Explosibility of Polyamide and Polyester Fibers
The current research is aimed at investigating the explosion behavior of hazardous materials in relation to aspects of particulate size. The materials of study are flocculent (fibrous) polyamide 6.6 (nylon) and polyester (polyethylene terephthalate). These materials may be termed nontraditional dusts due to their cylindrical shape which necessitates consideration of both particle diameter and length. The experimental work undertaken is divided into two main parts. The first deals with the determination of deflagration parameters for polyamide 6.6 (dtex 3.3) for different lengths: 0.3 mm, 0.5 mm, 0.75 mm, 0.9 mm and 1 mm; the second involves a study of the deflagration behavior of polyester and polyamide 6.6 samples, each having a length of 0.5 mm and two different values of dtex, namely 1.7 and 3.3. (Dtex or decitex is a unit of measure for the linear density of fibers. It is equivalent to the mass in grams per 10,000 m of a single filament, and can be converted to a particle diameter.) The explosibility parameters investigated for both flocculent materials include maximum explosion pressure (Pmax), size-normalized maximum rate of pressure rise (KSt), minimum explosible concentration (MEC), minimum ignition energy (MIE) and minimum ignition temperature (MIT). ASTM protocols were followed using standard dust explosibility test equipment (Siwek 20-L explosion chamber, MIKE 3 apparatus and BAM oven). Both qualitative and quantitative analyses were undertaken as indicated by the following examples. Qualitative observation of the post-explosion residue for polyamide 6.6 indicated a complex interwoven structure, whereas the polyester residue showed a shiny, melt-type appearance. Quantitatively, the highest values of Pmax and KSt were obtained at the shortest length and finest dtex for a given material. For a given length, polyester displayed a greater difference in Pmax and KSt at different values of dtex than polyamide 6.6. Long ignition delay times were observed in the BAM oven (MIT measurements) for polyester, and video framing of explosions in the MIKE 3 apparatus (MIE measurements) enabled observation of secondary ignitions caused by flame propagation after the initial ignition occurring at the spark electrodes.
Study of the explosion reactions of sucrose, activated charcoal, polyethylene and lignite Part 1: Effect of variation in particle surface area upon explosion reaction
Abstract The rate of pressure rise (K St ) of explosion reactions in dust/air mixtures under atmospheric conditions is an important safety parameter for describing the kinetics of explosions. The value is used during the planning of protective measures like pressure release or suppression systems. The K St is not a value inherent to the substance, since it varies according to the shape of the test apparatus, ignition energy, time delay, and dispersion system, which all affects the degree of turbulence. Keeping these boundary conditions constant the K St is determined essentially by the chemical properties of the dust and its reactive surface area. 3–4 fractions differing in particle size distribution between 7 μm and 400 μm and in related specific surface area were produced from four carbonaceous dusts (activated charcoal, polyethylene, lignite and sucrose), and the K st values of the fractions were determined by experimentation. The experimental results were classified into four stages depending upon the suitable surface concentrations and the different processes involved. The stage in which dp/dt changes in surface concentration are most intense comply best with the Arrhenius equation. As a function of the specific geometric surface area, the K st value characterizes the chemical reactivity of the substance clearly and permits extrapolation to other particle size distributions.
Explosibility of cork dust in methane/air mixtures
Explosibility studies of hybrid methane/air/cork dust mixtures were carried out in a near-spherical 22.7 L explosibility test chamber, using 2500 J pyrotechnic ignitors. The suspension dust burned as methane/air/dust clouds and the uniformity of the cork dust dispersion inside the chamber was evaluated through optical dust probes and during the explosion the pressure and the temperature evolution inside the reactor were measured. Tested dust particles had mass median diameter of 71.3 mm and the covered dust cloud concentration was up to 550 g/m 3 . Measured explosions parameters included minimum explosion concentration, maximum explosion pressures and maximum rate of pressure rise. The cork dust explosion behavior in hybrid methane/air mixtures was studied for atmospheres with 1.98 and 3.5% (v/v) of methane. The effect of methane content on the explosions characteristic parameters was evaluated. The conclusion is that the risk and explosion danger rises with the increase of methane concentration characterized by the reduction of the minimum dust explosion concentration, as methane content increases in the atmosphere. The maximum explosion pressure is not very much sensitive to the methane content and only for the system with 3.5% (v/v) of methane it was observed an increase of maximum rate of pressure rise, when compared with the value obtained for the air/dust system. q 2005 Elsevier Ltd. All rights reserved.