Dust Explosion Causes and Hazards

What is a dust explosion ?

Refers to the dust in the explosive limit range, encountered heat (open flame or temperature), the flame instantly spread throughout the mixed dust space, chemical reaction speed, while releasing a lot of heat, forming a high temperature and a lot of pressure, the system The energy is transformed into mechanical work as well as light and heat radiation, which has a strong destructive power.

Dust explosion conditions

There are generally three conditions for dust explosions:

(1) Combustible dust is suspended in air at a suitable concentration to form what is commonly referred to as a dust cloud;

Any solid substance that is in a fine powder state is called dust. The dust that can burn and explode is called combustible dust; the dust that floats in the air is called suspended dust; the dust that settles on the solid wall surface is called deposition dust.

There are explosive dusts: metals (such as magnesium powder, aluminum powder); coal; food (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).

Dust generated during the production of certain factories and mines, especially the dust generated during the processing of some organic materials, can cause explosion combustion under certain conditions.

(2) There is sufficient air and oxidant;

(3) There is a fire or strong vibration and friction.

Dust explosion prevention measures

1, eliminate dust sources. The available dust removal measures include closed equipment, ventilation, dust extraction, dust extraction, or wetting and dust reduction. The fan for dust removal equipment should be installed on the side of clean air. In which flammable dust can not use electric dust removal equipment, metal dust can not use wet dust removal equipment. When starting the equipment, the equipment should be dusted and then turned on; when it is stopped, the opposite is true to prevent dust from flying. Every part of the dust workshop should be smooth. Try to avoid setting up any unrelated facilities (such as window curtains, curtains, etc.). Pipeline, etc. should not cross the dust workshop as much as possible, and should be laid in the wall to prevent dust from accumulating. In addition, if the conditions permit, spray water in the dust workshop, increase moisture in the material being crushed can also promote dust settlement, prevent the formation of dust clouds . In addition, cleaning in the workshop and timely manual cleaning are also a good way to eliminate dust sources.

2, strictly control the ignition source. Eliminating sources of ignition is the most practical and effective measure for preventing dust explosions. Among the common sources of ignition, sparks, static electricity, frictional sparks, open flames, surfaces of hot objects, and welding cutting sparks are the main causes of dust explosions. Therefore, it should be highly valued. The electrical equipment of the site shall be designed and installed in strict accordance with the “Specifications for Design of Electrical Installations for Explosion and Fire Hazardous Environments” to achieve the overall requirements of explosion protection. As far as possible, no mechanical equipment that may generate static electricity easily and generate sparks shall be installed or less installed, and electrostatic grounding protection shall be adopted. Measures. The material to be crushed must be strictly screened, stoned, and iron-absorbed to prevent impurities from entering the mill and creating sparks.

3, is to take reliable and effective protective measures. For smaller comminution devices, their strength can be increased and consideration should be given to preventing the explosion flame from propagating outward through the connection. In order to reduce the destructiveness of the explosion, pressure relief devices can be provided, such as using lightweight roofs, walls, or additional doors and windows for the workshop. However, it should be noted that the pressure relief device should be located close to the site where explosion is likely to occur, and not to the location where personnel are concentrated and main traffic routes; to reduce the amount of combustion gas, the inert gas (such as nitrogen) is added to the mixture of dust and combustion-supporting gas, reducing Oxygen content is also one of the feasible methods.

Dust explosion hazard

First, dust explosions are extremely destructive. Dust explosions cover a wide range of areas. Coal, chemical, pharmaceutical processing, wood processing, food, and feed processing sectors all occur from time to time.

Second, it is prone to secondary explosions. The first explosion air blast blows up the dust deposited on the equipment or on the ground. In the short time after the explosion, a negative pressure is formed in the central area of ​​the explosion. The surrounding fresh air is filled in from the outside to the inside, forming a so-called “return”. "Wind", mixed with the rising dust, caused a second explosion under the ignition of the first explosion. In the second explosion, the dust concentration is generally much higher than that of an explosion, so the power of the second explosion is much greater than the first time. For example, in a sulfur powder plant, an explosion occurs inside an attrition mill. The explosion wave propagates along the gas pipeline from the attrition mill to the cyclone separator. A secondary explosion occurs at the cyclone separator. The blast wave is generated at the cyclone separator after the explosion. The cracks spread to the workshop, causing sulphur dust that settled on buildings and process equipment, and exploded.

In addition, dust explosions can produce toxic gases. One is carbon monoxide; the other is a toxic gas that is decomposed by explosives such as plastics. The generation of poisonous gas often causes a large number of human and livestock poisoning after the explosion, and must be given full attention.

Dust explosions over the years

● March 1987

Harbin Linen Textile Factory caused a fire caused by a dust explosion and caused 58 deaths and 177 injuries.

● February 2010

An explosion of corn starch dust occurred in Hebei Qinhuangdao Hongye Starch Co., Ltd., resulting in 19 deaths and 49 injuries.

● April 2011

On the 1st, the aluminum dust parts polishing shop of a vehicle company in Jinyun, Zhejiang Province, exploded in the workshop and killed 5 and injured.

On the 19th, a dust explosion occurred at Jiashan Wood Factory in Zhejiang, and 6 people were burned.

● May 2011

An accidental explosion of combustible dust occurred at the polishing plant of the Foxconn Chengdu company, killing 3 people and injuring 16 people.

● August 2012

An aluminum dust explosion occurred in a residential building in the Ouhai District of Wenzhou City, causing it to collapse and burn, causing 13 deaths and 15 injuries.

● April 2014

An explosion of stearic acid dust occurred in Dongchen Town Shuangma Chemical Co., Ltd., Rugao City, Nantong City, Jiangsu Province, resulting in 8 deaths and 9 injuries.

● August 2014

In the production process of the automobile hub-light shop, the development of the Zhongrong Metal Products Co., Ltd., Kunshan City, Jiangsu Province, exploded. Seventy-five people were killed in the accident and nearly 200 were treated in hospital.

Extended reading :

What are the harmful effects of dust on the body under normal circumstances?

According to the nature of dust, can be divided into three categories: inorganic dust (mineral dust, such as silica, asbestos, coal, etc.; metallic dust such as iron, tin, aluminum and other compounds; artificial inorganic dust, such as cement, diamond, etc. ). Organic dust (including plant dust, such as cotton, hemp, flour, wood; animal dust, such as fur, silk, bone dust; synthetic organic dust, such as dyes, pesticides, synthetic resins, etc.), mixed dust (The above two kinds of dust are mixed together).

According to different chemical properties, dust can cause fibrosis, poisoning, sensitization and other effects on the human body, such as: fibrosis caused by free silica dust. Dust less than 5 μm in diameter (aerodynamic diameter) is more harmful to the body and can easily reach deeper respiratory organs. The concentration of dust is also related to the degree of harm to humans.

Specific impact on physical health

Systemic action: long-term inhalation of higher concentrations of dust can cause diffuse, progressive fibrosis in the lungs of systemic diseases (pneumoconiosis); such as inhalation of toxic dust, such as lead, copper, zinc and manganese, can be dissolved in the bronchial wall and be absorbed , from the blood to all parts of the body, causing systemic poisoning. Lead poisoning is chronic, but poisoning can cause acute attacks of poisoning if the person has a fever, or eats certain drugs and excessive amounts of alcohol. Excessive inhalation of copper fumes may cause hemolytic anemia; zinc may oxidize when burned. Zinc fumes cause a malaria-like "metal fume fever" after inhalation; long-term inhalation of manganese and its oxide dust or fumes adversely affects the central nervous system, respiratory system, and digestive system.

Local action: In contact with or inhalation of dust, it first produces local irritative effects on the skin, cornea, mucous membranes, etc., and produces a series of lesions. If dust acts on the respiratory tract, it can cause hyperactivity of the nasal mucous membranes in the early stage, and the telangiectasias can form hypertrophic rhinitis for a long time. Finally, atrophic rhinitis is formed due to insufficient supply of mucosal nutrients. Can also form pharyngitis, laryngitis, trachea and bronchitis. Action on the skin, can form acne, folliculitis, pyoderma, such as lead dust immersed in the skin, there will be some small red spots, known as "lead rash."

Carcinogenicity: Exposure to dust such as nickel, chromium, and chromate can cause lung cancer; contact with radioactive mineral dust can easily lead to lung cancer; asbestos dust can cause skin cancer.

Infection: Some organic dusts, such as tattered cloth, animal skins, grains, etc., are often accompanied by pathogenic bacteria, such as filamentous fungi, actinomycetes, etc., and can cause pulmonary mycosis in the lungs of dust particles.

Effect of dust on the lungs: Pneumoconiosis caused by long-term inhalation of productive dust is a common occupational disease with a greater risk of harm. Due to the different nature of dust, there are differences in the pathological changes caused by lung tissue. Dust-induced lung diseases can be divided into three categories.

1, pneumoconiosis. On April 18th, 2004, the Ministry of Health and the Ministry of Labor and Social Security promulgated the Catalogue of Occupational Diseases according to their etiology. They were classified as silicosis, electrofused lungs, and caster lungs, and 13 pneumoconiosis diseases. Pneumoconiosis is an incurable disease from the current medical level. Therefore, in the "Mechanical Manufacturing Enterprise Safety and Quality Standards Assessment Criteria," the classification of hazard levels of exposure to productive dust (one of four levels) and occupational health monitoring are important One of the evaluations.

2. Dysfunctional lung disease. Some production dusts, such as tin, antimony, bismuth, etc., can be deposited in the lung tissue after inhalation, present general foreign body reactions, have little or no significant impact on human health, and can be gradually reduced after treatment or detachment from dust. disappear.

3, organic dust caused by lung lesions. Pulmonary inflammation, pneumoconiosis and other diseases caused by organic dust are extremely rare in the machinery manufacturing enterprises. Because there are few studies on the causes of organic dust, the pathogenic mechanism is inconsistent. At present, it has not yet been defined as an occupational disease.

How to make personal protection for dust

According to the hazards of the dust on the human body and ways of injury, targeted personal protection. Dust (or poison) on the human body has three ways: First, inhalation, through the respiratory tract into the body: the second is through the body surface skin sweat glands, sebaceous glands, hair follicles into the body; third is ingestion, enter the body through the digestive tract.

Then for personal injury protection measures:

One is the way to cut dust into the respiratory system. According to different types of dust, loading different types of dust masks, respirators, (to some toxic dust should also wear a gas mask); second is to block the dust on the skin contact. Correct wear overalls (some need to wear rompers, hooded overalls), helmet (the human head is sweat glands, skin fat and hair follicles are more concentrated parts) glasses, etc.: The third is to prohibit the dust on the job site to eat, smoke, drink water Wait. The above content refers to "safety production technology", "safety production management" and other books.

In addition, improving the working environment is much better than wearing protective equipment.