Fowler Associates Labs

Static Electricity can play havoc with cochlear implants

Plastic playground slides can zap hearing devices and force kids to play in silence

As reported by Eric Hand
St. Louis Post-Dispatch

Six-year-old Taylor Zinderski slid down a plastic slide and slipped into silence.

It was October at a church playground. Taylor, deaf for almost two years, ran to her father. She told him her cochlear implant -- an electronic device that lets her hear -- had suddenly fizzled.
It had been zapped by a static electric shock. Chris Zinderski hadn't switched off his daughter's implant because he didn't believe that static could really be a problem.
"Now I've learned my lesson," he said.

Plastic slides studied

The shock didn't ruin Taylor's implant, but it did require an inconvenient trip to an audiologist. Static electricity is so much of a worry and hassle for the deaf that Washington University electrical engineer Robert Morley has a grant to study one of its main sources: plastic playground slides.

As playground slides evolve from metal to durable, cheap and colorful PVC plastic, deaf children face a sad choice: Don't play, or turn off their implants and play without sound.
Some playgrounds, such as new "all inclusive" ones, have deliberately included metal slides, which don't produce static electricity. But many others don't -- including some that are supposed to be accessible to disabled children.

"Every time I look, there's another we can't go to," said Peg Jones, the mainstream coordinator at St. Joseph Institute for the Deaf in Chesterfield, Mo.

In the name of science

Morley, who helped pioneer digital hearing aids, got a small federal grant to study the issue. His first task: See how much static a slide can make. He sent his two daughters down St. Louis-area plastic slides hundreds of times, wearing different clothes.

Static electricity occurs when a "positive" material sheds electrons by rubbing a "negative" material that attracts them. Good static-producing combinations include wool and PVC plastic, hair and rubber, and skin and polyester. Cotton, paper and steel are neutral.

The resulting charge on both objects can dissipate slowly in humid air, or cause a shock if it touches something that is grounded, such as a person, a car -- or the metal pole that Morley had his daughters touch after each slide.

Humidity is a factor

The type of clothes and length of the slide didn't matter much. But humidity did. In the cold, dry air of winter, Morley's daughters achieved charges of about 10,000 volts. Morley says that in the dry air of Tucson, Ariz., a colleague measured 20,000 volts after a slide.

In coming months, he will apply those voltages to test implants, which are rated to withstand 8,000 volts, according to Doug Miller, an engineer with Cochlear Americas, one of the manufacturers of the devices.

Cochlear implants can cost more than $50,000. They require a delicate surgery to insert a wire into the snail shell-shaped cochlea. A hearing aid outside the ear picks up sound and converts it to an electrical signal that is broadcast through the skin to the internal device, which electrically stimulates the auditory nerve.

Miller and Morley both stress that static electricity is not a threat to the internal part of the implant. It can only zap the external equipment and force a trip to the audiologist for recalibration.

Miller says it will soon be a nonissue, as deaf people move to newer implants that can withstand more static. New rules will require a rating to 15,000 volts, and most companies test the devices at even higher levels, he says.

Spray away the static

But until then, each room at the Moog Center for Deaf Education in St. Louis County will keep a bottle of diluted fabric softener for spraying down staticky kids and carpets. On a cold November morning, family school director Betsy Brooks watched for signs of static.At recess out on a wood and metal playground, the children played with their implants turned on. Taylor sailed down the metal slide, her mop of curly blond hair bouncing in the air. Jones feels sorry for the children who have to turn their implants off."It's a completely different experience to go down the slide without the wind and the 'whee,' " she said.

January 2006

UPDATE: Allowing the children to wear our new Static Friendship Bracelet* may help this problem or make it become obsolete.