Abstract: The invention provides methods, systems and devices for installing thermal barriers in openings or gaps in or between structures such as walls, ceilings and floors. At least one firestop block is positioned in the holes or gaps formed by the wall and a fluted metal deck of the ceiling or floor. The walls can be gypsum walls, which may have a metal track at the top or bottom, or could be block walls made of concrete or similar material. The firestop blocks are made of fire resistant material such as hydratable cement or intumescent materials. A flexible or flowable firestop material that is operative to cure or harden, such as elastomeric sealant or silicone, or hydratable cementitious slurry, is introduced into the space between the firestop block and the hole or gap, as a sealant or filler.