthersville, Missouri to his home in Sikeston.  His recovery forced him to lay on his side for three months, putting him back in his pre-treatment condition.

In 2009, he sued GM, Amerigon, the seat heater supplier and Sapaugh Motors, which sold him the Escalade. The GM bankruptcy stayed the litigation against the automaker, but the case against the other two defendants proceeded, with GM providing legal guidance. DeFeo says that the case ended in a mistrial after Amerigon violated the court’s orders by injecting false testimony into the trial. The judge also imposed monetary sanctions against Amerigon, and the Cole case settled before a second trial.

“Terry Cole lost everything he had gained,” DeFeo says. “It’s major damage, it’s the plastic surgery, it’s pain, it’s expensive. It’s a significant life-changing injury and they will have skin breakdown again.”