It would be really hard to start a fire with an Arduino with 5V USB power. You might fry some components, but even then, they usually just stop working (with a

It would be really hard to start a fire with an Arduino with 5V USB power. You might fry some components, but even then, they usually just stop working (with a little magic smoke if you're lucky, but typically not) and you lose a dollar or two. Don't let a genuine fear of safety issues stop you from tinkering with low-voltage hobby electronics. Stay away from 120/240VAC mains power of course, but an Arduino and the 5VDC from a USB charger is a pretty forgiving environment.