What types of dust may explode?
Dust explosion refers to a dust cloud formed by mixing combustible dust with air in a confined space. Under the action of an ignition source, the formed dust-air mixture burns rapidly and causes a chemical reaction in which the temperature and pressure rise sharply.
Dust explosions are often accompanied by aluminum powder, zinc powder, aluminum processing grinding powder, various plastic powders, intermediates of organic synthetic drugs, wheat flour, sugar, sawdust, dyes, bakelite ash, milk powder, tea powder, tobacco powder, coal Production and processing sites where dust, plant fiber dust, etc. are generated.
Combustible dust is suspended in the air at an appropriate concentration, forming what is often referred to as a dust cloud.
Any solid substance in a fine powder state is called dust. Dust that can burn and explode is called combustible dust; dust floating in the air is called suspended dust; dust that settles on solid walls is called deposited dust.
Explosive dust includes: metals (such as magnesium powder, aluminum powder); coal; grain (such as wheat, starch); feed (such as blood meal, fish meal); agricultural and sideline products (such as cotton, tobacco); forest products (such as paper powder, wood powder); synthetic materials (such as plastics, dyes).
The dust generated during the production process of some factories and mines, especially the dust generated during the processing of some organic substances, may cause explosion and combustion accidents under certain conditions.
Five elements of dust explosion to improve industrial safety awareness
Dust, like other substances, has a certain amount of energy.
Explosion limit is a very important concept and has great practical significance in fire and explosion prevention work:
(1) It can be used to evaluate the explosion hazard of combustible gases (steam, dust), as a basis for classifying combustible gases and determining their fire hazard categories. Our country currently classifies combustible gases with a lower explosion limit of less than 10% as first-class combustible gases, and their fire hazards are classified as Class A.
(2) It can be used as a basis for design, such as determining the fire resistance level of a building, designing a factory ventilation system, etc. It is necessary to know the explosion limit value of flammable gases (steam, dust) present in the place.
(3) It can be used as the basis for formulating safety production operating procedures. In places where combustible gases (steam, dust) are produced, used and stored, in order to avoid fire and explosion accidents, the concentration of combustible gases (steam, dust) should be strictly controlled below the lower explosion limit. For this reason, when formulating safety production operating procedures, corresponding preventive measures should be taken based on the explosion hazard and other physical and chemical properties of combustible gases (steam, dust), such as ventilation, replacement, inert gas dilution, detection and alarm, etc.
Dust explosion is a dangerous phenomenon that occurs in some industrial places, such as grain warehouses, wood processing plants, chemical plants, etc. Dust explosions can cause huge losses and even endanger people’s lives. So, how do dust explosions form? Generally speaking, a dust explosion needs to meet the following five conditions, which are the so-called “five elements of dust explosion”.
- Combustible dust
Combustible dust refers to solid particles that can undergo oxidation reactions in the air and release heat. There are many types of combustible dust, including organic matter (such as sawdust, flour, coal dust, etc.) and inorganic matter (such as metal powder, sulfide, etc.). Combustible dusts are characterized by a higher surface area and lower ignition temperature, making them more likely to ignite.
Air is the oxidant of combustible dust, that is, the medium that provides oxygen. Air contains about 21% oxygen, which is enough to support the combustion of combustible dust. Of course, not all air can cause dust explosions. It is also necessary to consider the effects of other components in the air (such as moisture, inert gases, etc.) and factors such as temperature and pressure on dust explosions.
- Ignition source
Ignition source refers to an external energy source capable of converting combustible dust from its normal state to its active state. Ignition sources can be open flames (such as sparks, flames, etc.), high-temperature objects (such as resistance wires, light bulbs, etc.), electrostatic discharge (such as friction, contact, etc.), mechanical impact (such as metal collision, hammering, etc.), chemical reactions (such as Spontaneous combustion, self-explosion, etc.), etc. The size, form, location and duration of the ignition source all influence the occurrence of a dust explosion.
- Mixing ratio
Mixing ratio refers to the ratio of combustible dust to air. Different types of combustible dust have different minimum and maximum explosive concentrations. That is to say, within a certain range, an explosion can only occur when the mixture of combustible dust and air reaches a certain ratio. If the mixing ratio is too low or too high, there will be a lack of sufficient contact area or reaction speed between combustible dust and air, thereby suppressing the explosion.
- Confined space
Confined space refers to a physical boundary that can limit the spread and dissipation of combustible dust and air mixtures. A confined space can be a container (such as a tank, a box, etc.), a room (such as a warehouse, workshop, etc.), a pipe (such as an air duct, a delivery pipe, etc.), etc. The function of a confined space is to make the mixture of combustible dust and air uniform and stable within a certain space. It also prevents the high-temperature and high-pressure gas generated by the explosion from escaping, thereby increasing the power of the explosion.
The interaction between them constitutes the necessary conditions for dust explosion. As long as any one of these elements is missing, dust explosions will not occur. Therefore, in industrial production, to prevent the occurrence of dust explosions, we must start from these five aspects and take effective measures, such as removing combustible dust, controlling the oxygen content of the air, eliminating ignition sources, adjusting the mixing ratio, and improving sealing space etc. Only in this way can the safety of the working environment and the health of personnel be ensured.