Assessment of Fire Retardancy

FIGURE 5.6 Peak of heat release rate plotted against irradiance (a) PP-g-MA and PP-g-MA/5 wt% A (b) Epoxy and Epoxy/5 wt% D. 

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An obvious utility for the type of modeling described is to evaluate the effect of exchanging one material for another in a composite or an assembly or even the addition of a new material, perhaps one of high toxicity but with a low burning rate. It can be used to evaluate the contribution of a material that does not become involved until the later stages of a fire. The model has the potential of assessing the trade-offs of flammability vs. toxicity often encountered with the use of fire retardants. 

T.R. Hull, Challenges in fire testing Reaction to fire tests and assessment of fire toxicity. In Advances in Fire Retardant Materials, D. Price and A.R. Horrocks (eds.) Woodhead Publishing Ltd., Cambridge, U.K., 2008, Chap. 11, pp. 255-290. 

FIGURE 15.21 Using the Petrella plot for comprehensive and reasonable scientiflc assessment of flame retardancy by comparing different approaches, or by comparing the effects for different irradiations. THE stands for the Are load and PHRR/tig for the fire growth rate hence, the two most important fire risks are monitored at the same time. An ideal flame retardancy would decrease both hazards significantly as is the case for the combination of both flame retardants on the left (comparison of HIPS), HIPS/Pmd, HIPS/Mg(OH)2, and HIPS/Pmd/Mg(OH)2) and for low external heat flux on the right (comparison of PA 66-GF and PA 66-GF/Pred for different irradiations). 

T.R. Hull, K. Lebek, A.A. Stec, K.T. Paul, and D. Price, Bench scale assessment of fire toxicity, in Advances in the Flame Retardancy of Polymeric Materials Current Perspectives Presented at FRPM 05, Schartel, B. (Ed.), Herstellung and Verlag, Norderstedt, Germany, 235-248, 2007. 

The assessment of the contribution of a product to the fire severity and the resulting hazard to people and property combines appropriate product flammabihty data, descriptions of the building and occupants, and computer software that includes the dynamics and chemistry of fires. This type of assessment offers benefits not available from stand-alone test methods quantitative appraisal of the incremental impact on fire safety of changes in a product appraisal of the use of a given material in a number of products and appraisal of the differing impacts of a product in different buildings and occupancies. One method, HAZARD I (11), has been used to determine that several commonly used fire-retardant—polymer systems reduced the overall fire hazard compared to similar nonfire retarded formulations (12). 

The use of flame retardants came about because of concern over the flammabiUty of synthetic polymers (plastics). A simple method of assessing the potential contribution of polymers to a fire is to examine the heats of combustion, which for common polymers vary by only about a factor of two (1). Heats of combustion correlate with the chemical nature of a polymer whether the polymer is synthetic or natural. Concern over flammabiUty should arise via a proper risk assessment which takes into account not only the flammabiUty of the material, but also the environment in which it is used. 

One problem associated with discussing flame retardants is the lack of a clear, uniform definition of flammabiHty. Hence, no clear, uniform definition of decreased flammabiHty exists. The latest American Society for Testing and Materials (ASTM) compilation of fire tests Hsts over one hundred methods for assessing the flammabiHty of materials (2). These range in severity from small-scale measures of the ignitabiHty of a material to actual testing in a full-scale fire. Several of the most common tests used on plastics are summarized in Table 1. 

Flammability. The fire hazard associated with plastics has always been difficult to assess and numerous tests have been devised which attempt to grade materials as regards flammability by standard small scale methods under controlled but necessarily artificial conditions. Descriptions of plastics as selfextinguishing, slow burning, fire retardant etc. have been employed to describe their behaviour under such standard test conditions, but could never be regarded as predictions of the performance of the material in real fire situations, the nature and scale of which can vary so much. 

The symposium was planned as a state-of-the-art meeting, focusing on the basic science. Program areas included high heat polymers, fire performance of polymers, hazard modeling, mechanism of flammability and fire retardation, char formation, effects of surfaces on flammability, smoke assessment and formation mechanisms, and combustion product toxicity. 

Figure 15.21 (right) uses the Petrella approach, to assess the fire risks of both PA 66-GF and PA 66-GF/Pred at different external heat fluxes.54 55 81 Thus, the assessment is valuable for different applications, fire scenarios, and Are tests, as these correspond to different external heat fluxes and define different demands on Are retardancy in terms of the long duration and growth of a Are. The data for both materials show that with increasing heat flux the Are hazards increase in terms of Are growth, as expected, since a higher irradiance results in an increase in fuel production rate. The THE of... 

Cone calorimeter in standard atmosphere (to assess the effectiveness of nanoparticles and intumescent fire retardants and also measure heat release rates (HRRs) and product yields)... 

It is intended to use these properties for the assessment of alternative flame retardants (FRs) (including nanoparticles, phosphates, and inorganic metal oxides) in comparison with brominated fire retardants by quantitatively assessing ... 

In this test, a small sample of material (127 mm x 13 mm, or 5 in. x 0.5 in.) is exposed vertically to a small Bunsen burner-type flame from underneath (in the UL 94 V test) and the results show a rating, ranging from V-0 (best), through V-l, V-2 to B (for Burn). Materials with a B rating on the UL 94 Vertical test can also be tested in the less severe UL 94 HB (for horizontal burning), where the assessment is whether a flame spread rate of 4in./min is achieved. It is the most widely used fire-test specification for plastic materials, especially fire-retarded ones, and forms the basis of the famous Yellow Card used by ULs to list the plastic materials. The results from these tests are almost invariably found in a variety of specifications and data sheets. 

The focus of this program was to evaluate the environmental profiles of chemical flame-retardant alternatives for use in low-density polyurethane foam.93 The program was a joint venture between the Furniture Industry, Chemical Manufacturers, Environmental Groups, and the EPA to better understand fire safety options for the furniture industry. It assessed 14 formulations of flame-retardant products most likely to be used in this application. The project began in December 2003 and the report was issued in September 2005.94... 

The compatibility of a colorant is assessed not only on the basis of the ease with which it can be mixed with the base resin to form a homogeneous mass but also on the requirement that it neither degrades nor is degraded by the resin. In relation to product functional properties, incompatibihty of a colorant can affect mechanical properties, flame retardancy, weatherability, chemical and ultraviolet resistance, and heat stability of a resin through interaction of the colorant with the resin and its additives. Flame retardancy, for example, may impinge directly on the performance of a colorant. Pressure to produce materials with lower levels of toxic combustion products can involve organic fire retardant additives that interact with the colorant either to negate the effect of the additives or affect the color. 

Furthermore, the human health section of the EU Risk Assessment has concluded that the fire retardant additive TBPBA carries no risks, and the EU Scientific Committee on Health and Environmental Risks (SCHER) has confirmed the EU (Risk Assessment) conclusions that TBPBA presents no human health risk. TBPBA is a brominated flame retardant (used in electrical equipment including computers, televisions, and in printed wiring boards (PWB), and so on [21],... 

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