Small heat source ignition test

Examples of Small Heat Source Ignition Tests.355... 

Examples of Small Heat Source Ignition Tests 14.2.2.1 UL 94 20-mm Vertical Burning Test... 

Specimen thickness affects performance in the test as was recently demonstrated in a study involving 18 plastics.20 The materials were tested in two thicknesses, 1.6 and 3.2mm. Specimen thickness did not affect the rating for most materials but for some the rating changed from V-0 to V-2 (two materials), from V-0 to not rated (one material), and from V-l to not rated (one material). Small heat source ignition test standards therefore nearly always require that at least the minimum end-use thickness be tested. 

A large number of flammability tests have been developed to evaluate the ignition propensity of a wide range of materials exposed, usually for a short duration, to a small heat source. For example, the most recent compilation of ASTM lire standards includes 30 small heat source ignition tests.21 When adding methods that use an electric arc, hot wire, hot surface, etc., instead of a flame and those developed by other standard organizations (NFPA, UL, ISO, IEC, etc.), the total number of tests is in the hundreds. 

Fire safety codes and regulations have requirements that are based on small heat source ignition tests. The objective of these requirements is to greatly reduce the probability of a relatively benign ignition source causing a major catastrophic lire (first strategy in the NFPA 550 Fire Concepts Tree). 

However, good performance in a small heat source ignition test can give a false sense of confidence as far as a material s behavior is real fires is concerned. Performance in the test depends on how it is measured, i.e., how the pass/fail or classification criteria are defined. Whether a material will ignite in the test depends on many factors such as... 

Small heat source ignition tests generally appear to be very sensitive to the composition of the material and some are therefore ideally suited to serve as a tool for formulation development and quality assurance of fire-retardant-treated products and materials. The equipment is inexpensive, only a small quantity of material is needed, the results are usually reasonably repeatable and reproducible, and a qualified laboratory technician can run many tests in a short time. 

Flammability tests are typically associated with the first strategy. A small specimen (linear dimensions of the order of centimeters or inches) of a polymer is exposed to a small heat source (Bimsen bumer-t5q)e flame, hot wire, etc.) for a short duration (seconds). Pass/fail criteria are based on ignition of the specimen during exposure, formation of flaming droplets, and/or sustained flaming or smoldering after removal of the heat source. 

Once ignited they produced considerable amounts of heat and smoke. Flame retarded flexible PU foams became available in 1954-55, i.e. within a few years of flexible PU foams becoming available in commercial quantities(22). These FR PU foams contained trichloroethyl phosphate or brominated phosphate esters and resisted ignition from small flame sources. Unfortunately they may burn when subjected to a larger ignition source or when covered by a flammable fabric and may then produce as much heat and more smoke than the standard grade of PU foam(3). This was identified by UK room tests in the early 1970 s and has been confirmed more recently by furniture calorimeter tests at the NBS(21). 

In most commercial references to FR -PBT blends, what is really meant by FR is that the materials are ignition resistant - not impervious to fire. With limited heat sources, such as in the UL-94 test [52] or the glow wire test [53], the FR blends will resist ignition or self-extinguish a small flame. However, in a large fire, these resins will bum, usually with a smoky flame. 

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