Did my dryer actually catch on fire or what happened to this sweatshirt?

That's almost certainly a chemical reaction from the BLC rather than a mechanical failure in your dryer. If the machine itself were getting hot enough to actually ignite fabric, the **thermal fuse** or the high-limit thermostat would have tripped and cut power to the heating element long before you saw a charred hole. Modern dryers are packed with safety sensors specifically to prevent what you're describing.

BLC is usually a pretty harsh alkaline or acid-based cleaner, and those chemicals are notorious for eating through organic fibers like cotton. When a chemical like that sits on the fabric, it starts a process of degradation that stays invisible untill you add a catalyst. The high heat of the dryer cycle acts as that catalyst, accelerating the reaction and basicly "cooking" the fibers until they carbonize. That's why it looks like it caught fire; in a sense, a chemical fire happened right on that patch of fabric. If this were a legitimate dryer fire caused by a failing heating element or a lint buildup, you wouldn't just have one clean hole in a single garment. You’d have scorching on multiple items, a heavy smell of smoke in the drum, and likely some discoloration on the dryer’s enamel. The fact that it's localized to where a splash would hit the shoulder is the smoking gun here.

You relly don't need to scrap the unit. Just to be safe, wipe down the inside of the drum with a damp rag to make sure no chemical residue is left to ruin the next load. If the dryer still tumbles and heats without making any weird grinding noises or smelling like burning plastic, it's perfectly fine to keep using. Just keep the keg cleaning setup away from the laundry area in the future.

That's wild, I had no idea cleaners coud just sit there and 'wait' for the heat to kick in like that. Makes me wonder if I should be more careful with my stain removers too. If a thermal fuse actually did blow during a real fire, whould the dryer just stop working entirely or would it keep spinning without heat? I'm always worried about the lint trap being the culprit, but the idea of a chemical reaction is way scarier becasue you can't even see it happening until it's too late. Is there any way to test if those sensors are still working properly or do we just trust they'll trip when they need to?

To answer that fuse question—ussually, if the thermal fuse pops on an electric dryer, the motor still runs but the heat stays dead. It’s a one-way ticket to a cold load of laundry. If yours is still heating, the safeties are intact.

One other thing to keep an eye on is the felt seal around the drum. If those get old and start sagging, a small piece of a garment can get stuck in the gap while the drum spins. It creates high-speed friction that literally chars the fabric in seconds. It looks exactly like a fire but it's just mechanical heat. Given the BLC splash though, I'd bet my house on the chemical reaction.