Dust Explosion Safety
Dust Safety Science has released its annual Combustible Dust Incident report 2023 which captures and details combustible dust incidents from around the globe.
The report shows that in total, 263 fires and 53 explosions caused 94 injuries and 62 fatalities during 2023. Comparatively 163 fires and 50 explosions caused 89 injuries and 49 fatalities during 2022.
163 fires and 52 explosions resulted in 215 injuries and 69 fatalities during 2021.
Before that, in 2020, 165 fires and 60 explosions caused 88 injuries and 10 fatalities.
Over 4 years Dust Safety Science have logged 754 fires, 215 explosions, 486 injuries and 190 fatalities from more than 40 countries
In 2023, 66% of the fatalities recorded occurred due to dust explosions. Of the injuries, 86% occurred due to explosions and 14% occurred due to fires.
From the global incident data, food and wood products made up over 79% of the fires and explosions recorded, 74% of the injuries and 24% of the fatalities. Coal was the most deadly material this year, accounting for over 68% of this year’s fatalities. This is largely due to a tragic mine explosion in Sutatausa, Columbia and fires in Panguan, China and Karaganda, Kazakhstan.
Fatal explosions involving metal this year included an aluminium melting furnace in Brazil, and an explosion during a 3D printing dust collector filter exchange in Shanghai, China. A paper products facility fire in Washington and a coal dust explosion in West Virginia contributed one injury each.
Under the category “unknown” and “other”, 4 injuries
and one fatality resulted from one explosion at a battery manufacturing plant in Sweden and three fires in a laundry facility, tire manufacturing facility and storage silo fire, respectively.
In 2023, storage silos demonstrated the highest percentage (36%) of combustible dust incidents with 93 fires and 20 explosions reported. Dryers and dust collectors were the next biggest sources of incidents, accounting for 18% and 13% each.
Only three dust collector explosions were recorded in 2023 compared to 10 in 2022. These included a flash fire which occurred during a filter change at a 3D printing facility in Shanghai that killed two workers and injured two more, and a dust collector explosion in Wismar, Germany that injured two.
Of the incidents where the equipment is known, 21 fatalities came from elevators/conveyors, 10 from storage silos, two from dust collectors and two from an aluminium melting furnace explosion. The 21 fatalities from conveyor belt systems are attributed to two coal mine fires in Panguan, China and Karaganda, Kazakhstan, respectively.
ATEX Explosion Hazards have been providing solutions to these problems for 50 years. To understand these issues we have written papers specific to most industries, that have issues with explosion safety, especially where dust is the primary hazard.
Dust Explosion Safety in Chemical & Pharmaceutical, Dairy, Food and Beverage, Cement and Biomass.
To be a real explosion hazard, the dust or fine powder needs a Minimum Explosion Concentration; MEC of typically 30 to 60 g/m3 enough fuel to sustain an explosion. You cannot see your hand on the end of your arm at 30 g/m3; this is not a light dust loading. The explosibility KST (explosion severity) of most powders is typically 50 to 200 bar m/s or less. That is 200 bar/s in a 1-m3 vessel, reaching typically a Pmax (maximum explosion pressure) 9-10 barg. European guidance defines explosive dust as less than 500 micron and fines as >100 micron. Explosion tests are standardized at 63 micron. Metal dust or some pharmaceutical dusts can be higher up to 500 bar m/s.
Ignition energies may differ for similar substances with differing moisture content and particle sizes. They may be as low as the static discharge experienced when taking off a synthetic fibre jumper, or as high as that from a ‘fixed flame’ such as a gas fired boiler. In evaluating the self-heating properties for biomass pellets or dairy powder, there are limitations to basket tests when scaled up to large silos installations.
Strength of vessel. It is important to know the strength of the plant, so that one can design the protection system within that vessel containment. Take care of transition points and socks. The weakest part of most plant is the roof. In old plant, this could be lower than 0.1barg but in modern plant typically 0.3 to 0.7 barg. Fluidbed and cyclones can be very strong with filters usually 0.5 to even 1 barg.
Select the appropriate Zones/Equipment.
Simple things like a viewing lamp have caused fires and explosions in plant. Obviously, do not use any equipment, instrumentation or tools, which generate an ignition source.
Train your staff
Wherever there is the potential for harm at the workplace, this also implies that the work organization must meet training requirements.
Prevention. Outside the above, there are systems that can minimise the probability of a fire or subsequent explosion. Temperature sensors are useful to control process conditions but tend to be too slow to detect a fire. Spark detection has been tried but with limited success. In the milk industry it causes more trouble than it is worth and most plant operators now favour ACOM i.e. ATEX CO monitoring.
Protection
Once the explosion starts, you need to mitigate the consequences. Venting is the preferred option but only if you can vent the flame outside. The flame from large vessels can do a lot of damage in a congested site. Due to product upgrades flameless vents are now accepted even in the Food industry, for small vessels venting inside the building is feasible.
Explosion Suppression is an alternative when venting is not feasible, using Hot Water or Powder fast fire extinguishing usually in fluidbeds and cyclones. Explosion Isolation is possible using rotary valves if they are ATEx approved, barriers using hot water and powder between the driers, fluidbeds, cyclones and bag filters are common.
Maintenance
Maintenance, should never be done while the plant is running especially blockages and hot work. Proper risk and method statements even for regular maintenance should be in place and supervised by a competent person. Ensure the plant is returned back to the operator in a safe condition.
Changes
Modern companies are now in the business of multiple ingredients, where the hazards and their properties are different with each product having different safety implications. Some factories can be processing various products in one week, which product is their worst-case scenario? Is one product stickier, is it more susceptible to self-heating, leading to the possibility of smouldering nests. Review your safety assessments.
