Dust Explosion Safety
Dust Safety Science has released its annual Combustible Dust Incident report 2021 which captures and details combustible dust incidents from around the globe.
The report shows that in total, 163 fires and 53 explosions caused 215 injuries and 69 fatalities during 2021. Comparatively 165 fires and 60 explosions caused 88 injuries and 10 fatalities during 2020.
250 fires and 75 explosions resulted in 118 injuries and 8 fatalities during 2019.
Before that, in 2018, 213 fires and 68 explosions caused 114 injuries and 23 fatalities.
Over 4 years Dust Safety Science have logged 960 fires, 357 explosions, 720 injuries and 126 fatalities from more than 40 countries
In 2021, one mine explosion and subsequent dust fire in Gramoteino, Russia impacted the data more than any other incident, accounting for over 49% of the year’s injuries and 73% of the fatalities.
Of the other injuries, 83% occurred due to explosions and 17% occurred due to fires. For the other fatalities, all but one were due to dust explosions.
From the global incident data, food and wood products made up nearly 75% of the fires and explosions recorded, but only 23% of the injuries and 12% of the fatalities. Coal was the most deadly material, accounting for over 53% of the injuries and 87% of this year’s fatalities. This is largely due to the catastrophic mine explosion and subsequent ventilation fire in Russia. Twelve metal dust injuries, and the lone fatality, were results of two separate aluminium dust explosions. The other four injuries involved an explosion at a zinc powder facility. The nine injuries from textiles were sustained in an explosion at a packaging production plant. Under “Other,” two injuries came from explosions involving rubber dust. Four workers were also injured in an unspecified chemical dust explosion at a pharmaceutical plant.
The report lists some of the most severe incidents that occurred in 2020, including the December 3 explosion at Wessex Water’s treatment plant near Bristol which killed four people and injured one. In terms of the materials involved in combustible dust incidents, food and wood products made up over 75% of incidents and resulted in 57% of the injuries and 40% of the fatalities. Similarly, wood processing, wood products, agricultural activity and food production also make up a large portion of the overall fire and explosion incidents, a historical trend when it comes to combustible dust incidents. The report shows that storage silos had the highest percentage of combustible dust incidents in 2020 with 30 fires and 13 explosions reported. This differs from 2017 and 2018, which found collections systems to have the highest number of incidents.
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; it 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.
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.
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, 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.
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.