Miller Magazine Issue: 135 March 2021

75 ARTICLE MILLER / march 2021 Abstract In this study, dust explosions experienced in various industries and the characteristics of these explosions have been examined and their effects on the milling industry have been evaluated. Measures to be taken within the businesses operating in the milling sector according to the legislation in force in Turkey have been evaluated. 1. Dust explosions and its characteristics Dust explosion is the general name for an explosion that takes place when the density of particles in the air exceeds a certain limit and is ignited by a spark or similar effect. Such explosions, which can occur in almost every sector in to- day's industry, are crucial in terms of facility safety and occupational health. According to the definition of the American National Fire Protection Asso- ciation standard; Regardless of particle size and shape, flammable solids suspended in the air or in any oxidiz- ing environment and carrying the danger of ignition or explosion is considered as explosive dust. Dusting is the tendency of dust to form suspended clouds and hung in the air. [1]. Dustiness is also a term used to determine the respirable fraction and assess health risks. It may occur during operations such as transport, unloading, filling, weighing, especially in enterprises where dust-forming components are processed. About 130 years ago, Holtzwart and VonMey- er (1891) experimentally proved that explosive dust clouds can be ignited by inductive electric sparks. [2]. It has been reported that a dust density of 10 and 1000 grams per cubic meter or cloud is sufficient for dust explosions to occur. [3]. Major explosive dusts in the food industry can be listed as sugar dust, flour, starch, milk powder, cocoa, instant coffee dusts, spice dusts, and custard dust. Dust is generally defined as particles that can hang in the air and sink depending on the conditions. It has been reported that particles with a size of 0.1 micron and smaller hang in the air, while particles with a size of 0.1-10 microns cannot hang in the air. [4]. It should be taken into account that the stagnant air en- vironment can only occur in situations where air circulation is limited, such as in warehouses and silos. Fibers, snips or dusts of various characteristics stem- ming from solids can create an explo- sive atmosphere. [5]. Solids with a size of roughly less than 500 μm and that can hang in the air for a certain time are also considered dust. [5]. It is known that the intensity of the explosion caused by the formation of flammable clouds in the air and the spread of the flame depends on the concentration of oxygen and flammable material in the environment. [6]. It has been experimentally demonstrated that dust explosions do not occur at concentrations below or above the specified density value. [7, 8]. Moreover, it has been proven that all kinds of dust with diame- ters below 0.5 mm are more or less explosive. [5]. The moisture content of explosive dusts affects the explo- sion intensity. It is known that the dry dusts increase the intensity of explosion [5]. The maximum and minimum values of dust explo- sion parameters are uncertain because the probability of explosion depends on certain accidental variables [9]. This situation makes it difficult to clearly deter- mine the time when dust explosions may occur and the appropriate conditions that may cause an explosion. It has been reported that when a pressure wave hits the flame or the mixture in front of the flame is turbu- lent, the flame may become turbulent and at this stage of the flame propagation, pressure wave may accumu- late and shock wave may occur in front of the flame [3]. In general, the first perceptible shock wave and vibrations occur 25 milliseconds after the first moment of explosion. Approximately 60 ms after this stage, the dust in the outside environment sticks up and is dispersed. The Figure – 2: Primary and secondary explosion [16] Figure – 1 Flame propagation speed in dust explosion [15] 3 ms 6 ms 10 ms 10 ms