Decal fire

My daughter put a decal from her med school on the rear window of her Corolla some 6 years ago.
When she used the rear defogger for the first time this year, the decal caught fire filling the car with smoke.
Has anyone heard of this happening?
Do you think it is a problem with the defogger or the decal?

I’m guessing there was some metallic film in the decal that shorted out the defroster, with the age/heat helping to make the decal flammable.

First time I owned a car with the rear-defogger the owners manual said NOT to put a sticker of any kind over the wires. Ever since then I’ve heeded that warning. Although I am surprised the decal caught on fire. I’ve put my hands on the wires when it’s on and it doesn’t get that hot. I suspect the decal might have some time of conducting element in it. Although I’m surprised that it would. You would think that the Med-School would have come across this by now…unless they are using a new sticker.

Yep, a foil based decal will short out the live circuit of the heating element.
Do they issue a decal for the outside ?

Maybe the decal caused a hairline crack in one of the conductive lines, creating a high resistance hot-spot.

If your daughter gets shocked by sticking a knife into a toaster, are you going to blame the toaster or the knife? This is pretty much the same situation here.

Stickers should never be applied over the defroster wires, however this knowledge isn’t intuitive and the mistake not unheard of. These are some of the things we often learn only from experience.

Fortunately nobody was apparently hurt.

Sincere best.

That makes me wonder about using a piece that decal to fix the 1 non functioning strip in my rear window defogger. It seems other repairs are a little more costly.

So the decal was there for 6 years, she’s been using the defroster every year, and this year it catches fire?

If this was the chain of events, I’m with circuitsmith in saying that the wire was gradually damaged and developed a hot spot.

Maybe a paper type decal that dried out over time due to sunlight until it reached the point that not much heat was needed to set it on fire?

Most of the new decals are the vinyl self-stick/removable ones now and they shouldn’t be a problem. I had two on for years since 9/11 and never had a problem. Guess I could see it shorting out if it was the right material though.

If a metal decal shorted across a couple inches of trace it would create a low resistance cold zone and make the rest of the trace not under the decal run hotter due to reduced overall resistance.

I’m surprised, very surprised the FUSE didn’t blow before anything caught fire…

Maybe it was a sticker for the ‘Hindenberg Medical School’…

Aged plastic can get flammable, maybe just a little hot spot set it off…

If the decal shorted across a couple of inches of trace, it would make the rest of the trace run hotter, but the decal itself may have heated up from carrying the current.

It would take a lot for the fuse to blow, especially if it was a small hot spot on the grid. These fuses are usually 30A and above, and the whole grid would have to be drawing more than that for a while. What happened was probably a ‘glow fault’, which causes home fires and property damage far more than dead shorts do. Rarely will a fuse blow, and this type of fault is not detectable by an arc fault breaker. Think of the aluminum wire used in homes about 50 years ago and you’ll be on the right track, I think. It wasn’t the wire that was at fault, but the interface between the wire and the terminals of wiring devices creating hot spots.

You might smell stickers burning, but I smell a lawsuit. Toyota has deep pockets. Medical schools have deep pockets. I hear the finest lawyers have ads on the back cover of the Yellow Pages. (joking of course)