[ EMF-Link Home
| Online Store
| Comments ]
FDA is receiving inquiries about reports that electromagnetic interference (EMI) can cause some power- driven wheelchairs and scooters to move unexpectedly. The following can be used to answer questions.
The agency has investigated this matter and determined that EMI can cause unexpected movement in some power-driven wheelchairs when they are turned on. Not all brands and models of power wheelchairs and scooters have this problem. Some have greater immunity levels than others that may protect against EMI.
Common sources of EMI include cellular phones, CB radios, TV and radio stations, amateur (RAM) radios and police, fire and ambulance radios.
After receiving reports of problems, FDA tested sample wheelchairs and scooters in its laboratories and obtained information from manufacturers and users about possible EMI- related incidents. As a result of its review, the agency last May asked wheelchair manufacturers to take steps to protect powered wheelchair users from the potential hazards of EMI.
FDA required all firms to clearly label wheelchairs and scooters with the immunity level, or else state that the immunity level is not known. It also required them to label wheelchairs and scooters to warn users of the potential hazards of EMI.
The agency also asked manufacturers to:
FDA first learned of a possible problem with motorized wheelchairs from a complaint in June 1992. As a result, the agency began testing sample wheelchairs in its laboratories. Those tests, on several brands of power-driven wheelchairs and scooters, revealed that most -- but not all -- of those sampled were susceptible to interference at various radio frequencies. In some tests, the brakes released. In others, the wheels moved uncontrollably. Sometimes both occurred at once. The extent to which this happens in actual use is not known.
In early 1993, FDA began inspecting facilities of all domestic and foreign motorized wheelchair and scooter manufacturers to gather information on the problem. The agency reviewed warranty and complaint files and looked at any manufacturing practices that could contribute to this type of problem.
The inspections revealed numerous complaints about erratic, unintentional wheelchair movement, sometimes resulting in injuries. It is unclear, however, exactly what caused the chairs to move in those cases. In addition to EMI, unexpected movement can be caused by failure of an electronic component or by user error.
In May 1993, FDA sent letters to all U.S. manufacturers asking them to provide any information they had about possible problems with radio wave interference, including complaints, reports of injuries and studies on power-driven wheelchairs. In July 1993, the agency alerted consumer groups that represent wheelchair users about the possible problem and requested similar information.
An estimated 10, 000 motorized wheelchairs and 50, 000 motorized scooters are sold annually in this country.
FDA has been receiving inquiries about reports of possible electromagnetic interference with some electronic medical devices. The following can be used to answer questions.
The agency has received a number of reports in recent years of possible EMI-related problems with medical devices--some resulting in serious injury and death.
Electronic medical devices can be susceptible to interference if they are not designed to be protected against it. Common sources of EMI include cellular phones, police, fire or ambulance mobile communications equipment, radio and TV transmitters, amateur radio transmitters and CD radio transmitters.
There have been reports, for example, that patient breathing monitors failed to alarm when needed because of radio wave interference that cellular phones, when used too close to an electronic medical device, have interfered with the device's operation; and that radio wave interference causes some power-driven wheelchairs to move unexpectedly.
Because of these reports, FDA has increased its vigilance of possible EMI-related problems and has been working with manufacturers and voluntary standards organizations to improve the electromagnetic compatibility (EMC) of devices.
In response to reports about wheelchairs, FDA conducted a preliminary review to see if they could be affected by EMI. The agency determined that radio waver, can cause unexpected movement in some power-driven wheelchairs and scooters, but the extent and severity of the problem is not yet known. FDA tested wheelchairs in its laboratories; initiated an inspection of wheelchair manufacturers; and asked manufacturers and consumer groups that represent wheelchair users to provide any information they have an the problem. In May, FDA asked manufacturers to assure that all new wheelchairs have at least a reasonable immunity to EMI, that the chairs be labeled with immunity level and that purchasers be warned about the possibility of EMI and instructed on how best to avoid it.
Because of reports several years ago of unexplained failure of apnea monitors to alarm when a patient stopped breathing, FDA engineers investigated the susceptibility of these devices to EMI. FDA laboratory tests showed that most commercial monitors could malfunction when exposed to relatively low radio frequency strengths, which could result in failure to alarm.
One product in particular was found to be unusually sensitive to such interference. FDA required the manufacturer to recall the monitor and correct the problem. The agency has since established an electromagnetic compatibility (EMC) standard for all breathing monitors. The agency has also investigated problems with an anesthetic gas monitor, a device used to monitor the amount or anesthesia given to a patient. FDA had received several reports that the machine sometimes displayed erroneous gas concentration readings during surgery, but none mentioned EMI as a possible cause. However, further investigation revealed that the problem was caused by EMI from the electronic knives used during surgery. The manufacturer corrected the problem by changing the gas monitor's software.
In addition to investigating specific reports of possible EMI problems and testing devices in its laboratories, FDA is initiating steps to require medical device manufacturers to design and test their products to ensure they are electromagnetically compatible.
In addition to requiring an EMI immunity level for wheelchairs, FDA currently requires that all new respiratory devices and implanted pacemakers moot a rigorous FDA guideline for ENT before they can be approved for marketing. The agency plans to develop similar guidelines for other medical devices as needed.
FDA is also working with the International Electrotechnical Commission to develop international EMC standards for medical devices.