In previous articles on ATEX, I try to simplify the language and complexities that have grown around the EU directives. Despite all the technical solutions on offer, we know “people cause explosions not plant”.
Statistically we have many more fires than explosions. Dust explosions, are not considered a common hazard but we should be aware that fire is a leading indicator to dust explosions. If end-users and their employees believed dust is not just a house keeping issue, unlike liquid or gas fuels, but a true hazard that could kill or flatten their plant, they might handle it differently. Dust measurement levels are very difficult to define in g/m3 or mm layer thickness, do we trust in the real on site conditions versus a worst-case scenario.
In 2017, a corn dust explosion killed 5 workers and injured 14. Two days earlier, they had a major fire in a dust collector on the roof of the plant. Fires without a subsequent explosion can lead to complacency or the normalisation of risk.
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The burning smell and signs of smoke 30 minutes earlier should have initiated an automated evacuation alarm but since there were no alarms on the control panel, they did not think it was an issue. By the time, they had identified the impact mill problem, the filter had blown off, and dust and flame engulfed the building followed by secondary explosions. The use of radios and language difficulties further confused the communication for the eventual evacuation call.
Fuel handling (normally coal) in the Cement, Steel and Power industry, traditionally had a very good explosion safety awareness. They were one of the few industries to use self-reclosing explosion doors and pressure shock resistant silos. Now the fuel has changed to alternatives such as sludge pellets, wood pellets, tyres and various waste streams.
Fires are now becoming a big problem and explosions are happening in areas never protected before. The Management of Change requires these industries to share with other industry, what is best practice under these new circumstances. Creating new forums through trade associations and expert guidance. These platforms can share generally without fear of reprisal and revise best practice.
The mountain pine beetle, a bug the size of a grain of rice, killed pine forests, the area almost three times the size of Vancouver Island. If you are looking for the cause of the sawmill explosions that killed four workers and injured dozens more in 2012, the beetle is a good place to start.
Virgin wood usually has a high moisture content therefore less dust, but wood killed by this bug comes in dry! Useless as lumber this wood is pelletised for fuel. This alternative fuel must be stored indoors to keep it dry and if swapped for damp coal (normally stored outside), as an alternative fuel, it becomes a very big headache, as a fire and explosion hazard.
A plastics recycling plant had an explosion in 2020 eventually fined $88,000 dollars but they had received citations for the company permitting dangerous amounts of combustible dust to build up on surfaces that possibly could ignite due to open electrical equipment in the area, in 2014, 2016, 2017 and 2018!
We were monitoring a car shredder plant and the control room window blew in on our colleague. The operators just laughed and put the window back in its frame, stating that happens at least once a week but the plant is built to take it. The plant was eventually moved from the docks area to a remote industrial site, as the neighbours became more upwardly mobile. Can mitigation measures reduce risk to a point where it no longer matters?
Safety driven by regulations and penalties does not always create best practice. Incidents have been recorded shortly after recent inspections, this may create new acceptable hazards levels, procedures and existing mitigation measures may create practical drift, uncoupling practise from procedure, as existing safety levels have been reinforced by perceived compliance. This compliance, does it mean a revised acceptable risk that no longer poses a significant threat. Is compliance the end goal?
The classic hidden dust above a false ceiling, precipitated over years due to a faulty aspiration system, propagated the initial explosion throughout the plant. An inspection by an external consultant may not be aware of the hazard above. Did any maintenance staff ever lift a ceiling panel?
Steam pipe cut by an angle grinder in an empty tallow silo, cleaned earlier. The hazard had leaked into the pipe over years. The contractor assumed it was safe to proceed. A confined access permit had been issued.
Many surveys have been conducted post incident and one set of employees can state the plant was “spic and span” to “I was covered in dust every day”.
Roof windows fitted on top of silo penthouses back in the 70’s are frequently bolted down. Nobody realised they were explosion relief for the silo venting system. Safety needs to be regularly reviewed and recorded. Training programmes should not be just about compliance but ensuring continuity of basic safety practises.
Some old silos still have wooden hatches on the silo roof, but there is no data to support their weight over the vent area Kg/m2 i.e. vent efficiency, did anyone review the original silo strength figures allowing for the condition of the silo walls after 50 years. ]
- What is the strength of the penthouse walls?
- Where are the drawings?
- In the penthouse above the silos, is there restricted access during filling operations?
- Do they brush or vacuum the surplus dust?
- Is there horizontal surfaces for the dust to accumulate?
- How much dust is too much?
Can anyone end-user afford to CFD model the primary silo explosion into the penthouse and the secondary explosion effects through the skylight opening to outside.
Food and pharmaceutical companies keep their plant clean for both reasons of hygiene and product quality. This is normal accepted practise. In animal feed, recycling and wood processing industry this is not common but the dust hazard is the same for all of the above.
There is now huge responsibility placed on employers to comply with regulations, directives, and standards while at the same time keeping their employees safe. We can get lost in the mire of paper reports, procedures, hazard area classifications, risk assessments, while forgetting the need for good training and competency in process safety, connected to relevant best industry practice.
Managing, controlling and understanding your processes and its people are the best basis of safety. Directives, regulations and standards are there to support this basis of safety. Compliance is not a comfort blanket for safety. Keep sharing your experiences.
