Source: Ministry of Emergency Management of the People's Republic of China
September 14, 2023 at 14 o'clock
Shanghai Hanbang United Airlines Laser Technology Co., Ltd. (hereinafter referred to as Hanbang Company)
A dust deflagration accident occurred
As of 17 September
The accident resulted in 2 deaths and 2 serious injuries (90% and 70% burns were caused by the seriously injured)
Basic information of the accident unit
Founded in 2017 with a registered capital of 41.46 million, Hanbang is a private enterprise with 89 employees, mainly engaged in the research and development and sales of metal powder bed laser additive manufacturing (hereinafter referred to as metal 3D printing) equipment, with a total sales revenue of about 150 million yuan in 2022.
The accident occurred in the workshop of the R&D center of Hanbang Company, and the dust involved was aluminum alloy dust (Al content 87%, Mg content 9%, Si content 1.5%).
The metal 3D printing process adopted by Hanbang (see Figure 2) is: in the molding room, the metal powder is coated into a micron-sized dust layer on the substrate, and the dust is melted and rapidly solidified on the substrate under the action of the laser. The workpiece manufacturing is completed by stacking the "print" layer by layer.
The metal 3D printing equipment supporting dust removal system is used for dust removal in the molding chamber, and the dust removal system adopts a first-stage cyclone dust collector and a second-stage filter cartridge dust collector. The printing equipment and supporting dust removal system operate under argon protection (see Figures 3 and 4).
2 deflagrations
Restore the accident history
On September 14, the operator prepared to replace the filter element of the filter cartridge dust collector in the workshop.
At 11:32, the first deflagration of the filter cartridge dust collector occurred. The operator immediately extinguished the fire, and the deflagration did not spread further.
At 13:40, the operator transferred the filter cartridge dust collector to the outside of the workshop to replace the filter element.
At 14:01, the operator turned on the filter cartridge dust collector.
At 14:02, the operator poured water on the filter element of the filter cartridge dust collector, and the second deflagration of the filter cartridge dust collector occurred.
Preliminary analysis of the causes of the accident
After on-site investigation, questioning personnel, and viewing surveillance videos, it was preliminarily judged that the cause of the accident was:
At about 11:30 a.m., before replacing the filter cartridge dust collector filter element, the operator "humidified" the filter element, sprayed tap water into the filter element and the dust collection barrel, the water and aluminum alloy dust contact exothermic reaction to produce hydrogen, due to the small size of the dust collection barrel, the accumulated hydrogen concentration in the barrel is high, when the operator disassembles the dust collection barrel, due to static electricity or mechanical impact and other reasons caused by local deflagration in the dust collection barrel. The dust collection barrel and the dust collector cavity are separated by a butterfly valve, and the local deflagration is not propagated to the cavity.
At about 14:02 p.m., the operator transferred the filter cartridge dust collector to the outside of the workshop, after opening the box door, the suspected operator found that there was high temperature smoke in the filter element area, and then the operator directly poured water on the filter element, which quickly caused the reaction to be out of control under high temperature conditions, causing spontaneous combustion and bursting of dust, resulting in deflagration in the box, resulting in burns for surrounding employees.
At present, the exact cause of the accident is still under further investigation.
The field of metal 3D printing
Security risk warning
Metal 3D printing is an important production process in the additive manufacturing industry. According to the news of the Additive Manufacturing Industry Development (Guangzhou) Forum and 2023 Additive Manufacturing Industry Annual Conference held on June 28, 2023, in the past ten years, the overall additive manufacturing industry in mainland China has achieved good development, and additive manufacturing has experienced the metamorphosis from R&D innovation to industrial scale development, and is currently widely used in aerospace, medical, automotive and other fields, covering product design, prototype manufacturing, mass production, tooling fixtures, support maintenance, etc., and the scale of the industry continues to grow. The industrial scale will grow from about 1 billion yuan in 2012 to 32 billion yuan in 2022. There are more than 1,000 enterprises in the additive manufacturing industry chain, and the number of regulated enterprises with additive manufacturing as their main business has increased from more than 20 in 2016 to nearly 200 in 2022. Among them, the number of enterprises with revenue of more than 100 million increased from 3 in 2012 to 42 in 2022.
Wu Xiaoyu, director of the dust explosion-proof room of Wuhan Safety and Environmental Protection Research Institute of China Steel Group, introduced that metal 3D printing product processing and equipment manufacturers are different from the "typical" dust-related explosion-related enterprises we have previously impressiond, but the risk of dust explosion accidents is no less than that of any traditional aluminum-magnesium metal products processing enterprise. This new process technology has not attracted enough attention in the previous research and risk prevention and control in the field of dust explosion, and great attention should be paid to the research and development process of 3D printing equipment and the dust explosion risk in the manufacturing and processing process of 3D printing technology, and effective prevention and control measures should be taken.
Xiao Qiuping, member of the Dust Explosion-proof Sub-technical Committee of the National Safety Standards Committee and director of the Safety Engineering Center of the Shanghai Research Institute of Chemical Industry, introduced that aluminum alloy powder is a relatively common raw material in metal 3D printing, and most of them use micron-level aluminum powder, which itself is flammable and can release flammable gas (hydrogen) when exposed to water.
The explosion mechanism is mainly: aluminum powder and water reaction to release hydrogen will also produce heat, when the amount of water is sufficient, the heat can be dissipated in time, will not cause heat accumulation; However, in the semi-dry and semi-wet state, due to poor thermal conductivity, the heat released by the reaction is easy to accumulate in the aluminum powder pile, resulting in the phenomenon of temperature rise, and the higher the temperature, the more intense the reaction of aluminum powder and water, the more heat accumulated, which will often lead to spontaneous combustion of aluminum powder. In addition, in the metal 3D printing process, there is also a high risk of dust explosion, because the particle size of the aluminum powder used is very small, and the possibility of dust explosion and the consequences of explosion are relatively high.
In view of these explosion risks, the following protective measures are recommended:
●First, strengthen process risk control. It is recommended that the metal 3D printing and its filtration process adopt an inert gas protection method, and monitor the oxygen concentration data in real time to ensure that the relevant processes operate at low oxygen concentration and avoid combustion and explosion accidents during the manufacturing process.
● The second is to clean up and dispose of waste powder in time. After the production is completed, in the process of cleaning and disposal, it should be avoided to use water for local "humidification" treatment in confined spaces such as filters and dust collection bins; If a large amount of water is used to soak the waste powder, it should be done in an open space to prevent hydrogen accumulation.
● The third is to strengthen emergency response. When aluminum powder is on fire during production or disposal, sand can be used to cover the fire when the fire is light, and dust should be avoided during the fire extinguishing process; When there are no fire extinguishing conditions and the fire-related equipment can be moved away from a safe area, it can be allowed to burn itself; It is strictly forbidden to use water or foam extinguishing agents to extinguish fires to avoid the expansion of the consequences of accidents.
Safety tips for dust explosions
Dust explosions are made up of combustible dust
Heat sources are encountered within the explosion limit range
(open flame or high temperature).
Dust explosions are extremely hazardous
It often results in large casualties
Summer temperatures are high
Dust explosion accidents are prone to occur
Vigilance is needed
Five elements of dust explosion
Combustible gas: A certain oxygen content is the basis for dust combustion.
Combustible dust: dust that can be burned by oxidation reaction with combustion gas.
Ignition source: a high-temperature heat source that can cause the temperature of the local dust cloud to increase sharply and burn.
Dust cloud: A combustible dust cloud suspended in the air and reaching the lower explosion limit.
Confined space: The dust cloud is confined to a relatively confined space.
Features of dust explosions
Multiple explosions are the biggest feature of dust explosions.
The first explosion gas wave will blow up the dust deposited on the equipment or the ground, and a negative pressure will be formed in the central area of the explosion in a short time after the explosion, and the surrounding fresh air will be filled from the outside to the inside, mixing with the raised dust, thereby causing a secondary explosion. In the case of a secondary explosion, the dust concentration will be higher.
Safety management of dust-related explosion-related enterprises
Relevant regulations
Which enterprises are specifically referred to by dust-related explosion enterprises?
Article 2 of the "Provisions on the Safety of Dust Explosion Prevention in Industrial and Trade Enterprises" These provisions shall apply to the dust explosion-proof safety work and its supervision and management of metallurgy, nonferrous metals, building materials, machinery, light industry, textile, tobacco, commerce and trade enterprises (hereinafter referred to as dust explosion-related enterprises) that have the risk of combustible dust explosion.
What should be included in the enterprise dust explosion-proof safety management system?
Article 7 of the "Dust Explosion-proof Safety Provisions for Industrial and Trade Enterprises" Dust-related explosion-related enterprises shall establish and implement a dust explosion-proof safety management system in combination with the actual situation of the enterprise. The dust explosion-proof safety management system shall include the following contents:
(1) Dust explosion risk identification, assessment and control;
(2) Investigation and treatment of hidden dangers of dust explosion accidents;
(3) Safety operation procedures for dust operation positions;
(4) Special safety production education and training for dust explosion prevention;
(5) Dust cleaning and disposal;
(6) Operation, maintenance, overhaul and maintenance management of dust removal systems and related safety facilities and equipment;
(7) Emergency handling and rescue of dust explosion accidents.
Dust-related explosion enterprises
Criteria for determining major hidden dangers
Under what circumstances are the relevant enterprises judged to be major accident hazards?
Article 11 of the Standards for Determining the Hidden Dangers of Major Accidents in Industrial and Trade Enterprises An industrial and trade enterprise with a dust explosion risk shall be judged as a major accident hazard under any of the following circumstances:
(1) Where the dust explosion hazard place is set up in a multi-storey building (structure) with a non-frame structure, or there are employee dormitories, conference rooms, offices, rest rooms and other personnel gathering places in the dust explosion hazardous place;
(2) Different types of combustible dust, combustible dust and combustible gas and other media that are likely to aggravate the explosion risk share a set of dust removal systems, or different buildings (structures) and different fire prevention zones share a set of dust removal systems and dust removal systems are interconnected;
(3) The dry dust removal system does not take any kind of explosion prevention and control measures such as explosion relief, inerting, explosion suppression, etc.;
(4) When the metal dust removal system such as aluminum and magnesium adopts the positive pressure dust removal method, or when other combustible dust dust removal systems use positive pressure to blow dust, no measures such as spark detection and elimination are taken to prevent ignition sources;
(5) The dust removal system adopts gravity settlement chamber dust removal, or uses dry roadway-type structures as dust removal air ducts;
(6) The dry dust removal system of aluminum and magnesium and other metal dust and wood dust is not equipped with a lock gas ash discharge device;
(7) The electrical equipment of dust explosion hazard places such as dust collectors and dust collection silos divided into 20 zones does not meet the explosion-proof requirements;
(8) Before crushing, grinding, granulating and other process equipment that is prone to produce mechanical ignition sources, iron, stone and other debris removal devices are not installed, or the air duct connected to the sanding machine by wood product processing enterprises is not equipped with spark detection and elimination devices;
(9) Where measures to prevent hydrogen accumulation are not taken at the collection, stacking, or storage sites of spontaneous combustion of metal dust in case of humidity, or waterproof and moisture-proof measures are not taken at dry collection, stacking, or storage sites;
(10) The dust cleaning system has not been implemented, resulting in serious dust accumulation at the work site.
Dust explosions cover a wide range
The harm is unimaginable
Please take precautions