After four years of writing magazine articles and blog entries, there is
something that irks me to no end. Safety police. (Eye protection. Ear
protection. Push sticks. Yes we all know those should be used in the
shop.) If we try to work taking every safety precaution out there, we
would be dressed as if we’re defusing a bomb and unable to bend our arms
enough to actually flip the machine switch, or we would never attempt
to work because we would be scared to make a move. (You have to gauge
your level of acceptability, then move accordingly.)
a worthwhile nugget of safety information arrives. Something beyond the
normal eye and ear protection and push stick droning. This week that
nugget came from Bob Rozaieski. Bob expressed concern over the heating
of galvanized pipes that I use when bending string inlay in the Line
& Berry Chest from our December 2010 cover project (tour the chest here, then order a copy of the magazine here).
It seems that heating galvanized pipe to a red-hot temperature releases
fumes of zinc oxide (zinc is the coating on the pipes).
what Bob wrote: Just got my Dec. issue and was reading about Glen’s
awesome line & berry chest. I had to comment on one thing I saw in
the article though. I noticed that Glen recommended using a heated
galvanized pipe to bend the stringing. You may want to be careful with
this, or choose a different pipe. If you get galvanized pipe too hot, it
can put off some nasty fumes that can make you pretty sick in a high
enough dose, and at minimum be pretty irritating to your throat and
lungs. A better alternative might be to use the black iron pipe and
simply strip the paint from it before heating. That way you wouldn’t
have to worry about the galvanic fumes in the event that the pipe gets
For the record, if you heat the bending pipe too hot
– cherry red is “too hot” – the fumes should begin. I say “should
begin” because I don’t know if that happens or not. I didn’t get my pipe
that hot. There’s no need to get the pipe that hot. Also, if you heat
the pipe beyond what’s necessary to steam the water that’s in the string
out, your string will burn (that I did do a couple times!).
I wasn’t aware of the fume potential, so I checked into it. My “go to”
site for quick information is the Occupational Health & Safety
Association, OHSA for short. Here is what OHSA lists as the potential
symptoms: Metal fume fever: chills, muscle ache, fever; dry throat,
cough; lassitude (weakness, exhaustion); metallic taste; headache;
blurred vision; low back pain; vomiting; malaise (vague feeling of
discomfort); chest tightness; dyspnea (breathing difficulty), rales,
decreased pulmonary function. (Sounds like small print read during a
medicine commercial on television.)
In a study with two hours of
exposure at the OHSA Permissible Exposure Limits, subjects reported an
inflammatory response involving the release of cytokines thought to
mediate the symptoms of metal fume fever (elevated body temperature,
myalgia, cough, fatigue) that peaked about 9 hours after exposure. Prior
zinc oxide exposure resulted in the development of some tolerance
(desensitization) to these effects.
I will heed this advice –
that’s why I passing this along to you – and I appreciate Bob sending it
in. However, if you happen to get the pipe so hot as to fume, I doubt
you’ll be working and breathing these fumes for two hours nonstop, nor
will you have this kind of exposure. But you should be warned.
I said above gauge your level of acceptability. If you’re concerned
about zinc oxide fumes, follow Bob’s advice and use black iron pipe
that’s been stripped. Or you can heat your galvanized pipe to cherry red
in a well-ventilated area so all the zinc has fumed off, then go back
inside the shop to begin bending your stringing.
I received a message from saw maker Mike Wenzloff about his
run in with zinc oxide. He was once poisoned while cutting up some
galvanized strapping one day with a torch. It was a good fall day with
plenty of breeze blowing from behind me and across the work and away. He
says, “That was an intense couple days of thinking I would die.” I
respect Mike and believe he was going to temperatures much hotter than
we need to for bending. I dug a little deeper into zinc oxide to
discover that zinc boils at 1652 degrees Fahrenheit and melts at 788
degrees. I’m going out on a limb here to say that zinc has to melt in
some way prior to giving off fumes. In our in-shop experiment (which
Chris Schwarz filmed and is posted below), the temperature the
galvanized pipe reached was just below 500 degrees. That’s well below
the melting point of zinc. At that temperature the wood had significant
burning which is something you don’t want to happen when bending string –
you should look to get the pipe heated to about 350 degrees (much lower
than the melting point of zinc). I continue to say that using a
galvanized pipe is OK for steam bending sting inlay. There is no need
“metal fume fever” worries.
Here’s a fact about zinc oxide and
metal fume fever if you should ever run into this issue. Fumes from zinc
oxide fully dissipate from your body in a few hours, the effects are
not cumulative as they are with sun exposure or lead poisoning and it’s
said that drinking a half-gallon of milk will help offset the effects of
metal fume fever. Got Milk.
For another furniture project from Chester County, go here to pick up the October 2009 issue and build the Inlaid Bible Box.
To watch a video from Rob Millard of curved inlay, click here.
For more information on bending wood, read Jon Benson’s book “Woodworker’s Guide to Bending Wood” Order a copy here.