Analysis of typical accident cases of enterprises involved in metal dust explosion

Dust explosion refers to the formation of a dust cloud when combustible dust mixes with air in a confined space. Under the action of an ignition source, the dust-air mixture formed burns rapidly, causing a chemical reaction with a rapid increase in temperature and pressure. Common combustible dusts includeMetaldust,fooddust,feeddust,treedust, resindust, coal dust, etc.Metal dustEspecially aluminum-magnesium dustProportion of explosion accidentsThe risk is the highest and causes many casualties, so it requires special attention and prevention.

one、Basic information of the accident

2023Year7moon4day10hour47Located in Chang'an Town, Dongguan City, Guangdong Province, Dongguan Huamao Electronics Group Co., Ltd. (hereinafter referred to as Huamao Company)BFactory buildings3In the grinding workshop on the first floor, a dust explosion occurred when a manual grinding wheel was used for grinding.1People were seriously injured.2Huamao mainly produces mobile phone structural parts and hardware structural parts. The main processes includeCNC　Processing, polishing, cleaning, oxidation, dyeing, shipment, etc.

2. The workshop involvedDust collection and treatment process

2021Year10In January, Huamao Company separated its former manual sandblasting workshop into two with gypsum board walls. The larger workshop served as a sandblasting inspection room, while the smaller workshop was temporarily converted into an aluminum alloy polishing room (the workshop involved in the incident). This renovation was completed independently by the company without a design plan or hiring a third-party contractor.

picture1　Elevation diagram of the dust removal system in the grinding workshop

aluminumThe alloy product grinding and polishing workshop uses sand grinders and sandpaper to grind and polish the surface of aluminum alloy products. The dust generated is mainly aluminum alloy dust (AL　content97.7％，Mg　content0.83％In order to meet the environmental protection requirements, Huamao Company has set upCOULDThe plastic (polyurethane) hose absorbs the aluminum alloy dust generated at the workstation and discharges it intoPP　The plastic (polypropylene) main exhaust duct (through the floor slab and connected to the roof fan) uses a multi-blade fan to blow the dust in the main exhaust duct into the roof water tank for sedimentation and collection.

three,The accident

7moon4On the morning of the same day, Huamao Electronics Company organized its employees to carry out the grinding work as usual. The workers on duty in the grinding workshop11people.6People carry out grinding operations,5People perform deburring operations.

10hour47point34Second,11Workers are carrying out grinding operations normally.

10hour47point35Seconds later, smoke and dust were ejected from the dust removal pipe above the grinding line in the workshop.

10hour47point36Seconds later, a violent explosion occurred in the dust removal main pipeline of the workshop grinding line.

10hour47point37Second－46Within seconds, several small-scale explosions occurred in the workshop, and then the workshop was engulfed in fire and thick smoke.

picture2Aluminum alloy parts grindingpicture

Figure 3Dust explosion site

picture4Grinding table after dust explosion

Four,Analysis of the cause of the accident

Direct cause:A large amount of aluminum dust accumulated in the horizontal ducts at the front of the fans in the dust removal system of the aluminum alloy grinding and polishing workshop. The raised dust mixed with air and reached the minimum concentration for a dust explosion. Two bolts securing the bearing seat of the multi-blade fan impeller near the partition wall loosened and fell off, causing the fan to vibrate violently. The impeller then deviated, causing intense friction with the casing, generating mechanical sparks that ignited the cloud of aluminum alloy dust raised in the fan cavity and the horizontal duct at the front of the fan, causing the initial explosion. The blast wave then sprayed from the rooftop duct into the workshop through the branch hose of the duct interface, dispersing the aluminum alloy dust accumulated in the duct into the workshop, triggering multiple deflagrations.

picture5 The bearing seat fixing bolts loosen and fall off

picture6 Friction marks between the fan wheel and the fan casing

V. Major Issues Exposed by the Accident

First, enterprisesSelf-modified aluminum product grinding and polishing workshop without dust explosion safety design; Second,The fan of the dust removal system was not maintained regularly, and potential safety hazards such as loose bolts fixing the bearing seat and deviation of the wind wheel were not discovered and eliminated in a timely manner.Third, there was a lot of dust accumulated in the air duct, which caused a secondary explosion and caused casualties.UsedWetThe dust removal system does not meet national standards.

6. Lessons from the Accident

Industrial and commercial enterprises with combustible dust explosion hazards should strictly implement the "Regulations on Dust Explosion Prevention and Safety in Industrial and Commercial Enterprises" (Order No.6No.) and other requirements.

1．Strictly design dust explosion-proof safety facilities.The design and construction of safety facilities for new construction, reconstruction and expansion of dust explosion-related engineering projects in dust explosion-related enterprises shall comply withNational and industry standards such as "Dust Explosion Safety Regulations"Design and construct.

2．Take effective measures to prevent dust ignition sources.Aluminum, magnesium, zinc, titanium, etc.Metalor combustible dust collection systems generated by metal alloys，Strictly prohibitedPositive pressure blowing process is adopted.The fan blades of the dust removal system should be made of conductive materials that do not produce sparks during operation.Dust removal system air ductStrictly prohibitedPPplasticpipelineto prevent static electricity from causing sparks.

3．Strict daily inspection and maintenance of equipmentThe fan and blades of the dust removal system should be installed tightly and operate normally without collision, friction or abnormal noise. During inspection and maintenance, tools that produce collision sparks should not be used.

4．Clean up dust in time.The dust in the dust removal pipeline should be cleaned regularly. The dust inlet pipe of the dust collector of the polishing and grinding processing system of aluminum and magnesium products should not exceed1mmThe workplace, equipment and facilities shall not have a thickness greater than0.8mmof dust.

5．Standardize the use of wet dust removal systems.The wet dust removal system for aluminum and magnesium dust should be equipped with a liquid level and flow rate monitoring and alarm device interlocked with the grinding and polishing equipment. Keep the workplace and the dust collector body well ventilated to prevent hydrogen accumulation and timelyClean the mud in the circulating water pool regularly to ensure the water quality is clean. It is strictly forbidden to operate the wet dust collector dry.