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.
Partial inerting of dust clouds using a modified standard minimum ignition energy device
Abstract Partial inerting is an important but underutilized mitigation technique in which minimum ignition energy (MIE) of a dust cloud is increased through inerting, reducing the risk of an accidental dust explosion or more accurately, a dust deflagration. This technique has wide application potential in numerous chemical and general manufacturing industries. The Kuhner MIKE3 is the predominant apparatus for measurement of the minimum ignition energy (MIE) of combustible dusts worldwide. The current version of the MIKE3 device is not specifically designed to measure partial inerting minimum ignition energies. The purpose of this work is to demonstrate that a properly designed add on purge device and technique can accurately produce partial inerting MIE results with an existing MIE device. The purge device ensures complete purging of the Hartman dust dispersion tube with the desired gas concentration before experimentation. The same gas is then pulsed into the dispersion tube producing the dust dispersion for ignition testing. This approach leads to uniform testing conditions in the tube with respect to gas concentration which is essential for producing proper measurements. Additionally, experiments show the turbulence generated by the purging technique did not significantly affect the MIE measurements. Therefore, an important finding of this work is that purging the tube before partial inerting MIE testing results in a proper characterization of the relationship between the MIE and oxygen for the dust. The findings therefore demonstrate the need to amend existing or develop new standards for this type of dust testing. The effect of these modifications and techniques are demonstrated by the experimental determination of the partial inerting curve for Niacin (CaRo15) using the Kuhner MIKE3 apparatus.
Prevention and mitigation of dust and hybrid mixture explosions
The results presented in this article focus on the importance of the prevention and mitigation of dust and hybrid mixture explosions. The main objective is to demonstrate the use of the inherent safety principle of moderation to achieve a significant reduction of the risk of explosions. Experiments and a companion modeling study were conducted with a test matrix composed of various size fractions of polyethylene powder together with concentrations of hydrocarbon gas (ethylene, hexane, and propane). The results quantitatively show the increased hazard posed by fine particle sizes of dust and the addition of flammable gases. There are clear implications for industry in terms of moderating the risk of an explosion.