Any solid substance in fine powder state is called dust.

1. Combustible dust:dust that can burn and explode

2. Suspended dust:dust floating in the air;

3. Deposited dust:dust settled on solid walls

4. (Combustible dust can only explode when it is in the form of suspended dust)

2. What is dust explosion

Dust explosion refers to the explosion phenomenon that occurs when combustible dust suspended in the air touches a fire source such as an open flame or electric spark. Because tiny particles of solid matter have a much larger surface area than blocks of the same weight, they can easily catch fire.

3. Conditions for dust explosion

Combustible dust explosion should meet three conditions:

1. The dust itself is explosive;

2. The dust must be suspended in the air and mixed with the air to an explosive concentration;

3. There must be a source of ignition sufficient to cause a dust explosion.

Remarks:All three are indispensable

(i) Which dusts are explosive:

It is generally believed that the dusts of the following seven types of substances are explosive:

1. Metals (such as magnesium powder and aluminum powder);

2. Coal;

3. Food (such as wheat, starch, corn flour);

4. Feed (such as blood meal, fish meal);

5. Agricultural and sideline products (such as cotton, tobacco);

6. Forest products (such as paper powder, wood powder);

7. Synthetic materials (such as plastics, dyes).

(II) Appropriate concentration

Within the explosion concentration (explosion limit) range. What is the explosion limit of suspended dust?

The lowest and highest concentrations that can cause dust to explode are collectively referred to as the explosion limits. If the concentration is outside the explosion range, the dust will not explode.

For example:The range of explosion limits of PVC powder:lower limit 63g/m³, upper limit 500g/m³. Below 63g/m³, or above 500g/m³, there will be no explosion.

(III) Fire sources causing dust explosions

As long as the temperature of the fire source exceeds the required auto-ignition point of the dust, it will explode.

Common ignition sources in the production process

1. Friction and impact sparks in the equipment. According to statistics, the explosion accidents caused by friction and impact of crushing and grinding equipment alone account for 57%.

2. Electric sparks and static sparks. Electric sparks caused by electrical equipment failure.

3. Smoldering and spontaneous combustion of deposited dust. Dust (10~20mm) deposited on heated surfaces such as lighting devices, motors, and hot surfaces of mechanical equipment will burn after being heated for a period of time.

(IV) The process of dust explosion

Step 1:Suspended dust is rapidly distilled or gasified under the action of heat source to produce combustible gas.

Step 2:Combustible gas mixes with air and burns.

Part 3:The heat generated by the combustion is transferred outward from the combustion center, causing the adjacent dust to further burn. In this cycle, the reaction speed continues to accelerate, and finally an explosion occurs. (The whole process lasts for tens of seconds)

4. Characteristics and hazards of dust explosion

It is extremely destructive

1. It is easy to produce a secondary explosion. The negative pressure state formed by the explosion sucks the dust to form new suspended dust, resulting in a secondary explosion. This continuous explosion will cause serious damage.

2. It lasts for a long time, generates great energy, and has great destructive power and burning degree. Especially in relatively closed pipe spaces, the pressure rises faster than in open spaces.

3. A large amount of heat is released, and the combustibles will be severely carbonized locally, causing serious burns.

4. Poisoning can occur, accompanied by carbon monoxide poisoning and poisoning by explosive decomposition products.

V. Dust explosion fire fighting measures

The effective extinguishing agent for dust explosion accidents is water, especially mist water.

For dust fires in workshops with large areas and long distances, it is important to take effective separation measures.

6. Working principle of CCD-500 explosion-proof dust meter (dust meter)

Real-time monitoring of on-site dust concentration through explosion-proof dust meter (dust meter) can effectively reduce the risk of dust explosion.

CCD-500 explosion-proof dust meter adopts laser light scattering technology, which uses laser beam to irradiate dust-laden airflow to make the beam produce scattered light. The higher the dust concentration, the greater the intensity of scattered light, and the dust concentration is measured.

The light scattering method determines the dust concentration in the air of public places. There is no need to weigh it. The dust concentration value can be directly read, and the fastest measurement can be achieved in 0.1 minutes. It has the advantages of being fast, sensitive, stable, small, light, noiseless, easy to operate, safe and reliable. On the one hand, this method has high sensitivity and requires a small amount of sample, and can omit or simplify the sample processing steps, so the sampling time and analysis time can be greatly shortened;on the other hand, this method does not require sample storage, thereby avoiding or reducing various possible error factors in the analysis method. The CCD-500 explosion-proof dust meter has passed the explosion-proof test experiment and can be used in dangerous workplaces and high-concentration dust environments in Zone 1, Zone 2, Group ⅡB, T4 and below, and can safely and quickly display the on-site dust concentration value in real time.

Users can set the alarm concentration threshold according to different locations. When the dust measurement concentration reaches this value, the dust meter automatically starts the alarm device to achieve an over-standard warning. The dust meter can also be linked to a spray, fog cannon or air exchange device to form a dust online monitoring system that integrates monitoring, alarm and dust reduction. The rapid dust measurement of dust meters and the coordination of dust reduction equipment will greatly reduce the dust concentration in the workplace and prevent explosions caused by continuous increases in dust concentration.