The risks of explosion
For a Fire you need 3 components of the Fire triangle; Fuel, oxygen, and ignition. An explosion is just a very fast fire, creating high pressures in a contained vessel. For Dust to explode you need Containment and dispersion.
The earliest Dust Explosion recorded 1785. Boy shoveling flour from one level to another by naked candle light had his face and arms scorched. It blew out the windows and released frames into the street. Another boy saw the flame coming from across the warehouse and jumped off a scaffold and broke his leg. The accident was report to be due to the dryness of the corn as there had not been any rain for the last 5 to 6 months in the Piedmont area!
Lies, dam lies and statistics, but the trends are always the same. There are about 2 dust explosions in Europe per day. Between 25 to 50% of these are in the Food industry, followed closely by the Wood and Paper industries at 20 to 30%, the remainder can be distributed between the metal, Chemical and fuel industries. The highest ignition sources are Mechanical Friction, smouldering product and hot surface auto ignition. Welding, electrostatic discharge and faulty electrical equipment are in single percentages. The statistics do not indicate the highest risk which is from “human failure to maintain and manage a safe plant”!
Historical UK reports:
William Primrose and Sons Ltd operated a provender mill in Glasgow which exploded on the 10th Nov 1911, killing 5 people including 3 children playing nearby. Their grinding process was very dusty and had no dust collection system. The room was lit by naked gas lights, and one was on such a long rubber hose that it could be moved around the room. Dust accumulations on the beams were not cleared adequately.
Exactly two weeks after the Glasgow explosion, the premises of J Bibby and Sons in Liverpool experienced the same fate, only this time the toll was 39 dead and 101 injured, figures hard to imagine in factories which today run with such minimal labour. Bibby’s were a more go-ahead firm, with electric lighting and a sprinkler system. They handled cotton cake and assorted meals. The machinery was belt driven, and the official report supposes that a dust cloud was formed when a belt broke. The ignition source was not possible to identify with certainty, but matches and electrical equipment were the most likely cause of the spark.
Bibby’s managed it again in Liverpool in 1930, when an explosion in the top floor of a silo building killed 11 and injured 32. Rice flour, sunflower seeds and soya bean meal were used in the processes. Self heating of the sunflower seedcake seems to have been the cause of an initial fire, but the heat spread between silos, and initiated an explosion, when hanging dust fell, while an adjacent silo was being emptied. Among the recommendations was ‘the provision of recording thermometers on the silo.
In the USA,gigantic explosion of flour dust destroyed a mill in Minnesota on May 2nd, 1878, killing 18 workers at the Washburn A Mill. In the late 1970s a series of devastating grain dust explosions in USA grain elevators left 59 people dead and 49 injured Here we can see the dynamics of an explosion in a bucket elevator.
France-Blaye-1997
A grain terminal which killed 11 people in 1997 Six of the victims were found in the offices. The sudden nature of the incident and the close proximity of the silo to the offices meant that they had no time to react and their bodies were found at their workplaces. Significantly sized pieces of debris from the explosion were found up to 100 meters from the silo although one piece of breeze block, weighing approx. 10 kg was reported to have been discovered at a distance of 140m.
1982 Grain Silos Metz France
News Report one day after the explosion: "After clearing debris for 24 hours the toll is now known: four dead, one seriously injured and eight missing , they could possibly still be alive buried under many tons of beams and cement. A spark from a blow torch could have caused the catastrophe’ The concrete silos were 70m tall, held barley, and the report stated that 4 out of 10 cells in the complex were seriously damaged"!
On May 11, 2004, the ICL Plastics factory (commonly referred to as Stockline Plastics factory), in the Woodside district of Glasgow in western Scotland, exploded. Nine people were killed, including two company directors, and 33 injured, 15 seriously. The four-storey building was largely destroyed. The Cause was a corroded LPG tank leak; the gas explosion may have caused a potential dust explosion. HSE indicated that the explosion was due to an ignition of gas released by a leak in a pressurized petroleum gas pipe. Report:
- Failing to maintain pipes carrying hazardous gas.
- Failure to ensure the safety of staff and visitors.
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Failing to carry out suitable and sufficient risk assessments
Wood Paper Dust:
The combination of high powered grinders, and kilns drying chips and dust to a low moisture content make these plants dangerous. Almost all the manufacturers have experience of dust explosions at their plants. One employee died at Egger UK in Hexham in 1989 when a dust explosion spread through the plant and somewhere between 20 and 30 explosion vent panels opened inside the building. Sonae built a new plant at Kirkby, Merseyside, and they placed vented silos and other vented equipment inside the building. That exploded in 2002, knocking over an internal wall, and injuring one employee. They were prosecuted in 2006, and a £70,000 fine imposed in Liverpool Crown Court.
The Aluminium Powder Co in Anglesey, exploded 16th. July 1983 injuring two men and causing very extensive damage on-site.
Energy from1 gram Aluminium = 6 gram of TNT.
The most recent incident on 7 February 2008, which has caught international news was the sugar dust explosion inat a Port Wentworth, Georgia Imperial Sugar refinery killed 14 people and injured over 40. An explosion, possibly caused by static electricity, igniting fine sugar dust that had become too dry -–. They had enclosed the bottom of the silo conveyor to prevent spillages, which subsequently blocked and acted as a confined path way for the propagation of the flame throughout the plant. There are some great videos from the Chemical Safety Board CSB explaining this and other events.
