Smoke and toxic gas emissions

Smoke can be defined as a mixture of particles, liquid aerosols and gaseous products resulting from a combustion process. The toxicity of the gaseous products is of prime concern as a direct threat to life. 

Obscuration is typically measured in the NBS smoke chamber (ASTM E 662). This is a small scale laboratory test of a sample exposed to a radiant energy source, either with or without an adjacent pilot flame to ignite the gases from the material. 

The attenuation of a beam of visible light is recorded against time to derive the specific optical density. The standard heat flux is 25 kW/m.  

Testing involves identifying the nature, concentration and injurious effects of the major gaseous species. The rate of evolution of the toxic species will in turn depend upon the type of fire. 

The concern is primarily within confined spaces like buildings and transport. The need for large scale tests is apparent and this has been tackled in various ways, for example, 

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The performance of aluminium hydroxide/magnesium hydroxide-filled systems can be enhanced by incorporation of zinc hydroxystannate in halogen-free rubbers giving reduced smoke and toxic gas emission, coupled with higher flame retardancy. This action will be complimentary to the water release and endothermic effects of aluminium hydroxide/magnesium hydroxide filler systems. 

In halogen-containing rubbers, zinc hydroxystannate can be substituted as a non toxic replacement for antimony trioxide to reduce smoke and toxic gas emission. Zinc hydroxystannate does not pigment the rubber and can be used to produce clear or translucent products. 

Polyetheretherketones (PEEK) have excellent properties for use in advanced polymer composites, including low flammability, low smoke and toxic gas emission, and broad chemical and solvent resistance. PEEK... 

PAEK find applications in the automotive, chemical process, oil and gas, aerospace, medical device, telecommunications and electronics industries. They are often used because of a combination ol properties which goes far beyond temperature resistance and includes resistance to wear, chemical environments, hydrolysis, sterilisation and fire together with biocompatibility, purity, low smoke and toxic gas emission and electrical performance. 

Applications for PEEK in the aerospace industry include critical engine parts as the polymer can withstand high temperatures and the tribological interaction of dry and lubricated material contacts. In aircraft exterior parts, PEEK provides excellent resistance to rain erosion, while for aircraft interior components, its inherent flame letardancy and low smoke and toxic gas emission reduce hazard in the event of a fire. In aircraft electrical systems, the polymer is used for manufacture of convoluted tubing to protect wires and fibre optic filaments. PEEK is also used to protect the wire harnesses used in commercial aircraft engines. 

CAL 133. California Technical Bulletin 133 is a test of the fire hazard associated with upholstered furniture (22). The test is carried out by igniting a standard fire source directiy on the piece of furniture being tested. In the most recent version of the test, the fire source is a gas flame. Smoke, heat, and toxic gas emissions are measured dufing the test. A related test, BS 5852, uses various wooden cribs as the fire source (23). 

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

Three pultrusion grades of phenolic resin systems are used (3-4) and they provide high flame retardancy, phis low smoke ant toxic gas emission in fires. 

Density Test) and toxic gas emission (DraegerTube Toxic Gas Test). For certain parts of the aircraft, FAA also requires the materials to pass either a 12 second or a 60 second vertical bum test. In addition, aircraft manufactures may have additional requirements on the flammability of the materials. Table 1 summarizes the performance of OSU resin against typical FAA requirements. Especially noteworthy are the OSU heat release values that not only meet, but also exceed OSU 65/65 standards (<55/55). At the same time, OSU resin generates a very low amount of smoke and toxic gases during burning. 

The potential fire hazard presented by waste tire stockpiles has been realized a number of times in the past decade. Several stockpiles have burned until their tire supplies were exhausted which, depending on weather conditions, may be a few days to more than a year. Air pollutants from tire fires include dense black smoke which impairs visibility and soils painted surfaces. Toxic gas emissions include polyaromatic hydrocarbons (PAHs), CO, S02, NOj, and HC1. Following tire pile fires, oils, soot, and other materials are left on site. These tire fire by-products, besides being unsightly, may cause contamination to surface and subsurface water as... 

Aluminium trihydrate (ATH) and magnesium hydroxide (MDH) have been shown to create low smoke levels and much reduced toxic gas emission (245,390). The activity of these materials is a function of the vaporisation of their water of hydration. 

Phenolic resins exhibit excellent dimensional stability with a constant use temperature range of 180-200 °C, excellent resistance to chemicals, moisture, and heat and favorable behaviour against fire and smoke. The predominant consideration in the use of phenolic resins as a matrix resin in fibre-reinforced composites is fire behaviour. Phenolic-based composites perform better under fire conditions compared with epoxy- or vinyl ester-based composites. This is due to their delayed ignitability coupled with low heat release, low smoke evolution with little or no toxic gas emission, and capability to provide significant strength retention (70%)... 

These fillers are of great industrial importance, and are the main subject of this chapter. They owe their fire retardant effectiveness to their ability to decompose endothermically at polymer pyrolysis temperatures, with the release of inert gases such as water. Thus, unlike some other flame retardants, they are able to combine a high level of flame retardancy, with low smoke and low toxic and corrosive gas emissions, and are thus becoming of increasing importance. One of the simplest such materials is aluminium hydroxide (also known as alumina trihydrate, ATH). 

Table 8.7 Typical limits for toxic gas emission in NBS smoke chamber, 25kW/m, flaming and non-flaming ...

Extremely low smoke emission. PEEK has been claimed to have the lowest toxic gas and smoke emissions of any plastics material. 

Marine vessels are effectively self-contained units in which the ability to escape is limited and so apart from the structural components it is essential that the textile content which comprises a significant fire source has some level of recognised fire retardant or even resistant property. In addition it is preferable that the individual vessel compartments and cabins and other occupied spaces have fire safety devices such as sprinklers and fire resistant bulkheads so that any fire is contained for as long as possible. More importantly, because of the nature of the confined nature of the vessel, toxic gas and smoke emission hazards are significant and must be contained. 

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