Fire-blocking products work by creating a thermal barrier, temporarily containing the fire, allowing fire fighters more time to extinguish it. The FireLock line of non-combustible caulks and fillers from BDA Corp., Greensboro, N.C., blocks the toxic fumes, as well as the actual flames. The product has been tested and approved by the American Society of Testing Materials for the E-136 and E-119 codes and exhibits flexibility when pipes expand and wires move.