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
