Burn specialists, a safety advocacy group and the National Highway Traffic Safety Administration (NHTSA) are investigating instances in which heated car seats allegedly burned drivers or passengers. Some concerns stem from malfunctioning seat heaters, but others arise with seats that function as the manufacturers intended, but are being used by people who lack sensation in their lower extremities.
During a six-year period, NHTSA received 138 complaints about malfunctioning seat heaters, with reports ranging from a burning smell to visible flames. Sixty-nine of the accounts involved some mention of fire, according to an Edmunds analysis of complaints made to NHTSA's Office of Defects Investigation (ODI) from January 1, 2005 to March 31, 2011.
NHTSA began conducting an analysis of seat heater problems after Sean Kane, president of Safety Research & Strategies Inc. and Dr. David Greenhalgh, chief of burns at Shriners Hospitals for Children, Northern California and chief of the burn division at University of California, Davis, wrote letters in February raising concerns. Heater temperatures that exceed human tolerance pose a particular risk for people with little or no sensation in their lower extremities because of such conditions as paralysis, Kane and Greenhalgh wrote.
Greenhalgh, who has researched burn thresholds, told Edmunds that the most conservative approach would be to set a 105-degree limit for the heaters. Ideally, people with paralysis in the lower limbs should avoid using the heaters, he said.
Karen Aldana, a NHTSA spokeswoman, declined to comment on how long the agency's investigation will take. Part of the analysis will involve determining "whether the frequency and severity of this condition may create an unreasonable risk to safety," the federal agency said in a statement.
The Alliance of Automobile Manufacturers also is looking into the issue, according to spokesman Wade Newton. He declined to review and comment on the Edmunds findings.
In the NHTSA complaints reviewed by Edmunds, some consumers described a burning odor or seeing smoke. Burns usually occurred on the back or the bottom area. One complainant said that the burning smell started shortly after he put the car into Drive. Within a mile, according to the report, "I felt intense heat on my left side and saw smoke coming out of the seat. Upon exiting the car, I saw that my seat was on fire."
Mercedes and BMW were the two makes most frequently involved, with 34 and 27 complaints, respectively. Twenty-eight of the Mercedes complaints involved the M-Class or the GL-Class.
When provided this data, Mercedes replied with a brief comment via e-mail, saying the company was aware of "instances in which the seat heaters caused relatively minor irritation — similar to a bee sting."
A number of factors might influence the heating intensity. Most frequently, it's stress to the seating surface caused by people getting in and out of the car over a long period, Mercedes said in its statement. Over time, that process "could lead to a break in the electrical wire of the heating mat," wrote Mercedes Product and Technology spokesman Robert Moran. The seat heating function also can be deactivated through a plug connector beneath the seat, he wrote.
Kane, who also is looking at NHTSA complaints, described the federal agency's data as incomplete and not reflective of the full range of heater problems, which might only emerge in other forums, such as hospital records.
He reported talking to a Kansas City physician who has treated five heater-related burns. As of mid-March, Kane estimated that he would compile reports of more than 150 such problems, based on NHTSA data and consumer or physician feedback.
But any burn that could be avoided is one too many, he stressed. "The key issue is very simple," Kane said. "If a seat heater exceeds human tolerance for burns, it should be considered defective. There is no reason for it."
In his February letter to NHTSA Administrator David Strickland, Kane recommended that the federal agency reexamine its approach and "categorize seat heaters that exceed well-established human tolerance as defective and encourage automakers to recall them."
People with paralysis are among the most vulnerable because other car occupants can move or turn down the heater, Greenhalgh said. In a 2003 article in a professional journal devoted to burns, he described a 48-year-old paraplegic man who suffered third-degree burns during his initial drive in a new car with a seat heater.
Greenhalgh's research has shown that a burn takes at least 8 hours to develop when the skin is in contact with an object of at least 109 degrees.
Once the skin is burned in a weight-bearing area, such as the buttocks, it's difficult for the wound to heal, and the injured people "basically can't sit" during that time, he said. In February, he wrote to the National Mobility Equipment Dealers Association, a nonprofit trade organization focused on car and driving modifications for people with disabilities, supporting the concerns raised by Kane's group.
Safety protections vary not just between different car manufacturers, but even among models produced by the same manufacturer, Kane said. In a separate February letter to the automobile alliance, Kane credited some manufacturers with taking prudent measures, such as equipping cars with heaters that shut off after a designated period of time or setting a temperature threshold of 105 degrees.
"But other manufacturers leave it to the occupants to determine when to turn off the heated seat feature and some have no visual telltale to alert occupants that the seat heater is on," he wrote.
