Yes, a residential wall light switch can catch fire even when the toggle switch is flipped to the "Off" position. The root cause of this hazard is that line-voltage electrical wires remain continuously connected to the top terminal screws inside the switch box regardless of switch position. If terminal screws loosen due to thermal expansion or wire nuts fail, high electrical resistance and continuous micro-arcing will keep generating extreme localized heat behind the wall plate, melting the plastic housing and igniting surrounding framing. You can troubleshoot fire risks safely by shutting off the breaker. You can verify that your corrective action is successful when cutting power, removing the wall plate to inspect for scorched wiring, and tightening all terminal connections eliminates the hidden heat source.
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