Fixture fire

[cornbread]

Looking for some help in trying to determine what cause the fixture fire we had in our plant. Photo?s 1 thru 4 shows the damage. Luckily for us the problem was spotted quickly and fire extinguished. My concern is we have other fixtures of this type and how likely are they to fail in this manner.

A few notes about the photo?s.
The light fixture was removed and the photos were taken in our electric shop.
The original bulb (Sylvania Metalarc" 400 watt) had two holes in the glass globe near the middle of the bulb. The bulb you see in the photo is a replacement, we wanted to see if the fixture still worked, and it does. Unfortunately when the original bulb was removed it shattered. What is not shown in the photo is the bottom plastic bezel of the fixture, it completely melted and fell to the ground. Note the fixture was fuses properly, and the fuse did not blow. The correct bulb wattage was installed.

Has anyone seen a fixture fail in this manner? Any thoughts on what failure mode prompted the fixture to catch fire? Any feedback would be greatly appreciated.

 

[augie47]

Thoiught:
MeaL Halide can rupture...I'm told especially in the later life.
NEC 420.130(F)(5) addresses this by requiring type "O" lamp or a containment barrier. Possibly a lamp rupture with hot elements striking a "plastic" reflector.
Uneducated opinion only.

 

[peter d]

Thoiught:
MeaL Halide can rupture...I'm told especially in the later life.
NEC 420.130(F)(5) addresses this by requiring type "O" lamp or a containment barrier. Possibly a lamp rupture with hot elements striking a "plastic" reflector.
Uneducated opinion only.

I agree - this was a meltdown from lamp failure. If you leave a MH lamp operating beyond its rated life, there is a good chance it will fail catastrophically. I'm sure we've all changed our fair share of MH lamps that was nothing more than removing the base and what's left of the arc tube, cleaning out all the broken glass.

So, the moral of the story is - change those lamps in regular intervals. Also, if you leave a MH lamp in too long, you are paying for electricity but not getting much light. Light output declines dramatically beyond rated life.

Regarding O rated lamps, it would not be required in this "luminaire" since the OP mentioned it had a bottom shade.

 

[don_resqcapt19]

I agree - this was a meltdown from lamp failure. If you leave a MH lamp operating beyond its rated life, there is a good chance it will fail catastrophically. ...

I wouldn't say a good chance as less than 5% fail in this manner. Also this type of failure is almost always in a lamp that is left on 24/7. A 15 minute shutdown once a week will prevent most failures of this type.

 

[LarryFine]

I won't argue with those who have experience with this kind of failure, but what's left of the reflector sure looks like it was heated from below, and the ballast housing is rather clean.

Now, if MH failures cause spewing of hot gas and/or molten metal through the mentioned holes in the globe, then I could grasp that better.

So, I'm just curious: what is or was below the fixture?

 

[cornbread]

Appreciate the replies. Thanks to your feedback I've done several google searches on halide lamps and getting myself up to speed on the problems these lamps can cause. Again many thanks !!!!

 

[cowboyjwc]

I won't argue with those who have experience with this kind of failure, but what's left of the reflector sure looks like it was heated from below, and the ballast housing is rather clean.

Now, if MH failures cause spewing of hot gas and/or molten metal through the mentioned holes in the globe, then I could grasp that better.

So, I'm just curious: what is or was below the fixture?

Thanks Larry, I was having a hard time figuring that damage out my self. I know it's just plastic, but it's pretty heavy duty plastic and I figure that it would have to get pretty hot to do that kind of damage.

I too have never seen that kind of damage on a MH fixtue so I will say that I am certainly not an expert.

 

[don_resqcapt19]

The arc tube in these types of lamps operate at about 1800?F and 400 psi. If the tube exploded and the fragments stuck to the plastic shade, I could see this type of damage.

 

[cornbread]

So, I'm just curious: what is or was below the fixture?[/QUOTE]

The light was in our drum storage wharehouse.

 

[ironman3452]

i use to relamp home depots and in the 4 years i only saw this once, it was caused by a worker with a lift, he had hit the fixture with the forks and broken the bulb, the fixture had a glass shield on the bottom and it contained the hot parts.

 

[K2500]

Relamping a 1000 w once, and the arc tube had ruptured but the outer envelope didnt shatter. The glass had streched and a small hole at the tip of the bubble. Fixture was charred. It was almost like the arc didnt extinguish when the tube broke.

Is that type of failure common? The fixture was metal so no fire, but will the arc continue even with the arc tube broken?

 

[K8MHZ]

Relamping a 1000 w once, and the arc tube had ruptured but the outer envelope didnt shatter. The glass had streched and a small hole at the tip of the bubble. Fixture was charred. It was almost like the arc didnt extinguish when the tube broke.

Is that type of failure common? The fixture was metal so no fire, but will the arc continue even with the arc tube broken?

Decades ago I saw a friend of mine throw a snowball at a streetlight and hit it so the snowball swirled around in the housing before falling back to the ground. The glass broke due to thermal shock and the filament continued to burn, increasing it's brightness tremendously, for 15 or 20 seconds before popping out.

I could see a potential fire hazard if that were to have happened in a warm building instead of outdoors in a typical Michigan winter where we had to warm the snow up in our hands to get it to stick together enough to make a suitable projectile.