The dangers of combustible dust

WHAT IS COMBUSTIBLE DUST ?

Combustible dust is any material (finely divided solid particles) that has the ability to disperse in the air, ignite and cause an explosion when exposed to a source of combustion. Combustible dusts may include materials that are in the physical state of powders, flakes, fibers, etc. Some of these materials are not usually combustible, but they can burn or explode if their particles are the right size and present in the right concentration. Thus, any activity that creates dust should be examined more closely to see if the dust is combustible. Dust can accumulate on surfaces such as rafters, roofs, suspended ceilings, ducts, crevices, dust collectors and other equipment. Under certain circumstances, if the dust is stirred up, a large explosion can occur. Accumulation of even small amounts of dust can cause significant damage.

Whether in the wood industry, the synthetic materials industry, the chemical industry such as plastics or paint, the food industry such as flour or sugar, or the textile industry such as cotton and the metal industry such as aluminum or magnesium, combustible dusts are present in a large number of industries.

Combustible dust explosions can occur in all branches of industry when the products handled are in the form of fine particles and when they are oxidizable materials.

Deflagration

Deflagration is the term used for combustible dust explosions. In fact, a deflagration is a fire like any other fire, and when there is a fire, there is also a substance of some sort that will burn and release heat, gas, particles, and sparks. However, when it comes to dust explosions, this deflagration happens so quickly that the heat mixed with gaseous fuels, such as carbon dioxide, creates such intense air pressure that it creates an explosion. This type of explosion can destroy the area where it occurs. Dust explosions should not be underestimated.

HOW TO DETERMINE THE RISK OF EXPLOSION?

In order to determine if the location could be subject to a potential explosion or fire hazard, there are several variants to analyze.

You must consider the size of the particles, the way they are dispersed in the environment, the ventilation properties, the air currents that can circulate the dust, the sources of combustibles, the places where the dust can accumulate, the organization of the premises with physical obstacles. Then, evaluate the premises with a qualified person in order to have a precise idea of the level of danger and risk. Several professionals can guide you in a process like this : safety engineer, industrial hygienist, dusting engineer, etc.

What is important to know is that when it comes to factories in Canada, there are obligations in the presence of combustible dusts. Administrators must comply with NFPA standards by conducting a risk analysis. This analysis must be completed by a qualified engineer and the results must be available at all times in the plant.

 

The engineer will analyze:

  1. The particles circulating in the air are combustible
  2. Particles that are created by manufacturing are combustible
  3. Places where dust may have accumulated.
  4. The effectiveness of the processes in place to control the dust
  5. The presence of combustion sources
  6. The probability of explosions and accidents related to these factors

Of course, to maintain a safe and healthy environment, it is necessary to remove as much dust as possible by using dust collectors that are adequate for your type of application.

The economic sectors identified as the most at risk are the wood industry, the food industry, plastics, and metals.

HOW CAN COMBUSTIBLE DUST FROM VARIOUS MATERIALS CREATE AN EXPLOSION HAZARD?

Wood

When wood dust is not properly controlled, serious explosions or fires can occur. It is when there is a large accumulation of wood dust that the hazard is present. This accumulation occurs particularly in small, confined areas where the dust cannot be seen, or in large, virtually inaccessible areas. One of the most important things in preventing wood dust explosions is to prevent any accumulation, no matter where it occurs.

When it comes to woodworking shops, where wood is the most used material, the area will be considered a medium risk building. In an environment where one finds large quantities of fine dust like wood flour, that would be considered as a building with very high risk.

It is very important in these cases to have dust collection equipment that allows effective control of the dust. Medium and high-risk areas must be cleaned frequently to avoid any accumulation of combustible dust.

Sugar

Sugar presents a combustion hazard when it is in a dehydrated or dust form. An explosion of fine sugar dust can generate a pressure exceeding 100 psi in enclosed processing equipment in less than 100 milliseconds. The industry has recently updated tools to manage such a risk in the form of standards published by the National Fire Protection Association (NFPA). When sugar dust and air are mixed in a confined space, an explosion is very likely. Filtration equipment handling combustible dust will almost certainly contain a hazardous concentration of material under normal operating conditions. Other equipment may only temporarily include a combustible load of hazardous material, perhaps at startup, shutdown, during charging or discharging. However, when the combustible load is present, the hazard is no less serious. If the presence of a combustible load cannot be eliminated, protective measures are required.

Plastic

There are two main classifications of plastics: thermoplastic resins and thermosetting resins. Thermoplastics can be melted by heat to be reshaped afterwards. Thermosets do not have this ability. After the polymerization of this resin, the shape created cannot be changed, unlike the polymerization of thermoplastic resins.

Therefore, thermosetting resins will be used more to resist heat and allow a certain durability. On the other hand, thermoplastic resins will allow the creation of a multitude of plastic objects, including several plasticizers, flame retardants, and other additives to the resin and allow them to be reshaped for other purposes. It is in the process of polymerization and final production of the plastic object that there may be some risk of a large accumulation of combustible particles that carry the same risk of creating an explosion or fire as wood.

Coal

Coal dust is created when coal is crushed, ground, or pulverized. If it becomes airborne outside the controlled environment in which the coal is crushed (an environment where equipment is adapted to combustible materials), this dust can be hazardous. High-capacity conveyor systems are capable of moving several thousand tons of coal per hour. A small portion of the particulate material is released and becomes airborne.

It can then be deposited on various surfaces and eventually create a thick layer by accumulation. These particles often accumulate in places that are difficult to access. A single spark can cause an explosion that can potentially paralyze the activity of a thermal power plant.

Metals

All activities involving the manufacture of any metal object carry the risk of creating an explosion or a fatal fire. It is therefore necessary to be vigilant when this type of material is at the source of manufacture. In fact, 5 factors combined can lead to an explosion: 1) a concentration of fine, easily oxidized dust 2) a source of ignition 3) an oxidizer such as oxygen 4) a confined space/semi-enclosed area. 5) combustible dusts (metals) that act as a fuel since many are potentially flammable when exposed to the air, especially when they are in the form of metal powder.

Pharmaceutical Industry

Dust generation in the pharmaceutical industry occurs during most stages of bulk material handling, grinding, granulating, pelletizing, coating and even packaging. Due to the fine nature of this dust, it can deflect quickly and travel long distances to land on surfaces and in cracks in your facility. This dust can pose several challenges including cGMP issues, cross-contamination of parallel processes, employee exposure from contact with the harmful dust, and potential deflagrations due to the combustible nature of the dust. Improper handling and ineffective containment of process dust can result in OSHA fines, downtime for cleanup, and even personal injury or death.

STATISTICS

The different industries

When we look at the statistics concerning explosions in the different industries, we can quickly see that there are more cases in the wood industry, accounting for 42% of the cases of explosions. It is followed by the food industry, which represents 31% of the cases. The next largest number of cases are in the chemical and pharmaceutical industries, in the metal industry and in the cereal industry.

The wood industry

The wood industry accounts for 77 cases of explosions over a 27-year period. A little more than half of the cases come from wood panel manufacturing sites, representing 55% of the explosions. For each explosion with human consequences, there is an average of 2.5 injuries, of which 1.3 are seriously injured, and 0.2 deaths.

The food industry

In the food industry, out of 56 cases of explosions, more than 60% of them are the result of an explosion alone, while 34% are followed by a fire. 50% of the cases result in casualties, with an average of 5 injuries and 2 deaths for each explosion with human consequences.

Sources of ignition

There are several possible ignition sources causing explosions in these different industries. A large portion is from unknown sources, 44%.

CASE STUDIES

Case #1

2017 Corn Dust Explosion: a combustible dust explosion occurred at this corn milling facility. The explosion caused the complete collapse of the building and railcar loading dock. A total of five employees were killed and 14 were injured.

Case #2

Sugar Dust Explosion in Georgia, February 7, 2008: this company has been producing sugar for over 100 years. The explosion damaged a portion of the processing area, packing buildings, palletizing area, silos, and the bulk loading area of the railroad cars. The explosion was fueled by large accumulations of combustible sugar dust throughout the packing house. There were 14 fatalities and 38 injuries.

Case #3

2017 Corn Dust Explosion: a combustible dust explosion occurred at this corn milling facility. The explosion caused the complete collapse of the building and railcar loading dock. A total of five employees were killed and 14 were injured.

Case #4

Phenolic resin dust explosion in Kentucky, February 20, 2003: the plant was producing fiberglass insulation for the automotive industry. A fire in the malfunctioning furnace ignited a cloud of phenolic resin dust that had been generated while cleaning a production line. The dust explosion caused considerable damage to the production area. 7 people were killed and 37 injured.

Case #5

During welding work, on May 6, 2016, a wood mill in Amos, Quebec experienced an ignition of combustible dust in a planer bucket that resulted in a fatal burn victim of one of the workers.

Case #6

At Fabrimet, in Drummondville, in January 2022, a confined fire occurred in a dust extractor. No injuries were reported as the firefighters responded quickly. This plant manufactures electrical pylons made of galvanized steel, a dangerous steel when welded since it reaches a 6th stage of chromium oxidation called hexavalent chromium. The particles of this material are very harmful to health when breathed in and obviously carry the risk of creating explosions when confined in a place where they are accumulated.

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