2002

Cellphones make wheelchair dangerously uncontrollable

(IEEE EMC Symposium)

In the Netherlands recently a wheelchair unintentionally drove off a subway-platform, badly injuring the person in it. Her insurance company started an investigation with help of an EMC laboratory, who found out that the chair would move uncontrollably in a field of only a few Volts/meter at 1.89 GHz.

The chair’s manufacturer argued that it complied with the relevant EMC product standard for wheelchairs. But the radiated susceptibility test in this standard did not go beyond 1GHz and the judge decided that the manufacturer could have known that 1.89 GHz was a commonly used cellphone handset transmitter frequency.

The manufacturer was sentenced because he had put an unsafe product on the market.

1994

FDA advises wheelchair manufacturers to warn against EMI risks

(FDA document)

Dear Powered Wheelchair/Scooter or Accessory/component Manufacturer:

The information contained in this letter is pertinent to manufacturers of powered wheelchairs, motorized scooters, and related accessories and components.

Technological advancements in the design of powered wheelchairs, coincident with the proliferation of devices that emit electromagnetic (EM) energy (especially communication devices), have caused us to become increasinqly concerned about electromagnetic interference (EMI) with powered wheelchairs. We believe that EM energy (or signals) in the environment can pose a potential hazard to users of powered wheelchairs and motorized scooters (collectively termed powered wheelchairs) by causinq these devices to move unintentionally. This problem could be exacerbated with the addition of accessories or customizinq components to the powered wheelchair.

We have received many reports of erratic, unintentional powered wheelchair movement. There have been instances in which this has resulted in serious injury. It is unclear how many of these incidents have resulted from EMI, but, based on our own field and laboratory tests, as well as information obtained from manufacturers and users of powered wheelchairs, we believe that EMI is one of the causes.

After evaluating this information, we believe that certain steps are necessary to provide information to protect powered wheelchair users from the potential hazards of EMI. These steps, which are outlined more fully below, include:

the establishment of a minimum recommended immunity level to interfering radiated electromagnetic energy;

product labeling to warn users of the potential hazards of EMI, provide information about the risks and how to avoid them, and identify the immunity level of the powered wheelchair (if known);

a recommended educational program to warn users of the potential hazards of EMI and provide information about the risks and how to avoid them; and

soliciting of reports of EMI problems and continued monitoring to evaluate the full scope of the problem.

2003

Immunity issues with pacemakers

(IPEM Conference)

Pacemakers have always been designed with interference in mind. When they sense signals outside of the normal signal range of 10 to 300 beats per minute they go into an 'interference mode' and pace in a backup safety mode. This will keep the patient alive but will make them feel very unwell. All modern pacemakers have bi-directional radio telemetry systems that allow the cardiology technician to send instructions to the pacemaker. The digital coding is robust, but it is an obvious point of entry for interference signals.

In general mains signals do not cause problems with pacemakers. Surgical diathermy can be a problem. There have been some reports of pacemakers being damaged and some currents being conducted down the lead and causing myocardial tissue fibrosis, with consequent loss of pacing function, but these are extremely rare. Arc welding has long been known to be contraindicated for patients who have pacemakers. The problem is mainly with spot welding as the interference generated can appear at roughly cardiac frequencies. There have been isolated reported cases of ventricular standstill when a therapeutic ultrasound unit's lithotripter is synchronised to the P wave of the ECG. RF physiotherapy equipment using pulsed and CW at 27MHz can cause interference problems - care needs to be taken and an expert involved in any discussion about patient treatment.

GSM mobile phones can be a problem when held very close to the pacemaker site. This is due to the 22Hz bursts of 900MHz signal at switch on and switch off, and 8.3Hz bursts during the ring phase. Patients are told to use the phone with the ear opposite the pacemaker site and not to keep it in their breast pocket. Otherwise there are no problems. Transcutaneous nerve stimulators (TENS) are common sources of interference. They can cause complete inhibition of pacing and potential death. Patients who require TENS above the waist should be individually evaluated by the pacemaker clinic and safe levels of operation established.

A number of recent reports have indicated that Electronic Article Surveillance (EAS) systems in shops can be a problem. These normally only occur when pacemaker patients linger close to the security gates. Under some extreme circumstances the field can be sufficient to cause the pacemaker to revert to its emergency reset conditions. This is not life-threatening but can make the patient feel very unwell.

External pacemakers are particularly prone to interference because they have a much longer lead and the system is not entirely screened within the body. Such systems carry a high risk in the hospital environment and patients need to be kept well away from physiotherapy departments which have potentially life threatening sources of interference. Mobile phones and hospital radios can also cause problems that may initiate dangerous cardiac arrhythmias.

1994

RF interference in ambulance

(Wall Street Journal)

Medical technicians taking a heart-attack victim to the hospital in 1992 attached her to a monitor/defibrillator. Unfortunately, the heart machine shut down every time the technicians turned on their radio transmitter to ask for advice, and as a result the woman died. Analysis showed that the monitor unit had been exposed to exceptionally high fields because the ambulance roof had been changed from metal to fibreglass and fitted with a long-range radio antenna. The reduced shielding from the vehicle combined with the strong radiated signal proved to be too much for the equipment.

1994

Talking EEG Machine

(Compliance Engineering)

This case involved EMI that prevented proper testing of surgically implanted probes used in monitoring specific portions of a patient's brain activity. With probes in direct brain contact, the potential between any two points is measured on an EEG machine. The EEG provides critical feedback to the surgeon during surgery. This particular EMI manifested itself on the analog plotting needles of the EEG machine as a modulated signal easily recognized as speech-hence a talking EEG machine! The EMI-caused noise was so severe that it completely masked the EEG signals and made the machine alarmingly ineffectual during surgery. The signal was from a local AM radio station, and the noise during surgery was from common impedance coupling between the EEG machine and the operating table. Bonding the EEG with the operating table eliminated the EMI and restored the critical brain monitoring function.

2001

Interference clouds future of multi-billion police radio project

(The Register)

The future of a £2.5 billion project to provide British police with a radio network has been thrown into doubt amidst fears that the technology could interfere with hospital equipment and even breath test devices or speed detection kit. Early trials of the equipment have led police forces to advise officer to switch radios off when in hospital environments, instead of simply refraining from transmitting as is the case with current kit.

The concern expressed by police is the latest twist in the controversy surrounding the provision of a next generation network for the emergency services, called Airwave, or the Public Safety Radio Communications Project, a contract for which was signed last year. The technology behind the system Tetra, (or Terrestrial Trunk Radio), uses handset that transmits signals to base stations at regular intervals and concern centres around the fear that these pulses could affect other equipment.

All British forces should have the technology available by 2004, but as police in Lancashire become the first force to go live with the system, another early pioneer has broken ranks to air its concerns. Police from the channel island of Jersey, which is going through pre-implementation testing of the technology, is advising its officers to be much more careful about using the equipment than was the case with previous kit. Because of fears of interfering with hospital equipment, the States of Jersey police have imposed tough rules on using equipment and ordered the lowest powered handset available.

The testing also threw up concerns that, according to a statement issued by the Jersey Police, "if a speed detection device external radio interference, it was rendered inoperative". There are also concerns about breath testing devices. According to reports police are being advised that they can only do breath tests 10m from handsets or 35m from more powerful car transmitters. This has raised concerns that the system, the price of which has already been a source of discontent with the old bill, will be turned off in many situations. The Police Federation has raised concerns that operational effectiveness and even police safety will be damaged, and not improved, by the introduction of the technology.

A spokeswoman for the suppliers of the technology, BT Quadrant, said that the equipment used complied with international standards. She compared the equipment to GSM phones which also have to be turned off in hospitals.

A spokesman for the Police Information Technology Organisation (PITO), which is managing the Airways project, said it was working with police to devise revised operational guidelines so that safety is not compromised. He admitted there was a potential for interference and that tests were ongoing, even as the first network was been rolled out in Lancashire, to determine how bad interference might be. In the long term a technological solution would have to be devised, he added.

Police radios can trigger positive breath test

(The Register)

If you're ever asked to do a breath test by the police you might do well to insist that they turn off their radios before you blow into their breathalyser.

The advice comes from an ex-copper who wrote to us after we printed a story about police concerns about interference from next-generation handsets. He writes: "When at the Metropolitan Police training school, it was taught that PCs should not press the PTT (push to talk) button on the personal radio whilst waiting the requisite forty seconds for the lights to (hopefully) go red. Never. "Oh, no - indeed. Definitely not. Especially if the subject was being 'griefy'. Honest."

He adds that the idea that that a PC might surreptitiously give a quick burst of transmit on his radio whilst his partner was administering the breath test to an uncooperative suspect, was similarly frowned upon.

It's worth noting here that, at least in Britain, the actual charging and conviction of drink driver suspects relies on a different test which is administered at police station. Our correspondent explains the technique was used to annoy awkward customers. "This merely gave the opportunity to cause inconvenience, spend time filling out the forms, apologise profusely and sincerely (again, honest) afterwards, give the driver back the keys to his car and advise him where he might find a cab to drive him back to it. At four in the morning.

"Oh dear. Terribly sorry, but we are not insured to give you a lift if you are not a prisoner anymore. Sir. No cash on you, then it's a long walk back, in the rain," he added.

Another reader, who worked for the St. John Ambulance, a first-aid volunteer service, recounts a time on duty when he saw a policeman using his radio to trigger a positive result on a breath test. Apparently it was all a bit of innocent fun and the guy was using the trick in a rather strange attempt to chat up a woman he fancied. Our man in the St. John's Ambulance service says that ambulance radios can have the same effects on breathalysers. It's not that we condone drink drivers, but if you're ever pulled up (and assuming you're not too drunk in the first place) now you know what to look out for. Let's be careful out there.

Hand portable transmitters and cellphones interfere with medical equipment

Many types of hospital equipment are susceptible to RF radiation from hand-portable mobile radio transmitters – diagnostic equipment such as ECGs, EEGs, pulse oximeters and other physiological monitoring equipment; and therapeutic equipment such as infusion pumps, ventilators and defibrillators. Physiological monitoring equipment is very sensitive – hence very susceptible.

The type of modulation employed by the mobile transmitter can be significant. For example, an external pacemaker withstood a GSM signal (modulated at 217Hz) at 30V/m field strength, but TETRA modulation (17Hz) caused interference at 3V/m.

York EMC Services recommend a distance of 1.2 metres be maintained between typical hand-portable transmitters and medical equipment. Rice and Smith (Canada) found that 10 out of 14 devices failed with a 0.6W mobile phone at distances of under 500mm. Irnich and Tobisch (Germany) tested 224 devices and recommend a safe distance of at least 1 metre (but 1.5 metres for emergency services’ mobile handsets, because they are more powerful). The U.K.’s Medical Devices Agency tested 178 devices and found that 4% exhibited effects with mobile transmitters at 1 metre distance, although only 0.1% of them had serious problems at that distance (Bulletin BD 9702).

It is estimated that 1 out of every 200 patients admitted to US hospitals die due to medical errors, an annual rate exceeding that due to road accidents or heart disease. In the vast majority of cases, excellent physicians and medical staff make such errors because they do not have access to appropriate information (e.g., medical textbooks, correct dosages for medication; patient health history records, etc.). At least some of these deaths would be preventable if wireless information technology were widely used to make the necessary information quickly and easily available wherever it is needed throughout a hospital. However, the associated increased RF emissions may cause increased medical-device malfunctions.