Gallery: Low pressure intumescent resin: This product is suitable for use in passive fire protection in general, and in firestopping and interior fireproofing in particular. The small, orange chunk on the bottom right is capable of growing into the large black object above and to its left. This type of intumescent is typically highly endothermic and contains a considerable amount of chemically bound water in hydrates. As this is released, it cools adjacent materials. Such intumescents are useful as ingredients in firestop pillows and in paints used for fireproofing purposes. They do not produce enough expansion force to be used in plastic pipe devices, where the intumescent must squeeze shut a melting plastic pipe or conduit. Piped covered with a thin-film intumescent spray fireproofing product called unitherm. When the flame from a blow-torch is applied, the intumescent sodium silicate expands, forming a layer of insulation which slows down heat transfer to the pipe underneath. Hydrates within the coating give up their water content, maintaining a temperature near the boiling point of water, 100^oC. The critical steel temperature is ca. 540^oC. Once the water is spent and enough heat has gone through the char, the steel can reach and exceed its critical temperature and then lose its strength. The time this takes determines the fire-resistance rating