An intumescent mesh has a flexible grid with a plurality of strands that form a series of openings in the flexible grid, and an intumescent coating applied to the flexible grid. The intumescent coating is made of an expandable graphite and a polymer-based carrier as ingredients and having an activation temperature above which the intumescent coating swells. The grid is sized such that the intumescent coating permits airflow through the flexible grid until the intumescent coating is exposed to temperatures at or above the activation temperature, whereupon the intumescent coating swells to seal the openings and prevent air flow through the flexible grid.