Dust is a common problem for many of us in the work place, particularly in manufacturing processes. Dust in the work place comes in many forms from wood dust and metal shavings to chemical powders and biological dusts (like skin from podiatry and chiropody) and more.
Many dusts can also be flammable and create potentially explosive atmospheres which can pose significant risks to not only the lives of the employees but also property and infrastructure.
In order to know how to properly control hazardous dusts in the work place then we need to understand what the dust is, how it is created and the dangers it poses.
What is dust?
In terms of extraction dust is classified as solid particles that can be either supplied (from applications such as powder weighing, sampling and more) or process generated (from applications such as cutting, crushing, grinding and more). This also includes fibres and powders.
Airborne dusts created from these applications is able to be breathed in and can be further divided into two groups: Inhalable and Respirable.
Inhalable and Respirable dust
Inhalable dust clouds are partially visible with particle sizes ranging from between 10 microns and 100 microns (a human hair is around 100 microns and the human eye cannot see below 30 microns). Inhalable dust can easily be breathed into the mouth, nose and throat. Once here the dust can cause irritation to the soft tissue and, depending on the materials the dust has come from, may cause more severe or lasting damage.
Respirable dusts are usually invisible to the naked eye. They have particle sizes below 10 microns and are small enough to be breathed deep into the lungs. This means they can get lodged in the soft tissue of the lung’s alveoli and bronchioles. Once in this far the dust can cause serious damage ranging from reduced lung capacity to masses, chronic illnesses and even cancer.
Particles above 100 microns are not inhalable as they to large to be breathed in. These heavier particles will fall out of the air and settle on the floor and surfaces around the process. Dust extraction systems do not handle these particles, they are only effective at capturing and removing airborne inhalable and respirable dusts.
Dust clouds contain both inhalable and respirable dusts in varying degrees. Some materials (like chemical powders) will contain more respirable dust then inhalable, whereas wood dust for example, will tend to contain more inhalable dust then respirable.
How to control airborne dusts
As with all hazardous substances COSHH has specific regulations on controlling dusts in the work place and a COSHH Assessment should be carried out to identify the hazards.
- What is material the dust being created from? – i.e. saw dust, metal dusts, powders, grain dust, flour dust etc.
- How is the dust being created? (process and source)
- How much is being created?
- Who is at risk from the dust?
- How are they at risk? – is it toxic, flammable, corrosive, an irritant etc.
Once you have identified these then control measures can be implemented.
- Can you change the way the dust is created to create less?
- Can you remove the operator from the immediate area?
- Can you use less harmful materials or one that will produce less dust?
The last control is a dust control LEV system. Most dust control LEV systems use dust collector/ filter extractor units like our LS500E Dry Dust Extractor.
Process and Source
Careful consideration needs to be made when specifying a dust extraction system. In order for the LEV system to be effective the applications process and source need to be understood.
The process is how the airborne dust is created, for example, in woodworking the process is the act of cutting, sanding and so forth. The source is the point at which the process creates the dust. By understanding the process, the source can be understood and therefore effectively captured and controlled.
The strength of the source also needs to be considered, which is the speed, shape and density of the dust cloud produced by the source as well as its direction. The further the dust moves away from its source the larger the cloud grows and the harder it becomes to contain, control and extract.
Image credit HSG258: Controlling Airborne Contaminates at Work.
Capturing the Dust
Capturing the dust effectively is important as dust clouds will mix with air and disperse more, the further away they are from the source, making them harder to contain and remove and increase the risk of exposure to near by workers.
Most dust extraction systems will work by dragging the dust backwards, to the side or downwards. Hood type and placement is essential in ensuring the dust cloud is captured and removed before it reaches the operators breathing zone.
Examples of how to do this include a dust hood or canopy to contain and remove the dust as it is created. This are great for billowing dusts from applications like sack emptying or powder weighing. It could be an extraction arm with a nozzle (usually a flared or trumpet shape) placed in the line of the containment cloud jet. It could be on-tool extraction that consists of a high-pressure extractor and a hose mounted directly onto the tool to extract the dust as it is created at the source before it becomes a contaminate cloud jet. On-tool extractors are common for sanding applications where the operator and tool may move over large areas. Then there are also downdraft benches such as our range of AirBench's, these work by pulling the contaminate down through a top grille into filters before the dust can reach the operator.
For some applications that can produce large amounts of dust a dust control booth may be required. These are purpose-built extraction systems that completely enclose the operator, process equipment and application in a self-contained environment and can be referred to as process rooms, spray booths, spray rooms and more. These extraction rooms often have extraction one end and draw air across the room, dragging clean air in from one side and taking dirty air out the other.
As dust booths don’t stop the dust from entering the operators breathing zone prior to being extracted additional controls like air fed masks and filtered masks, eye protection and other PPE is required to work in the extraction room. Extraction rooms like these are ideal for applications that cover large areas like spraying or sanding vehicle body work and are often costly.
Most dusty applications create dust that can’t be extracted straight into the atmosphere. This is either because the application creates to much dust or the dust is to harmful. Virtually all dust extraction systems will have a filter of some kind in the system. This could be an inline filter such as a panel filter, pre-separator cyclone or even electrostatic scrubbers or wet scrubbers.
Commonly the filters will be part of the extraction unit itself. Most dust extractors are often referred to as a dust collector as the extraction unit usually comprises of a fan, filters, a dust collection bin and the clean air exhaust. Most dust collectors have a filter cleaning system, this can be manual or automatic and is usually a shaker type system where the filters are vibrated some how or an air cleaning system (reverse pulse jet).
We cover the different types of dust filters in more depth in our Filtered Extraction section but it is important to ensure the right type and grade of dust filters are used in the LEV system. Using the wrong type or grade of filter could result in the LEV system being ineffective and not cleaning the air properly before it is exhausted or the filters could be blinded too quickly resulting in constant cleaning and emptying and decreasing the filters life span.
One consideration that is commonly over looked is the combustibility of the dust you are extracting. We cover combustible dusts in more detail in our Combustible Dust section but it is vital you understand the dangers combustible dust can pose. It is also wrong to assume that the dust you are using is not combustible. Most dusts from Sugar and Coffee to wood and metals and plastics have a combustibility rating (ST class or Kst value) and additional factors like dust particle size, ignition sources, explosion/ fire control and others need to be considered when specifying and LEV system.
Some contaminates and applications may also fall under the Dangerous Substances and Explosive Atmosphere Regulations in which case further considerations may be needed such as the ATEX 95 and ATEX 137 directives.
Dust is not always an obvious health hazard as the majority of particles that pose the most risk are respirable and are too small to see, so we often don’t realise we are even breathing it in. The damage these dusts can cause can often take years to manifest. When it does, it is often too late and the damage can be permanent.
It is vital to understand the materials you are using, the processes and sources of hazardous dust. From cutting wood to chemical powder mixing. LEV systems need to be tailored to not only these three things but also must have the correct filtration and make allowances for the dusts combustibility.
It is also important to remember dust extraction systems are not hoovers and will only capture and remove inhalable and respirable dusts. Larger dusts particles, swarf and shavings will still drop out of the airstream and collect in the work place. Good housekeeping is also essential in controlling dust exposure.
Vodex Extraction Services
Vodex Ltd has over 30yrs experience in handling fume extraction and we offer a whole range of extraction products for fumes and vapours. We have worked in a very wide range of applications. As always if you need any further information, have any questions or just want to chat about your application or requirements then please feel free to contact us. Its really easy to do.
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