The world is a complex mix of concepts and concepts are made of blends of laws. These then manifest as the physical world that we see. A person is made of several concepts of life, matter, energy, and soul. Salvos's attack makes the law of fire overwhelm the other laws and throws everything out of balance.
But it is worse than that. He doesn't just create random errors, he infuses everything else with fire so that even if you survive his attack, the damage of the law of fire will still be lingering in your body. And fire wants to spread as long as it has been started. So even if you survive being dunked in a lake of fire, the lake of fire will continue to be with you.