"Home Guy" wrote in message ...
Malcom Reynolds wrote:

Half of the 3-dozen 4-lamp fixtures I have are mounted to a
concrete ceiling, so you tell me what exactly is the fire
threat there.

The other half are mounted _under_ a suspended ceiling.

what's under those fixtures, surely nothing flammable

You mean what happens if an electronic ballast gets so hot that
something melts through not only it's own steel casing, but also the
steel shield in the center of the fixture that covers the ballast and
the wires? And then once through the shield, some flaming bits drop
down and melt through the lexan light-diffuser sheet?

What exactly are we talking about here? The acidic blood of the
creature in Alien?

Uh, no. Ballasts are "black boxes; but that's as dramatic as it gets.
Fluorescent ballasts, both magnetic and electronic, have for years been
equipped with thermal protectors to avoid overheating and fires plus the
smoke, smell and dripping black tar (sometimes laced with PCBs) emitted from
failing ballasts. It's a U.L. requirement called "Class P" protection.
Most Class P ballasts have thermal switches that reset automatically when
the ballast cools off; a few don't so the ballast has to be replaced if it
overheats. A fluorescent lighting fixture which cycles on and off every few
minutes is likely the victim of a failing or overheated ballast -- perhaps
due to the wrong lamp being used.

Tomsic