Hello all, There is a HUGE difference between the frequencies used by
ultrasonic cleaners and ultrasound medical equipment.
And yes, you can certainly hurt yourself in an ultrasonic.
When my cousin was finishing her degree at the School of Mines in
Golden, CO, one of her classmates was rushing to complete the
preparation of hundreds of thin section specimens of minerals for
his master’s thesis. He was working long hours and running right up
against his deadline. One evening he just figured that it was
ridiculous to have to fish around in the ultrasonic cleaning chamber
for his rock slices which were wickedly difficult to catch with the
big tweezers he had. So he just reached in and fished the slices
out. He did this many, many times that night with the big ultrasonic
tank on the entire time. This was in direct violation of stated
safety policy of the department, which was posted on big signs
around the lab.
By the next morning he could not hold a pencil, his fingertips hurt
so badly. They were bright pink and starting to look puffy. Finally
he went over to the school clinic and they checked him over. When he
told them what he’s been doing, they took an x-ray. He had
thoroughly destroyed the bones in this fingertips – they showed up
as gray ghosts on the film, not nice, tight, white bones. Basically,
the doctor told him that the sound waves had given him the most
complete set of stress fractures he’d ever seen. Not to mention the
soft tissue damage – the pinkness and swelling was due to bleeding
deep in the tissue.
It took a long, long time to heal, and wow, did it hurt like hell.
Don’t go there.
I realize that an anecdote is not convincing for many folks, so I
went looking for more detailed safety discussions on the kind of
ultrasound we use in our cleaners. To my chagrin, there is very
little out there. There is an excellent general FAQ on ultrasonic
cleaners and how they work at cleansonic.com/ultrasonic_faq.htm This
explains the physics of cavitation nicely in layperson’s terms. You
will have a much better understanding of what your cleaner is doing
(or not doing) and why you need to have some kind of detergent in
the water in order to accomplish anything. To check if your cleaner
is working properly, you can immerse a little square of aluminum
foil suspended from a bit of wire, and in a few minutes you should
have nice little perforations all over the foil. This site explains
the procedure nicely, and yes, it surely does work. And it certainly
illustrates how vigorous the energy in that little tank really is:
strong enough to shake bits of aluminum right out of their nests.
Ever dropped in pearl and watched what happened? Since the sound
waves travel especially well in liquids, and you are basically a
liquid in a sack made of skin, you can see how there is a potential
problem here.
As for the issue of tissue damage, check out the “Guidelines for the
Safe Use of Ultrasound, Part II – Industrial and Commercial” at the
Canadian government’s informative Consumer & Clinical Radiation
Protection site. Specifically:
www.hc-sc.gc.ca/hecs-sesc/ccrpb/publication/safety_code24/toc.htm
Click on the “contact exposure” headings. They do mention the
scarcity of research on this topic. There has been one study with
volunteers, who did confirm that putting your fingers in a tank can
hurt. (I would suspect that there are ethics problems in pursuing
this further with human subjects.) The article says:
"Contact exposure can in some cases provide nearly 100% energy
transfer to tissue… For example, high-power ultrasonic waves are
used in ultrasonic cleaners and cell disintegrators because of their
destructive and violent effects. It is certainly reasonable to
assume that relatively intense cavitation activity occurs in the
water (or solvent) baths of such devices… “The literature on
devices such as ultrasonic cleaners and tissue homogenizers is
confusing: these devices do not appear to be as hazardous as
expected, given the effects they were designed to create.
Nonetheless, although reports of biological effects are surprisingly
rare, exposure to the liquid-bourne ultrasound from these devices
clearly can cause tissue injury, and protection measures are
necessary.”
In conclusion, this is not an urban legend. This is physics. Renate,
please stop using your ultrasonic tank to clean your fingers. Just
because it “feels much the same” as medical ultrasound: it is not,
and this is not a safe practice.
Anne Hollerbach
