Metal is a good conductor of heat. Diamond is the leading thermally conductive material—hardly a concern for owners of commercial buildings—but silver and copper are also highly conductive. Silver has a 429 W/m•K, which is a unit of measurement for thermal conductivity, and is a component of many appliances. Copper (398 W/m•K) is commonly used for manufacturing conductive appliances. Hot water pipes are among the products that use the conductive properties of copper. Concrete and brick have low thermal conductivity, as does insulation.
Heat transfer can also occur through radiation. Heat is transferred through the air due to electromagnetic waves. Heat spreads in multiple directions until it connects with an absorbent object. Through radiation, a fire can spread through windows, lighting materials on fire and causing a quick spread that can destroy other buildings.
Intumescent coatings
Intumescent coatings, or paint, is applied to structural elements and prevents objects from losing their strength in a fire and plays an important role in passive fire protection. Intumescent coatings were first patented in 1948 and have been part of the building landscape since 1960.
An intumescent coating expands in a fire and forms a thick protective foam layer, called a char, that insulates the object from the fire. The foam forms a barrier between the fire and the object. Some intumescent products can expand to more than 100 times their original thickness. As the product expands, it becomes much less dense. It works as an insulator that keeps high temperatures away from structural components or protected openings.
The chemical reactions that take place during expansion absorb heat. The coating reacts when its temperature reaches or exceeds 120 C (248 F), and the charring effect insulates and reduces the transmission of heat. It also releases water vapour to help cool the object.
The duration of protection of products with intumescent coatings differs but is generally between one and two hours. The load bearing capabilities of steel should not be impaired with that duration, allowing more time for evacuation and firefighter response.
Intumescent coatings contain several raw materials, including ammonium polyphosphate, melamine, pentaerythritol, and titanium dioxide. As the temperature rises, chemical reactions within the coating occur and forms the foam. As the char forms, the intumescent layer provides a barrier against the heat of the fire.
