I’ve been running wiring in my house and had to drill from the basement up into a first floor wall cavity. Must have gone through 2-3 inches of wood, including the plywood flooring and a sole plate. The spade bit was duller than anticipated, resulting in a rather long drilling process–and a damn hot drill bit at the end.
I’ve drilled through other wood supports before and have wondered if the friction from a dull bit could ignite the dry wood. My concern: an unseen fire erupting in a wall cavity. IIRC, I’ve drilled wood before to the point that it started smoking a little.
I’d say not unlikely. Same principle as with a fire drill, right? I’ve certainly been able to induce smoking this way. However, I’d say you’re safer drilling overhead, in that the fine dust that would serve as tinder will tend to fall out. However, I don’t think it’s that likely that you could leave a small ember in the hole that would erupt into a fire later. As soon as you get smoke, you know you have a problem. Solution: rapidly spit into the hole. Then carefully sharpen your spade bit with a mill file.
It almost happened to me. I was drilling through a wall footer blind, using a flex extension through a hole in the drywall. The bit either hit a reall hard knot or a nail/screw. I thought the wood was just really tough, so I applied more pressure. After a few seconds, I realized the drill bit wasn’t going anywhere, so I pulled it out of the hole in the drywall. As I sat there thinking about what to do next, smoke started coming out of the hole. At first just a bit, which I thought was just from heating, then a bit more, so I ran to the kitchen, grabbed a glass of water and poured it into the hole.
If I hadn’t stayed there and just walked away, I’m not sure what would have happened. It was probably just wood smouldering, but there was plenty of sawdust in there from the drilling, so it’s entirely possible that it could have fully ignited and burned the house down. I learned a good lesson from that.
Problem is, unless you’re blessed with X-ray vision, you never quite know. When operating a drill, knotty wood may “feel” not much different than electrical conduit. Imagine sinking a cobalt bit into a live 110-volt service.
BTW, the “smoking” wood that I referenced above occurred when I hit a resinous knot.
There might be a risk if the drill broke out of the side of the timber, behind the plasterboard - because embers (if any are actually produced) might drop down inside the cavity and fall onto something that would act as tinder, but even then, it seems fairly unlikely that a fire would break out - from my limited experience of attempting to light fires by friction, I can testify that lots of air flow is required. It’s possible, but pretty unlikely and even less likely to erupt into a blaze without conspicuously smouldering for a while.
This can be dramtically affected by the age of the wood involved. The ignition temperature of wood lowers with age due to chemical changes. Drop a spark on fresh wood and it goes out. Drop it on a 100 year old stud or sill and the outcome may be quite different.
Problem is, unless you’re blessed with X-ray vision, you never quite know. When operating a drill, knotty wood may “feel” not much different than electrical conduit. Imagine sinking a cobalt bit into a live 110-volt service.