Smoke density rating

Material LOI (%) Char yield (%) Average heat rate release (kWm ) Smoke density rating... 

Metal chelates lower decomposition temperature (decrease thermal stability of material), increase char yield and limiting oxygen index, and improve smoke density rating. They are useful S5mergistic additives for Al(OH)3 and Mg(OH)2. Their two major functions are catalysts of dehydrochlorination and char formers. 

These foams are characterised by higher thermal resistance, low smoke density rating, lower thermal condnctivity and higher friability than rigid PU foams. More recent chemical modification (cyclic imide groups, carbodiimide groups, etc.), of PIR foam provides relatively low friability and excellent thermal stability. 

It is well known that freshly formed oxides have high surface areas and in addition, can be cata-lytically active,52 thereby promoting both carbon deposition and subsequent oxidation processes.53 The reduced combustion rate arising from the effects of the fire-retardant filler also contributes to lowering the rate of smoke evolution and, by improving oxygen to fuel ratios, further limits levels of smoke density.1... 

Fire testing was performed according to 14 CFR Part 25 for heat release rate (HRR), smoke density, and flame resistance [22], HRR was measured using retaining wires on the sample holder in an attempt to prevent melt dripping. At least two samples were tested and averaged to obtain reported values. 

Chapter 6 Smoke test. The test is based on the National Bureau of Standards (NBS, now NIST, National Institute of Standards and Technology) smoke density chamber, which has also been standardized as ASTM E 66239 (see also Section 4.1.1). The test exposes a vertical test specimen ca. 75 mm x 75 mm (3 in. x 3 in.) to an incident radiant heat flux of 25kW/m2, from a radiant heat burner for 4 min, in the presence of an open-flame pilot burner. The test applies to the same materials as the heat release rate test. The acceptance criterion is an average maximum specific optical density of smoke that does not exceed 200 (no units). 

The unfilled grade of PAI is rated UL 94 V-0 at thicknesses as low as 0.008 in. and has an oxygen index of 45%. PAIs are extremely resistant to flame and have quite low smoke generation. Some reinforced grades have surpassed the FAA requirements for flammability, smoke density,... 

ASTM E 906 Heat and Visible-Smoke-Release Rate Test (based on Ohio State University Release Rate Apparatus). In this test the specimen is injected into an environmental chamber through which a constant flow of air passes. A radiant-heat source is used to produce the desired heat flux in the specimen, which way be tested horizontally or vertically. Combustion may be initiated by a number of different methods. The changes in temperature and optical density of the gas leaving the chamber are monitored, and from the resultant data the heat-release rate and visible anoke-release rate are calculated. Toxic-gas release and oxygen consumption rates may also be measured. 

The apparatus of the Austrian standard, ONORM B 3800 Teil 1, 1979, is essentially identical to the XP-2 chamber. Solid specimens of 30 mm x 30 mm x 4 mm or expanded specimens with a bulk density below 100 kg/m of 60 mm x 60 mm x 25 mm are tested until the specimen has been completely consumed, but not longer than 15 min. On the basis of the highest smoke density measured during the test procedure, the materials are rated into 3 groups as shown in Table 4.1. 

The rate of increase in smoke density is another parameter which can be obtained from the curve of the specific optical density vs. time as follows ... 

Table 3.1 depicts the flame spread and smoke density values for various premium fire retardant resins. All products meet a class 1 flame spread rating with the phenol resorcinol product providing an outstanding value of 10. 

A special grade meets the demand for halogen-free materials for pultruslon, resin transfer moulding, filament winding, and hand lay-up processes, giving highly retarded composites at a comparatively low addition rate. With this additive, at approximately 50 parts per hundred resin (phr), the Epiradiateur NF 92-501 test - one of the most stringent in Europe - can be passed with a classification of Ml, where 250 phr is required with aluminium hydroxide. With epoxy resins, the same low smoke density is produced as with polyester laminates, at addition levels of 20-50 phr. The aviation standard FAR 25.8 53 can be passed with an addition of 25-35 phr. A liquid-form additive is available where no powder additive can be used. 

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