This really worries me: I own three laptops, use a fourth for work and thus I often have three — and sometimes four — laptops fully-charged at home. What exact

This really worries me: I own three laptops, use a fourth for work and thus I often have three — and sometimes four — laptops fully-charged at home. What exactly are the parameters under which an unattended laptop may catch fire? Only when the laptop itself is running? Only if running and heat exchange is impeded? I honestly don't know, and that worries me.