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Wood dust: Controlling the risks

Date posted: 5 October 2015

There are a number of health and safety risks associated with environments where wood dust is produced, and this article aims to highlight the key hazards – and offer practical suggestions as to how they might be controlled.

Fine dust poses the greatest risk, and alongside tiny particles of wood dust can also contain bacteria, as well as moss and fungal spores. Fine dust can be inhaled deeply into the lungs where it can cause the most significant damage. Fine dust also tends to travel further from the cutting area, so it is critical to clean surfaces regularly to prevent it from building up in the workshop.

Key health & safety risks

Wood dust can cause some serious, irreversible health conditions such as skin disorders; rhinitis; asthma; and a rare type of nasal cancer. Settled dust can also pose a slip and trip hazard in the workplace.

Wood dust is also flammable, with the potential to cause a fire or, rarely, even an explosion. Most wood dust fires start inside dust extraction equipment.

High risk activities

There are certain woodworking activities that produce large quantities of wood dust, including:

  • machining work such as sawing, routing and turning
  • sanding, whether by hand or by machine
  • using compressed airlines to blow dust off furniture or other objects before spray painting, etc
  • hand assembly of machined / sanded components
  • the processing of composite boards (e.g. MDF)
  • the bagging of dust from dust extraction systems
  • cleaning up once the work is finished, especially if sweeping up / using compressed airlines

The HSE advises that compressed airlines should be avoided as their use poses a high risk.

Legal considerations

Wood dust is covered by the Control of Substances Hazardous to Health Regulations (COSHH), which provides information about employers' legal requirements to protect their workers from health risks posed by hazardous substances at work.

Employers (including contractors) must undertake an appropriate and sufficient risk assessment – then take the necessary steps to prevent or adequately control exposure.

Where it is not “reasonably practicable” to prevent exposure to wood dust, control of that exposure is only deemed 'adequate' if:

  • the principles of good practice for the control of exposure are applied. This is set out in Schedule 2A to the COSHH Regulations, and includes the requirement to provide suitable personal protective equipment, such as respiratory protective equipment (RPE), combined with your other control measures, such as Local Exhaust Ventilation (LEV), if adequate control cannot be achieved;
  • any workplace exposure limit (WEL) is not exceeded. Both hardwood and softwood dusts have a WEL of 5 mg/m3. These are limits placed on the amount of dust in the air, averaged over an eight-hour working day.
  • for a substance that has the potential to cause cancer or occupational asthma (such as wood dust), exposure is reduced to as low a level as is reasonably practicable (ALARP). So even if your control measures (e.g. LEV) reduce exposure to below the WEL, but there remain improvements that could further reduce the exposure, then you should make these improvements if reasonable and practicable.

Employers must always consult their workers (or their representatives) when assessing risks and making decisions about control measures – remembering that effective communication and co-operation are vital if control measures are to be taken on board by their workforce.

Effective control of wood dust exposure

Fine wood dust gets suspended in air. Capturing the dust basically involves controlling the movement of this dust-filled air. This can be a tough job, however, because the high-speed rotating blades and cutters of most woodworking machines act like fans - creating strong air movements.

The ideal solution is to use a fixed Local Exhaust Ventilation (LEV) system to control the dust at source, as it is being produced. This contains the air movement and therefore the dust. Some LEVs are more effective than others, however – for example, many designs fail to control the dust because the hood design is wrong. Hoods need to be designed to contain, receive and control the air movements. In some instances, the hood(s) used to hold the dust are incorporated into the machine housing or guards.

Bear in mind that you may need to use RPE as a temporary safeguard to control exposure while engineering controls are being developed / modified, or to offer extra protection for short-term jobs such as cleaning up and maintenance that generate high dust levels.

To clean up, use vacuum equipment that meets a minimum of the dust class M (medium hazard) classification, and completely avoid using compressed airlines or hand brushing, particularly on clothing, as these methods create dust clouds and simply redistribute the dust.

LEV requirements

As well as capturing the fine wood dust, the LEV design also needs to remove larger/heavier chips and shavings.

In the woodworking industry the LEV often extracts from different combinations of machines at different times, so the airflows through the hoods are not fixed – meaning the LEV system cannot be ‘balanced’. The balancing process involves getting the required airflow to control the wood-dust cloud at each hood in the system after initial installation, and is achieved by establishing the various airflows in each branch, hood resistance, etc.

Having a single fan and filter system that supplies suction to a number of machines means that:

  • The system needs to be designed to operate the maximum number of machines that will be used at any one time, so you will need to know the maximum number of hoods that the fan can extract from and still manage to control the dust. Help management of the system to ensure the number is not exceeded by clearly displaying a plan in the workplace that shows which combinations of hoods can be open.
  • You need to open and close dampers as required to ensure there is the correct volume flow rate (VFR) at the machines in use. It is possible to do this automatically but usually depends on the operator doing it manually. The easiest way to monitor whether the dampers are in the right position, and that the airflow is correct, is to fit airflow indicators to the hoods.

Employers (and contractors) should also read “INDG 408 Clearing the air: A simple guide to buying and using local exhaust ventilation (LEV)”.

The basics of LEVs

  • Aim to have an LEV system that is effective yet straightforward, robust and demands minimum maintenance.
  • You can check whether it is effective by using either a dust lamp or a smoke generator (see below ‘Testing whether your LEV controls are working’).
  • Ducts need inspection doors to enable you to check for (and clear) any blockages.
  • The design should be able to supply the correct VFRs, which will vary according to the type of woodworking machine -- but must be high enough to keep the dusty air within the hood and then take the dust / chippings away through the ducting to the filter.
  • Ductwork needs to be large enough in diameter to allow the correct VFR to be maintained, but not too large that it reduces the air transport velocity to below that required to effectively transport wood dust / chippings. Get advice on this from a competent LEV engineer.
  • Train a responsible worker to effectively manage your LEV controls to maintain optimum system performance, referring to a comprehensive user manual that covers the entire LEV system (either from your supplier, or created by yourself).

The design of the hood(s)

The hood is key to successful control of wood dust. Invest time in ensuring that the hood design is correct, bearing in mind that:

  • Most machines require more than one LEV hood.
  • The LEV hoods must be designed to enclose and receive the air movement produced by the woodworking machine's moving parts.
  • The hoods should be as close as possible to the source, and positioned so that they receive the dust-laden air stream. The more you can enclose the source, the better you will control the dust -- and this will demand lower VFR, ensuring a lower running cost.
  • Match the hood volume airflow to the airflow created by the woodworking process. If you get the right hood and achieve the right extraction airflow you will also achieve effective control.
  • If the process you are trying to control is outside of the LEV hood, and the hood airflow therefore has to reach out and capture the dusty air, do not expect more than is realistic about the ‘reach’ of these hoods.
  • Poorly-designed hood and duct connections can cause a blockage of splinters and shavings.

The design of the duct

You want to achieve smooth airflow through the ductwork – to limit wasted energy and reduce noise. To do this, avoid tight bends; take extra care at duct junctions; and avoid lengthy sections and numerous bends.

Only modify your original extraction system (e.g. by adding extensions) if the impact of this on the whole system has been adequately assessed by a competent person.

Bear in mind that the LEV system will then usually need to be recommissioned to be sure that control of the dust is still effective and to establish a new set of performance parameters to use at the ‘thorough examination and test’. BS EN 12779 recommends allowing lengths of flexible ducting to be longer than 0.5 metres only if it is vital to accommodate the movement of the woodworking machine. Apart from the fact that flexible ducting costs more than rigid sheet metal ducting, it is best to keep it to a minimum wherever possible because:

  • it is easily damaged / blocked
  • it increases the resistance to airflow, therefore reducing the system’s efficiency and costing more to run.

Flexible ducting also needs to be earthed – to avoid the risk of static build-up. You can do this by creating a connection from the flexible ducting’s metal helix to the adjacent rigid metal ducting.

The right type of fans and air cleaners

When choosing a fan, consider the following key factors:

  • The fan needs to be capable of delivering the total airflow necessary for the maximum number of machines that you might use at any one time.
  • The overall resistance of the system (influenced by junctions, bends, and so forth); how much noise it will generate; and any space limitations. If you can place fans and air movers outside the workroom this will reduce noise impact and will also keep ductwork within the workspace under negative pressure – and any leakage inwards.
  • If you are extracting larger volumes of wood waste, a settlement vessel / cyclone before the air is presented to the air filters will reduce the burden on filters and ensure filter bags last for longer.
  • Look into recycling options for wood waste, such as using it to heat your workshop or sell on to a recycling firm.
  • To avoid risk of fires / explosions, ensure air cleaners are designed and positioned with this potential hazard in mind – preferably outside, away from walkways and work spaces. Wherever it is necessary enclose the units and fit them with suitable explosion relief, which will vent to a safe area in the event of an explosion.  In some scenarios it may be cost-effective to install a fire spark detection system.

Testing whether your LEV controls are working

Dust lamps

Cheap yet highly effective when used properly, a dust lamp is a handy tool for identifying dust leaks and other problems, and checking whether your extraction system is working effectively.

Wood dust would not normally be visible to the naked eye, but is with this lamp. Fixed onto a tripod, the lamp is then pointed towards the area where you want to check for a dust cloud. Turn off other lighting to get the best view. Set the lamp to its ‘on’ position, then shift around so you can look back up the beam of light, at a slight angle – using a book or board to shield your eyes from the main beam, and recording what you see with a video or camera.

Smoke generators

As the name suggests, these devices produce variable amounts of smoke (for prolonged periods of time) enabling you to make air movements visible. Smoke tests need to be undertaken with the woodworking process running. This means you can simulate wood dust clouds in terms of size, velocity and behaviour, confirm that the dust is being contained within a hood; and spot any draughts / air currents that need resolving.

Checking and maintenance

It is a legal requirement to regularly check and maintain the health of your LEV system (COSHH regulation 9). Always follow the instructions in the user manual, which should include regular ductwork / hood checks to ensure there are no blockages or signs of damage; filter checks and cleaning as required.

Read 'INDG 408 Clearing the air: A simple guide to buying and using local exhaust ventilation (LEV)' for further details.

Airflow checks

Ensure you have procedures in place to check the correct VFR is entering the hood(s), such as making sure the VFR has not been reduced due to a blockage, or an incorrectly closed damper that needs to be opened.

The HSE advises fitting airflow indicators to offer you a clear and continuous way of checking that the VFR is correct and that the hood is working as it ought to. This is vital for unbalanced LEV systems, e.g. those used in woodworking, where the operator has to
regularly adjust dampers manually as machines are in and out of operation.

More time-consuming alternatives for monitoring air velocity include using an airflow meter, or visually checking the effectiveness using a dust lamp / smoke generator – but these also tend to work out more expensive in the long run.

Some LEV system suppliers now include airflow indicators with new installations, or can retro-fit them to older, existing systems – although these will then need a recommissioning test.

 

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