hi all, I stumbled onto this info posted like 5 years ago by someone on the cozy builders forum, and thought it was good enough to share. Bottom line, you want to *always* wear a P100 respirator (not paper mask) when sanding our aircraft. Very cheap insurance.
FROM COZY BLDRS FORUM: Every once in a while a topic comes along where I actually know something about how to answer it. In my real job I create particles that you're supposed to inhale. I work on dry-powder inhalers (DPIs), specifically in what is called Chemistry, Manufacturing, and Controls (CMC). When I'm really on my game they look like this: (dead link) This is opposed to working on our fiberglass airplanes, where we create particles you are NOT supposed to inhale. I am providing insight from the point of view of someone that makes particles, not as a medical doctor and not as an industrial hygienist. Sorry for the very long-winded reply, but this is a SERIOUS safety issue that I think people take way too lightly. Inhalation of particles can be completely safe, or absolutely dangerous, depending on the chemical composition of the particle, the aerodynamic size of the particles, and the total amount of exposure. Your airways classify by aerodynamic particle size. Anything larger than 25 microns is unlikely to actually make the trip through your nasal sinus or through the back of your throat without being stopped by the mucus membranes and expelled. When you blow your nose when you're done working and get a tissue full of very white snot, that's what it is. Particles less than 10 microns are likely to make it past the first 3 branches of your bronchi. Particles less than ~0.5 micron will make it to your deep lung, and then be expelled right back out. This is actually what keeps people that smoke relatively healthy for such a long time. The particles are so small the vast majority come right back out. The critical sizes you care about then are between about 10 and 0.5 micron. They will go in and stay there. I'll take each for the case of you inhaling aerosolized glass fibers and microballoons. Microballoons supplied by Aircraft Spruce are a 3M product called K20. You can reference the data sheet that is on ACS's website here: http://www.aircraftspruce.com/catalog/pdf/3MGLASS%20BUBBLES.pdf In it you will find that the baloons are made of soda-lime borosilicate glass. You will also find they have a median diameter of 60 microns, an x10 of 30 microns, and an x90 of 90 microns. This is all good information as far as inhalation is concerned. Your lungs and nasal cavity are a pretty efficient filter of certain aerodynamic particle sizes. Because we're talking about spheres, the aerodynamic particle size and the geometric particle size are nearly identical. The vast majority of the microballoons are above the cutoffs where you should be concerned, but 10% of them are in the range that could get to your deep lung. That isn't to say that by sanding them you haven't broken the larger particles down into smaller pieces that will get into your deep lung and stay there. >From a chemical point of view, borosilicate glass is a pretty inert material. Your body isn't going to absorb it, but that creates another problem. The particles go in, and your body doesn't absorb them, so they stay right there. The glass fibers are a similar story, with a critical difference. The morphology of the particles is, well, fibrous. The longs strands of glass (and by long we're talking ~100 microns here) have an aerodynamic particle size that can be two orders of magnitude smaller then their lagest physical dimension. They "fly" like a 2 micron particle when they can be 100 times that in length. So they are quite able to make it well into your deep lungs and then lodge there and become a serious irritant. Again, the glass is largely inert, but this is a double edged sword because that means they will stay there for quite some time. These two characteristics (largely inert, large physical size to aerodynamic size) are what makes asbestos such a hazard. The next thing to consider is the amount of exposure. For particle inhalation there are EPA standards for what a person can tolerate on a day-to-day, 8 hour exposure for job safety issues. Typically these levels are such that if you were to look across a well-lit room you would not be able to see the dust in the air. Sanding micro and fiberglass is multiple orders of magnitude above this level. So, we have a material where at least 10% of the microbaloons, and potentially much more than that of the fiberglass is able to get to your deep lung, made from materials that are mostly biologically inert, so they are going to stay right there for a while. And you're exposing yourself to potentially orders of magnitude more than the EPA considers acceptable on a day-to-day basis. This is all entirely preventable by wearing a proper dusk mask at all times. I put mine on when I get to the hangar, and try to leave it on until I leave. I certainly always have it on when cutting class, sanding, etc. The type of dust mask makes a big difference too. The little paper masks with a single small elastic band are totally useless. They will not seal to your face, and give you a false sense of security. Buy filtering face masks that are rated NIOSH N95 or better. More information here: http://www.cdc.gov/niosh/npptl/topics/respirators/disp_part/n95list1.html You can get them at Home Depot, Lowes, etc. If you're not paying about $1 each for them , they are the wrong ones. Make your life easier and buy the type with an exhalation valve and you'll be less tired at the end of a building session than if you don't have one. It is fine to re-use them as long as you store them, face up, in a plastic bag between uses. If you contaminate the face seal taking it on or off, throw it out and use a new one. -- Kevin _______________________________________________ Search the KRnet Archives at https://www.mail-archive.com/[email protected]/. 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