Dust explosions often occur in production and processing sites accompanied by aluminum powder, magnesium powder, zinc powder, zirconium powder, cobalt powder, iron powder, aluminum processing grinding powder, PCB cutting, PCB destruction, various plastic powders, intermediates of organic synthetic drugs, corn starch, wheat flour, sugar, sawdust, dyes, bakelite ash, milk powder, tea leaf powder, tobacco powder, coal dust, plant fiber dust, etc. The personnel injuries and property losses caused by dust explosions are incalculable, such as the explosion at the Kunshan factory in Jiangsu on August 2, 2014, which resulted in 75 deaths. Explosion is a safety accident caused by aluminum dust encountering open flames. To save unnecessary and irreversible losses and protect the personal safety of workshop personnel, strict compliance with production regulations should be implemented to prevent accidents before they occur.

1、 Formation of dust explosion

Dust explosion refers to the phenomenon where dust particles suspended in the air and rapidly burning within the explosive limit range cause flame propagation, resulting in high temperatures and high pressures in a relatively enclosed space. For example, a pile of flour is difficult to ignite with an open flame, but when we blow this pile of flour into a closed space, it forms dust and comes into full contact with the air. When encountering an open flame, the entire space of flour dust is ignited instantly. Imagine if in mass production, the flour dust inside the entire workshop is ignited by an open flame, resulting in a huge explosion power and incalculable personal injury and property damage.

2、 Related industries involved in dust explosions

1. Grain, food processing, feed

Grain depot, flour mill, food processing plant, feed mill

2. Wood processing

Door companies, flooring factories, timber factories, furniture factories

3. Metal powder production

Magnesium powder, aluminum powder and other powder production factories

4. Metal processing

Automotive parts factories (wheels, brake pads, front grille, decorative strips), aluminum alloy parts factories (cylinders for pneumatic valves), precision metal processing enterprises (laptop, tablet, and mobile phone frames), locks, motorcycle parts, hardware daily necessities, other aluminum products, titanium alloy processing.

5. Production and processing of plastics and resins

Plastic and powder production, spray coating, wind turbine blades, PVC pipes, synthetic resins

6. Light Industry

Food deep processing (starch, glucose, fructose), sugar, instant noodles, various blended beverages (coffee, milk powder), seasoning factories (dry seasoning, soy sauce factories), malt factories, breweries.

Pharmaceuticals, pesticides, dyes

Tea and tobacco

7. Chemical industry

Sulfur, coal chemical industry, petroleum coke

8. Energy and Building Materials

Thermal power generation, cement, ironmaking

9. Textile

Linen, cotton textile, synthetic fiber textile, down product factory

10. Port

Coal terminal, grain terminal

11. Solid waste treatment

Destruction of printers, copiers, and computers

Destruction of PCB circuit board

other

threeTheIn productionFormation of dust clouds

· The continuous existence of dust/air mixture due to the process itself

For example, lifting (bucket elevator, belt clamp), horizontal conveying (buried scraper, belt conveyor), crushing, mixing, rotary drying, spray drying, fluidized bed drying, pneumatic conveying, dust removal, etc.

· Sedimentary dust is disturbed during maintenance and cleaning processes

· The shock wave generated by the initial explosion lifts up the deposited dust layer.

· Dust combustion leads to the peeling and falling of the dust layer

4Types of dust involved in dust explosions

1. Grain, agricultural products, and food dust

For example, corn starch, wheat flour, coffee, sugar, milk powder, soybean flour, fish bone powder, mixed feed, tobacco, corn cob, etc.

2. Wood dust

This includes associated dust generated during wood processing, wood powder (used for producing cellulose), and debris from papermaking and wood based pellet biofuels.

3. Metal powder or metal dust

For example, aluminum powder, magnesium powder, zinc powder, zirconium powder, cobalt powder, iron powder, etc.

4. Non metallic elemental substance

For example, sulfur, phosphorus, silicon, etc.

5. Polymers such as plastics and synthetic resins

ABS、 Polyethylene, polypropylene, phenolic resin, epoxy resin, etc.

6. Coal based substances

Lignite, bituminous coal, anthracite, peat, coke, petroleum coke, etc.

7. Chemical dust

Pharmaceutical industry dust

Herbicides and insecticides

intermediate

Antioxidants, slow-release agents

8. Textile fibers

Including natural fibers (such as cotton, linen, wool, down) and chemical fibers (such as polyester, spandex, acrylic, etc.)

5Five elements of dust explosion1. Combustible dust; 2. Oxygen; 3. Fire source; 4. Restricted space; 5. Spread.

VIThe development of dust explosionsprocess

The first step is the rapid dry distillation or gasification of suspended dust under the action of a heat source to produce combustible gases; The second step is to mix combustible gas with air and burn it; The third step is to transfer the heat released by the combustion of dust to nearby suspended or blown dust through thermal conduction and flame radiation. These dust particles are heated and vaporized, causing the combustion cycle to continue. As each ring is laid, the reaction rate gradually increases, and through intense combustion, an explosion is formed. This explosion reaction, as well as the speed of the explosion flame, explosion wave, explosion pressure, etc., will continue to accelerate and increase, and develop in a leapfrog manner.

7Main hazards1. It has extremely strong destructive power; 2. It is prone to secondary explosions. The first explosion wave blows up the dust deposited on the equipment or ground. In a short period of time after the explosion, negative pressure is formed in the central area of the explosion, and fresh air around fills in from the outside to the inside, forming a so-called "return wind". It mixes with the raised dust and ignites the second explosion under the residual fire of the first explosion. During the second explosion, the dust concentration is generally much higher than during the first explosion, so the power of the second explosion is much greater than that of the first one. 3. It can produce toxic gases, mainly carbon monoxide and toxic gases from the decomposition of the explosive itself.

8、 Dust testing standards and testing items