Smoke generators, hazards

These materials are developed from the polyetherimides introduced by General Electric (see also Section 18.14.2). At the time of writing one grade, Ultem Siltem STM 1500, is being offered. It is of particular interest as a material for wire and cable insulation, as it not only has excellent flame resistance coupled with low smoke generation but also avoids possible toxic and corrosion hazards of halogenated polymers. This can be of importance where there are possible escape problems in the event of a fire, such as in tunnels, aircraft and marine (particularly submarine) vessels. 

No information was available to the committee on the quantity and composition of the offgases from the processed TRBP bins when they are in the smoking rooms. It is not clear that the design will provide adequate abatement for the smoke, and no provision appears to have been made for abatement of the carbon monoxide. The misting process employed in these rooms and the associated carbon filters may not remove the smoke generated from the contents removed from the TRBPs. If the smoke is not adequately managed, a visible plume whose composition is unknown but that could contain hazardous air pollutants will be emitted from this part of the plant. 

Guidance for controlling combustible materials is provided in Chapter 5 of the SNL ES H Manual. Materials used in construction must meet criteria established to limit the combustibility, flame spread and smoke generation potential of the materials. Minimization of combustible materials is also achieved by good housekeeping practices to reduce unnecessary items and lower the overall fire load. Periodic assessments, which work in conjunction with housekeeping, are conducted to identify any materials or hazards that need to be removed. 

The practical approach to containment should be defense in depth, so a spill tray suitably lined with absorbent paper on a bench of suitable design and construction (raised edges/stainless steel or laminate) in a designated area would be suitable for very small quantities of nonvolatile material. As the activity and volatility of the material increase, the tray should be itself held within the partial containment provided by a ventilated fume cupboard or slit box. (The linear flow rate through any working aperture of a ventilated enclosure should be at least 0.5 m sec for nonvolatile materials and at least 0.75 m sec for volatiles such as iodine.) If there is an external radiation hazard as well as the potential for contamination, then appropriate shielding must be used but care should be taken not to disturb the enclosure air flows. (Checks should be made with a smoke generator if there is any doubt.)... 

The characteristics that are measured in a fire test are indicative of the performance of the material under the conditions of the test and are therefore referred to as fire-test-response characteristics. They may or may not be indicative of the hazard of a material under actual fire conditions. The most common fire-test-response characteristics that are measured in fire tests are the ease of ignition, flame spread, heat release, smoke generation and toxic potency of smoke (20,25). 

As mentioned earlier, smoke is one of the hazards associated with the burning of polymeric materials. It has been identified as the cause of death in many instances. Any additive that will reduce the smoke generation of a given material is beneficial. 

As an alternative to blowing agents, in 1980 lightweight void-forming pellets or manufactured from ultrafine ceramic foam p = 100-200 kg/m have been introduced for PP. Teepull from Filtec are stable to 1050°C, do not generate smoke or hazardous gases and resist attack by most chemicals. They are used to form foams. 

Further dechlorination may occur with the formation of substituted diphenyhnethanes. If enough aluminum metal is present, the Friedel-Crafts reactions involved may generate considerable heat and smoke and substantial amounts of hydrogen chloride, which reacts with more aluminum metal, rapidly forming AlCl. The addition of an epoxide inhibits the initiation of this reaction by consuming HCl. Alkali, alkaline-earth, magnesium, and zinc metals also present a potential reactivity hazard with chlorinated solvents such as methylene chloride. 

The carbon black generated by a fire from a rubber source increases the smoke density other products are highly toxic and often corrosive. The halogens, phosphates, borates, and their acids evolved during a fire corrode metals and electrical and electronic equipment. Hence many of the fire retardants described below cannot be used in situations where the toxic gases evolved will create their own hazards. In these cases inorganic hydroxides are used, at filler-type addition levels. Aluminium hydroxide and magnesium hydroxide are used as non-toxic fire retardant systems. 

Because of the lack of suitable standard rate of heat, smoke and toxic gas generation tests, the 1988 UK regulations are based on ignition resistance of individual materials. This contradicts the basic requirements for the fire testing of composites and of hazard related tests and as such it may be possible to develop materials which meet the requirements but which produce hazardous products. 

Results from the NBS Cone Calorimeter have been shown to correlate with those from real fires. Moreover, it measures properties very relevant to fire hazard, in particular heat release, the most important of them. The OSU Calorimeter will measure many of the same properties. Furthermore, the results generated by both instruments have similar significance because of the good correlation between them. Smoke measurements are only relevant to fire... 

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