Buying guide for Best fireplace screens Why do you need a fireplace screen for your fireplace? Well, as fire burns a log, cellulose inside the wood turns to gas. This gas expands and ruptures the cell walls to produce that familiar, soothing crackle. Every once in a while, these gases collect and build up enough pressure to create a small explosion or pop. These pops can launch flaming pieces of wood a good distance from the fire, creating a safety hazard.