I came across this safety warning while surfing for general information (and while waiting for lenses and stuff to come in).

Metal Halide Safety Notice

The gist of it is right here:



Since we're essentially building our own MH fixtures here, it's worth knowing the potential issues and designing appropriately.

Essentially, I would interpret this to mean that pj boxes should be designed to allow for the potential for the MH lamps to explode. That means... well, I don't know what that means. Definitely put flashing on the interior? Reinforced walls? Forget about saving the internals if the lamp explodes, you really want it to not cause a fire, and not blow metal and glass fragments at your family.

UV filtering is definitely called for. Most MH lamp fixtures are positioned well away from people, in very high ceilings and such. Ours will be/are pretty close to the viewers. Are we running risk of skin cancer after prolonged exposure?

Have these potential problems been discussed?

The key word here is "potential." Not all MH lamps will explode at end-of-life, and that life is pretty long (20,000 hours). That means years of explosion-free service.

On the other hand, it also means that, years from now, after this discussion is long forgotten, your MH lamp might "fail non-passively." Better to design this assumption into your pj now, and not take risks.

I don't know how to design for an exploding lamp. Strong, reinforced, heavy exterior casing makes more sense intuitively, but I don't know how much force we're talking about. Substantive materials might result in a fragmentation grenade effect.

Lightweight materials (ala Jones' overhead projector) won't provide blast protection, but might shred easily.

And I think there's a reason commercial fixtures are made of metal, and positioned well away from people.

Am I blowing this out of proportion here? Yikes.

All right, found an OSHA warning. The full text is here http://www.electriciansupplies.com/pdf/hid_psds5.pdf

Lamps do not present any hazard if intact. However, if not intact, the following toxic materials may be released.

NIOSH/OSHA Occupational Health Guidelines for Chemical Hazards and/or NIOSH Pocket Guide to Chemical Hazards lists the following effects of overexposure to the chemicals/materials tabulated below when they are inhaled, ingested, or contacted with skin or eye:

Lead - Ingestion and inhalation of lead dust or fume must be avoided. Irritation of the eyes and respiratory tract may occur. Excessive lead absorption is toxic and may include symptoms such as anemia, weakness, abdominal pain, and
kidney disease.

Mercury - Exposure to high concentrations of vapors for brief periods can cause acute symptoms such as pneumonitis, chest pains, shortness of breath, coughing, gingivitis, salivation and possibly stomatitis. May cause redness and irritation
as a result of contact with skin and/or eyes.

Barium Peroxide - May be fatal if swallowed. Harmful dust. Avoid skin and eye contact.

Quartz, Fused - Fibrosis of the lungs causing shortness of breath and coughing has been associated with silica exposure.

Sodium - Skin contact can cause thermal and/or alkali burns. Fumes from burning sodium are highly irritating to skin, eyes and mucous membranes.

Glass - Glass dust is considered to be physiologically inert and as such, has an OSHA exposure limit of 15 mg/cubic meter for total dust and 5 mg/cubic meter for respirable dust. The ACGIH TLVs for particulates not otherwise classified
are 10 mg/cubic meter for total dust and 3 mg/cubic meter for respirable dust.

Aluminum Oxide (Alumina) - Alumina is a non-toxic material which is very low in free-silica content. Sharp-edged particles can irritate the eyes, perhaps the skin, and definitely the mucous membranes of the respiratory tract.

Yttrium Vanadate - Inhalation of vanadium compounds can cause irritation of the nose, throat, and respiratory tract. Eye contact and prolonged, repeated skin contact may also cause irritation. Studies of workers exposed to this material
showed no evidence of chronic or systemic effects.

PROCEDURES FOR DISPOSAL OF LAMPS
---------------------------------------------------------------------------------------------------------------------------------------------------------------
If lamps are broken, ventilate area where breakage occurred. Clean-up with mercury vacuum cleaner or other suitable means that avoids dust and mercury vapor generation. Take usual precautions for collection of broken glass. Place materials in closed containers to avoid generating dust and mercury vapor.
It is the responsibility of the waste generator to ensure proper classification of waste products. To that end, TCLP tests should be conducted on all waste products, including this one, to determine the ultimate disposition in accordance with applicable federal, state and local regulations.

Well, just be over-cautious and replace the lamp after 10,000 hours of service.

Our cases are plenty ample to contain a lamp explosion. Generally if one did explode the outer jacket of the lamp would contain it, but not in all cases. In all of the time I've been doing this I've never heard of anyone who's had a lamp explosion.

I have to agree with Brain that it seems unlikely one of these would explode. It did remind me of something however (and forgive me if it has been covered). Are MH lites vulnerable to fingerprints as halogen are? If so we should be very careful in the handling/installation of our bulbs.

yeah i was wondering about finger prints also - would be nice to know

No, a jacketed MH lamp is not sensitive to fingerprints. The inner quartz envelope would be, if you could touch it...

Given that these lamps have a life of 20,000 hours, and they don't all "fail non-passively" (I like that phrase ), I'm not surprised that this is rare, and that nobody's heard of this happening on a pj recently. We need to check back here in, say, 7 years. And that's for someone who leaves the projector on 8 hours a day, 7 days a week.

I think I'll make sure I build the box strongly, use metal flashing on the interior, and hope for the best. If the bulb ever explodes, I'll make sure it's not on fire, and dispose of the whole thing. If the explosion is self-contained in the box, all the toxic stuff will be in a tidy package (darn, lost that LCD!)

The best way to avoid an explosion is to not run the lamp more than the recommended life span.

Brain, what about those UV filters? When are they being added to the store?

I have found further cautions for those people who are working with the lamps directly, with their projectors open.

http://members.misty.com/don/shortarc.html#hz

UV filter should be on the store this weekend.

Doing further searches... This time I didn't record all my sources, because I was ranging all over...

Some facts I have found:

- It may be that people haven't been building pjs long enough to run into the problem, but there are plenty of examples of MH aquarium lights that have exploded.

- The outer jacket provides no explosion protection. Explosion of MH lamps is a possibility that needs to be accounted for (still, it is stressed that everything says POSSIBLE, NOT PROBABLE). Best protection is to house lamps in a fixture designed to contain the explosion.

- There is no way to predict if your bulb is going to explode. It is more likely if the bulb is used beyond its listed life, or if you see severe discoloration on the bulb. However, sometimes it might just explode with no visible indicators at all.

- The main two disadvantages of MH lights cited for aquarium users is the possiblity of explosion, and UV burns for the fish and aquarists if improperly shielded. If not for these two disadvantages, MH bulbs would be considered the ideal light source (cheap, bright, correct color, long life).

- Strong recommendation not to exceed 15 minutes of exposure to an unshielded MH bulb, or risk sun or eye burns. Never look straight into the lamp. There is a potential for temporary or permanent blindness.

- Color temperature of MH bulbs have a tendency to change over time. Best fix is to use an electronic ballast (I think Brain already has that one covered).

- Recommendation to keep the bulbs clean and oil free. Avoid sudden temperature shifts. (Don't wipe it with something cold, then turn the lamp on.) Best cleaning material was some sort of alcohol (pure alcohol? rubbing alcohol?)

- Generally 400W MH bulbs should be air cooled. (MH dive lights are usually water cooled). I think that one's covered as well.

I think I agree that our pj boxes are going to contain the explosion. There is a strong metal reflector that will absorb half of the immediate blast, aluminum flashing to pick up most of the rest, and the entire assembly box is made of rather thick wood. I think I'll choose plywood over MDF.

(Of course, if we're wrong, you will send splinters and superheated glass or toxic metals into your family and friends. ) But hey, what are friends for?

An alternative is to search for a MH fixture that was designed to contain the explosion, but is still suitable for providing a point light source.

to be honest here i think that this could happen - but people get hit by lighting also - anything you do in life there is a risk - i really dont think this thread needs to go over kill - just my thoughts -

I too think this is a doubtful situation, but one thing to add to the "safety" mix would be our exhaust fans. E.g. if there is a cloud of vapors/dust from a bulb exploding, it's gonna go right out the back end. So much for that "nice tidy package" to throw away. Seems like even if it is a remote possibility, people should figure out a way to design their enclousures to 1) withstand a bulb explosion, and 2) figure out something with their fans/venting so that they don't have any vapors/dust distributed beyond their projector if a bulb does explode.

You're right, I completely forgot about the fans. Having not built anything yet, I still forget the obvious.

Anyways, I'd still do the same thing. The box should contain most of the contaminants, glass, and metals that did not turn to vapor or dust. OSHA suggests ventilate the room well.

Ventilating the cooling system elsewhere is probably impractical.

As for whether or not metal halide lamp explosion is a real issue or not, just do a google search with the keywords "metal halide lamp explosion" and make up your own mind.

here is what i found on the web -------------

Each year in the U.S., approximately 73 people are killed by lighting and more than 1,000 are injured. In most lighting fatalities, victims die from cardiac arrest caused by the surge of electricity through the body. For those who survive lighting strikes, many will suffer long-term effects including memory loss, personality changes, fatigue, irreparable nerve damage, chronic pain and/or headaches, difficulty sleeping and dizziness. Only a few victims suffer burns, and many of these are
minor.

--------------------------------------
The metal halide lamp fires and then either burns dull or the arc extinguishes?
Usually the ballast and lamp are not receiving enough power. Metal halides pull a high current. Usually the
problem is either there is too great a load on the circuit or the extension cords are of a small wire size and
can™t handle the power needed by the ballast. Use only heavy duty extension cords and try running a ballast
off a circuit from another part of the house.

Can I operate a ballast and lamp together which are designed for different wattages?
Each wattage lamp and ballast are designed together for optimal performance and safety. If you over drive
the lamp it may explode and shorten the life of the ballast and lamps. If you under drive the lamp it will also
shorten the life of both components and also may explode. Do not mix different type wattages of lamps and
ballasts.

http://www.marinedepot.com/md_viewItem.asp...B4413&ast=&key=


----------------------------------------
In extreme cases, inappropriate operation may cause the lamp to explode in the growroom. Lamps can also become damaged due to power spikes from the electricity supply. In the unlikely event that this is a re-orruring problem, spike and surge suppression circuitry can be obtained.
http://www.blunt.co.uk/cat/light/250w-400w-600w-air-cool/

Well, almost every commercial projector uses metal halide lamps and those cases are typically plastic and the fans exhaust the lamp air just like ours.

Did a little more searching. Apparently there are some MH bulbs that are rated for "open" enclosures available. From what I understand reading the web pages, it suggests that these type of bulbs reduce the chance of an explosion and hence, are designed for said "open" enclosures. Would this be a better bulb to use in order to reduce the risk?

Our lamps ARE in enclosures. If it explodes it will NOT make it past the tempered glass, nor will your 3/4" case be affected negatively.

Fuse your circuit, (use the smallest amp fast burn fuse you can make work, mine is 5A fast burn). Then purchase a "good" surge suppressing power bar.

Lets not be paranoid... If you use the specs found in the lumenlab guide for the enclosure you should be safe enough. If my bulb did blow, the 3/4" MDF enclosure would more then handle the explosion!

Worst case, if the bulb did explode what do you think is going to happen? Do you believe it will blow apart a 3/4" MDF or plywood monster box???

Dare I say that people should be worried about that thin plastic Sony Home Theater projector if that is the case?

Oh, and if you think aluminum flashing is going to help... Ha, shards would blow through aluminum flashing before they ever penetrated 3/4" plywood.

This is a non-issue. Use common sense when working with a bulb like the MH 400W.

Cheers,
Lee

I am an electrician were I work and have changed a lot of the MH and HPS lamps. I think what they mean by a failure is something different than just the end of the bulbs life.

Normally the bulbs just go out or will light for a little while and then restart again.

I have never seen one explode and we change them with the power off but still very hot.

Here is the product sheet on the EYE lamp currently recommended by the Guide.

http://www.eyelighting.com/tb/MH/multimeta...52-78-51886.pdf

It cites the following that might cause a "non-passive failure" (their term is "unexpected lamp rupture.")



I found on the OSHA site that there is a standard for building high intensity discharge (HID) fixtures. That is UL 1598 Luminaires. Anyone have access to UL standards, who can say how strong we need to make these?

Sorry if I sound a little obsessive-compulsive, but I'm a little obsessive-compulsive. I read the warning labels, and was a bit alarmed. I do not think this is a high likelihood, but I do want to take sensible precautions, and I did not just want to shoot in the dark and hope for the best.



I have no clue if a bulb explosion would be contained by 3/4" MDF or plywood. (I think I said that up front.) How do you know?

I did take a look at a commercial projector, and noticed that under the plastic outer shell, there is a lot of metal, particularly around the bulb. Commercial projectors also have a much smaller bulb, so probably a much smaller amount of damage if it did rupture.

My thought on the aluminum flashing was that it would help contain the initial flare, reducing the chance of fire. The plywood would have the job of stopping the shards. Steel plates might work better, but that might cause design problems with the heating. At least, half the bulb is covered in stainless steel (the reflector.)

To keep this in perspective, the risk of MH lamp explosion is probably very low. The potential for fire or injury is high if it does happen. Thus, there are industry standards for the commercial products to address those risks.

However, you only risk fire or injury if the bulb ruptures. Follow common sense, treat the bulb with care, and don't exceed the bulb specifications, and you'll be fine.

BTW, you may have seen an MH lamp explosion if you have ever been at a gymnasium or ballfield when someone hit the lights with a ball. Don't do that with your pj

If someone is trying to keep track of how many hours their bulb has on it, be it for safety concerns or for other reasons, an hour meter should be easy enough to install if you are running 12V in your fan setup. Lots of different styles/looks - this is just one example....

Guys,

This really is getting out of control; yes you need to follow safety procedures when working with 120V electricity and a 400W MH bulb. That said we should not be over paranoid about this setup, I can tell you that MH bulbs are the sh*t when it comes to saltwater setups, do you really think that acrylic splashguards would be stronger then a 3/4" plywood box??? Lets be real here guys, the EYE BT28 has an inner bulb of about 1.5" and an outer re-enforced case for gas leakage and UV protection. This outer case also acts as a barrier for the inner bulb. Would this outer glass stay intact if an explosion did occur? The outer glass might stay intact, then again it might not, either way our box will stop the glass shards. Heck I bet the tempered glass would hold up under a MH explosion.

Cheers,
Lee

I don't think I'm being paranoid, and don't appreciate the comment.

According to EYE, there are several important things, consider:

1) The currently recommended EYE bulb is rated for an "Enclosed" fixture ONLY. Eye does make other bulbs that are rated for "Open" fixtures.

2) Contrary to your faith in the outer glass bulb protecting you, they specifically state, "The arc tube and outer jacket may unexpectedly rupture..." - meaning that indeed, the outer jacket CAN break (e.g. explode)

3) They also state that the bulbs must be operated in an ANSI fixture that has the same rating as designated for each bulb.

4) They state that "The radiation from this lamp may cause colored objects to fade unless an adequate fixture is used." (i.e. our screens DO need UV protection)

Although I have yet to see a MH bulb explode, and believe it may be a very uncommon event, I can not imagine it having the explosive force to blow the box apart. The explosion is not what concerns me. The contaminants from a bulb that exploded floating around my house does.

Go back earlier in the thread - these bulbs contain nasty stuff. There's no denying that. And ***IF*** a bulb exploded (however unlikely), the box, as designed, is going to spew all that crap around your viewing area. Maybe that's no big deal to you, but for those of us who have small children, exposure to things like lead IS a big deal.

You may very well have no concerns about a bulb explosion. That's fine. It may very well never ever happen to anyone building one of these projectors and all this "overdesign" is for naught. But calling other members "paranoid" for wanting to "build a better mousetrap" because they have justified concerns is unwarranted.

I'm quite surprised at all the resistance to examining possible ways to improve the safety of these projectors. WHY?? This forum is called "Intelligent Video Projector Design" - doesn't it follow that enhancing the design to alleviate an individual's safety concerns SHOULD be in this area?

Alright, I don't like the direction this is going... I may have to exercise my Moderator Veto, but i don't want to do that.

Movieguy, I think you're over reacting. Nor said "we should not be over paranoid about this setup", Not "Movieguy, you're being paranoid and irrational! Give it up, and stop scaring the customers!" No, that's something I might say, but certainly not Nor.

Really Movieguy, I don't think he meant it like you're taking it. It seems to me as an impartial observer that Nor was merely trying to aleviate some of your concerns, not trying to insult you.

Calm down, take a few deep breaths and relax.


Now to Nor: I'm with you, I've worked around MH lights for years (never worked WITH them before, as I have with this project, but still around them) I have never seen an explosion and have no fear of one, but if they want to discuss the possibility of one, Let 'em discuss it to their hearts content.

Ok now, let's not take these comments as personal attacks. Norlander is simply tempering the argument with some well needed balance. Movieguy, it is also entirely possible that your car's gas tank will some day explode, and a caveat is needed for proper safety in handling the gas and maintaining the condition of the fuel supply. It is good you are concerned about safety and are considering ways to improve the design, no arguments there. It is possible that too much emphasis on the rather remote dangers are over blown as well. A commercial projector's lamp generally has no outer envelope at all and is vented to the room directly by the fan. The lamps in a commercial projector also operate at higher temperatures and pressure due to their smaller size. If explosion is such a risk how could they just vent the lamp directly to the room? Fluorescent lamps contain mercury and other toxins but they are ubiquitous in our lives. UV is a concern that is well mitigated by the tempered glass and acrylic lens. For those who are especially concerned we offer the UV acetate. Please folks, keep the debate friendly.

Ok Movieguy128, I did not mean to anger you. The quote above clearly states "we should not be over paranoid". That could be interpreted badly I suppose, and for that I do apologize. You are correct in the fact that working for better safety is always a good thing. I don't think I ever denied that?? What I am trying to say is many people have MH bulbs in their houses, and anyone with a reef tank setup using an MH bulb takes the chance of exposure to the contents inside. If you do a little research you will see that even if the bulb explodes the amount of exposure is so very little that you have a better chance of poisoning your children with Teflon overheating then an exploding MH bulb. "IF" the bulb does explode carry the pj outside and vent your house. You can always setup a dryer style vent system and vent directly outside from the box fan exhaust.

What would happen if that MH bulb in the Sony Home Theater projector blew-up?

Here is some info on MH safety... Note that it states "Prolonged or frequent exposure"... I must remind you that prolonged or frequent exposure to the sun can have harmful consequences.

MH MSD by Phillips lighting
Cheers,
Lee

Movieguy128,

I wanted to respond ("friendly mind you ") to some of your posted remarks.



We are using an enclosed fixture "projector light chamber is enclosed".



If you read my former post you will see that at no time did I say the outer jacket would protect you. Yes, you do need an enclosure for these bulbs, under no circumstances should you run your projector with an exposed bulb. (You might have to test things with the lid off, in that case use every precaution)



When I hear the word fixture, I think of the entire bulb enclosure with ballast and mogul base... They have no choice but to say you need an ANSI approved fixture, we in fact do use the M59 ANSI approved mogul base with approved tri-tap ballast.



Yes, brainchild has stated this many times in the last few weeks. You do need to be careful of exposure to the bulb, just like you need to be careful of over-exposure to the sun.

Thanks,
Lee

Guys -

All my point was with Norlander (and others previously within the thread) is that if someone wants to design their projector with an extra degree of safety in mind, they should be allowed to without being subjected to comments that can be interpreted (whether meant that way or not) as condecention by other members. Positive/creative input, GREAT! Poo-Poo'ing ideas to help improve the design with regards to safety - not so great.

If I interpreted Norlander's comments as "over agressive" - I'm sorry. But I also think my comments are being interpreted the same way. The crux of my point was what's wrong with trying to build a "safer" projector? If someone wants to incorporate some of the ideas that come out of this thread, fine. If not, that's fine too. But my main point is that folks shouldn't squash the creative suggestions just because they don't subscribe to the need.

Hopefully this post will be interpreted in the spirit it was intended.

Agreed Movieguy128 I am sorry if I seem over aggressive, the written word at times is not a good method of conveying intention. I suppose that is why we have the smiley faces

I guess bottom line, I feel the projector design is as safe and in most cases safer then commercial level projectors. With all the testing and approval needed to allow for a device to be operated within a consumer’s home, I am going to guess that the commercial level projectors have been deemed safe.


Cheers,
Lee

Just an observation:

Are not the huge lamps I see in department stores and building supply stores using MH bulbs? They look the same anyway, and they are all "hanging" out there above the public (dozens of them in each store). I even took an extra look upward this weekend while out at my local building supplies store, and the lights up above look like MH bulbs, and there were not even any glass covers over the bulbs. If this is the case, it seems as if these department stores are not too concerned about the bulbs exploding. Or perhaps where they are so high up it's not as much an issue?

I do myself plan on lining my box with metal around the MH section. My initial concern was heat/fire, but the question of gases also concern me now as I have 2 small children that would be watching projections in a somewhat small room.

That's a good point to bring up.

I can't speak for the individual stores you mention, however not all MH bulbs are rated for the same types of enclosures. The BT28 currently used by most of the folks here is rated by the manufacturer for use in an enclosed fixture only. ("E" class) Some bulbs are rated as suitable for use in "Open fixtures." The stores you cite should be using "O" type bulbs from what I interpret from the mfgs.' documentation. Whether they do or not, well, that's a separate question.

Although EYE states that "E" class bulbs should only be used in properly enclosed fixtures, without the knowledge of fixture design, I don't know what is "proper." The projector, as it is currently designed, *** may *** constitue a "proper" enclosure - but it just as easily *** may not ***. I simply don't know.

Personally, I can't imagine the bulb blowing apart the projector, but understanding the venting process of a "properly" designed fixture is a different matter. (i.e. the serious of spreading the contaminants in an enclosed area like a living room or home) Does "proper" mean air tight? Does it mean fans are OK to use? Again, I just don't know. These are questions I have, and based on them, I plan on tweaking my projector design to meet those criteria. Is this all overkill? maybe. maybe not. Again, I just don't know.

Whoa. Didn't expect the thread to take this turn when I last looked in.

The polite term for paranoia is "risk management."

Using the gas tank analogy, it's not that we're just concerned that our car's gas tank might explode. We're actually designing and building that gas tank, with no idea of all the considerations the engineers who build real cars had when they designed theirs.

Actually I deliberately chose to start this thread in the protected forums because I didn't want to alarm the many lurkers out there, and drive away any potential customers.

My thought was also that there would be more people more likely to look at this issue objectively. Bringing up safety issues is not an attack on the pj. It's an attempt to inform people so they can take appropriate precautions, and maybe come up with solutions.

We're all familiar (I hope) with the dangers of electricity, and how to properly handle it. Now that you know that the risks of MH bulbs, aren't you now going to handle the bulbs differently? Scattered in different threads are descriptions of people experimenting with the bulbs both in and out of the case. Don't they want to know about the potential risks, and mitigate them (or not) to their own satisfaction?

I see several possible solutions to the safety issue.

1. Find out what the commercial standards are for safely building high-intensity discharge (HID) lighting. Obviously, we're not required to build to those standards, but my thought is that they might describe what it takes to contain an explosion. Without this, we're shooting in the dark. Probably nobody here knows the actual force of an MH bulb explosion. (That's also a good thing, because that means the event is rare).

2. Replace the current EYE bulb with the one designed to contain the explosion and the toxic residue. It may be overkill, especially since our enclosures might be sufficient. But this would be a way of buying a solution that was at least designed by metal halide lighting engineers who were examining this specific problem.

3. Adapt the lumenlabs projector design to incorporate a commercially designed and engineered lamp fixture. (This is solution #2 in another form.) Floodlights are not a point light source, but perhaps the reflectors can be modified to fix that? In the project area, somebody from Germany was retrofitting a theatre light. Much more than I had in mind, but it's a potential fix.

I deal with risks for a living. You have to balance the probability of a negative event occurring, the cost of the negative event if it did occur, and the cost and effectiveness of mitigation.

The likelihood of being exposed to UV radiation with this bulbs is high (100%). That is because the bulbs generate UV (see the spectrum chart in the product brochure).

Put the bulb behind normal glass, and most of the effects of UV are shielded. Use UV filters, and the effects are removed almost completely. Mitigation is both cheap and effective.

If you simply ignore the risk, however, and damage the outer casing, the risk is high levels of UV radiation, IR radiation, possible UV burns and possible blindness.

When considering the possibility of an MH bulb explosion, the probability is clearly very low. You will find examples of MH bulb explosions if you look. You will also find many, many, many more instances of MH bulbs in common use that will never have a problem.

On the other hand, if it did blow and you aren't taking any precautions...

The basic design by Brain has 3/4" plywood and a good size box. IMCUO, (That's In My Completely Uninformed Opinion) that is probably sufficient to contain the explosion, especially if properly constructed. Other people are proposing smaller, lighter designs. Are those designs sufficient, too? ???

Another thought. The commercial products may be way over-engineered, because their concern is not so much customer safety, as product liability.

People who are building their own aircraft out of kits do not normally build in all the safety features found on a 747.

Sometimes the correct answer is risk acceptance.

Just get an explosion proof lamp. End of debate.

Technically wouldn't the lamp implode, since the interior is under vacuum pressure?

Actually the inner tube isn't under a vacuum. It is filled with pressurized gas and metal salts.

Brain, what happened to the UV filters? Were they going on the store last weekend?

I have an order of lenses and ballast pending. Is it possible to add to that order while we're waiting for the ballast to come in?

I've given it some time, research, and thought, and I've reached the following conclusions:

- The 3/4" plywood is probably plenty strong to absorb a full MH bulb explosion. You'll want to make sure the walls are strongly fastened together, and secure the lid. Brain's basic design works out.

- Those who are redesigning the box may want to keep the possiblity of explosion in mind. Use of just thin aluminum, plastic, or thinner MDF to save on the weight are losing out in strength (blast protection). If you try that two-lid design, don't forget to fasten both lids.

- The tempered glass provides some protection to an explosion. In this pj design, however, it's the fact that the bulb is sitting inside a thick plywood enclosure that provides the blast protection. The tempered glass is inside.

- If an explosion does occur, you will have toxic materials imbedded in the walls of the box. You may not want to reuse it for that reason. Toxic gases and dust will vent outside the box. Keep the area well-ventilated. It's not the initial exposure that is warned against, but long-term continued exposure. Also, turn off the electricity right away, and watch for fire.

- Take care when working with the bulb. Don't forget that it is emitting UV. Don't look straight into it. Don't scratch it. Use UV sunglasses, and avoid long-term direct exposure.

- I also found that the comparisons to commercial projectors don't fly. Most (as far as I could tell, it was all) commercial projectors use halogen light sources, not metal halide. Halogen bulbs are much smaller. Although they are HID lights and might explode as well, they contain less pressurized gas, and the pressure level itself is less. It may also release nasty materials, but again, those materials are not as bad as a metal halide bulb. That's why this is not as much of an issue for commercial projectors.

- If you have small children about, you may want to secure the pj box so they don't look inside or play with the interior.

Sorry AllThumbs, but all long life comercial projector bulbs are MH bulbs.

Projector bulb FAQ's

Cheers,
Lee

You're right. I was reading too much HowStuffWorks.com. Gotta admit, though, that the bulbs we're putting in these are much larger than the ones the commercial projectors use.

AllThumbs its a bulb not C4. You are making a mountian out of a mole hill here.

Man they haven't used halogen for 25 years...puhleese.

And the smaller lamps are under higher pressure and generally have no UV blocking outer envelope and are therefore more dangerous.

Hello People,

I am just starting to collect all parts for my projector, it means that I am much less than an "newie" . As far I understand this issue, there two main problems to confront:

1- The "explosion" istself. Solutions: strength the box, thicker tempered glass, something more? Someone knows the "force" of that event?

2- Metal gases. Possible solutions: a new circuit that allows stops all fans when there are not lamp in the mogul?, and add some metal adsorbant materials in all the vent holes ( I think in fine sponge metal or activated carbon, but I am not sure if them works)?

Finally, an old (and hated) professor from my University always says that "Lack of evidence, is not evidence". Nobody knows if this lamps will blow or not, our only solution in that case is be alert and cautious.

Greetings

We don't know this definitively. However, clearly the "explosion-proof" bulbs need to be built with some type of tempered glass. 3/4 inch plywood probably greatly exceeds the strength of most tempered glass that you would see on a bulb.

[ADDED IN EDITING] In addition, don't forget that half the bulb is covered by a stainless steel reflector. The remaining half would be dissipated largely by the tempered glass, then has to travel through the fresnels, the lcd monitor, and travel the length of the box, and finally has to overcome the 3/4" plywood. Overall, the basic design is probably more than sufficient. (Make sure the joints are strong, and the lid is secured.)

There is a UL standard for the building of light bulbs of all types that might have the answer, but someone has to buy it.



Really, this is a rare event. Following the warnings listed on the package would probably reduce the chances of it occurring. Avoidance is the best way to handle the metal gas issue.

Most of the measures that you might take to filter the outflow might also impede airflow and cooling, which could lead to other problems (lcd failure). I figure that if you avoid the potential damage or fire from any potential explosion, and are prepared to ventilate the area if one does occur, most of the risks are mitigated. In any case, I'd have no clue how to filter mecury vapor.

If your lamp blows, does your fuse blow? That would stop the fans, right?

For suggesting that people be aware of the published warning labels and figure the possibility into their designs? Hmmm.

You're probably relating the force to an incadescent bulb implosion. I would say that the force is probably greater than that, but less than C4. I don't think I would be saying that 3/4" plywood would stop it if I thought it was as strong as C4.



I don't think we know this as a fact. I haven't looked at the frequency chart for any of the commercial projectors. Anyways, commercial projectors were designed to be placed relatively close to people. These big overhead lamps were not. Since we're using the lamps in ways that they were not initially intended, shouldn't we be cautious?

In any case, I was trying point out some concerns that I encountered while researching the metal-halide lamps we are using. People are playing with and redesigning the projectors, and did not appear to be aware of any of these cautions.

If you don't think it's a concern, ignore it. (It's your life. Live it the way you want.)If you do think it's a possibility, plan for it.

I think I've said what I wanted to say on this issue. Ya beat me down, so I'll shut up now.

I've been studying lamps for the last 18 months. I've looked over 100s of commercial projector replacement lamp pdfs to compare specs, assemblies etc. I am here to tell you, they typically have no UV block and are under much higher pressure than the lamps we use. The reason these lamps are alllowed to be used is because the risk associated with lamp failure is minimal. The lamps we use are indeed designed to be used in habited environs. Have a look overhead on your next trip to Malwart, where metal halide is the lamp of choice. The enclosure-rated lamps we use are designed to be used in a high bay fixture with (surprise) a piece of tempered glass separating the lamp from you. The high bay fixture is openly vented for cooling purposes.

That said, there are real risks and it pays to be apprised of them. Do not go on vacation and leave your projector running! If the lamp explodes turn off the projector and don't let your kids play with the lamp debris! If your projector catches on fire put it out with a fire extinguisher!

From personal experience:

I have changed the MH lamps in the company parking lot, about 2 per month for the last 5 years.

I always wait until the lamp will not light to replace it (totally burned out). These lamps are on from 6:00PM to 3:00AM every day.

I have never opened a fixture to find bulb fragments from an explosion.

Regarding temperature changes, these bulbs have been exposed to 20 degrees fahrenheit and started fine (just slower due to cold ballasts). The physics involved with MH bulbs prevent a sudden temperature change. They arc then slowly warm up, thus increasing the outer envelope's temperature gradually. If they were instant-on then I could imagine potential problems, but that is not possible when considering the chemicals involved.

Basically, I see no problem with forced-air cooling of the bulb, and cannot foresee any explosion threats.

Why don't we just agree to disagree, and let this drop?

All along, I've been saying that metal halide is a possibility, not a probability. If it concerns you too, take appropriate precautions.

If you disagree, I'm never going to convince you otherwise. You won't convince me otherwise, either, especially when I read the warning labels on the side of the box, the manufacturer's fact sheet about the bulb, and the OSHA warnings issued by the government.

We are taking a bulb that is designed to be used for industrial applications, usually 15 feet overhead and left on for long periods of time, and instead putting it 2-4 feet from our kids, and turning them on and off more frequently. Those differences in use should have some impact; possibly reducing the life of the bulb; possibly stressing the bulb. I never argued that they weren't engineered for use around humans, just not 2 feet away from those humans. Those bulb designers did NOT have a DIY PJ in mind.

The reason there is a possibility of explosion is that the MH bulbs are under pressure. If something happens to rupture the glass (like something physical striking it), boom! The other possible cause is that some of the chemicals inside can deteriorate over time and crystalize, causing the bulb to spontaneously explode. Again, these events are not common. But they can and do happen. Hence, all the warning labels.

Everyone's tilting at windmills with this issue, trying to convince the other side.

Step back, take a deep breath, and let's go our own separate ways.