Zero International Inc.
Door sweeps with integral intumescent seals for both wood and metal doors can restore lost fire ratings due to excessive undercuts. Model 339FS has been tested for 20-minute fire-rated wood doors with undercuts up to 1.25 inches. It carries a 20-minute fire rating. Model 521FS carries a 90-minute fire rating based on testing with metal doors with undercuts up to 1.25 inches.