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Wood Dust Fire and Explosion

Wood Dust Fire and Explosion

What are the fire and explosion hazards of wood dust?

Wood dust is considered to be explosive if ignition of part of a cloud of wood dust results in the propagation of flame through the rest of the cloud. The burning of an unconfined wood dust cloud produces a flash fire. However, if the wood dust is contained within a full or partial enclosure, the pressure build-up can produce a destructive explosion. Its severity will depend on a number of factors, generally, the larger the volume of the exploding dust cloud, the more widespread its effects will be.

It is important to ensure that wood dust does not escape from collection systems and be allowed to build up within workrooms. If dust does accumulate, any primary explosion which occurs in a collection unit may stir up dust deposits within the building which houses the plant. Burning particles from the primary explosion can ignite the dust cloud resulting from it, leading to a secondary explosion that is usually more destructive than the first.

The explosibility of wood dust

You should assume that all wood dust is potentially explosive. . Wood waste usually has a dust explosion risk where the mean particle size is less than 200 microns, and where as little as 10% of the mixture contains dust less than 80 microns in size.

Explosive Wood dust is commonly produced by:

  • fine cutting (eg sanding) – which produces a dust of very fine particle size;
  • sawing and machining hardwoods – often producing wood waste containing considerably
  • more dust than that from softwood;
  • the processing of MDF, chipboard and similar boards by machining and sawing – which can be expected to produce waste containing much fine dust;
  • profiling and moulding components on routers, spindle moulders etc.

Sources of ignition for wood dust

Common ignition sources include naked flames, faulty or unsuitable electrics and impact sparks.

The sanding or hogging of off-cuts containing metal may produce friction sparks, which can cause sawdust to smoulder and subsequently be fanned into fires or explosions. Use dedicated collection systems for these operations. Consider spark detection and extinguishing devices where there are significant risks.

Hot work involving the careless use of welding or flame-cutting equipment has resulted in many incidents. To prevent this, plant should be isolated and thoroughly cleaned before work starts. Use cold cutting methods whenever possible.

Electrical equipment should be sited away from dusty areas. If this is not practicable, ensure it is adequately protected.

Collection systems for wood dust

There are three main types of system for collecting wood waste:

  • One or more woodworking machines are exhaust ventilated to a nearby collection unit within the workshop which does not form part of any other exhaust ventilation system.
  • Many (perhaps all) of the woodworking machines are ventilated to a collection unit, which can be some distance from the machines and may be inside or outside the workshop (see Figure 1).
  • One or more woodworking machines are exhaust ventilated to a nearby collection unit. These units deliver the wood waste into a larger collection unit, usually outside the workshop. This is known as a ‘through flow’ system.

Ductwork for wood dust

Make ductwork as short as possible with a minimum number of bends. The design should specify a minimum transport (or conveying) velocity of 20 m/s to minimise dust deposits. Use only conductive materials for ductwork so that any static electricity generated can be discharged to earth. Ductwork needs to be regularly inspected internally and cleaned to prevent any accumulation of dust. Suitable access points/hatches should be provided for this.

Collection units for wood dust

There are a number of different kinds of collection unit and the main types are:

  • unenclosed fabric filter sock collector;
  • unenclosed fabric multi-sock collector (see Figure 1);
  • enclosed fabric single-sock collector;
  • enclosed fabric multi-sock collector;
  • cyclone; and
  • bin or hopper.

Precautions for collection units where there is a risk of dust explosion

Collection units should normally be sited outside, away from areas where there may be people. If units have to be indoors, precautions will depend on the size of the collector; the size and construction of the room it is in; the number of people nearby; and how near they are to walkways and combustible materials.

To avoid the risk from secondary explosion or fire, it is essential to enforce good housekeeping practices to prevent the accumulation of wood dust within the building, eg a formal cleaning regime using appropriate vacuums fitted with HEPA-type filters.

Sock collectors (<0.5 m3/s capacity)

Unenclosed sock collectors would quickly disintegrate if the contents were ignited, but would not produce high explosion pressures or widespread effects. Fire risks may exist so, if unenclosed, do not position them within 3 m of workers, combustible materials or walkways. Alternatively, provide a suitable baffle or deflector plate or enclosure (see below). Enclosed sock collectors should discharge at the top to a safe place i.e. above head height.

Sock collectors (0.5–2.5 m3/s capacity)

Ignition of wood dust can lead to a jet of flame at head height, but an explosion is not likely. Where such collectors must remain within the workroom, provide one of the following precautions:

  • Total enclosure within a strong metal cabinet with either an air outlet large enough in area to act as explosion relief or explosion vents. Outlets or vents should preferably discharge to a safe place outside the workroom or, if inside, discharge at least above head height.
  • A baffle or deflector plate made of non-combustible material to direct flames or burning material to a safe place.
  • Ensure the fan can be turned off from a safe place if a fire starts in the filter. A 3 m separation between the filter and regularly occupied locations is likely to be adequate to protect employees.

Sock collectors (>2.5 m3/s capacity)

Site these outside or enclose them in a strong cabinet fitted with explosion vents that discharge to a safe place.

Cyclones for wood dust

Well-made cyclones of less than 0.5 m3/s volume (rare in woodworking) do not usually require explosion relief panels. Larger low-efficiency cyclones usually have large enough air outlets to act as an explosion vent, but the need for additional explosion venting should be assessed. Larger high-efficiency cyclones do not usually have large enough air outlets to act as effective explosion vents and so additional venting will be necessary. Where cyclone air outlets discharge to an after filter, both the cyclone and the after filter will need explosion-relief panels.

Bins or hoppers for wood dust

Where used to store explosible wood waste, these will require explosion relief appropriate to their volume. They should preferably be outdoors but, if indoors, additional explosion relief may be required on the building itself. There should also be a safe system of work for emptying bins and hoppers.

Interconnected plant for wood dust

Take precautions to prevent an explosion spreading between interconnected units of plant, such as collectors, cyclones, filters and incinerators. Collectors should discharge their collected wood waste through an explosion choke, eg a rotary valve, or directly into strong metal containers clamped firmly to the discharge outlets.

Sizing of explosion relief for wood dust

The simplest and most common method of protecting process plant against the consequences of a dust explosion inside it is to provide some deliberate weakness in the structure in the form of explosion relief vents. Suitably sized and sited vents will ensure any explosion within the plant will be vented safely.

Fire fighting

Consider installing a dry sprinkler system and a C-coupling for attachment to a fire-brigade hose (on new plant). Make sure access doors on silos are big enough to allow access for fire fighting. Use gently applied water (eg a spray or mist), not jets to extinguish fire, to minimise the disturbance of burning wood waste

Additional precautions for wood dust explosions

Users should take the following practical precautions to minimise fire and explosion risks:

Ensure there is a preventive maintenance regime for the entire collection system

  • Leave the fan running for some time after the machines have been turned off to ensure the ducts are empty when the air flow stops, and minimise dust fall-out in the ducting.
  • Keep the system dust-tight.
  • Replace seals, gaskets and covers as necessary.
  • Empty containers associated with filters regularly.
  • Take care to prevent metal objects entering the collection system.
  • Smouldering fires often precede explosions – if a fire is suspected, stop the air flow through the collection system before investigating the problem.

For detailed advice on assessment and specific control measures for your workplace contact our consultants.

For further information on workplace monitoring, testing and assessment click here.

Haztek: Servicing Sunshine Coast, Brisbane, Gold Coast and Regional Queensland

Wood Dust Exposure

Wood dust

What you need to know aboout wood dust exposure

Wood dust can cause serious health problems. It can cause asthma,  carpenters and joiners are four times more likely to get asthma compared with other workers. Work Health and Safety Legislation require that you protect workers from the hazards of wood dust.

Hardwood dust can cause cancer, particularly of the nose.

Settled dust contains the fine particles that are most likely to damage the lungs.

What you need to do to control wood dust exposure

Exposure limits for wood dust

Safework Australia have set exposure standards for hardwood (1mg/m3) and softwood (5mg/m3), these exposure standards must not be exceeded. These are limits placed on the amount of dust in the air, averaged over an eight-hour working day. However, you must reduce exposure to wood dust to as low as ‘reasonably practicable’.

Implement Control Measures for wood dust

Extraction for wood dust

Provide dust extraction (also known as local exhaust ventilation or LEV) at woodworking machines to capture and remove dust before it can spread.

Design the extraction system to take into account:

  • the number and type of machines to be connected to it, the ones that are used together and the layout of the workshop or factory. This information should be supplied by the user.
  • the machine manufacturer’s information or an experienced body’s information on required air flow and extraction vacuum for each extraction connection for each machine.

Educate workers about the risks from wood dust and the control measures required. They should know how to use the extraction properly. Fitting air flow indicators will help, as these will show them if it is working correctly, for example if dampers are open or shut and also if maintenance is required.

Keep the extraction system properly maintained and working correctly (it is a legal requirement to have it examined every year). Follow the extraction manufacturer’s guidance for maintenance requirements.

Sweeping Wood Dust and Compressed Air

Never sweep up or use compressed air lines as this will disturb the dust and allow it to become inhaled. Always clean up using a suitable vacuum cleaner with HEPA filters, or a vacuum attached to the extraction system.

Respiratory Protection for wood dust

For very dusty jobs such as sanding, additional protection may be needed and a suitable face mask should be worn as well as using the extraction.

Where you need to use RPE you should:

  • select the right mask and cartridge
  • ensure it fits properly by having it face fitted, and by being clean shaven
  • look after it / change it regularly in accordance with the manufacturers’ instructions

Health surveillance for wood workers

Because wood dust causes asthma any health effects must be picked up early. This can be done using health surveillance].

For most woods, low level health surveillance will do. When someone first starts in a job where they are exposed to wood dust they should fill in a questionnaire.

After six weeks they should then complete a follow up questionnaire and this should then be repeated every year.

These questionnaires tell you what to do if you think someone has been affected.

A higher level of health surveillance, including lung function testing, is needed for exposures to woods such as western red cedar which are a known asthma causing agent.

 For detailed advice on assessment and specific control measures for your workplace contact our consultants.

For further information on workplace monitoring, testing and assessment click here.

Haztek: Servicing Sunshine Coast, Brisbane, Gold Coast and Regional Queensland


A Strategy for Assessing and Managing Occupational Exposures

A Strategy for Assessing and Managing Occupational Exposures

Introduction to Assessing and Managing Occupational Exposures

In Australia we have a legal requirement to protect all who work on or visit our sites or premises from occupational illness or injury. To maintain competiveness in a global economy it is essential that this is achieved through an effective and efficient program. Prior to developing workplace monitoring or health surveillance programs a comprehensive understanding of workplace exposures is required to ensure appropriate cost-effective programs are developed.

Many people carry out risk assessment on a day-to-day basis during the course of their work. They note changes in working practices, they recognise unsafe working conditions and practices, and often they take appropriate corrective action. However risk assessments need to be conducted systematically to deliver real and lasting benefits to worker health.

The American Industrial Hygiene Association (AIHA) Strategies for Assessing and Managing Occupational Exposures prescribes a methodology which when adopted provides a systematic and cost-effective program for assessing workplace exposures. This program has been adopted for use in the Australian work environment through the Australian Institute of Occupational Hygienist (AIOH) Simplified Occupational Hygiene Risk Management Strategies Guidelines.  The guideline has been developed to meet Safework Australia’s requirements and will assist in achieving compliance with the Model Work Health & Safety Laws which will be enacted early 2012.

Occupational Health Hazard Identification

Health hazard identification is the first step to develop an occupational hygiene program. This process will develop a list of the stressors that the workforce is potentially exposed to. These will be under the categories of Chemical (Solvents, Pesticides), Physical (Vibration, Heat, Noise), Biological (Mould) and Ergonomic. The health hazard identification needs to be conducted in consultation with operational staff, the process usually involves:

  • A review of the materials/chemicals and their material safety data sheets (MSDS);
  • A review of the process, including exposure scenarios e.g. the tracking of trace amounts of highly toxic substances;
  • A walk-through survey, and consultation with operational personnel regarding processes, equipment, materials used, physical environment, products / by-products, etc;
  • A review of documented monitoring or information from similar types of assessments;
  • A review of reported incidents.

Establishing Similar Exposure Groups for Occupational Health Hazards

The next step is to establish Similar Exposure Groups. A Similar Exposure Group (SEG) is a group of people having the same general exposure profiles because of the similarity and frequency of the tasks they perform and materials and process with which they work. A properly defined SEG provides the ability to use data from a relatively small sample of the exposure population to predict the likely chronic health exposures of the group as a whole.

Risk Assessment for Health Hazards

Assessments involve qualitative and semi-quantitative risk assessments that are performed to identify potential exposures that require inclusion in the monitoring program. This is a risk management process to establish the priority exposures for further review and uses surrogate data, modelling and the judgment of the hygienist, engineers, managers and operators. Resources for health surveillance and workplace monitoring can then be focused on the priority areas where further information is required to define exposures.

Health Surveillance

Health surveillance, of a person, means monitoring the person to identify changes in the person’s health status because of exposure to a hazardous chemical.

The Workplace Chemicals Model Regulations require that health surveillance be conducted when:

  • there is a significant risk to the health of a worker arising from exposure to a hazardous chemical listed at Schedule 3; or
  • a risk assessment identifies a significant risk to the health of a worker arising from exposure to any hazardous chemical and there are valid techniques for detecting indications of the health effect; or
  • a valid method for determining biological exposure exists for a hazardous chemical and there is uncertainty, based on reasonable grounds, as to whether a safe level may be exceeded.

The Model Work Health and Safety Regulations provide specific requirements for health surveillance for workers conducting specified lead work or certain asbestos removal or maintenance work.

Blanket heath surveillance programs (full health surveillance for all workers) are extremely expensive. They disrupt workforce scheduling and create unnecessary anxiety with the workforce (why am I getting health surveillance for asbestos when I have been told that I do not work with asbestos containing material).

Systematic hazard identification and risk assessment to determine occupational exposure profiles assists with focussing health surveillance on the groups where a need has been identified.

Workplace Monitoring

Monitoring means to survey regularly all measures which are used to control hazardous chemicals in the workplace. This includes the monitoring of atmospheric contaminants, but does not include biological monitoring which is an element of health surveillance.

The Workplace Chemicals Model Regulations require that monitoring is undertaken to determine the concentrations of hazardous chemicals in the workplace when:

  • there is uncertainty, based on reasonable grounds, as to whether an exposure standard may be exceeded or;
  • monitoring is necessary to determine whether there is a risk to health.

Blanket monitoring programs are extremely expensive and can disrupt workforce scheduling.

Systematic hazard identification and risk assessment to determine occupational exposure profiles assists with focussing monitoring programs on the groups where a need has been identified.

Our Experience ?Assessing and Managing Occupational Exposures

Our principal consultant, Maurice Barnes, has professional qualifications in Science, Occupational Health and Safety and Occupational Hygiene and is a Chartered Profession Member of the Safety Institute of Australia and a Member of the Australian Institute of Occupational Hygienist. Maurice has over 15 years experience in the field of occupational health and safety including experience conducting audits and risk assessments for waste and treatment facilities including sewerage treatment plants.

Recent projects completed by our principal consultant include:

Conduct health hazard identification and risk assessment and develop health surveillance and monitoring programs for Australian Navy Ships and Submarines. This project was completed on behalf of the Defence Centre of Occupational Health under direction from the Defence Minister.

Assistance to regional councils in the conduct of risk assessments and development of work method statements for their waste water and treatment facilities including the sewerage treatment plant.

Conduct of detailed risk analysis and personnel exposure monitoring for maintenance personnel exposure to contaminated soil and water during site remediation work.

Some Benefits of implementing a Strategy for Assessing and Managing Occupational Exposures

Cost Savings for Health Surveillance Program

Without systematic hazard identification and risk assessment a blanket health surveillance program is often implemented.  Through implementing a strategy for assessing and managing hazards a targeted health surveillance program can be adopted. The below table shows estimated costs of a blanket health surveillance program compared to a targeted approach for a workforce with 500 operational people.

Type of Assessment Full Assessment Partial Assessment Minimal Assessment Total Cost / Year
Cost of Assessment $600 $400 $200  
Blanket Health Surveillance Program 500 employees - - $300,000
Targeted Health Surveillance Program 100 employees 200 employees 200 employees $110,000

The cost of a health surveillance program is not necessarily a new cost for organisations, in many cases health surveillance is already conducted i.e. medical checks for all workers who conduct confined space entry and hearing assessments. Adopting a systematic strategy is about integrating and targeting resources so that they are effective and compliance is achieved.

Cost Saving of Workplace Monitoring Program

Similar savings can be made in workplace monitoring programs. This is harder to quantify as we don’t yet know what monitoring is required. In a lot of situations using this assessment methodology allows risk assessments to be conducted using surrogate data (exposure data from other workplaces) and modelling, again providing significant savings. In some situations surrogate data and modelling is more reliable and provides stronger evidence of the exposure profile as it draws from large assessment programs that an individual organisation could not resource.


The cost savings in health surveillance and workplace monitoring are advantages of adopting this strategy but they are not the main benefit. A thorough understanding of exposures allows the occupational hygiene program, including control efforts, to be prioritised to protect employees and manage exposure related risks.  It also puts the organisation in position to manage the unpredictable changes that will occur both in knowledge of health-effects of environmental agents and in society’s tolerance of workplace exposures.

Development of a comprehensive exposure assessment program is encouraged because a comprehensive program is the best way for organisations to understand and manage the ever-broadening realm of occupational health related risks.

For detailed advice on assessment and specific control measures for your workplace contact our consultants.

For further information on occupational health and hygiene hazards click here.

Haztek: Servicing Sunshine Coast, Brisbane, Gold Coast and Regional Queensland