Fire testing, method development

Fire-test method development has followed two separate but complementary paths. One path, theoretically oriented, is characterized by the measuring of scientifically-meaningful fire properties, such as mass loss and rate-of-heat release. This approach also includes the development of mathematical models incorporating these properties to predict propagation and flame spread. A new lab-scale apparatus, the "cone calorimeter" developed at NIST is an example of the hardware now available to measure these fire properties. 

Fire test methods attempt to provide correct information on the fire contribution of a product by exposing a small sample to conditions expected in a fire scenario. Methods can be viewed in two ways the first entails the strategy of the fire test, ignition resistance or low flammabiUty once ignited the second addresses the test specimen, a sample representative of the product or a sample of a material that might be used in the product. Fire science has progressed markedly since the older test methods were developed and it is known that the basis for many of these tests is doubthil. Results from older tests must be used with great care. 

In a joint research project in Sweden under the main title "Fire hazard - Fire growth in compartments in the early stage of development (pre-flashover)" (1, 2) a number of different factors have been studied. In the process of developing a full-scale fire test method - "room-corner" configuration - for surface lining materials, Nordtest NT-FIRE 025, the emission of smoke and gas was studied. That study covers data from thirteen different single and... 

A number of modern full-scale fire test methods have been developed for products, relying on heat release rate measurements, such as those involving testing of upholstered furniture (ASTM E 153792 and CA TB 13391), mattresses (ASTM E 1590,85 CA TB 129,82 CA TB 603,88 16 CFR 1633,19 and ASTM F 1085 [Annexes A1 and A3]171), stacking chairs (ASTM E 1822172), electrical cables (ASTM D 5424,173 ASTM D 5537,174 and UL 1685123), plastic display stands (UL 1975),175 other decorative items (NFPA 289,176 a generic furniture calorimeter test), electrical equipment (UL 2043),120 or wall-lining products (NFPA 265,116 NFPA 286,115 ASTM E 2257,177 and ISO 9705178). In fact, room-corner tests are now being used in the codes, as alternatives to replace the... 

As discussed earlier, a number of organizations and technical committees develop fire-test methods or specifications that are specific to some particular material or product. It is not possible to cover all of them in this work and they are usually publicly available from the responsible organization via their website. 

A number of fire tests for polymeric materials have been developed, during the past several years, by the International Standards Organization (ISO). Hopefully, these tests will replace the present national test methods, which often correlate badly with each other. I he development at ISO is aimed at describing the fire properties of polymeric materials comprehensively, with test methods chosen so as to be applicable to all types of samples. At present, the ISO fire test methods are published as standards (ISO R 1182-79 for non-combustible materials, ISO R 1326-70 and ISO R 1210-70 for flame spread, etc.), or as draft for development (DP 5657, ISO/TC 92 N 531-79 as an ignitability test). One can only sympathize with using certain complex fire hazard indices for describing material behavior in fire... 

Sorathia and co-workers [51] investigated the use of smaller scale fire test methods. From these investigations, two methods, differing in concept and technique, were developed. The methods developed by the UL in the late 1950s are still in use today and are described in the Approval Standard for Class 1 Roof Covers, FM 4470 [52] and Fire Test of Roof Deck Constructions, UL 1256 [53]. 

Most importantly, none of the methods have, been sufficiently checked to assess how well they reproduce the gas yields or even the LC50 values from the appropriate segments of real-scale fire tests. To begin this process, a comparison procedure has been developed and a few materials have been checked using the NBS bench-scale combustor and the N-gas method (14,15). 

A comparison of results for fire effluents from full scale and small scale fire tests has to be done in steps. A full scale fire is a developing event where temperature and major constitutions changes continously. A small scale fire test either take one instant of that developing stage and try model that or try to model the development in a smaller scale. On a priority one level rate of heat release, temperature, oxygen concentrations and the ratio of C02/C0 concentrations have to be similar for a comparison. The full scale fire experiments reaches a temperature of 900 C at the moment of flashover, while the small scale fire tests are reaching temperatures just above 400 °C for NT-FIRE 004 and the cone experiments. For the DIN 53436-method the temperature was set to 400 °C. 

The FPL vertical wall furnace used in our study was described in some detail by Brenden and Chamberlain (6). This furnace is normally used to evaluate the fire endurance of wall assemblies. The basic guidelines for the furnace test method are given in the ASTM E-119 standard (5). The method was designed to evaluate the ability of a structure to withstand a standard fire exposure that simulates a fully developed fire. The furnace is gas fired, and its temperature is controlled to follow a standard time-temperature curve. A load may be applied to the assembly. The failure criterion can be taken as time at burnthrough, structural failure, or a specified temperature rise on the unexposed side of the wall—whichever comes first. The construction of the furnace is not specified in the ASTM E-119 standard. 

In a penalty test, a property cf the system is modified to reduce the probability of the desired result. For example, to predict safety, a particular expl train interface may be tested with a standard donor and a more sensitive acceptor conversely, to predict reliability, a less sensitive acceptor material is used. If this probability is reduced sufficiently, it is possible to obtain mixed responses (that is, some fires and some no-fires) with samples of reasonable size, and to develop data from which the mean value of the penalty and its standard deviation (as well as confidence limits) can be established. These estimates can be used iri statistical extrapolation to estimate safety or reliability under the original design conditions. The term VARICOMP (VARIation of explosive COMPosition) was coined by J.N. Ayres for a method developed at the Naval Ordnance Lab, White Oak, in the 1950 s and early 1960 s (Ref 1)... 

SABRE Method. Acronym for Simulated Approach to Bayesian Reliability Evaluation. An advanced approach to designing a reliability test program developed at PicArsn, the objective of which was to design a test program of minimum sample size for artillery fired atomic projectiles. Called the SABRE method, the program uses mathematical modeling, Monte Carlo simulation techniques, and Bayesian statistics. It is a sophisticated system devised to test items that cannot be tested because of their atomic nature. The aim is to determine the risk factor and to predict what will happen when the projectile is fired... 

In that frame, the use of a plane-plane rheometer has been evaluated. The purpose of the experiment carried out in the rheometer is not to mimic fire testing (this is not possible since the heating rate [slow ramp vs. quenching], heating source [convection vs. radiation], sample size, and boundaries effect are different) but to develop a test method that will permit the characterization of the char strength when exposed to pressure (in that case compression force). 

In some cases, it is not possible to evaluate a material or product (combination of materials) in a bench-scale test in a manner that is representative of its end-use. For example, it is difficult to use a bench-scale test method to evaluate the effect of joints on the fire performance of a thick sandwich panel that consists of a plastic foam core and metal skins. In this case, a room test is used to assess the reaction to fire of the materials. It is also very difficult to assess the fire performance of complex objects such as upholstered furniture based on the reaction-to-hre characteristics of the object s components. Large-scale reaction-to-hre tests have been developed to evaluate these complex objects. 

The LIFT apparatus is used in conjunction with an instrumented exhaust stack to qualify finish materials for use on ships that sail on international voyages and need to comply with the SOLAS (Safety of Life at Sea) regulations developed by the International Maritime Organization (IMO). The method is described in ASTM E 1317 and in Part 5 of Annex 1 to the IMO Fire Test Procedures (FTP) code. 

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