Mankind can feel different aspects of fire. It can provide beneficial ways of living, such as heating source for cooking, warming people and a source of energy for many mechanical devices. On the other hand, fire implies another kind of severe hazard to human being. As a room catches fire, it generates heat, and even toxic and corrosive substances that cause fatal and properties loss. Thus it initiates many scientists and engineers to work together for obtaining a systematic solution to alleviate the loss.
Hence many fire testing methods and models have been developed for assessing the fire hazard. The evolution can be seen in Fig. 1.1.
In the very early days, the testing method basically was only used to evaluate the fire performance of material in a bench scale under an assigned environment. These bench scale tests usually were only provided result of pass or fail without any detailed information.
However, they served as the baseline for the fire safety regulation. As the advance of material science and technology, many new materials are developed and the above-mentioned test method may not get along with the progress of technologies as expected. Therefore, a revolution testing methodology, termed as reaction-to-fire, was developed in the era of 1990.
The Cone Calorimeter (ISO 5660) [1] was the representative testing apparatus. The reaction-to-fire properties of building materials include the flammability, combustibility, toxicity, heat release rate…etc. Among
them, heat release rate is an important parameter to characterize a fire. It describes the total energy release of a material, or upholstery furniture, or a confined space during burning. As pointed out by Thornton [2] and then Huggett [3], there exists a more or less an approximate constant of heat release per unit mass of oxygen consumed for a large number of organic matters. This constant is given as 13.1MJ/kg of O2. Therefore heat release rate can be measured by using Oxygen Depletion Method (or Oxygen Consumption Method), which is a well-known method and widely adopted for both bench-scale and large-scale experiments in many fire laboratories all over the world.
The general goal of fire safety regulations is to provide life safety and sufficient property protection in case of fire. In order to achieve this goal, combustibility of materials, fire protection of structures, evacuation arrangements, and relative locations of buildings are set to define how buildings should be designed and constructed for their respective use.
Traditionally, fire testing and classification systems are developed individually in different countries, each with its different background and circumstances. A wide variety of requirements has thus been drawn up.
However, as a result of the development of transportation facilities and international trade, the harmonization of standards and fire classification systems has become an issue of increasing importance. Canada adopted the cone calorimeter (ASTM 1354) [4] to make classification for the fire performance of building materials in 1992. In the Building Standard Law (BSL) of Japanese, it has already adopted the heat release rate obtained from the cone calorimeter (ISO 5660) [1] as the test criteria to replace the
original JIS A 1321 [5], equivalent to Taiwan CNS 6532 [6]; Method of Test for Incombustibility of Interior Finish Material of Buildings. In the European Union (EU), the development of the Euroclass system, EN 13823 [7], was completed in 2002. It defines the fire performance classification of building productions and building components by using the single burning item (SBI) test.
Since 1990s, EU planed to adopt the cone calorimeter test (ISO 5660) [1] for the small-scale test and the room corner test (ISO 9705) [8] for large-scale one. However, it was difficult to obtain the satisfactory correlation between the test results obtained from cone calorimeter and room corner tests respectively, after several years of research. Of course, the room corner test could show the real reaction-to-fire behaviors of materials in a fire, but it cost a lot of time and resource. On the other hand, the small scale fire test of cone calorimeter cannot exhibit the reaction-to-fire properties in the situation of a real fire. Therefore the EU developed a medium-scale test, called single burning item test (EN 13823 [7]), to make a compromise. It was carried out since 2002, and now the building materials, which are intended to be sold in EU, must comply with the proper standard of the SBI test except the fire door of buildings.
In addition, for harmonization of fire standards for trains the EU wanted to develop a standard, called prEN 45545-2 [9], to replace all national corresponding standards. According to prEN 45545-2 [9], the burning behaviors of passenger seats for railway vehicles should be tested by including the complete passenger seat, upholstery and head rest, seat shell and arm rest. Test methods consists of ISO 9705(Furniture Calorimeter)
[8], ISO 5660 (Cone Calorimeter) [1] and ISO 5659-2(Smoke chamber with FTIR) [10]. The FTIR (Fourier Transformation InfraRed spectroscopy) is used for analyzing toxic components. However, this proposed standard is not perfect enough to carry out yet.
As becoming a member of WTO, the corresponding testing standards and classifications of Taiwan inevitably must harmonize with the ones that are popular adopted by the other countries. Although the cone calorimeter test method (CNS 14705) [11] has not become the legal criteria of classification yet in Taiwan, it is expected to be adopted like Japan in the near future. Table 1.1 lists the criteria of classification of the cone calorimeter [1], the surface [6] and single burning item tests [7], and the room corner test (ISO 9705) [8] are also included.
Table 1.1: The apparatus and criteria of classification Test apparatus Criteria of classification
Cone calorimeter test
Canada: CAN/ULC S 135-1992 Taiwan: CNS 14705
Japanese: NO.5 Article 1, NO.6 Article 1 and NO.9 Article 2of the Building Standard Law
EU: prEN45545-2(Draft) Surface test Taiwan: CNS 6532 Single burning item test EU: EN13823
Taiwan: CNS protocol Room corner test EU: ISO 9705
Norway: NS 3919 1.2 Literature review
The first application of Oxygen Depletion Method in research was
done by Parker [12] on the ASTM E-84 tunnel test. Later, it was applied to a room fire test [13]. During the late of 70`s and early in 80`s this principle was refined at the National Institute of Standards and Technology (NIST). The first version of test standard of cone calorimeter (ASTM E1354) [4] was announced in 1990. ISO also announced the cone calorimeter test as ISO 5660 [1] and room corner test as ISO 9705 [8].
For ISO 5660 and 9705, the measurements and calculations of the heat release rate are similar, whereas the major difference is the magnitude of heat release rate which sustained.
Chen et al. [14] tested eighteen different wall-covering materials according to Chinese National Standard (CNS) 6532, equivalent to Japanese Industry Standard (JIS) A1321, and ASTM E1354 (Cone Calorimeter). A comparison of test results was presented, and a qualitative relationship was developed between the performances in the two methods.
Tsantaridis and Ostman [15] tested 30 products separately by cone calorimeter, SBI and room corner test. They found that the occurring times of the first peak of heat release rates for these three tests are in the good correlation. The comparisons of FIGRA (Fire Growth Rate) indices, defined in Chapter Two, of 30 products showed that the R2 of correlation between cone calorimeter and SBI is about 0.85, SBI and room corner test is about 0.92, and cone calorimeter and room corner test is about 0.76.
The burning situation of materials in SBI was found very similar to that of Cone Calorimeter.
Heskestad and Hovde [16] used the experimental data of 17 products,
which are obtained from the full- and bench-scale tests, to consider the influence of the combustion conditions on the full scale smoke production.
All these materials caused the occurrences of flashover within 10 min in the ISO Room Corner Fire Test. The smoke to heat ratio SQ (m2/MJ) was used to compare smoke generation rates between these two tests. Plastics did produce more smoke yields than wood-based materials in both tests.
However, no simple correlations were found between full scale and bench scale for smoke yield. An accurate empirical smoke prediction model by using bench scale fire parameters was presented to predict the full-scale smoke production rate at a heat release rate of 400kW.
Messerschmidt and Hees [17] studied the SBI tested data, which are obtained from fifteen laboratories of EU. They found that the test results for some materials tested in different laboratories show very different behaviors with each other. The reason discussed was the sensitivity of oxygen analysis instrument, indicating that the operation of oxygen analysis instrument must be careful in order to avoid the error.
Hakkarainen and Kokkala [18] developed a one-dimensional thermal flame spread model, which was used to predict the rate of heat release in the SBI test on the basis of the cone calorimeter data. The features of the measured and calculated heat release rate curves were compared for 33 building products. The fire growth rate indices (FIGRA) were calculated to predict the classification in the forthcoming Euroclass system.
Although the model used cone calorimeter data could not simulate the heat release rate of SBI perfectly, the model still can provide the correct classification for 90% of the products studied.
Hees et al. [19] developed a prediction software tool by using the test data obtained from cone calorimeter (ISO 5660). The user-friendly software package, called cone-tools, allows users to predict the major classification parameters of HRR and FIGRA in the SBI and room corner tests. The results showed that the predictions are satisfactory, implying that the tool will be powerful for the product development by industry.
Comparison between the SBI test results and data of cone-tools, it was shown that cone-tools could predict the accurate classification of EU up to 90%. Comparing with the room corner test results, the correction of prediction for the classification of EU was about 85%.
Axelsson and Hees [20] tested the sandwich panels, which were already tested from the previous Nordtest project. In that project, it was shown that the correlation between the SBI test method (EN 13823) and both the ISO 9705 and ISO 13784 part1 was insufficient. New data, tested by Axelsson and Hees on sandwich panels, were generated by using the European product standard prEN 14509. They were compared with ones from Nortest project. It showed that the correlation between the data from the full-scale test and SBI was not satisfactory. In addition, the SBI test method for sandwich panels would give irreproducible results so that the classifications could not reflect the real fire behaviors of the panels.
1.3 Scope of present study
This thesis intends to find the correlation among the fire performance tested data for the selected materials, which are measured from the Cone Calorimeter (in both vertical and horizontal positions),
Surface and Single Burning Item (SBI) tests. These measured data are analyzed in advance and then tried to correlate. Finally, the proper suggestions will be made for the fire performance criteria of classification for Taiwan according to these results.
Chapter Two
TEST APPARATUS AND EVALUATION METHODS
This chapter will introduce four kinds of apparatus, which are the cone calorimeter, surface test, elementary materials test and SBI test, respectively, and their test procedures. The calculation methods for the Cone calorimeter and SBI tests are presented as well. Those fire parameters obtained from Cone calorimeter are especially crucial for the application of fire modeling.
2.1 Cone calorimeter
The ISO 5660[1] for cone calorimeter test is a bench-scale fire test method for assessing the contribution that the product tested can measure the rate of evolution of heat during its involvement in fire. The main parts of the apparatus are a cone-shaped radiant electrical heater with a temperature controller, spark igniter, weighing cell, holder of specimen, gas analyzer instrumentation, calibration equipment, smoke system and exhaust gas system. The picture and a schematic configuration of the cone calorimeter are presented in Figs. 2.1 and 2.2, respectively.
2.1.1 Introduction for cone calorimeter apparatus 2.1.1.1 Cone-shaped radiant electric heater
The electric heater is able to be of capable of horizontal or vertical orientation. The active element of the heater shall consist of an electrical heater rod, rated at 5kW at 240V, tightly wound into the shape of a
truncated cone (see Fig. 2.3). The heater is encased on the outside with a double-well stainless steel cone, packed with a refractory fiber material of approximately 100kg/m3 density. The irradiance from the heater is capable of being held at preset level by means of a temperature controller and three, type K, stainless steel sheathed thermocouples. The heater is capable of producing irradiances on the surface of the specimen of up to 100kW/m2. The irradiance is uniform within the central 50mm × 50mm area of the specimen, to within ± 2% in the horizontal orientation and to within ± 10% in the vertical orientation.
2.1.1.2 Load cell
The load cell for measuring specimen mass loss has an accuracy of 0.1g and it preferably has a measuring range of 500 g and a mechanical tare adjustment range of 3.5 kg.
2.1.1.3 Specimen holders
There are two kinds of specimen holders, horizontal and vertical orientations, showed in Figs. 2.4 and 2.5. The bottom of the holder is lined with a layer of density (nominal density 65kg/m3) refractory fiber blanket with a thickness of at least 13 mm. When testing on the horizontal orientation, the distance between the bottom surface of the cone heater and the top of the specimen is adjusted to 25 mm by using the sliding cone height adjustment. In the vertical orientation, the cone heater height is set so the centre lines up with the specimen centre. A retainer frame and wire grid are used when testing intumescing specimens in the horizontal orientation and can also be used to reduce unrepresentative edge burning of composite specimens and for retaining specimens prone
to delamination.
2.1.1.4 Exhaust gas system
The exhaust gas system with flow measuring instrumentation consists of a high temperature centrifugal exhaust fan, a hood, intake and exhaust ducts for the fan and an orifice plate flow meter. The exhaust system is capable of developing flows from 0.012m3/s to 0.035 m3/s. A restrictive orifice with an internal diameter of 57mm is located between the hood and the duct to promote mixing. A ring sampler is located in the fan intake duct for gas sampling, 685mm from the hood. The flow rate is determined by measuring the differential pressure across a sharp edge orifice (internal diameter 57mm) in the exhaust stack, at least 350mm downstream from the fan.
2.1.1.5 Gas analyzer instrumentation
The instrumentation incorporates a pump, a filter to prevent entry of soot, a cold trap to remove most of the moisture, a by-pass system set to divert all flow except that required for the oxygen analyzer and a further moisture trap. The detail part of instrumentation is shown in Fig. 2.6.
2.1.1.6 Smoke system
The smoke detection and measurement system employs a 0.5mW Helium-Neon laser operating at 632.8 nanometers. The laser system provides a means of obtaining the extinction coefficient based upon the degree of visual obscuration caused by suspended particulates in the exhaust stream.
2.1.1.7 Heater flux meter
The heater flux meter is the Gardon (foil) or Schmidt-Boelter (thermopiles) type with a design range of about 100kW/m2. The target receiving radiation, and possibly to a small extent convection, shall be flat, circular, of approximately 12.5 mm in diameter and coated with a durable matt black finish. The target shall be water-cooled. The instrument shall have an accuracy of within ±3% and the repeatability within 0.5%. It is positioned at a location equivalent to the centre of the specimen face in either orientation during this calibration.
2.1.1.8 Calibration burner
The burner is constructed from a square-section brass tube with a square orifice covered with wire gauze through which the methane diffuses. The tube is packed with ceramic fiber to improve uniformity of flow. The calibration burner is suitably connected to a metered supply of methane of at least 99.5% purity.
2.1.1.9 Optical calibration filter
Calibration of the smoke system is by operator insertion of pre-calibrated neutral density filters. Two high-quality optical filters of approximately 0.3 O.D. (Optical Density) and 0.8 O.D. are provided with precision fabricated keyed positioning holders. The manufacturer’s optical density curve is provided with each filter.
2.1.1.10 Ignition circuit
External ignition is accomplished by a spark plug powered from a 10 kV transformer. The spark electrode position is 13mm above the center of
the specimen in the horizontal orientation and 5mm above the top of the holder in the specimen plane in the vertical orientation.
2.1.2 Specimen construction and preparation for cone calorimeter 2.1.2.1 Specimens
Unless otherwise specified, three specimens shall be tested at each level of irradiance selected and for each different exposed surface.
The test specimen has an area of 100 mm × 100 mm and a maximum thickness of 50 mm. For products with normal thickness of greater than 50 mm, the requisite specimens shall be obtained by cutting away the unexposed face to reduce the thickness to 50±3 mm.
2.1.2.2 Conditioning of specimens
Before the test, specimens shall be conditioned to constant mass at a temperature of 23±2°C, and a relative humidity of 50±5% in accordance with ISO 554.
2.1.2.3 Preparation
A conditioned specimen is wrapped in a single layer of aluminum foil, of 0.03 mm to 0.05 mm thickness, with the shiny side towards the specimen, covering the unexposed surfaces. Composite specimens are exposed in a manner typical of the end-use condition. They are tested with the retainer frame and also prepared so that the sides are enveloped with the outer layer(s) or otherwise protected. If using retainer frame and wire grid, they shall be specified in the test report.
2.1.3 Test procedure for cone calorimeter
1) Check the CO2 trap and the final moisture trap. Replace the sorbents
if necessary. Drain any accumulated water in the cold trap separation chamber. Adjust the distance between the bottom of cone heater and surface of specimen. This distance shall be 25mm.
2) Turn ON the computer and type CONE2A. The Calibrate & Test Specimens option allows operator to start the AutoCal cycle for complete system calibration prior to performing tests.
3) Turn ON all calibration gas, air, water and methane supplies. N2 gas always shall be opened.
4) Change the Drierite, Ascarite and new 9cm filter if needed.
5) The computer program requests that all external exhaust blowers be turned off so a static pressure reading can be taken.
6) Turn ON external exhaust fans. The operator enters the desired Exhaust Flow Rate in m3/sec. Here we use 0.024m3/sec. When the reading is stable at the desired flow rate for 15 seconds, the AutoCal system will continue.
7) Choose YES or NO to use the last C factor. Select YES to use the last C factor. AutoCal will proceed to Heat Flux Calibration. Select NO to determine a new C factor. AutoCal will proceed to calibrate gas analyzers, smoke and weigh system to determining the new C factor.
8) For determining the new C factor, we first calibrate the laser system.
Insert the 0.8 O.D. filter and wait to read it completely. Repeat the procedure for the 0.3 O.D. filter.
9) For weigh cell calibration, operator is requested to place the
specimen holder, without specimen, onto the weigh cell platform.
10) Enter the weight of the specimen holder and adjust the mechanical tare for 0.00 ± 0.2 g.
11) With the specimen holder on the weigh cell, add a 500 gram mass.
AutoCal will detect the mass and tale a Span reading. Don't remove the specimen holder. Remove the 500 gram mass.
12) The CONE2 will display this screen until the cold trap temperature reading is below 9°C before proceeding with the analyzer Span.
12) The CONE2 will display this screen until the cold trap temperature reading is below 9°C before proceeding with the analyzer Span.