Watch that UV!

Tales of woe that teach. We learn best through failure sometimes
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This is for tales of woe that teach. We often learn quickest through failure that shows us how our thinking was off, and of course, sometimes it's funny at least in hindsight. Share your "Doh!" moments here.

Watch that UV!

Postby Jerry » Tue Nov 16, 2010 1:35 am

So, I have that box of Ultra High Pressure Mercury Vapor lamps. I looked at the spectrum and the lowest main peak was about 365nm, about the wavelength of a generic blacklight. Figured I would try to fire it up. Took my 60v/10A adjustable voltage/current power supply and hooked it to the ends and used a hand held tesla coil to get it going.

Worked! As seen in the photo. And felt in the sunburn on my left arm.

Ugh. That was saturday. Spent yesterday eating ibuprofen. Still red but not as sensitive.

Green color is from the white balance not being happy. I took a pic with my dSLR and will post that too.

Image
UHP Mercury Lamp by macona, on Flickr
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Re: Watch that UV!

Postby Doug Coulter » Tue Nov 16, 2010 1:47 am

Ow, been there with that one. Fe in a weld arc is pretty nasty too. 365 is the main Hg line, but not so much in the old blacklights -- they actually converted that to the 400's and filter out the 365 and shorter (325?) to some extent, else they'd do the same. The 365 line is what you get out of the clear quartz tubes used to erase eproms and sterilize water. Nasty stuff! I take it you left it on for a little while? Or, those were pretty high power, right? In that case, wouldn't take long at all to get burnt. I hate wearing gloves during welding, but....got tired of UV burns.

When I started messing with UV sources to expose the older type of PCB that needed UV, that streetlamp made so much ozone during warmup I had to put it into it's own box so I didn't breathe so much of it - a few ppm is nice, but this was like having elemental chlorine in the room. Once warmed up, at high pressure it makes more of a continuum of light, not all so concentrated in that one line. We found also that the O3 wasn't good at all for UV hardening glues and had to flood the box with argon to make it all work right with that source.

You may find that this effect goes away on warmup, or on plain old hours of use due to solarization of the quartz, which will then absorb the short stuff. At least it has on my source.

On the other hand, that short stuff is quite valuable inside a vacuum vessel to blast water and junk off the tank walls....I'm thinking about putting in some big xenon lamps I have here for that very reason, but heck, merc vapor might do it. Doesn't need to be very long to get a good job done, the warmup time of that streetlamp bulb (3-4 minutes) would do it fine.

How are your eyes? A little bloodshot now?
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Watch that UV!

Postby johnf » Tue Nov 16, 2010 2:19 am

Jerry
Silly boy
Quite a few years ago while working as an RF engineer we were developing a rural /emergency self contained Cellular system based on AMPS /TACS for rapid deployment. Of course we used a container 20' to house it in. I had the idea that the mast should be mounted dead centre of the container and a tapered metal lamp post was sourced. Works workshop didn't have the door width or welder to make the base so I said I would do it at home 8x8x0.25 RHS made the frame with a base of 0.75' thick steel to mount the lamp post on for the antennas.
It was a hot day so i'm welding with shorts on with 0.25" iron powder arc rods --these suckers need around 350- 450 amps to run. I am usually out doors so the legs didn't get hit but the UV went up inside the shorts to where the sun don't get to. I walked like a cowboy for two weeks.
The other incident did not get me directly but I rang the alarm bell. Some idiot talked me into a wheel of fortune tryout and we appeared at a local school hall. All was going slow so I (being a smoker at this point ) got up to go outside as I walked down the rows of people I noticed a group that looked like lobsters. Looking up I saw the roof was covered by Hg arc lamps but one fixture had the wire protector missing and the bulb had lost its outer envelope but was running funny kind of green /blue light.
I informed the organisers what was going on they laughed me away --20 minutes later 10 people hospitalised with third degree burns four needing skin grafts. I did give a statement to the police afterwards and got an apology from the organisers.
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Re: Watch that UV!

Postby Jerry » Tue Nov 16, 2010 2:43 am

250w lamp. Nope, only thing that got toasted was my arm where i was reaching past to adjust the current. I was kind of expecting getting arch flash in the eyes but nothing happened. I was shielding my eyes and I also wear glasses so that will filter out most of the UV. I think I ran the lamp for 2 minutes at the most. There is a nice demarcation on my arm where my sleeve was! There was no ozone created by the lamp.

I have heard stories where the outer envelope has broken on merc vapor lights and toasted people. Never from someone that had witnessed it.

Yep, not one of the brightest things I have done, well, lumens wise it was.

From what I read about using UV in the chamber you want low wavelengths, germicidal range. And I also worry about cooling on one of these. It would be pretty difficult to cool it in a vacuum. These that I have run at 150 ATM. Wouldnt want to be around if one 'sploded. Ill send you a couple if you want. I must have 30 of them.

I think one of the UV sterilizer lamps and remove the plastic base and mount to a feed through would be the way to go. Those lamps will create ozone if exposed. I know, I used to use them in my salt water tank. One night the lamp has slid part way out of the quartz tube into open air. When I came down stairs in the morning the ozone was pretty potent.

I have been cooked many times from welding. Especially tig. Tig creates a lot of short wave stuff that does create ozone. Plasma cutting can get you too when scarfing.
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Re: Watch that UV!

Postby Doug Coulter » Tue Nov 16, 2010 11:12 am

Ah, in my case I deliberately took the outer envelope off. I do get ozone (still, after a hundred hours or so of runtime) during warmup, before it becomes a high pressure lamp -- most of the mercury is still liquid at that point, and we're running on a little Hg and some Argon (I'm guessing). The color is different during that, a little, less of the output is in the visible range. I only get ozone for the first couple minutes, while the pressure hasn't built up yet, then it's more the longer waves that don't make it. It will sunburn you at any time, though. For ref, that's with a 250w lamp, I also have a 450, but after seeing what this one does, don't fire that big guy up.

My experience is yeah, in a vacuum you're not going to be able to keep it cool. The quartz-halogen bakeout heaters I have in there now are almost a foot long and half an inch diameter for 500w, which is about what it takes, and they get red hot fast -- takes a special clamp mount to thick copper to keep the leadin wires from melting at full power. Kind of fun to run them 30 sec and turn them off and see how long it takes them to stop glowing -- not the filament, the quartz envelope!

But what I noticed with these, which are wired for either half voltage (in series) or full, is that you get a pulse of out-gassing very fast when they are turned on, and that's most of the game. The pulse is faster and has much more H2 and O2 when they are at full volts and "whiter than white" -- lots of UV, but not as much as something meant for that. You get nearly all the good out of it in about 60 seconds of that, after that you're just wasting power and heating the tank in bulk (eg below the surface metal). In that short time, they don't heat up so much, so my thought with an in-tank source was that it wouldn't have to be on very long at all, and the louder the short wavelengths, the better. Then cut it right back off, or perhaps run in a very low duty cycle pulse-mode. I think this is also the reason that running a glow in argon, at fairly high pressure (so you can do it at all) then pumping back down gets you to base pressure so much faster than pumping alone -- even though you had to let in some argon to get up to glow discharge pressures. All that fierce UV just blasts water off the tank walls, and everything else with it. The the argon holds it in suspension while you pump it all back out.

Many people have noticed that one, so it's real -- if there's an alternate explanation, I'm all ears. Seems to work with any inert gas, argon is just cheaper than He.

I've melted plenty of stuff in a vacuum, it was one of those surprises that shouldn't have been -- intellectually I knew it's harder to get rid of heat in a vacuum, but...seeing a 100w bipin lamp running at 70v (about half power) quickly melting the #10 wire I had crimped around the leads was a demonstration of how much the good old air normally does for us. So as the old preachers used to say, there's a difference between "head knowedge" and "foot knowledge". Which is kinda why I put so much emphasis on this board about "doing stuff" rather than "talking endlessly about stuff". Guys who do stuff know things better, complete with the real-world caveats, than people who merely think about the same stuff.

And those are the ones who will be contributing to this particular forum -- it can't almost work until you actually try to make it work!

Note, NASA's "faster cheaper better" stuff has run into this, using what they call COTS hardware (commercial, off the shelf). Some idiot thought they could use things like standard computer motherboards in space apps....that's what happens when you let young academics near hardware design. Gimme a guy who has had to fix it as a tech over that, any day. He'll be far more savvy.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Watch that UV!

Postby Joe Jarski » Tue Nov 16, 2010 5:50 pm

Are there any tips for tactfully removing the envelope or is it a smash and grab operation?
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Re: Watch that UV!

Postby johnf » Tue Nov 16, 2010 7:59 pm

Joe
Its easy
I drilled a small hole with a diamond tipped drill to let the vacuum escape
Score all around @ the widest point of the globe with a diamond scriber then a bit of nichrome around the score pass enough current to get nichrome red hot---presto top half is off. now you can see inside and with ordinary pliers break away the rest of the outer being careful not to damge the inner bits.
note this does not work with self ballasting types but you could remove the heater and then use it in an ignitor type fitting
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Re: Watch that UV!

Postby Doug Coulter » Tue Nov 16, 2010 8:56 pm

I did the smash thing, just put it in a paper bag and tapped it with a hammer (outside, from upwind of course) -- it doesn't take much of a hit. In my particular bulb, the outer envelope was large (several inches diameter), thin glass -- very easy to break, coated with phosphor (don't breathe that, most of them are bad for ya). As John says, once you have a break, it's easy to use pliers on the rest. The inner bulb in my case was about 3/4" diameter and of thick quartz -- hard to break, I didn't have to be all that careful. I bought a "kit" of bulb, socket, ballast at the local electric supply store to work with.

The 250 watt size was the smallest they sold. I also got a 400w one, but it's just too much for most anything, so I don't use it. The somewhat longer exposure time the smaller bulb needs makes it easier to time accurately. PCB's in my glass contact print frame take about 4 minutes with laser printer art to do. With the 450w bulb, it'd be under two minutes probably, and there'd be too much heating during warmup.

I didn't get a big cloud of phosphor in the air when I did it, the stuff was stuck to the glass pretty well, but this is definitely a "your mileage may vary" sort of thing. I was able to see inside through a gap in the phosphor near the base, and so knew how to control the hammer tap so as not to hit the real bulb inside.

These are real useful sources for various photo-chemistry. I mounted mine in a big wood box, with a door, a reflector (aluminum flashing) and a shelf to put the things I'm going to expose on.
You get a lot of very short UV for the first couple of minutes, I find that I get more uniform results (with things that don't need the real short stuff) if I let mine warm up for 4 minutes before starting the exposure of the PCB, or my own resists made of pva and ammonium dichromate. I use a timer, and just pull the plug on the lamp at the end, then open the door to fetch my stuff, seems to work best that way. And that way I don't get so exposed to the UV. Basically, after the warm-up time, I just reach in there and take the light blocker (Al foil) off the thing I'm going to expose without having to actually look in there at all. It's gotten to be one of those things that just works around here, doesn't take a lot of fiddling anymore.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Watch that UV!

Postby Jerry » Thu Nov 18, 2010 2:15 am

Arms getting better. I had been eating ibuprofen like candy.

Heres a pic I took with my SLR. I think the light in the room was on and you cant even tell.

Image
IMGP6492 by macona, on Flickr
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Re: Watch that UV!

Postby Remy Dyer » Mon May 28, 2012 1:36 am

For those that are maybe not familiar with UV - I'd think the UV would be the greatest danger of the ionizing sources most new to the tech would have to deal with - your survey meter isn't going to catch it.

It all gets absorbed pretty shallowly in skin, so the volumetric dosage rate will be quite high.
Also that shortwave what's breaking up the O2 is probably even worse, owing to it's higher energy. I hear that shortwave UV optics are often run in N2 to keep them clear of the scattering losses from the O2 absorption.

On the plus side the skin cells hit hard probably just die outright - and so have less change of a melanoma if they don't get as far as fixing their DNA.

Any how, so long as one isn't using windows which happen to be transparent to the shortwave stuff, it shouldn't be too bad. I'd just use the good 'ole 1/r^2 rule, and keep close exposures down.
-- Remy
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