Boilover: Fire Aspects of the World Trade Center Terrorist Attacks Analysis

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Fire protection engineering calls upon the study of the behavior of fire and the impact on the engineering properties of building materials that influences the structural modeling of buildings focused at effective methods of protecting occupants subject to the potential threat of fire. A balanced study of the behavior of burning materials, and the inherent characteristics particularly when exposed to incident heat and the influence on engineering properties such as steel and concrete which are commonly used in the construction industry for the safety of life spurs thoughts about fire protection engineering. Therefore, Fire protection engineering unfolds thoughts about the study of the behavior of fire, the structural response of the effects of fire on different materials such as steel, the engineering behavior of concrete when subjected to fire, how these influences the structural modeling of a building, and the overall influence on the safety of the life of occupants in these buildings.

The Behavior of Fire

Furness and Muckett observe that once a material has been ignited, it evident that the behavior of fire on different materials it comes into contact with leads to the dissipation of large amounts of energy resulting in mass losses in the burning process while undergoing through a number of stages before it reaches its maturity stage (20). Fully developed fires are characterized by a behavior that significantly influence the approach used in ventilating buildings, the rate at which temperature rises, and the time it takes the fire to reach the maturity stage. These elements critically influence the characteristic behavior of burning materials and influence the impact on the overall design of a building (Cote, 32).

Burning behavior of materials

Cote argues that once a material has been ignited and undergoing the combustion process, the incident fire moves or spreads along the body of the material under the influence of a number of key parameters (23). These includes the intensity of the incident heat on the burning object, the composition of the burning fire, the ability of air that supports combustion to reach the burning fire, the mass of the burning material and its surface ratio, and the physical orientation of the burning fire and the burning material. However for a fire to fully exhibit its burning characteristics, its exposure to the oxygen that supports combustion should be excellent. Dols and Walton affirm the relation that implies that the amount of heat generated from a burning fire can be critically calculated using the relation, Q= (q/l)*αH, where Q is the amount of heat generated from the burning fire, q is the heat on the burning material measured per unit area, l is the hidden or the latent heat of combustion, and α H is the change in the heat of combustion (56).

Dols and Walton reinforce the idea that the typical properties of burning materials influence the intensity of heat generated during combustion, the rate at which heat is released from the burning material, and the actual characteristic and type of fire produced in the burning process (64). That also has the overall influence on the heat protection materials and the heat protection engineering approaches used by the fire engineers to ensure minimal destruction to property in the event of a fire.

On the other hand studies by Cote indicate that a fire usually burns with its intensity increasing to a specific value before it declines due to the decrease in the amount of the remaining fuel (34). In addition to that, the development and decline stages of a burning fire are influenced by the suppression techniques used and amount of oxygen available. It is also worth noting that the development stages of a fire are significantly influenced by the arrangement of burning materials.

Development stages

Bryan reinforces the fact that upon ignition the possibility of the fire spreading increases with the pattern used in the arrangement of the burning material (32). However the development is influenced by the arrangement of the burning materials and is usually under a significant influence by a sequential organization of the burning objects. It has been demonstrated by Klote that the firs ignition causes smoke that collects at the upper layers of a burning fire and acts a medium for transporting heat to the surrounding materials or objects (45). In addition to that, the heat that is absorbed by the smoke from the burning object is carried into the next object in the sequence thus subjecting it to ignition. The burning process is accelerated by the radiated heat from the smoke into the unburned materials causing them to get ignited and start burning (Klote, 69).

It is possible for objects that have not been ignited in a building to be ignited and start burning spontaneously from radiated heat. That is also particularly due to radiation effects that may cause local fires and various flash points in the process.

Once a number of objects have been ignited and burning, the fire may continue burning until it becomes fully developed. A fully developed fire is characterized by a number of properties such as steady burning as discussed below.

Fully developed fire

Klote sees a fully developed fire as being characterized by a steady burning behavior where the burning rate attains equilibrium level (23). The state of equilibrium may be due to the presence of factors such ventilation as is common with fires that burn under controlled conditions or due to the characteristics of the burning material. Fire protection engineers see the ventilation effect as being produced by the presence of openings into a room such as a door. The heating effect of a fully developed fire is significantly influenced by the rate of air transfer into the burning fire and the environments in general. Fire protection engineers also endeavor to provide accurate statistics on the behavior of a fully developed fire to identify and model the best approach of designing the best protection approach. In addition to that, such models provide a clear and precise way of studying the behavior and structural response to the effect of the burning fires on the engineering properties of steel, a commonly used construction material (Klote, 35).

A Structural Response

When building materials have been subjected to heat, their engineering properties get modified in the process. Certain levels of heat coming from a fully developed fire at times weaken a steel structure and may lead such a structure to succumb under any loads it supports leading to its collapse. Therefore, the study of the response of steel to a burning fire and the modifying effect of the fire is critical in influencing the approach used by fire protection engineers in designing and implementing adequate and reliable fire protection strategies and methods.

Furness and Muckett argue that engineering materials such as steel have specific fire resistance properties that can be ascertained by conducting standardized tests on each specific material. In addition to that, the tests provide data about the resistance rating of any material and the ability of a specific model of a building to satisfy a given fire protection criteria (100). However, it should be clear that fire protection engineers conduct such tests to obtain comparative values on the ability of a building constructed using specified material to withstand a fire before it succumbs to the fire and collapses (Nwosu & Kodur, 156).

To fully obtain reliable fire resistance values and appropriate ratings, structural members for a building should be evaluated against the structural properties such as the intensity of the applied load that is withstood by a member of a structure, the physical and chemical characteristics of the members and its role in the structure such as a supporting column, characterizing measurements of a member and the conditions it is subjected to at its boundaries, the intensity of the incident heat on any specific member, the category of the material used in the construction of a building such as a steel or concrete, and the impact of incident heat on the chemical and mechanical properties of the structural material.

The fire protection on any structure is significantly influenced by thermal and mechanical properties of the building materials. That is the case with steel. The thermal performance of a steel structure is influenced by the influence of the incident heat on the on the mechanical properties of steel (Furness & Muckett, 120).

Steel has been shown to lose its strength when prolonged heat is applied on it. The ability to sustain its properties decreases significantly and becomes easily deformed when subjected to prolonged heat. This is indicated by a drastic change in its modulus of elasticity under prolonged heat. However, fire protection engineers have shown that the ability of a steel structure to resists the effects of prolonged heat is influenced by specialized treatment of steel to resists stresses due to heat and other loads when a building is under fire. In addition to that, it has been demonstrated that cold-drawn and hot-rolled steel are commonly used in the construction process for the purpose of overcoming the heating effect on steel structures.

However, before an appropriate material is selected for construction, it is important to evaluate its fire resistance characteristics and compliance to subscription standards for building codes which have to be adhered to to meet standards for fire protection for buildings. These are achieved by conducting performance assessments using a definite criterion on construction materials.

Performance tests

Klote notes that performance tests are conducted to determine the structural behavior of building materials and fire protection properties of a building and the construction materials used in the structure based on ASTM E119 standard requirements (35). Construction materials are tested in environments with heat tests particularly on building assemblies and other areas of a building that may be exposed to heat. The ASTM E119 standard provides data based on a number of performance elements. However, it is worth adding that the ASTM E119 is comparative in nature.

Klote emphasizes that fire protection is effectively achieved by identifying the load bearing capacity of a structure subjected to heat to determine the limit or extent to which a structure can resists collapse before it gives way to the effect of heat (54). In addition to that, research has shown that the effect of separating two buildings on the overall effect on a structure when subjected to heat has the possibility of reducing the heating effect on a building. In addition to that, it is worth conducting a test on the integrity of building materials to determine the overall effect of heat on the structural strength of the materials and their conformance to the ASTM E119 standards (Klote, 78).

It is widely agreed that these tests are conducted on buildings that are prototypes of actual structures. The tests data can be applied to actual structures and building materials. Research shows that ASTM E119 tests are thermal and not structural in nature despite the fact that loads are applied in the test process. Fire protection engineers load the test floors largely to determine the fireproofing effect on the materials that are used in the test process particularly the ability to resist buckling while undergoing tests. They also study the gradual effect of the buckling on the ultimate structure of a building.

Furness and Muckett emphasize the fact that typical studies have established that different materials particularly different types of steel indicate different responses to the application of prolonged heat (150). However, from practical experience, there is no incident in which a steel structure under protection has collapsed under the heating effect of fire. The fire protection methods used in the typical example was largely spray protection. However, other practical examples have shown that steel structures rarely collapse under the application of large amounts of heat. The uniqueness in the ability of steel structures used in the construction process to maintain their structural composure has been largely attributed to the thermal conductivity of steel, the specific heat capacity of steel and other mechanical and chemical properties (Beyler, 22).

Having understood some of the properties of steel and the influencing properties rendering steel a structurally reliable material in the construction of buildings able to withstand the effects of heat, fire protection engineers have various methods of improving the properties of steel particularly for use in the construction industry to achieve adequate fire protection using a number of fire protection methods. These methods include insulating structural materials and the captive technique that enables fire protection to be effected in buildings by limiting the exposure of the construction material to the weakening effect of heat. Thus the effects are significantly reliable.

The insulating methods has been shown to consist of covering the structural material with spray, the application of materials such as boards, and other materials on the external body of the construction material. That creates a fire sensitive barrier limiting the ability of a fire to extend its effect to the insulated member. On the other hand, the captive method is based on the conductivity and the heat capacity of a specific material that is used to protect a building material from the thermal effect of heat. One of the protective materials is concrete. Concrete provide a protective layer as they inhibit the transfer of heat to the member of a structure.

Fire and Concrete

In fire protection engineering, it has been shown that concrete is a material that withstands high stress factors when subjected to varying thermal effects and at times extreme conditions. These properties vary with aggregate materials used to make a specific type of concrete. Concrete falls into a number of distinct categories with specifically varying properties. Among these are normal weight and lightweight concrete. Much of the construction of the floor of fire protected buildings is done using lightweight concrete (Klote, 55).

Light weight concrete

Klote confirms that engineering properties of light weight concrete, like steel and other building materials, gets modified based on the thermal effects on construction materials (23). It has been demonstrated that penalties due to heat alter the ambient temperature resistance of concrete though these properties remain largely unaltered compared with that of steel. The structural performance of lightweight steel under severe heat conditions is characteristically influenced by the spalling properties, thermal resistance, and mechanical behavior of these materials.

Another property heat protection engineers sanguinely consider when developing a fire protection for a building is the comprehensive strength of lightweight concrete. This property and other characteristics influence to a large extent the thermal behavior of lightweight concrete. It has been shown that, lightweight concrete is characterized by low thermal conductivity at intensely high temperatures, has minimum thermal expansion at such temperatures, and the value of its specific capacity is low at such temperatures compared with other types of concrete. It has been shown that the spalling effect on lightweight concrete, an effect of where concrete chips away from the surface due to the intensity of heat incident on a material is low for lightweight concrete, therefore an excellent material for fire protection in fire protection engineering. Therefore, the properties of the materials discussed above and their mechanical properties under the application of heat largely influence the modeling of a structure tom meet standard requirements for fire protection in fire protection engineering.

Structural Modeling

Beyler observes that under the influence of the behavior of building materials discussed above, fire protection can be efficiently achieved for buildings by modeling these structures under normal fires or specific fire scenarios (24). That is also in accordance with building codes requirements. In addition to that, numerical methods provide a clear modeling approach to modeling actual structures that are efficiently fire protected.

However, in the modeling process, a number of specific factors have to be considered. Among these is the severity of a fire, fire load, the surface area of the building under occupation, and the resistance of the materials used in the construction of a building. However, discussions of the materials such as concrete and steel has been done in the previous have been discussion.

Furness and Muckett concur with the fact that the severity of a fire can be numerically determined to provide reliable data to influence a cost effective modeling (250). Other inherent factors that influence modeling factors are based on an analysis of the fire development stages, the thermal properties and response of the modeling materials, and the structural behavior of the model assembly. The modeling of fire development provides information about the behavior of a structure and its exposure to heat, the thermal analysis is used to determine the thermal response and behavior of the construction members, and the structural behavior provides information about the ability of the structural components to maintain their integrity under various loads and stresses under different categories of fires (Beyler, 25).

The structural tests provide information about the effect of ventilations, fire protection strategies and techniques and specific methods that can be adopted for different scenarios of fire. However, a number of other computational and mathematical models have been designed though a number of them need further validations for practical applications in fire protection engineering. In addition to that models, detailed information has to be incorporated about life saving procedures in the event of a fire. These include notifications for imminent disaster and protect in place strategy particularly for tall buildings (Lataille, 29).

Safety of Life

Drucker argues that the ultimate goal of fire protection engineering is to ensure reliable methods are in place to ensure occupants of any buildings are safe in the event of a potential fire outbreak (23). In addition to that, buildings should be insulated from the effects of heat to maintain their structural strengths and not collapse under incident heat. To that end therefore, fire protection engineers have incorporated a number of life safety principles to ensure minimum or non occurrence of fatalities. These principles include real time notification through any means to promptly reach the target population or individual, automatic messaging systems tailored to convey an urgent message, and the use of fire protection personnel where appropriate (Furness & Muckett, 290).

Lataille notes that one approach to protecting people from the effects of a fire is to provide emergency exit route typically characterized by the egress system (33). The egress system is a typical escape concept that demands that fire protection engineers should provide sufficient space for evacuations to occur from a building engulfed in a fire, building should be designed to provide alternate exists without the possibility of blocking a operational escape route, and the escape routes should be designed to offer protection from the encroachment of fire from the rest of the building while remaining clear and easily accessible. In addition to that, the evacuation process should be either simultaneous with alternative areas provided for the escaping occupants with the sole aim of preserving the evacuees lives (Drucker, 33).

That is partly due to the fact that fire has a behavior of spreading very fast once an object has been ignites with the potential to cause overwhelming losses of property and people’s lives. Moreover, the behavior of a burning fire is influenced by the chemical properties of the burning material and bears a combined effect on the overall behavior of a structure and the member elements used to put up a structure (Milke, 222).

Summary

To provide significant protection for buildings and people’s lives that may be exposed to potential fire outbreaks with undesirable consequences, the fire protection engineering discipline demands that detailed knowledge of the behavior of fire be acquired, the structural response of the effects of fire on different materials such as steel that are used in the construction of buildings and other structures, the engineering behavior of concrete when subjected to fire, which is a commonly used construction material for different types of structures, and the effect of these factors in influencing the structural modeling of building, and the overall influence on the safety of the life of occupants in these buildings. Based on the above discussion, the behavior of a burning fire is influenced by the specific heat capacity of the burning material, the exposure of the fire and the burning object per unit area to oxygen, and thermal insulation provided by smoke in a burning environment leading to massive heat transfers. On the other hand, the thermal properties of building material such as steel and concrete have an influencing effect on the mathematical and other modeling techniques for buildings to achieve optimum heat protection capabilities in any building. On the other hand, it is important to critically consider life saving techniques such as evacuations and other emergency exists in the event of a potential fire outbreak in the whole discipline of fire protection engineering.

Conclusion

In conclusion fire protection engineering is a rich an area of study that provides information and focuses on the behavior of fire and its impact on engineering properties of building materials that influence the structural modeling of buildings focused at effective methods of protecting occupants subject to the potential threat of fire. It is an important area of study that seeks to identify the best approach to provide reliable fire protection for buildings and ensure the safety of occupants of all types of buildings by providing adequate fire protection methods and escape rotes in the event of a fire. However, there is need to conduct further research into the use of electronic surveillance systems to add value to other fire protection engineering methods to enhance and reinforce the level of security from any potential threat from fire.

References

Beyler, C. L. Analysis of the Fire Aspects of the World Trade Center Terrorist Attacks: Hughes Associates Inc. Baltimore, MD, 2002.

Bryan, J. L. Automatic Sprinkler and Standpipe Systems. National Fire Protection Association,Quincy, MA, August, 1990.

Cote, A. Fire Protection Handbook, 19th ed., National Fire Protection Association, Quincy, MA, 2003.

Dols, W. S., and G. N. Walton. Contam 2.0 User Manual: Multizone airflow and containmenttransport analysis software. NISTIR 6921, National Institute of Standards and Technology, U.S.Department of Commerce, Washington, DC, 2002.

Drucker, J. Presentation on the World Trade Center Fire Alarm System. Siemens Building Technologies. 2001

Furness, Andrew & Martin, Muckett, Introduction to Fire safety Management. Butterworth-Heinemann, 2007.

Klote, J. H. Fire Experiments of Zoned Smoke Control at the Plaza Hotel in Washington, DC.NISTIR 90-4253. National Institute of Standards and Technology. Gaithersburg, MD, 1990

Klote, J. H. Fire and smoke control: an historical perspective. ASHRAE Journal. 1994.

Klote, J. H. An overview of smoke control research. ASHRAE Transactions: Symposia. (1995)101-1

Lataille, Jane. Fire Protection Engineering in Building Design. Butterworth, Heinemann, 2002.

Milke, J.A. Estimating the fire performance of steel structural members. Proceedings of the 1999 structures conference ASCE381-384, 199.

Nwosu, D.I. & Kodur, V.K.R. Behavior of steel frames under fire conditions. Canadian Journal of civil engineering. 26, 156-157, 1999.

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