At 5:32 -0500 4/10/07, Sridhar wrote: Sridhar and Andy, Good suggestions below. I have a couple of additions, based on my (limited) experience working on the flight hardware on a couple of pretty contamination-sensitive projects I've worked on. Sorry for the delay, I was ( :-) ) working on one of the projects, albeit not one at the clean-room stage, rather than keeping up with my email. Painted metal is what we use for practically all of our work. With the right paint, it can be grounded (through resistors) to eliminate the chance of ESD; that's hard with plastics. Also, most of the instruments I've worked on are *very* sensitive to contamination below, and it precludes most kinds of plastic. Delrin, lexan, and a few others with extremely low outgassing properties are still OK, but there are a lot of plastics that are not allowed in the clean room. I expect this would be much less of an issue (except for the ESD considerations) for something other than UV optics or microchannel detectors. In my experience, sealing is a non-issue. In fact, practically all of our clean rooms, clean boxes, etc. have open apertures of one size or another, cracks, vents, etc. What *is* critical is that the volume have positive pressure maintained inside of it while any work is going on. Generally, with a good high-volume but low-pressure supply of clean air, all the dust is removed (blown out the apertures) within about 15 minutes of starting the supply. Of course, if the air supply fails or is shut off, we close things up pretty well and pretty quick, to keep dust from migrating back in. We also wipe down surfaces from time to time, so that whatever dust does manage to accumulate doesn't get stirred up during work. For wiping down, Isopropyl alcohol (um, propan-2-ol?) and lint-free wipes ("Kimwipes" brand, in the US) are the standards. One thing you may not have to worry about is the idea that to us silicone is a four-letter word. Silicone oils are *very* easy to inadvertently transport all over the work via accidental contact on a gloved finger, *very* hard to remove, and fatal to several of the detectors and optics we use. So we don't allow any of that kind of material in the clean room as a general principle. Danger, Will Robinson! I second Simon's caution - do not allow N2 to accumulate in the volume you are breathing out of! Even though the box is "sealed", N2 will be leaking out into the room. If enough of that happens before the room air is replaced (by an open window, or whatever) you die. We don't want that. A liquid nitrogen dewar is a good supply of clean nitrogen, but that may not be such a useful suggestion .... Meantime, with bottled, regulated nitrogen, you may well have issues with hydrocarbons (if you care about that). Hoses that have been used downstream (or even upstream) of vacuum pumps can have some of the lubricating oil on the inside. Many regulators have grease or oil which can get into the downstream side. If you choose to go this route, you might consider SCUBA gear and plain compressed air (and a filter). Most SCUBA equipment and air suppliers are pretty careful about atomizing oil into divers' lungs, so that can help you. In general, if it has a noticeable odor, it's got some sort of hydrocarbon outgassing or contamination, and we would not use it. Most folks have noses which give them a lot more information than they pay attention to. All that said, we don't use any of that for clean-room work. We use *only* a HEPA (HEPA is a key descriptor, here) filter on the output end of a good ventilation system. We are reasonably careful about the input supply (ie no diesel trucks parking right next to the air inlet), but that's about all. Paxton's comments (hey, if it's good enough for pizza, it's good enough for a hard drive :-) ) are very well taken here. We do use a liquid N2 dewar to supply purge gas which is tubed directly into some instruments to make sure humidity, fumes from drying adhesives, diesel fumes from outside, etc. do not get into the detector and UV optics, but that comes at a really low supply rate and I don't think any of those considerations are applicable to hard drives or to most electronics. A good HEPA filter on a high-volume air supply (ie one that exchanges air in the work area about once every 15 seconds or so) is really *all* you need, in my experience. Put the work upstream of the hands and tools, wipe down the work area with IPA and kimwipes, let the supply run for an hour or so before you start, and I think you should be down to a pretty low level of particulates. True, but see above. Letting the gas get out any (many) ways is OK, as long as it's getting out fast enough that none or not much can come back in. Good for flexibility with the work, bad for staying downstream of the clean air supply. If anyone is interested, I can try to grab pictures of some of our work setups around here. They are probably fancier than what you'd want, though. There are particulate counters, but not cheap. One idea for a test is to set up your work area, lay a *clean* mirror in it facing up, and leave it overnight. (or do some non-critical work in the area for a few hours). Then look at the mirror under a really bright light or (even better) a UV light. If it still looks clean, you are probably OK. I'm hoping Tony D. (and many others) chime in (or have already done) on this thread; I suspect there's much experience out there more applicable than mine. -- - Mark, 210-379-4635 ----------------------------------------------------------------------- Large Asteroids headed toward planets inhabited by beings that don't have technology adequate to stop them: Think of it as Evolution in Fast-Forward.