[Superstone]

I usually check on my growroom at lights-on every day.Today I overslept.When I went to the growroom my ballast was humming loudly and my 1000w Agrosun bulb was in pieces in my reflector.ALWAYS USE SAFETY GLASS WITH YOUR REFLECTORS!!!! This has been a public service message from camp Superstone.

[Midnight]

Flame defender is your friend.

[BigDawg]

blown bulbs don't usually catch on fire?

[habeeb]

Originally Posted by BigDawg

blown bulbs don't usually catch on fire?

no,

shards of super heated material touching things do

[BudGood]

Stuff like that is why I've always been nervous to run bare-bulb, it's always nice to have that extra bit of protection from tempered glass!

[gaiusmarius]

edited : bummer, that really shouldn't happen by it's self.

[PuReKnOwLeDgE]

I went down to a dark veg room last week myself. A 1000MH had blown but stayed contained inside the bulb itself, just the innner tube exploded. Never had a bulb go out ever so it was only a matter of time. Ballast is unhooked and going in for checkups and maintenance just in case.

[Superstone]

Also don't skimp on timers for your lights.Only use tork 1104,Intermatic T101,etc....Any mechanical timer mounted in a grounded metal box will be fine.Don't settle for anything less.
Back in the spring of 2000... I remember it like it was yesterday... I came home from work and went immedietly to the growroom like I always do.That day things were a little dark and the smell of electricity and burnt plastic filled the air. I was scared shitless and almost fainted when I realized the severity of this blow to my senses.
What happened was my cheap plastic timer got stuck,blew the fusable switch on my ballast,caught the timer on fire,and melted the electrical outlet.Luckily the circuit breaker switched off fast enough and saved the day...
This particular grow was in the attic where everything was surrounded by carpeting and wood.I've learned alot since then and now grow only in the basement where everything is surrounded by bricks,cinderblocks,cement board and metal.
EVERYBODY PLEASE BE SAFE!!!

[Superstone]

My safety glass saved my ass today.

[MIway]

Sounds like it was either run too long, or came with manufacturer defects in the arc tube... 70-700psi inside there.



End of life behaviour

At the end of life, metal-halide lamps exhibit a phenomenon known as cycling. These lamps can be started at a relatively low voltage but as they heat up during operation, the internal gas pressure within the arc tube rises and more and more voltage is required to maintain the arc discharge. As a lamp gets older, the maintaining voltage for the arc eventually rises to exceed the voltage provided by the electrical ballast. As the lamp heats to this point, the arc fails and the lamp goes out. Eventually, with the arc extinguished, the lamp cools down again, the gas pressure in the arc tube is reduced, and the ballast can once again cause the arc to strike. This causes the lamp to glow for a while and then goes out, repeatedly. In rare occurrences the lamp explodes at the end of its useful life.[3]

Modern electronic ballast designs detect cycling and give up attempting to start the lamp after a few cycles. If power is removed and reapplied, the ballast will make a new series of startup attempts.

Risk of lamp explosion

All HID arc tubes deteriorate in strength over their lifetime because of various factors, such as chemical attack, thermal stress and mechanical vibration. As the lamp ages the arc tube becomes discoloured, absorbing light and getting hotter. The tube will continue to become weaker until it eventually fails, causing the breakup of the tube.

Although such failure is associated with end of life, an arc tube can fail at any time even when new, because of unseen manufacturing faults such as microscopic cracks. However, this is quite rare. Manufacturers typically "season" new lamps to check for manufacturing defects before the lamps leave the manufacturer's premises.

Since a metal-halide lamp contains gases at a significant high pressure, failure of the arc tube is inevitably a violent event. Fragments of arc tube are launched, at high velocity, in all directions, striking the outer bulb of the lamp with enough force to cause it to break. If the fixture has no secondary containment (e.g. a lens, bowl or shield) then the extremely hot pieces of debris will fall down onto people and property below the light, likely resulting in serious injury, damage, and possibly causing a major building fire if flammable material is present.

The risk of a "nonpassive failure" of an arc tube is very small. According to information gathered by the National Electrical Manufacturers Association (www.nema.org), there are approximately 40 million metal-halide systems in North America alone, and only a very few instances of nonpassive failures have occurred. Although it is not possible to predict, or eliminate the risk, of a metal-halide lamp exploding, there are several precautions that can be taken to reduce the risk:

* Using only well designed lamps from reputable manufacturers and avoiding lamps of unknown origin.
* Inspecting lamps before installing to check for any faults such as cracks in the tube or outer bulb.
* Replacing lamps before they reach their end of life (i.e. when they have been burning for the number of hours that the manufacturer has stated as the lamp's rated life).
* For continuously operating lamps, allowing a 15 minute shutdown for every 7 days of continuous operation.
* Relamp fixtures as a group. Spot relamping is not recommended.

Also, there are measures that can be taken to reduce the damage caused should a lamp fail violently:

* Ensuring that the fixture includes a piece of strengthened glass or polymeric materials between the lamp and the area it is illuminating. This could be incorporated into the bowl or lens assembly of the fixture.
* Using lamps that have a reinforced glass shield around the arc tube to absorb the impact of flying arc tube debris, preventing it from shattering the outer bulb. Such lamps are safe to use in 'open' fixtures. These lamps carry an "O" designation on the packaging reflective of American National Standards Institute (ANSI) standards.

https://en.wikipedia.org/wiki/Metal-halide_lamp

https://www.nasa.gov/offices/oce/llis/0309.html