[MaxMax]

The connection between the pipe coming out of the back of the dryer and the vent to the great outdoors was not the culprit.

When your dryer cannot vent outside the pressure leaks inside the dryer and causes
excessive lint buildup which can catch fire. Also, if the dryer vent is longer then
ten feet you will have the same result. ALSO, any turns or 90s can also limit the exhaust causing buildup.

You "at the very least" have a venting problem.

[dfwgator]

You "at the very least" have a venting problem.

Sounds like the dryer needs to go to Anger Management class.

[Smokin' Joe]

I do not think the system would be as sensitive to back pressure if the parts fit more closely. A 1/8 difference in ID of one part and the OD of the part that fits over it is pretty extreme, imho, and invites a problem with lint blowing back into the machine.

Part of my concern is that we expect the tolerances to be a bit closer, at least when it can result in a fire, and would not expect the lint to build up where the exhaust air isn't ordinarily supposed to go, so I want people to be more aware of that as well.

While buildup in the vents will affect efficiency and may cause the dryer to overheat, buildup of lint inside the dryer case provides fuel which can combust when it builds up enough to come in contact with the element or its housing. You have to either take the back off to see or, with some of the newer dryers, the lower front panel and check for an accumulation of lint inside.

Neither the clothes inside (quickly removed) nor the inside of the vent pipe contained smoke or scorching. The fire was inside the dryer cabinet, not the usual air circulation circuit.

As for venting, that is about a 10 foot run with a pair of 90 degree turns in it, and we do periodically inspect that and clean it.

It was the internal lint buildup we were unaware of, we'd been watching the vents to make sure they were clear.