Story highlights Smoke can hide unconscious victims from firefighters

Firefighters have used thermal cameras to locate victims

New device projects thermal image into firefighters' masks

(CNN) What's the most dangerous thing in a fire?

If you think it's the flames or the heat, that's understandable: those are dangerous, too. But both from a victim's and a firefighter's perspective, the deadliest enemy is smoke.

Smoke causes more fire deaths than flames, according to the National Fire Protection Association , because people are incapacitated by fumes so quickly that they can't get to safety.

And it leaves firefighters blind, because it's impossible to see anything in a smoke-filled room.

That's why firefighting teams use special cameras that allow them to see through the smoke, rendering images based on heat rather than light.

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