SRS and BioInjury

NHTSA to Investigate Seat Heaters

Reprinted from The Safety Record, Volume 8, Issue 1, March 2011

WASHINGTON, DC – Will the National Highway Traffic Safety Administration determine that seat heaters exceeding human burn tolerance are defective, as other public health agencies do, or will they continue to argue that not enough people have been burned?

Safety Research & Strategies and a group of burn specialists asked NHTSA last month to help prevent serious burn injuries that injure disabled drivers and passengers by re-examining its approach to seat heater defect investigations by categorizing seat heaters which exceed human tolerance as defective and encouraging automakers to recall them.

“This is a very simple issue: We should not wait to see how many people are burned by a feature that exceeds well-established human tolerances before the product is considered defective,” says SRS President Sean Kane. “Just like the limits on hot water temperatures to prevent scalding injuries, vehicle manufacturers need to take similar steps with seat heaters.”

SRS has requested that regulators, manufacturers and the mobility community take immediate steps and adopt long-term strategies to prevent further harm:

Manufacturers should limit the maximum seat heater temperatures to the limits of human heat tolerances and set all seat heaters on a timer. These time and temperature limits should be codified in an industry standard.

The mobility adapters and automakers’ mobility programs should develop a protocol to automatically disconnect seat heaters for disabled drivers with lower body sensory deficits.

The mobility adapters should immediately send out warnings to their customers alerting them to the dangers of seat heaters.

NHTSA should re-examine its approach to seat heater defect investigations and regulations.

Currently, there are no government or industry-wide standards on seat heater design or temperatures. In the absence of regulation, 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. In other cases, seats get hot enough to burn holes through the seat cover.

NHTSA has been investigating seat heater malfunctions for more than a quarter century. In total, the agency has launched six investigations into seat heaters overheating since 1984. Manufacturers, either influenced by an Office of Defects Investigation inquiry or at their own instigation, have recalled more than 600,000 vehicles in 13 campaigns. Since 2000, however, the agency has closed five investigations into seat heater malfunctions involving Chrysler, Volvo, Mercedes and Volkswagen vehicles. In an investigation into Mercedes ML 320 seat heater malfunctions, the agency decided that based on the low complaint rate, no defect trend existed. In most cases, ODI came to the conclusion that the harm caused by burning seats was minimal.

SRS and doctors from the Shriners Burn Hospital asked NHTSA to align its policies with other federal public health agencies, such as the Federal Drug Administration and the U.S. Consumer Product Safety Commission which do not minimize the safety risk when consumers report even minor burns from a heating-generating product, such as an electric blanket.

But, NHTSA officials appear to be sticking with their current approach. In a USA Today story about the issue and the call for action, published on February 22, the agency responded:

“Mr. Kane has provided no data on the frequency of such injuries, but nevertheless, NHTSA is reviewing agency data to determine how widespread the problem is. As part of its analysis the agency will determine whether the frequency and severity of this condition may create an unreasonable risk to safety. Based on its analysis, the agency will determine what actions, if any, are needed to address this issue.”

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.

Seat burn complaints are common on vehicle owner Internet forums covering a wide variety of manufacturers – BMW, Mercedes, GM, Toyota, Volkswagen and Volvo. Consumers have been lodging complaints with tNHTSA since the 1980s. A December 2001 report from an Irvine, CA owner of a 1996 Volvo 850 is typical:

“After starting the engine, I switched the seat heater on and drove away. Within 2 minutes of driving, a sharp pain developed in my right buttock. Within seconds a trail of dark smoke rose from the same area. After lifting my bottom off of the seat and realizing the smoke was coming from the seat I shutoff the seat warmer. The result of the incident left a burn mark on my pants and a cigarette sized hole in my seat cushion.”

The agency has also specifically received seat heater burn complaints from disabled vehicle owners or their advocates:

“My client, Peggy Stephenson was a passenger in the front passenger seat of a 2009 Ford Taurus. She is paralyzed from the waste down and was unaware the seat heater was on for the entire 2 hour drive from Phoenix Sky Harbor Airport to Sedona, Arizona. She subsequently discovered that she sustained 3rd degree burns on the bottom of her buttocks from the seat heater being on…. I just read a section of the owner’s manual for the car and there is a warning that says in substance that individuals with spinal cord injuries can sustain burns even when the seat heater is used at low temperatures when used for an extended period of time. This owners’ manual warning was obviously not read by my client when she entered the rent-a-car. A seat that can burn someone is not acceptable under any circumstances. In addition, a warning should be posted inside the vehicle in plain view since car renters won’t read the owner’s manual. The car seat heater should be recalled before more injuries.”

A 2003 article in the Journal of Burn Care Rehabilitation described the case of a 48-year-old male paraplegic with decreased sensation in his buttocks who suffered third-degree burns, caused by the seat heater in his new minivan. The patient reported that the heater was on for 20 minutes before he noticed the pain. Researchers found that the vehicle was equipped with four heating panels. Their tests showed that they reached a temperature of 95°F, but the heating panel near his burns reached a localized temperature of 120°F. At this temperature third-degree burns can occur within 10 minutes.

The Standards

The ASTM standard safe touch temperature for heated surfaces, ASTM C 1055-03 (2009) Standard Guide for Heated System Surface Conditions that Produce Contact Burn Injuries, provides a burn injury threshold from unintentional contact and establishes a means by which the designer can determine the acceptable surface temperature of an existing system where skin contact may be made with a heated surface. The maximum acceptable temperature for a surface is derived from an estimate of probable contact time, surface configuration and acceptable level of injury. For industrial designs, a contact time of 5 seconds is established, but for consumer products, a longer 60 second contact time is proposed, and even longer to reflect the slower reaction times for children, the elderly or the injured.

The background of the standard reports that for a surface temperature below 44˚C (111˚F), no hazard exists for exposures sustained for 6 hours. As the temperatures of contact increase above 44˚C (111˚F), the time to damage is shortened by approximately 50% for each 1˚C rise in temperature up to about 51˚C (124˚F). At temperatures above 70˚C (158˚F), the rate of injury exceeds the body reaction time and blood flow has little effect on the level of burn.

In 2001, Amerigon, a major seat heater supplier to the auto industry, recognized the importance of limiting temperature in another one of its products: a temperature-controlled mattress. The company, in conjunction with MicroClimate Solutions, is marketing a heating and cooling mattress under the brand name YuMe. The bed’s maximum temperature setting is 104°F. The owner’s manual contains an explicit warning to certain potential users: “Do not use the heat/cool feature of this bed with an infant, a child, an incapacitated person, a paraplegic, or a quadriplegic. A person who is insensitive to heat or cool, such as a person with poor blood circulation, should not use the heat/cool feature of this product, or anyone who cannot clearly understand instructions and/or operate the controls.” However, Amerigon does not provide similar temperature limits for its automotive designs.

Other industries manufacturing heat producing devices used in proximity to human skin are required to employ temperature-limiting design parameters. For example, pulse oximeters have become essential devices for evaluating and monitoring patient oxygenation. Under FDA regulations, the maximum allowable temperature of the probe, which emits a small amount of heat into the skin in the process of signal detection, is set at 41˚C (106˚F). Experiments show that pulse oximeter probes are safe up to a temperature of 43˚C (109˚F) for at least 8 hours in well-perfused skin and that above that temperature, there is a risk of burn injury.

For more information, read SRS’s Briefing Paper on Seat Heater Burn Injuries and SRS’s request to NHTSA and the industry.

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