Hot smoke can be carried with the convection currents produced by the combustion process of the fire and will spread laterally across the ceiling, then upwards at every opportunity. Due to the buoyant nature of hot smoke, it can travel a considerable distance from the seat of the fire. The fire gases which are mixed in with the smoke, are both flammable and toxic. The majority of smoke will contain carbon monoxide (proportional to the available oxygen) along with other toxins, such as hydrochloric acid from the combustion of electrical conductor insulation, and compounds of cyanide from the combustion of synthetic upholstery foam infill. Such gases will quickly render people unconscious and cause death, this helps to explain why people who die from fires that occur whilst they are asleep tend not to attempt to escape. The effect of construction Depending on the design of the building will influence the rate of fire growth and the movement of smoke. The style and method of construction can play a major part in fire growth, as can the maintenance of structural elements. Large open-plan and open-floor buildings do very little to limit the free air that can feed a growing fire and flashover is a real possibility. It is important to check the construction of a building to see what easy paths are available for smoke and fire, to circulate around the building: It is important to check the construction of a building to see what easy paths are available for smoke and fire to circulate around the building: • Vertical shafts such as lifts and ducts. • Open stairways. • False ceilings. • Voids behind wall panelling. • Doors, which are ill-fitting, damaged or wedged open. • Cavities. Any holes in fire-resistant structures should be 'fire stopped' , to maintain the integrity of the construction. The materials used in the construction are also vital to the growth of the fire within the building. If the construction materials are non-combustible, the fire will only grow because of the contents of the building. Combustible building boards are often used as internal linings to walls and ceilings, but the fire growth rate of these materials can be reduced by treatment with fire-retardant paints. Therefore, to provide fire protection around internal timber doors, intumescent strips can be fitted at the edge of the door or frame. This will seal the gap in the event of a fire and can achieve 30 minutes of fire protection. Cavities are concealed spaces enclosed by the elements of a building (including a suspended ceiling) or contained within a building element. Sealing cavities can create difficulties, especially where construction techniques rely on through ventilation of the cavity. Cavity barriers can be put in place to restrict the penetration of fire and smoke to restrict the movement within the cavity. Barriers can be provided at the edges of cavities, including around openings. Cavity barriers can also be provided at the junction between an external cavity wall and a compartment wall that separates buildings. Insulated core panels Many buildings have insulated core panels as exterior cladding, or for internal structures and partitions. The simple construction of these panels enables alterations and additional internal partitions to be erected with minimum disruption to the business. They normally consist of a central insulated core, sandwiched between an inner and outer metal skin. There is no air gap. The external surface is then normally coated with a PVC
©SHEilds – All rights reserved FCV5 JUN 2021
Page 9 of 20
Made with FlippingBook Digital Publishing Software