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Minimising combustible dust risk in a confined space
The danger of a combustible dust explosion is a serious occupational health and safety (OHS) hazard in many industries across Australia, particularly in those sectors with confined space.
"Over the centuries, dust explosions have claimed many lives and caused significant injuries and property damage," said Graeme Cooper, managing director of industrial parts supplier Tecpro Australia.
"To many, dust can seem harmless. But if certain conditions prevail, it can pose a deadly problem," he said in a July 2013 statement.
Combustible dust is a common risk in contained environments – such as underground mines, mills and storage facilities – as the confined space allows dust to collect in high concentrations. Additionally, these industries often introduce friction, heat and sparks into a confined space, which can result in an explosion or flash fire.
In the past, materials that have caused a combustible dust explosion include coal, grain, flour, sugar, sawdust, magnesium, cotton and even powdered metals such as titanium and aluminium.
Employers in high-risk industries are encouraged to offer their employees sufficient confined space training to ensure the hazard of a combustible dust explosion is minimised.
When do dust explosions occur?
For a combustible dust explosion to occur, a number of factors must be in place. This includes a high concentration of dust, the presence of an oxidising agent – such as oxygen – and an ignition trigger. The source of ignition could be a flame or even just static electricity off an employee's clothing.
Dust is particularly dangerous due to its massive amount of total surface area – this means the material is highly flammable. Combustible dust becomes a more significant hazard in confined space, where it is easy for dust to collect in high concentrations.
"In settings where there is the odour of gas or flammable vapours, it's obvious that there is an explosion risk and people are usually quick to respond and combat the problem," Mr Cooper explained.
"In contrast, where there is a large build-up of dust, it may not necessarily make people in the area think about the possibility of an explosion risk."
Even when dust is not collected in a confined space, there is also the risk of a flash fire or other damage-causing event. Due to the highly flammable nature of some forms of dust, any introduced flame can cause fire to spread quickly through a dusty environment.
Combustible dust explosions are also a significant OHS risk due to the added danger of multiple explosions. The first blast may unsettle more dust around the worksite and the highly combustible material could be ignited by the heat or shock wave resulting from the first explosion.
"Smaller dust explosions can unsettle dust elsewhere, causing rolling explosions which can of course do great damage. It's best to be vigilant and proactive by eliminating or minimising the factors that can contribute to a dust explosion," Mr Cooper revealed.
Another danger posed by combustible dust explosions is the varying size and impact of an event. When low grade dust explosions occur, it can create a false idea of the danger of combustible dust. In particular, when no damage is sustained to property or people, employers often downplay the risk of dust in the workplace.
"If relatively minor dust explosions occur, sometimes people feel complacent and that the problem is more or less manageable. However this doesn't necessarily mean that future explosions won't escalate into a larger disaster," said Mr Cooper.
How can you minimise the risk of a combustible dust explosion?
There are a number of important methods to reduce the risk of a dust explosion in your workplace, including offering your staff confined space training and improving your cleaning procedures.
– Train employees to identify the hazards. Ensuring all employees are adequately trained to identify the hazards in their workplace will enable them to protect their own health and safety, while also reducing the risks to their colleagues. This includes identifying when dust poses a risk of combustion or explosion.
However, due to the diverse nature of dust particles, it is not always possible to correctly identify when dust may be combustible or not. It is therefore recommended that employers and employees assume all dust is a risk and keep their workplaces as dust-free as possible.
There can be similar issues when attempting to identify the ignition source. While it may be simple to avoid introducing flame into a confined space filled with dust, the presence of material likely to cause a static spark could be less manageable. This is because a number of everyday clothing items can cause static electricity, which means even an employee's clothing could pose a risk in a confined space.
An in-depth knowledge of confined spaces training is also important so employees are aware of what to do if and when an emergency situation occurs.
– Separate dust-causing processes from other work areas. If possible, removing the presence of dust from the worksite completely may be the simplest way of reducing the risk of an explosion. Similarly, preventing the introduction of an ignition source will have a similar effect.
This could include ensuring dust-causing processes – such as grinding and sawing – are performed in a separate building or room to machinery that could create sparks or heat from friction. Additionally, removing all dust from an environment is recommended before any welding or hot work is undertaken in a factory or other site.
– Ventilation and dust-collection systems. An adequate ventilation or dust collection system will reduce the risk of airborne dust in a workplace, minimising the hazard of explosions. These systems could include direct air out-takes in confined spaces, dust capture hoods on machinery and filters. It is important not to use fans or other devices that may just disturb the dust and increase the risk of airborne particles.
– Regular cleaning. When cleaning the worksite, it is crucial to identify all surfaces where dust could settle, including on top of machinery and any overhead structures. These hidden areas can pose a significant risk if a small explosion was to occur. The shock wave from any smaller event could disturb the dust in these locations, causing a second, larger explosion that results in more damage than the first.
Regularly clearing dust from the worksite will minimise the risk of explosion, so it is important to invest in a thorough housekeeping program. This cleaning process also needs to be tailored to a dusty environment, including using approved vacuums instead of brooms and water instead of compressed air. Cleaning in a high-risk area can also be performed wet to stop the combustible material from becoming airborne – for example, mopping a floor instead of sweeping, as the use of a broom can kick up dust.
You may also want to consider substituting any rough surfaces on machinery or the work site for smoother platforms and facades. This should help to make cleaning easier and will also discourage dust from settling on these surfaces.
If you'd like to learn more about minimising the risk of combustible dust explosions in a confined space, get in touch with AlertForce today!
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