Fire Safety In High Rise Buildings Environmental Sciences Essay

Around the world, from New York and Chicago to Seoul, Dubai, Hong Kong, and Moscow, new super-tall buildings are scraping the sky at unprecedented heights and speed of completion. Fire safety in high buildings has been a significant issue for architects for over 100 years. However, provision for occupant safety from such fires was only addressed in the 1970s. A high-rise building, by popular definition, is a completed, occupied structure for which the roof access level exceeds the maximum height of rescue capability from street level by the fire department (O’Hagan, John T. 1977).

Knowledge in the field of fire prevention is undergoing development and recognition that will allow buildings to be designed for fire safety more rationally and proficiently. After years of trial and error, concepts and criteria have been developed that enables to build high-rise apartment buildings that are safe. Much activity has been taking place today regarding fire safe design of buildings. Adequate fire prevention and protection is the key to the safety of occupants and buildings. To avoid the sources of fire and damage due to it, planning should be done at the architects’ table which results in a fire safe building design. If both active and passive fire defenses are used they provide reasonable safety from the effects caused by fire. Therefore, a well-knit plan, its realization in the design and construction of the high-rise apartment building executes a fire safe structure (Proulx, G. 2001).

Regardless of building construction, sophisticated fire detection system, fire protection, and fire-fighting apparatus used, a building is only as “people safe” as the building owners, managers, and tenant spokesmen want it to be. People cause fires by their acts of commission and omission, furnishings feed fires, and panic results in needless loss of lives and injuries (Kobes, M. 2009).

I have taken this topic because one day I was just standing outside a mall, where I just looked at a high rise building and thought how many people live in that building. What if any disaster occurs, how many families live in there and how many lives will be lost. The most common disaster for high rise buildings is fire, which can be caused by many reasons and is really hard to stop but if fire safety is considered while designing a building and proper evacuation plans are made this disaster can be easily averted. Therefore, I started reading about the fire safety of high rise buildings, the methods available for construction, prevention system used and evacuation models available. The report will provide a comprehensive and concise literature for anyone to understand the measures available to ensure the fire safety of such buildings.

1.2 Problems

Numerous questions have arisen as to the safety of occupants in high-rise buildings following the World Trade Center aircraft collision, fire and collapse. While occupant safety in buildings due to aircraft impact and collapse has emerged as a front page issue for the design profession, it is safety from fire that should represent the long-term focus in high-rise buildings. A great concern has developed among architects, engineers, government officials, and building code experts worldwide about the fire safety of such structures. The record of fires in high-rise building occupancies, with resultant fatalities, and heavy financial losses emphasizes the urgent need for instituting effective fire prevention, fire protection; adequate evacuation programming and planning to make sure losses will be minimal in the event of fire. Fire safety for such structures can be incorporated in their design, construction, and by development of a proper evacuation process (Bryan J.L., 2002).

1.3 Research Objectives

Understanding the fire risk associated with high-rise apartment buildings

Identifying the unique fire safety problems associated with high-rise buildings

Identifying strategies for providing fire safety in high-rise apartment buildings and how they relate to the building design and to the occupants

Understanding how fire safety strategies work independently, and together, to reduce the risk to occupants of high-rise apartment buildings

Chapter 2: Literature Review

2.1 Risk to life in high-rise buildings from fires

A exact risk to life from fire in high-rise apartments is not easily discernible due to the many deficiencies in data. However, by examining the factors, which make up fire risk, the higher probable risk in high-rise apartments can be identified. Risk is defined as the probability that an event will occur, multiplied by the consequences of that event when it does happens. The equation is shown as:

Risk = Probability x Consequences

The risk to life from fire is calculated based on all probable fires occurring at all probable locations in a building while examining the consequences of all of these fire scenarios (Beck, V.R. and Yung, D., et al, 1989). It can be seen then that the fire risk in a high-rise building would be significantly higher than in a low rise building since there is potential for more fire locations, and there will be greater consequences of the fire itself (e.g., stack effect) to a greater number of occupants. Hence, both the probability and the consequences would be much higher, so the resulting risk would be even higher. This higher risk results in greater demands for more fire safety in high-rise apartment buildings.

2.2 Design issues to be taken in consideration by designers

The earlier fires in residential high-rise building illustrate a number of points that designers should take into account:

• Unsuppressed fires in high-rise apartment buildings generate large amount of smoke that can spread vertically or horizontally in the building, even if the fire is limited to only one room or apartment. A contained, but not extinguished, fire can also cause significant smoke (Butcher, E.G. and Parnell, A.C., 1979).

• Vertical smoke spread is accelerated by wind and by “stack effect” which occurs when the inside temperature of building is greater than the outside temperature. Thus in winters, lower floor fires are likely to have the greatest extent of smoke spread to higher floors.

• Most damage, deaths and injuries are due to the spread of smoke in spite of the type of structure (steel or reinforced concrete).

• In fires which result in multiple deaths in residential high-rise apartment buildings, many deaths occur in the egress routes (stairways and corridors) because of smoke from a fire elsewhere in the building (Frantzich H., 1994).

• In apartment fires with doors left unlock or burned-through, smoke spreads to the corridors, shafts and upper levels.

• Sometimes, it is safer for building occupants to remain in their apartments or rooms compared to exit through smoke filled paths and stair-shafts.

• Appropriate instructions to occupants during a fire should be provided if it is expected from them to take specific actions (Proulx G., 2001, 2003).

Designers must realize the results of failure of built-in protection or the absence of proper occupant-based programs on risk to life for residents of high-rise apartment buildings. They must understand the way building and occupant-based safety need to work together and how fire risk is moderated by the fire safety measures that are employed. Simply following with a building code does not necessarily provide best possible fire safety.

2.3 Uniqueness about fire safety for high-rise buildings

The following represent some of the most considerable unique features as in why is the risk from fire is perceived to be so much elevated for high-rise apartment buildings?

1. Egress Systems -In high buildings the potential for crowding and slow movement in exit stairs exists due to the increased number of storeys and also because exit stairs do not normally increase in width as they go down. However, stair shafts also represent one of the main means by which smoke moves vertically (Jin T., 2002). In addition, the time taken by an occupant to descend a stairway significantly increases with the height of the building, which increases the potential for smoke exposure. The essential issue is that the building egress system should provide sufficient evacuation time before smoke reaches the lethal levels, and harms the occupants still remaining in the building.

2. Fire Department Access – Fire department can still reach only six or seven floors in a building even with modern aerial apparatus. Thus, exterior rescue and firefighting is limited to the lower floors. With a fire above the reach of ladders, firefighters have to move vertically inside the building and launch an interior operation at the same time when occupants are descending the exit stairs[6]. This however can result in delays in reaching and extinguishing a fire and can increase contamination of stair shafts if doors to exit stairs have to be left open to run hoses.

3. The Forces of Nature – Stack effect and winds cause a major impact on smoke movement in high buildings. The stack effect increases with the increase in height of building. Wind velocity and direction also affect the path of a fire. They are considerably less of a problem in lower buildings (Butcher, E.G. and Parnell, A.C., 1979).

4. Increased Density of Resident and Fuel Load – By adding floors to a building, the fuel and resident densities increase within a given building footprint. Regardless of horizontal fire barriers, fire tends to move in upward direction, and hence potentially adding more fuel and affecting more residents.

5. Complex Vertical Utility Services – A complex arrangement of pipes, ducts, cables and conduit run in vertical direction throughout high-rise buildings. As well as, fire protection water supplies should also be provided from the top or bottom of the building. Due to these vertical utilities, other fire problems may occur such as cables to fire systems may be damaged by fire on one level and it can affect many other floors.

6. Integrated Fire Problems – Now a days the high-rise apartment buildings are not standalone structures. Normally, they are situated above shopping malls or other commercial structures, above atrium buildings containing offices, or above subway systems. Each structure has its own exclusive fire safety problems and when it is coupled with those in a high-rise apartment building, special engineered solutions are required to ensure resident safety.

Each of these unique features creates a special problem which needs to be resolved before a designer can achieve a fire-safe high-rise building design. While the codes provide generalized solutions to many of the issues, designers must be aware of the issues and the requirement for unique solutions based on the fire safety engineering.

2.4 Basic fire-safety strategies

Designers must understand essential fire safety strategies. One of the most often used means to define these strategies is found in NFPA 550 – The Guide to the Fire Safety Concepts Tree (NFPA 550, 1995). The strategies of NFPA 550 are presented in the form of a tree with a number of branches which represent the individual strategies. The figure 1 shows upper four levels of that tree.

Figure 1: Fire safety concept tree

Each box given in the tree shows how the fire safety aims of the box above can be met. For the high-rise buildings, the objectives of building codes are to reduce loss of life and injury to occupants because of a fire, especially for those occupants outside the apartment of fire source. These, then, become the objectives, which should be met by the designer.

Prevent Fire Ignition Strategy – This objective can be achieved by two strategies as can be seen at the second level of the tree: Prevent Fire Ignition or Manage Fire Impact. It is assumed by the tree that, if the strategy is 100% reliable and effective in itself, the objective of the box above is met. While means to reduce fire ignitions are integrated in the design and operation of a high-rise building, figures show that fire ignitions will still take place (e.g., cooking, smoking) and thus the plan employed to achieve the objective is to control the impact of the fire.

Manage Fire Impact – To manage the impact of fire, a designer automatically thinks of compliance with the building codes – and that is often one way of achieving that objective. However, it is more suitable to follow the logic of the tree to determine which fire safety strategies to employ and how code needs fit into these strategies. The third level of the tree depicts how to achieve the aim of managing the impact of the fire (to reduce deaths and injuries): for that either the fire itself should be managed (Manage Fire) or those exposed to it must be managed (Manage Exposed). The “exposed” over here refers to the occupants, but could also be valuable property, the building or an necessary activity. Since no strategy is 100% reliable and efficient, architects (and the codes) will typically employ multiple strategies to manage both the fire and the exposed.

Manage Fire – It is the 4th level of the tree in Figure 1. It shows that the fire can be managed by any one of following three alternatives:

• Control the Combustion Process – It can be done by controlling either the fuel (construction materials and combustible contents) or the fire environment. Noncombustible construction and restrictions on the quantity and flammability of combustible materials are generally employed. However, interior wall and ceiling finishes, carpeting will burn, also the furnishings which the occupants move into the building. Hence thus, this strategy has some impact, but by itself it cannot achieve the aim; in particular, since there is no way to control the occupants’ furnishings.

• Control by Construction – It limits the growth of fire and movement of smoke using the construction elements such as walls and floors. Special fire-rated floor assemblies, enclosures, corridors, etc are provided to meet this goal. The structural stability of the elements for a certain duration under fire attack is a must piece of the strategy. Many case studies show that doors may not be closed or the firestops may be missing. Hence, Control by Construction will not essentially be 100% reliable and effective. But it does, provide another basic building block for safety against fire.

• Suppress Fire – Water is generally used to extinguish the fire, either automatically or manually. The standpipe systems provide the water supply required by the fire fighters, as well as for automatic sprinkler systems. The interior firefighting in high-rise apartment buildings is tough and is not always effective during the time needed for the evacuation of occupants. It has been shown in studies that sprinkler systems are highly reliable and effective, but not 100%. Hence, this strategy can act as another building block but cannot be totally relied upon by itself to meet the objective of fire management (O’Hagan, John T., 1977).

Manage Exposed – Since it is known that, in real life, the Manage Fire approach may not be 100% reliable and effective; approaches are required to manage the residents exposed to the fire. Two means to achieve this aim are provided by the fourth level of tree:

• Limit Amount Exposed – The number of residents that are exposed to the fire is limited. Since designers have little control over the numbers of residents in a building’s lifetime, this approach is one that is rarely employed at the design stage and is not addressed further.

• Safeguard Exposed – To protect the exposed from the impact of the fire, the design must either protect the occupants in place or move them to a safer location. Smoke-filled exits may make it more suitable for occupants in a high-rise apartment building to stay in their apartments (or particularly on their balconies) to “wait out” the fire. Which is a form of defend-in-place. A defend-in-place strategy should be undertaken only with the full knowledge and involvement of the responding fire department. This approach is often employed to protect occupants with limitations related to mobility when they are supposed to wait for assistance in a protected place or exit stair. Given the many problems with defend-in-place design and the currently-held idea that evacuation is essential, the alternative method of moving the exposed is usually used. Moving the exposed occupants requires that the designer provide: a way to initiate movement (fire alarm/voice announcement); a protected means to facilitate movement (adequate sized smoke-free exit stairs); and a safe destination, which is usually outside the building.

Figure 1, The Fire Safety Concepts Tree, provides designer with the strategies to achieve fire safety in high-rise apartment buildings. In fact, by looking at these strategies, the designer can see the many fire safety elements at present incorporated into building codes. Designers will typically use a combination of these strategies in seeking to attain the goal of fire safety (NFPA 550, 1995).