My train operation is located in my 3-car garage...suspended from the ceiling. Some of you have seen it...but, if not here's a YouTube video.
http://www.youtube.com/watch?v=_iscqVRNwoI
Since I suspended it from the ceiling, I used thick "pink construction" foam insulation for the base rather than plywood. I didn't want to make it so heavy as I am no engineer and, who knows, I could pull the whole house down.
Back during the summer...August...I was showing the operation to a relative. We weren't running trains...though I had powered up the layout for the first time in a couple of months. Suddenly, one of my switch motors sizzled and popped...and melted its way through two layers of foam. I had not tried to throw the switch or shown any attention to it at all. I chalked that off to "bad luck" and a freak, unexplained accident.
Tonight after about 1 month of not applying power to the layout, I did so...largely to charge up various batteries in engines around the layout. As I had done a zillion times before, I left it on...went back in the house...and spent some time (30 minutes?) looking at this forum and Trainorders.com.
For some reason, I decided it was time to go back to the garage...do a little cleaning up and turn off the layout. When I got there, I found one section ablaze...very scary...especially, since all that melting foam was now dripping onto all the junk (stored on the ground level of the layout) and setting it on fire as well. I panicked a bit...but ran back inside the house to the kitchen and grabbed the large fire extinguisher there. I discharged all of it before using a second, smaller extinguisher stored in the garage itself. I was not sure if I could get it under control...but, luckily, those two extinguishers were enough.
So...I don't know if this is a warning to never leave your layouts powered up and unattended...to not use foam as a basis for your track work...or to never use this particular brand of switch machine and motor that will go un-named...I am not sure.
I do know I am a very lucky guy to have gotten out there when I did...very lucky indeed. We could have lost it all.
I attached a few photos of the aftermath.