Dust explosion

Japanese: 粉塵爆発 - ふんじんばくはつ（英語表記）dust explosion

Also called a powder explosion. A violent explosion that occurs when fine particles of a combustible material are dispersed in the air and an ignition source such as a spark is applied. Coal dust explosions in coal mines are the most well-known, but they can occur with a wide variety of materials, including sugar, wheat, soybeans, tea, poppy, leather, plastic, silicon, magnesium, iron, and aluminum powders. The particle size is 1 to 100 μm, and the concentration limit is not constant depending on the air humidity, ignition conditions, and particle size, but the lower limit is said to be 10 ^-3 g for sugar and wheat, 7 x 10 ^-3 g for sulfur and aluminum, and 13.5 g for sugar per liter of air. The flame propagation speed is slower than in a gas explosion, but the amount of gas generated is large, so the maximum pressure is high and the destructive power is great. Various methods have been devised to prevent dust explosions, and one method is to scatter stone powder inside the mine. When the stone powder adheres to the coal powder, the heat capacity increases and the temperature does not reach the ignition temperature, which is 400 to 700°C.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

粉体爆発ともいう。可燃性物質の微粒子が空気中に飛散しているとき，火花などの点火源が与えられて生じる激しい爆発。炭坑の炭塵爆発は最も有名であるが，砂糖，小麦，大豆，茶，芥子 (けし) ，皮革，プラスチック，ケイ素，マグネシウム，鉄，アルミニウムなどの粉体まで非常に多くの物質で起る。粒子の大きさは 1～100μm ，濃度限界は空気湿度，点火条件，粒子径などで一定でないが，下限界は空気 1l あたり，砂糖，小麦は 10^-3g ，硫黄，アルミニウムは 7×10^-3g ，上限界は砂糖で 13.5g といわれる。気体爆発に比べ炎の伝搬速度は小さいが，気体発生量が多いため，最大圧力が高く破壊力も大きい。粉塵爆発の防止法は種々考案されており，炭塵爆発予防には石粉を坑内にまく。石粉が石炭粉に付着すると熱容量が大となり，発火温度に達しないからである。発火温度は 400～700℃である。

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