Spreading Of Fire In Hospitals Essay.
Chapter 2: Fire spread
The chapter discusses aspects of fire spread so as to understand spread of fire, fire transfer, and how fire moves or escapes.
Most fires spread quickly in buildings because of the presence of combustible materials like furniture, and flammable gases. Controlling of fire spread is easy in the first stage also referred to as the insipient fire. Nevertheless, fire can move swiftly and even reach higher speed limits in the presence of assistant factors found in gaps or penetration inside a building. Internally, spread of fire is common in obscured spaces, small wall gaps, and attic or roof spaces. Externally, fire spreads along the outside part of a building,
Research by the Building Research Establishment (BRE) on fire spreads inside buildings concluded that several factors resulted in separation of fire. Furthermore, it was also discovered that approximately eight and a half thousands fire that have separated from the room of origin (J S Hopkinson 1984). The specific percentage of a fire spread in hospitals where it is limited in the room of origin is 86%, where the fire spread beyond the room of origin is 10%, and 4% unrecorded spread (See appendix 1).Spreading Of Fire In Hospitals Essay.
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The three modes of transfer where fire spreads are convection, conduction, and radiation. However, the most dangerous transfer mode is convection because it has been proven that it results in most casualties and deaths. When fire starts in an enclosure, the smoke rises vertically towards the ceiling. The smoke produces a mass of toxic gases that will be trapped at the ceiling. Afterwards, the smoke spreads to various directions penetrating gaps found in floors, walls, or ceilings so as to escape to other locations either within the building or in buildings nearby.
Some materials like metal transfer heat quickly and this is through conduction method. This occurrence—conduction—can result in heat being transferred to combustible materials inside a building, which result in a fire. Similarly, radiation is like conduction but through the air, where a heated electric bar in a room can transmit heat towards a combustible material resulting in a fire.
2.2 Fire spread on internal linings
The spread of fire inside the building can be inhabited through making sure internal linings: adequately resisting spread of the flame over their surface, and if ignited, have a heat release rate or fire growth rate that is reasonable in the circumstances. In this case, internal linings signify, “materials or products used in lining any partition, wall, ceiling or other internal structure” (ADB 2006, p. 62). The above graph is mentioned in The Approved Document B2, where it briefly describes the requirements that need to be considered in this topic of area.
Spread of fire and its growth has a high chance of being affected by the type of material used in making the internal structure—wall, ceiling, and many more. Rounded areas inside buildings are significant for linings to spread fire, and also where a strong spread might inhibit occupants from escaping. Therefore, the lining material can enhance internal fire spread, by accelerating the ease of ignition, which the lining material gives off heat when burning.Spreading Of Fire In Hospitals Essay.
Hospitals and other healthcare enclosures are designed and constructed in a way that it provides acceptable fire resistance, and the building to have the ability to remain stable obtaining time for escape and extinguishment. Furthermore, the buildings are to have the capacity to prevent smoke and fire from spreading to adjacent buildings and other rooms inside the burning building.
Therefore, there are several ways fire separates in such insensitive building, where different factors assist the process of fire spread. Six ways are listed and include:
Fire spread via doorways: This is where fire spreads from origin room of corridors to occupied areas through exposed doors. Fire can also spread through fire resistant doors if they are held with fire debris, wedge, or lack of door closer.
Fire spread via walls and partitions: Fire Penetrates through non-loading partitions, and through unstopped ceiling voids.
Vertical spread, via stairways: Fire can be spread upward if a door has a direct opening with the staircase from the room of origin.
Via ceilings: Early stages of failure of lath and plaster ceiling giving spread of fire to locations above (room and roof) because of the damage of ceiling materials.
Via wall cavities: Ignition of combustible materials within and external wall during installation and maintenance process enabling fire spread through cavities to upper floors or roofs.
Via furniture (curtains): Fire ignites along the lower edge by bed covers or beddings. It could penetrate to combustible lining of ceiling void.
Structural elements in a building
The major structures are:
A column, beam, or other member forming part of the structure.
A load bearing wall.
The above listed elements should be protected from early failure so that such elements have a minimum time of fire resistance to maintain itself and not to collapse, or the capacity of the load-bearing not to fail. Resistance to fire penetration and resistance to heat transfer should be considered, so that such elements have the ability tackle fire hazards and meet the demanded consequences. The minimum fire resistance period provided by the element of the structure should meet the provisions that are mention as in table 2. (See appendix 2).
2.3 Fire spread on external walls
In hospitals it is crucial that the external wall is protected from fire. This is because external element could significantly influence the separation of fire in minutes or it could be in seconds in some circumstances through roof and wall penetrations to adjacent buildings or parts within the indicated building. The minimum time of fire resistance for external walls for a building with a height to the top floor not exceeding 5 meters should be 30 minutes fire resistance, and where the height exceeds 5 meters should be 60 minutes fire resistance. Hospitals or health care buildings having above 18 meters should have an external wall that limits combustion.Spreading Of Fire In Hospitals Essay.
2.4 Fire spread though cavities
Hidden spaces and cavities in buildings affect fire spread and their growth. Fire and smoke moves rapidly and continuously from where the fire sets through these cavities. Therefore, it is important to set up fire resisting barriers in these cavities control their sizes (Department of Health – Estates & Facilities Division 2007; HTM 05-02 2007. p.29). Also, concealed spaces and cavities should be subdivided to restrict fires and smokes separation. The Approved Document B (ADB), section 9 (concealed spaces) has provisions and requirements for subdividing in concealed cavities (see appendix 3).
Edges of cavities can be closed by cavity barriers or around the openings. It should be also between the junction of an external and internal wall and every compartment floor or wall. Compartment walls should be constructed to reach the ceiling or roof cavity and run up the full height of the storey to the compartment floor to have the required fire resistance. The minimum fire resistance period of a cavity barrier should be not less than 30 minutes when constructed. Dimensions of thickness of cavity barriers in a wall, partition, or around openings are listed below:
Not less than 0.5 mm thick for steel
Not less than 38 mm thick for timber
Not less than 12 mm thick for polythene sleeved mineral wool, mineral slab, calcium silicate, cement based or gypsum.
Cavity barriers should not be affected by the movement of building due to the subsidence or due to the temperature change or other factors such as failure when subject to fire to obtain best performance (see appendix 4).
Compartmentation refers to subdivisions of spaces provided inside a building separated from each other by either walls or floors of fire resisting construction. By this method, separation of fire is avoided and large fires are prevented from occurring. Therefore, all floors in health care buildings should be constructed as a compartment floor to prevent the listed threats (ADB 2006, p71; HTM 2007, p25).
The planning for the horizontal evacuation (PHE) concept is to sub-divide the locations provided for the residents by compartment walls and compartment floors to obtain the required protection in the event of fire. This is made to give horizontal escape into aligned protected areas. The aim of this process is to evacuate in a short period of time to the ultimate safety (place of safety). In health care buildings, at least three protected areas by compartment walls must be provided in each storey and all floors should be compartment floors. The following provisions need to be considered for such premises, as mention in Approved Document B:Spreading Of Fire In Hospitals Essay.
In any protected area, it should exceed 10 beds.
Protected areas should be sufficient in its area and large enough to accommodate its own occupants and the occupants escaping and arriving from aligned protected areas.
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