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.)
Occasionally, 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).
Here’s 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 over heated.
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!).
Admittedly, 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.
As 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.