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3 FIRE TESTING The objective of fire testing is to evaluate the ~reaction-to-fire. behavior of materials. Within the context of this report, the key element of a successful fire test is its ability to approximate the conditions that would occur in actual fires and to quantify ignition requirements, flame spread, mass burning rate, energy released, and combustion product composition. (See Appendix B for the American Society for Testing and Materials (ASTM) definition of these and other terms used in this report.) It is appropriate to examine here only those laboratory-scale tests that can provide input data for assessment of toxic hazard. This excludes many of the standard pass/fai} tests that are customarily used to establish compliance with specifications. To be of relevance to toxic hazard assessment, fire tests must provide analytical data such as heat release/mass burning rates, combustion product composition, etc. Preferably, they should be capable of testing composite specimen and even, in some cases, systems. There are two particular laboratory-scale fire tests that have been accepted as standards and supply data useful for the assessment of toxic hazard the cone calorimeter (ASTM, 1990) and the Ohio State University (OSU) rate of heat release method (ASTM, 1983a). In addition, the National Tostitute of Standards and Technology (NIST) furniture calorimeter (Babrauskas et al., 1982) has been used for furniture-sized systems. Although not providing comprehensive data, numerous other laboratory tests also may be useful in a limited way (e.g., ASTM 1983b, thermal gravimetric analysis). 17 1
18 CONE CALORIMETER In the cone calorimeter (Figure 3-1), specimens of a material are cut into 100 x 100 mm sizes, with the thicknesses varying from 6 to 50 mm. The specimen is heated by an electric heater in the shape of a truncated cone. The irradiance to the specimen can be set to any desired value from 0 to 100 kW/m2. If desired, external ignition of the specimen is provided by an electric spark. The mass of the specimen is recorded continuously through the use of a load cell. An exhaust system provides air flow rates of D.012 to 0.035 my/. Heat release is measured by using the oxygen consumption principle, which states that for most combustibles 13.1 MI/kg oxygen relates the amount of heat released during a combustion reaction and the amount of oxygen consumed from the air. Thus, it is necessary to measure only the concentration of oxygen in the combustion stream, along with the flow rate, to calculate the heat released. Data derived from tests using the cone calorimeter constitute a very large set, and can be analyzed in a multitude of ways. The most important variables that are presented include the following: peak rate of heat release (kW/m2~; Abaser extinction beam including \ temperature measurement \ Temperature and differential \ ~ pressure measurements taken here \ . Soot samole tube location blower ~ Is samples Cone heater ~ taken here ~ ;!~ Soot collection filters ~ ~ ~` / ( FIGURE: S-1. Cone calonmeter. Controlled flow rate ~~q Vertical orientation Exhaust hood Spark igniter SamDIe Load cell
19 · rates of heat release averaged over various time periods, starting with the time of ignition (kW/m2~; · effective heat of combustion (MJ/kg) (Ellis will be less than the oxygen bomb value of the heat of combustion, since the combustion is incomplete); specimen mass lost (by; mass loss rate (kg/s); time to ignition (s); · average smoke obscuration (m2/kg); and · average yields from the test sample of each of the measured gas species (kg/kg). OSU RATE OF HEAT RELEASE In the OSU method (Figure 3-2), the specimen to be tested is injected into an environmental chamber through which a constant flow of air pass- es. The speci- men's exposure is determined by a radiant heat source adjusted to produce the desired total heat flux on the spec- imen. The spec- imen may be tested so that the exposed surface is either hori- zontal or verti- cal. Combustion may be i.~nitiade~ PILoT FI_AME: ignition, piloted ignition of evolved gases, or by point ignition of the surface. The changes in temperature and optical density of the gas leav- ing the chamber are monitored, ~ ; ::::':: :1 L:;,.,: :';' 1''; ::;:':':1 ..... ,...... or.., ; L; -' '7~::- ,- SMOKE DETECTOR ,RADIANT PANEL ONTO GAS SUPPLY ADZ- AIR DISRIBUTION // PLATE _ ', me' AIR INLET FIGURE S-2. Schematic of the OSU test appartus.
20 and from this data the release rates of heat and visible smoke are calculated. Rather than by using the oxygen consumption principle, heat release is calculated from temperature differences between the air entering the chamber and leaving it; however, use of the oxygen consumption principle has also been reported (Tsuchiya and Mathieu, 1989~. It is beyond the scope of this report to critique the two methods described; however, it is important to note that both tests use relatively small sample specimens. In response to the need for the testing of systems (e.g., furniture), larger-scale heat release rate calor~me- ters have been used. NIST FURNITURE CALORIMETER- The NIST furniture calorimeter (Figure 3-3) was developed as a technique for measuring the rates of heat release of free-standing combustibles burning in open-air conditions. As with the cone calorimeter, the apparatus uses the oxygen consumption as the measuring principle. Since it is intended to measure the burning of large objects that can sustain their own burning once suitably ignited, no external radiant heat is usually provided. (By contrast, in the cone calorimeter, where small-scale specimens are measured, external radiation is necessary to represent the effects on the specimen of adjacent items or portions of the same item burning.) Similar to the cone calorimeter, the furniture calorimeter also contains a load cell' a laser photometer for measuring smoke density, and gas analysis equipment. The furniture calorimeter at NIST exists in two versions: a low-capacity version (for fires not much over 1000 kW) and a high-capacity version (for up to about 7000 kW). The ignition source is typically a natural gas burner having a nominal 180 x 150 mm face and is operated at the 50-kW level for 200 s. Those conditions approximate the fire behavior of a small trashfilled plastic wastebasket. In addition to furniture, other full-size objects such as television cabinets'- business machine housings, electrical cables, and electrical circuit boards have been used in the NIST calorimeter (Babrauskas et al., 1988~. Tests have shown that under certain conditions the open-air large-scale measure- ments made in the furniture calorimeter can be directly transferred to the room fire situation (Babrauskas, 19841. The limits of this relationship have not been fully explored. The use at the Southwest Research Institute (Schubmann and Hartzell, 1989) of a room-size calorimeter for measuring the heat release of upholstered furniture also has been reported (Figure 3-4~. FULL-SCALE FIRE TESTING A problem with many small laboratory-scale fire test methods is that they often cannot simulate the interactions between the components of a system, or even between systems, as would occur under the high-energy conditions of a fire. Most materials are not employed singly but are used in a composite or system. Floor coverings are systems; an item of upholstered furniture is a system. The fire performance of individual components may not be reflected in the fire performance of a system. For example, the fire performance of a piece of upholstered furniture depends collectively on the frame, the filling, the fabric, \
21 Exhaust Blower Bleed Valve Variable I AdiUstable Sleeve ~ - ~ Smoke Meter ~ i ,~r~ Gas Sample Ring - , .Velocity Probe ~ Pressure //( \\ ~ Thermocouple Ring 0.~ Variable - between ! 0.9 ! and 1.53 Pressure Transducer , cc ~ . , , ~ ·.u~ ~ ~ - ~ ^ ^ D. Exhaust 1( Water Cooled Skid FIGURE Sag. View of the furniture calorimeter. ~ Water Spray All dimensions in meters ~1 1
22 GAS ANALYSIS PROBE / _ - a' ~1 -^ 1_ ~ W ~ SMOKE PHOTOMETER ~ ~ ~V'_ _ l _ EXHAUST 1 _~ ~ 1 ~~= ~ _,_ _ ~ BAFFLE / /l AL STACK AIR INLET_ /^' ' -//~iSTRIBUTION MAN IFOLD / Got I / ~LOAD CELL FIGURE Sad. Schematic of room calonmeter. and the construction designing! together, not singly. An uncontrolled fire may involve many systems interacting with one another. Thus, fulI-scale fire tests are useful to evaluate such large-scale phenomena. The costs of full-scale tests can be high, and, with few exceptions, they are not used directly for toxic hazard assessment. In Darticular. assessment of the contribution of anv ., _ _ . ,~ _ , _ _ _ , one particular material or product to toxic hazard in a full-scale fire test is difficult. A major utility of such large-scale tests Is to help validate the use of fire models for predicting fire growth and to provide visual documentation. Guidance for the conduct of such large- scale tests is available (ASTM, 1977~. CONCLUSION Fire growth moclels require' as input, information on the heat release/mass burning rates of the products involved in the fire scenario. These data are inferred from certain laboratory fire tests, some of which have been or are being adopted as standards both in the United States (ASTM) and also internationally (International Organization for Standardiza- tion). Among such tests are those involving the cone calorimeter, the OSU rate of heat release calorimeter, and the NIST furniture calorimeter.
23 REFERENCES to ASTM. 1977. Standard Guide for Room Fire Experiments," ASTM E 603, American Society for Testing and Materials, Philadelphia, PA. ASTM. 1983a. "Standard Test Method for Heat and Visible Smoke Release Rates for Materials and Products, ASTM E 906, American Society for Testing and Materials, Philadelphia, PA. ASTM. 1983b. "Standard Test Method for Specific Optical Density of Smoke Generated by Solid Materials, ASTM E 662, American Society for Testing and Materials, Phila- delphia, PA. ASTM. 1990. Standard Test Method for Heat and Visible Smoke Release Rates for Materials and Products Using an Oxygen Consumption Calorimeter, ASTM E 1354, American Society for Testing and Materials, Philadelphia, PA. Babrauskas, V. 1984. "Upholstered Furniture Room Fires Measurements, Comparison with Furniture Calorimeter Data, and Flashover Predictions, Journal of Fire Sciences, Vol. 2, pp. 5-19. Babrauskas, V., ]. R. Lawson, W. D. Walton, and W. H. Twilley. 1982. reupholstered Furniture Heat Release Rates Measured with a Furniture Calorimeter,. NBSIR 82-2604, National Bureau of Standards, Washington, DC. Babrauskas, V., R. H. Harris, R. G. Gann, B. C. Levin' and B. T. Lee. 1988. Fire Hazard Comparison of Fire-Retarded and Non-Fire-Retarded Products, NBS Special Publication 749, U.S. Department of Commerce, National Bureau of Standards, Gaithersburg, MD. Schuhmann, I. G. and G. E. HartzelI. 1989. Inflaming Combustion Characteristics of Upholstered Furniture,. Journal of Fire Sciences, Vol. 7, pp. 386-402. Tsuchiya, Y. and I. F. Mathieu. 1989. Measuring the Degree of Combustibility Using OSU Apparatus and Oxygen Depletion Principle,. Proceedings of International Confer- ence on Fires in Buildings, Toronto, Canada, September 25-26, 1989, Technomic Publishing Co., Inc., Lancaster, PA, pp. 27-30.