The Use of Standard Fire Curves for Determining Fire Resistance - Assignment Example

RUNNING HEAD: Standard Fire Curves Analysis of Standard Fire Curves in Determining Fire Resistance & How and Why the application differs from that of Onshore and Offshore Application Name: Instructor: Course Unit: Date: Introduction In the late 1890’s New York established an up-to-the-minute strategy that deemed it necessary for structures to be erected of columns, floors, walls and any fundamentals that were fire resistive, defined as “the ability of an element to withstand the effects of fire for a specified period of time without loss of its fire separating or load bearing function”. Therefore, Fire resistance is a measurement of the capacity of the building to refuse to give in to; cave in, fire spread, and any other collapse for the duration of exposure to a fire of specific severity. By severity I imply to the caustic effect of a fire, or a computation of the vigor that could bring about collapse or if not go ahead to breakdown as a consequence of the fire (ASTM 1993). The fire resistance capability of a structure can be verified by way of experiments or by calculation models. Experimentally the structure is exposed to a fire test carried out in agreement with procedures summarized in standards. During calculation, fire resistance is estimated using numerical models or else simplified formulas. From these different temperature-time curves are plotted and are being utilized in the present day, although in accordance with the nation and relevance. Figure 1 contrasts the ISO 834 test, the hydrocarbon fire (ASTM E1529), and external fire exposures to the standard ASTM E119 curve. This paper although analyzes the use of standard fire curves in determining fire resistance, and further more illustrates how and why the approach varies for onshore and offshore applications (Cobb, 2006). Source: Grosshandler, W. 2002, “Fire resistance determination & Performance prediction”, Research p. 13 Fig. 1: Alternative temperature-time curves for fire resistance tests. Analysis of Standard Fire Curves for Determining Fire Resistance: To shield a structure in opposition to the expensive effects of fire, one is required to make use of approaches. These approaches incorporate principally, fire containment which is more often than not attained by devising structure fire barriers, this is, walls and floors, with the intention that the fire is restricted inside the enclosure of fire source for a period of time; this is, containment is the capability of structure restrictions to resist disclosure to fire for a definite time. This time limit, known as fire resistance, should be sufficient for the fire barriers and the structural fundamentals sustaining them. The standard fire curves are utilized to achieve the time to failure supported on fire resistance decisive factors. These decisive factors can be patented in 3 modes; thermal failure described as mean temperature rise of 140°C or a local maximum of 180°C on the closed face higher than the ambient temperature; integrity failure illustrated as flames or hot gases piercing through the apparatus; and stability failure identified as the loss of load-bearing capacity of structural components (Gewain & Troup 2001). To establish fire resistance, exposures, this is, time-temperature relationships, are required to be identified. Its characteristics include; the fire is understood to be dynamic inside the entire enclosure, independent of the definite dimension of this enclosure; the fire by no means decays, not even in spite of everything combustible being worn out; and it does not depend on the compartment’s fire load nor on ventilation conditions. Conventionally, fire resistance is established by rendering a structure part to standard furnace experiment. The experiment is run pending failure of the heated part to take place, based on the failure decisive factors earlier acknowledged. There are many equations overriding the time-temperature fire curves for various standards globally. Equation (i) corresponds to the International Standards Organization’s standard ISO 834 time-temperature fire curve: Tg = To + 345 log10 (8t + 1) (i) Where Tg is the average furnace temperature in °C, To is the ambient temperature in °C, and t is the time in min (ISO 1999). Equation (i) is then used to plot the standard fire curve as in Figure 2 below. Source: The University of Edinburgh 2000, “Prescription vs. Performance”. Available from: . [1 May 2010]. Fig. 2: Standard Fire Curve Although the standard fire curves have been utilized in the designing of structures there are deficits in their creation and purposes. These include; one the curve is founded on an unrestrained column, this is pinned joints, which is hardly ever the circumstance in actual structures.   Although the column is intended to be basically sustained, in authenticity this could not be factual owing to the nature of bond.  For that reason this curve does not take into account the interactions created by the sum total of the structure actions; secondly the trend of the standard fire is established by directing the gas phase temperature in the furnace.  The implication of this is that, it generates an unnatural fire state of affairs since it does not encompass a limiting factor for instance exhaustion of fuel or be short of ventilation. The variations in the heating rate, fire intensity and duration involving the standard and real fires can give rise to unusual structural behavior. Such as, a short duration high temperature fire may give rise to peeling of concrete revealing steel reinforcement owing to the thermal shock. While a long duration low temperature fire may bring about a higher mean temperature in the concrete components bringing about a greater decline in concrete strength (Grosshandler 2002, p.13). Thirdly, basing on the latter statement, the standard fire curve does not generate a pragmatic model; another position to reflect on is that the temperature will persist to amplify with time for this reason no cooling occurs. Lastly on this, is that, standard fires do not at all times correspond to the majority brutal fire situations. Structural components intended to endure standard fires could not succeed to endure in real fires. Such as, the present place of work have a propensity for enclosing bulky magnitudes of hydrocarbon combustibles in embellishment, furnishings, electronics devices, in variety of polymers and other artificial materials. As a result, the fire turns out to be extra rigorous than the predictable standard fire. How and why the Approach Varies for Onshore and Offshore Applications: The onshore and offshore fire resistance determining applications utilizes the hydrocarbon curve method; this is because the burning rates for some materials for instance chemicals are well excessive of the rate at which point for example, wood would burn. Per se, there was a call for a different coverage for the aim of running tests on structures and objects utilized within the petrochemical industry, and consequently the hydrocarbon curve was established. The curve reaches 1000oC in approximately seven minutes. It corresponds to ignition of hydrocarbons for purposes that include aviation fuel fires, vehicle fuel fires and fires in the offshore industry. The temperature trend of the Hydrocarbon fire curve is illustrated by equation (ii) below (Lie 1994). T = 20+1080*(1-0,325*e-0,167*t-0,675*e-2,5*t) equation (ii) Where; T is the gas temperature in the fire compartment or near the member [°C]; and t is the time [min]. The reasons for these applications are; the standard fire curves in determining fire resistance doesn’t account for situations involving hydrocarbon fuels. Thus the hydrocarbon curve method is utilized for establishing the fire resistance reaction of structural components and fire-containment elements that are incorporated in structures exposed to hefty hydrocarbon pool fires. Unintended fires intermingle with their surroundings, if this is pipe-work, apparatus and configurations in process plants in petrochemical industry, or amenities on offshore oil and gas systems. For plant plan and risk evaluation, vigilant best approximations and vagueness ranges are necessary for several combustion limitations. These take account of release rates, flame size and shape, heat output, thermal radiation to its environment, and the heating-up of structures, pipe-work and items of equipment. The hydrocarbon curve is based on the temperatures that would be anticipated from a fire taking place within a comparatively open space where a number of dissipation of the heat would occur or several additional conditions where there is no considerable control to the flow of air to the burning pool fire. On the other side the standard fire curves are based on compartment fires. Also the hydrocarbon curve is in real sense a test-specific item and can vary from test apparatus to test apparatus. The standard fire curve is derived from tests and is experientially based; nevertheless the hydrocarbon curve is based on experience, judgment, and a record of tests in relation to the dimensions of the temperatures related to hydrocarbon fires. Lastly the thermocouples in hydrocarbons are bare and hence record the real temperatures of the gases liberated from hydrocarbon combustion (Babrauskas & Williamson, 1979). Conclusion: Even though there are weaknesses and limitations of presupposing the standard fire curves and component design, the straightforward and most frequent performance-based approaches for instance the hydrocarbon curve in onshore and offshore applications, have been established based on the outcomes and examinations from standard fire resistance tests. Even if the prescriptions pointed out above could provide a ballpark figure of the character and size of the time-temperature curves of fires, there is still significantly plenty of effort that requires to be embarked on. This involves the array, magnitude and geometry of the combustible material, in addition to the effect of various habitations. As a final point, all these aspects necessitate supplementary analysis and justification. References: ASTM E1529, 1993, “Standard Test Methods for Determining Effects of Large Hydrocarbon Pool Fires on Structural Members and Assemblies”, American Society for Testing and Materials, Philadelphia, USA. Babrauskas, V., & Williamson, R.B., 1979 “Post-Flashover Compartment Fires – Application of a Theoretical Model,” Fire and Materials, vol. 3, no. 1, pp. 1-7. Cobb, F. 2006, Structural Engineer’s Pocket Book. Heinemann, Elsevier Butterworth. Gewain, R.G. & Troup, E.W.J., 2001 “Restrained Fire Resistance Ratings in Structural Steel Buildings,” AISC Engineering Journal, 2nd Quarter, AISC, Chicago, IL, USA. Grosshandler, W. 2002, “Fire resistance determination & Performance prediction”, Research Needs Workshop: Proceedings, NISTIR 6890, p. 13 ISO 834, 1999,Fire-resistance Tests- Elements of Building Construction, International Organization for Standardization, Geneva, Switzerland. Lie, T.T., (Ed.) 1994, “Structural Fire Protection, American Society of Civil Engineers”, Manuals and Reports on Engineering Practice, No. 78. The University of Edinburgh 2000, “Prescription vs. Performance”. Available from: . [1 May 2010]. Read More