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ILLUSTRATION

DUST AND FUME EXTRACTION

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ILLUSTRATION (B)

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Dust and Fume Extraction GUIDELINES FOR THE CONTROL OF DUST AND FUMES IN THE WOODWORKING AREAS OF SCHOOLS Types of dust control systems All dust extraction units should include:

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A hood that will catch contaminants at its point source of generation,

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A duct system through which contaminated air will pass from the hood,

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An air cleaning system preventing pollution of the general atmosphere and

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A fan.

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STAND ALONE OR PORTABLE DUST EXTRACTION EQUIPMENT Stand alone and portable extraction units draw air and dust from their source of origin filtering out dust, shavings etc. before returning the air back into the local environment area. Each unit is made up of the typical elemants of a dust control system, including its own individual power source (single of three phase electric motors).

FIGURE 1

STAND ALONE PLANT Older models of dust extraction systems as shown in FIGURE 1 have the following characteristics:

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Cotton or canvas collection bags,

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Relatively a stationary unit in comparison to modern more portable types,

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Requires frequent emptying and cleaning of the dust bag and its surroundings to maintain efficiency,

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Noise emissions can be quite high due to the resonant effect of its enclosed metal cabinet and interior fan design.

FIGURE 1 clearly displays the leakage of fine to medium sized dust particles, a common feature with older type models of dust collection systems.

FIGURE 2 ‘Hour-glass’ Style Stand Alone Plant

Modern Portable Extraction System

FIGURE 2 shows the updated models of extraction systems that have differing design considerations in comparison to FIGURE 1. The unit on the left accumulates fine dust particles in the filter element while heavier particles and shavings collect in the disposable clear plastic bag forming the lower chamber.

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The filter element is cleaned by either rotating a paddle via a top mounted handle or by the external application of compressed air. The unit on the right does the same process but instead of a filter at the top and a disposable bag at the bottom, a reusable cotton/canvas bag is used. In both cases, dust is contained during the maintenance process. This unit features:

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High efficiency filtering (upper chamber) to purge air flow of particles as small as three microns in size,

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Efficient disposal or reusable collection of waste. The use of clear plastic disposable bags ensures that the cleaning or maintenance staff are not exposed to wood dusts,

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Lower noise levels emissions, lower than the levels or woodworking machinery,

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Ease of mobility of the unit enabling greater workspace flexibility,

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Easy maintenance of the filter,

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Able to service multiple machines.

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FIGURE 3 FIGURE 3 shows a system that allows for the collection of coarser waste products into a drum before the air is filtered to collect smaller particles. It should be noted that if this system is used, then a disposable bag should be used for safe handling of the wastes.

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Dust and Fume Extraction Back Advantages of stand alone systems •

Readily adaptive to changing requirements of the workshop layout whether it be the purchase of new machinery or rearrangement of machinery.

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Dust control operation directly matching operations. If only one or two lathes are in current use, only those machines are serviced.

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Compatible with air-conditioned environments. Air is returned back into the workshop environment once filtered instead of being released into the atmosphere once collected like that of the ducted system.

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There is no deterioration of the unit as it is not exposed to outdoor elements (sun, wind rain etc) unless it is not well maintained.

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Quite cost effective in comparison to the ducted system.

Disadvantages of stand alone systems

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This type of equipment does not incorporate a fume extraction function unlike the ducted system that exhausts fumes into the atmosphere. Stand alone equipment recycles filtered air into the environment.

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Unless a two stage filtering system is used as in FIGURE 3, then care must be taken to ensure that metal sparks are not drawn into the system as this could result in igniting the dust filter.

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When using multiple systems the noise level emissions generated can be quite considerable.

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These systems consume a considerable amount of workshop floor space unlike the ducted system which does not intrude noticeably into the work areas.

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DUCTED AIR AND FUME EXTRACTION EQUIPMENT Ducted systems are comprised of the basic components as that of the stand alone and portable systems ie. hood, ducting, filtering and a fan. The main function of the operation is situated on the outside of the workshop building in which air is drawn out into the atmosphere. An example of this type of system can be seen below in FIGURE 4 with the dust collection bin is circled.

FIGURE 4 Since this system performs a fume extraction function it is well suited for both woodworking and welding operations.

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Advantages of ducted systems: •

Performs both functions of dust and fume extraction,

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Due to the cooling effect of long length metal ducting, it is less susceptible to spark damage,

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Noise emission levels are lower than that of the stand alone or portable systems,

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Designed for long-term rigidity with plenty of reserve capacity to cope with heavy demand,

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Conserves vast amounts of floor space area as only the grated vents are what is visible to the eye. The main body of the system is outside the building and the ducting is in the ceiling.

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Due to the permanency of the system, superior engineering practices can be put in place.

Disadvantages of ducted systems:

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Long-term financial gain as it is a quite expensive outlay to begin with,

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More susceptible to weathering,

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Can be exposed to vandalism unless well fenced,

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Not compatible with air-conditioned workshops due to the great amounts of air that the systems draws out of the building,

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These systems have been designed to meet real demand therefore there is no capacity to reduce operations to match limited machine use. In the educational environment it may not be used as frequently.

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This system can generate high levels of noise emissions that can spread through all workshop area due to the characteristics of metal ducting.

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Due to its permanent status, there are limits to its adaptability to any changes in the workshop layout ie. the purchase of new machinery or the deployment of small portable machines (scroll saws etc).

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Dust collection bin sizes can be quite small to cope with the quantity of sawdust and shavings calling for a more frequent maintenance plan to be enforced. This can be seen in FIGURE 5.

FIGURE 5

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Dust and Fume Extraction POWER SUPPLY All portable and stand alone extractors have a mains power cable and should be plugged into a separate power point as that of the machine preferable a ceiling mounted adaptor. The user should turn on the portable or stand alone dust extraction system before the wood working plant receives power. Most modern equipment of this type uses 240 volt single-phase power. Refer to the manufacturers Users Manual for any power supply compatibility issues.

SIGNING REQUIREMENTS Dust collection areas must be properly signed indicating a dust hazard. Instructions for servicing should be clearly stated and appropriately positioned on each unit. Personal Protective Equipment requirements need to be indicated in the signage relevant to this equipment. Signing should state ‘For Authorised Use Only’ in the immediate vicinity of the machine.

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Dust and Fume Extraction ELECTRICAL TESTING OF FIXED PLANT Refer to the department’s Occupational Health, Safety and Injury Prevention Guide for the Principal or Manager Manual in sections; •

Machinery

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Electrical

It is suggested that the following processes as part of good practice, are undertaken on a programmed basis for each individual item of fixed plant: 1. Visual checking of the physical integrity of: •

Electrical cables

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Switch boxes

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Switch buttons

Evidence of overheating (e.g. discolouration, odours etc) should be investigated. Machinery locations should be dry and clean. 2. Operational Checking. All switches must operate properly. Under no circumstance should a switch e.g. emergency stop button be mounted but not connected. Particular attention should be paid to the proper function of any machinery guard switches. Qualified electricians must be employed to make repairs and written confirmation of this work must be supplied by them for your records.

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Dust and Fume Extraction TESTING Systems should be tested for adequate airflow under worst case conditions. That is, for stand alone units, when the bag is due to be changed or the filter requires cleaning. Ducted systems should be tested when all vents are fully opened. Adequate air-flows must be maintained under all circumstances.

FUME EXTRACTION Research has indicated, that some manufactured materials, specifically, some plywoods and particle boards, may under some circumstances emit formaldehyde fumes. These fumes are hazardous and should be dealt with by fume extraction machinery. It is important to note that machinery involved in the machining, sawing or sanding of the materials mentioned above should have in place appropriate dust extraction units that also function as fume extractors. This will mean that only dust extraction units that vent outdoors should be employed.

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ADMINISTRATIVE CONTROLS It is important that there should at all times be a high standard of workroom and plant cleanliness. Indications of sawdust residues around plant and machinery must be regarded as indicators of system failure and any problems rectified as a matter of urgency. Adequate supplies must be held of disposable items eg. dust collection bags. Under no circumstances are cleaning or maintenance staff to be exposed to dust particles while servicing the machines. Disposable items must not be recycled or emptied. It should however be appreciated that plastic dust bags or bin liners may in themselves be a hazard if their use is not monitored. It is strongly recommended that a portable vacuum cleaner be employed to collect any residual sawdust and chips from general workshop areas. Some timber varieties may be particularly hazardous and should be avoided if possible the table below lists some of the common timbers and the risks involved in their use. Name Alpine Ash

Possible Health Hazard Irritation to nose, eyes and throat, dermatitis

Eucalyptus delegatensis Blackbean

Irritation to nose, eyes and throat, dermatitis

Castanospermium Australe Blackwood

Irritation to nose and throat, dermatitis asthma

Acacia melanoxylon Coolibah Eucalyptus microtheca

Dermatitis

Crows Ash

Dermatitis

Flindersia Australia

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Dust and Fume Extraction Back Name Douglas Fir (Oregon)

Possible Health Hazard Irritation to nose, eyes and throat, dermatitis, nasal cancer

Pseudotsuga menziesii Ebony

Irritation to nose, eyes and throat, dermatitis

Diospyros spp European Beech

Nasal cancer, dermatitis

Fagus sylvatica European Boxwood

Irritation to nose, eyes and throat, dermatitis

Buxus sempervirens European Walnut

Irritation to nose, eyes and throat, dermatitis, nasal cancer

Juglans regia European Elm

Irritation to nose, eyes and throat, dermatitis, nasal cancer

Ulmus spp Grey Box Eucalyptus microcarpa

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Eczema, irritation to nose and throat

Dust and Fume Extraction RECOMMENDED MAINTENANCE SCHEDULE Dust and fume extraction units are not a high maintenance machine, and it is strongly suggested that a programmed maintenance schedule is developed for this equipment and that time is allocated specifically for maintenance purposes. A typical maintenance routine requires dust collection bags to be emptied daily and that they be shaken removing fine dust particles trapped within the weave of the fabric. Cleaning or maintenance staff are at risk of being exposed to frequent or unacceptable amounts of wood dust. It is therefore of utmost importance that persons wear the appropriate Personal Protective equipment for maintenance purposes. The table below is offered as a guideline. The Dust And Fume Extraction General Maintenance Schedule Maintenance Operation

Daily

Check Switch gear and examine for observable defects.

Monthly

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Check Electrical wiring for visual damage.

* * (or weekly if required)

Empty or replace full bags. Check adequate airflow of the units as may require new filter (operating correctly).

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Check work safety area/walk ways and ensure there is no concern of a trip hazard.

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Check inventory availability of spare collection bags.

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Weekly

* TABLE 1

Dust and Fume Extraction WARNINGS

WARNINGS •

Ensure adequate dust protection in use if certain timbers are being used.

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Maintenance instruction clearly stated.

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Ensure that metal is not machined near permanent stand alone systems as can create a fire hazard.

It is especially important that filters are maintained and that there is sufficient inventory of bags in place when needed. There is serious risk of side effects due to long term exposure to dust particles of various timbers when machined in woodworking plants. Dust masks should always be worn in extremely dusty conditions. This also applies to fumes from welding machines.

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HOOD OR DUST COLLECTOR DESIGN The Circular Saw (Or Table Or Bench Saw) This machine produces heavy particle-type dust, but some fines may be produced depending upon the type of timber being sawn. They nearly all have some ventilation control to accommodate saw dust waste. Hood Design Criteria 1. The minimum capture velocity: 10 metres/second. 2. Position: as shown in the diagram. 3. Exhaust volume: to match the blade diameter, (see table). 4. The hood size; determined by (1) and (3). 5. Hood entry loss*: 1.0 slot vp plus 0.25 duct vp (where vp = velocity pressure). Field Testing 1. Use accurate calibrated instruments. 2. Measure velocity at hood entrance. Capture velocity must be greater than 10 metres per second. 3. Measure velocity in ductwork. This must exceed 18 metres per second. 4. Check exhaust volume for size and saw diameter.

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TABLE, RIP, MITRE SAWS

SAW DIAMETER mm

EXHAUST VOLUME litres/second

Up to 400 inc

165

Variety with dado

260

Duct velocity = 18 metres/second Entry loss = 1.0 slot VP + 0.25 duct VP

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The Planer-jointer This machine produces a very heavy wood chip, but because of its high speed, small amounts of wood dust can be generated. Hood Design Criteria 1. The minimum capture velocity: = 10 metres/second. 2. Position: as shown in the diagram. 3. The hood exhaust volume: to match the knife length, (see table). 4. The hood size; determined by both (1) and (3). 5. The hood entry loss*: 1.0 slot vp plus 0.25 duct vp (where vp = velocity pressure). * Hood entry loss is expressed in imperial units ie; inches, water gauge, and vp (velocity pressure) = ( V ) 2 where V is the air velocity (4005) expressed in feet per minute. Field Testing Using accurate calibrated instruments, check:1. Velocity at hood entrance : must exceed 10m/second 2. Duct velocity : must exceed 18m/second Copyright © 2004.

3. Exhaust volume : appropriate for knife length.

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KNIFE LENGTH mm Up to 150 inc

165

Over 130 to 300 inc

200

Over 300 to 500 inc

260

Over 500

370

Duct velocity = 18 metres/second Entry loss = 1.0 slot VP + 0.25 duct VP

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EXHAUST VOLUME litres/second

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The Thicknesser This is similar to the planer or jointer. It produces a very heavy wood chip, but because of its high speed, small amounts of wood dust can also be produced. Hood Design Criteria 1. The minimum capture velocity: 10 metres/second. 2. Position: as shown in the diagram 3. The hood exhaust volume: to match the knife length, (see table). 4. The hood size: determined by both (1) and (3). 5. The hood entry loss: 1.0 slot vp plus 0.25 duct vp (where vp = velocity pressure). Field Testing Using accurate calibrated instruments, check:1. Hood capture velocity: must be greater than 10m/second 2. Duct velocity: must be greater than 18m/second 3. Exhaust volume: to suit knife length

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KNIFE LENGTH mm

EXHAUST VOLUME litres/second

Up to 150 inc

165

Over 150 to 300 inc

200

Over 300 to 500 inc

260

Over 500

370

Duct velocity = 18 metres/second Entry loss = 1.0 slot VP + 0.25 duct VP

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Dust and Fume Extraction Back The Band Saw This type of cutting machine can produce extremely fine particles of dust. The Hood Design Criteria 1. The minimum capture velocity: determined by hood size and exhaust volume. 2. Hood position: as shown (top and bottom). 3. Exhaust volume: as shown for various blade sizes, (see table). 4. The hood size: determined by blade width (and 1), (see table). 5. The hood entry loss: 1.75 vp in duct riser (at point A) (where vp = velocity pressure). Field Testing Using accurate calibrated instruments, check:1. Capture velocity : as per table 2. Exhaust volume : as per table 3. Duct velocity : greater than 18 m/second

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BLADE WIDTH mm BOTTOM

TOP

TOTAL

Up to 50

165

165

330

over 50 to 75

165

260

420

Over 75 to 100

260

370

640

Over 100 to 150

260

520

780

over 150 to 200

260

660

920

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EXHAUST VOLUME litres/second

Dust and Fume Extraction Back The Sander (Belt And Disc) a. Horizontal Belt Sanders These provide for extremely dusty situations and produce very fine dust. The Hood Design Criteria 1. The minimum capture velocity: determined by exhaust volume and belt width. 2. The hood position: as shown in the diagram(s). 3. The exhaust volume: to be determined by belt width, (see table). 4. The hood size: to be determined by belt width, (see table). 5. The hood entry loss: 0.4 vp (for tapered take off) (where vp = velocity pressure). Field Testing Using accurate calibrated instruments, check:1. Capture velocity : as per table 2. Exhaust volume : as per table for belt width 3. Duct velocity : greater than 18 m/second.

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BELT WIDTH mm HEAD END

TAIL END

TOTAL

Up to 150

210

165

370

over 150 to 225 inc

260

165

420

Over 225 to 350 inc

370

210

585

Over 350

520

240

780

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EXHAUST VOLUME litres/second

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b. The Disc Sander This produces dusts similar in size and characteristics as the Belt Sander. The Hood Design Criteria 1. The minimum capture velocity: determined by exhaust volume and disc diameter (see table). 2. The hood position: as shown and determined by disc size. 3. The exhaust volume: shown for disc size, (see table). 4. The hood size: determined by (1) and (3), (see table). 5. The hood entry loss: see note +. Field Testing Using accurate calibrated instruments, check:1. Capture velocity : as per table 2. Exhaust volume : as per table by disc size 3. Duct velocity : greater than 18 m/second.

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DISC DIAMETER mm

TOTAL EXHAUST VOLUME litres/second

Up to 300 inc

165

A

Over 300 to 450 inc

210

A

* Two bottom branches ** One top and two bottom branches Duct velocity = 18 metres/second + Entry loss (Depends on hood design) = 1.0 slot VP + 0.25 duct VP

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APPLIES TO DUCT

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c. The Drum Sander This produces extremely fine dust as in A and B. The Hood Design Criteria 1. The minimum capture velocity: determined by exhaust volume and drum service area (see table). 2. The hood position: as shown. 3. The exhaust volume: determined by drum surface area, (see table). 4. The hood size: decided by (1) and (3) (see table). 5. The hood entry loss: see note + = 1.78 vp plus 0.25 duct vp (where vp = velocity pressure). Field Testing Using accurate calibrated instruments, check:1. Capture velocity : as per table 2. Exhaust volume : as per table by drum surface 3. Duct velocity : greater than 18 m/second.

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DRUM SURFACE square metres

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TOTAL EXHAUST VOLUME litres/second

Up to 0.13 inc (and less than 250 mm)

165

Over 0.13 to 0.26

260

Over 0.26 to 0.45

360

Over 0.45 to 0.9

520

Over 0.9 to 1.5

660

Up to 0.13 inc (and less than 250 mm)

165

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The Wood Lathe a. Slot Control This machine can produce a variety of sawdust sizes depending on whether the operation is used for cutting or for sanding. The Hood Design Criteria 1. The minimum capture velocity: should not be less that 10 metres/second. 2. The hood position: as shown, but should be designed and positioned to move laterally, and be allowed to move towards or away from work. 3. The exhaust volume: when aspect ratio (a/b) > 5:1 Q(M3/seconds) = 4 LXVx where X is distance of work piece from hood £ 200 mm. 4. The hood size: as shown with b = 0.8 maximum work length = 600 mm. 5. The hood entry loss: 1.78 vp slot + 0.49 vp duct (where vp = velocity pressure). Field Testing Using accurate calibrated instruments, check:1. Capture velocity : greater than 10 m/second 2. Exhaust volume : as per table 3. Duct velocity : greater than 18 m/second. Copyright © 2004.

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Alternative Hood Capture for Lathe

The Hood Design Criteria 1. The minimum capture velocity: 0.75 metres/second across total face. 2. The hood position: as shown, but should be designed and positioned to move laterally, and be allowed to move towards or away from work. 3. The exhaust volume: minimum to be 165 litres/second (see table). 4. The hood size: as shown with b = 600 mm and width determined by (1) and (3). 5. The hood entry loss: 1.78 vp slot + 0.25 duct vp (where vp = velocity pressure).

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Dust and Fume Extraction Back Field Testing Using accurate calibrated instruments, check:1. Capture velocity : greater than 0.75 m/second across total face. 2. Exhaust volume : greater than 165 l/second. 3. Duct velocity : greater than 19 m/second.

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Dust and Fume Extraction GLOSSARY

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D.O.L.

This is the actual ON/OFF control switch for this machine.

Collection bags

Cotton/canvas reusable bags that are used to collect small to medium sized dust particles. Clear disposable bags are also available.

Ducting

A sheet metal pipe designed to be hidden in the ceiling allowing dust and fumes to pass through into the main extraction system.

Fan

Winged rotating device situated in the body of the system creating a vacuum of air to draw up the dust or fumes (with the ducted system) from the workshop.

Filter

A removable thin material made up of fine holes like that of a fine sieve through which the air and dust particles pass. The dust particles are trapped in the material and the air is left to circulate back into the workshop.

Collection Tube

A plastic cylinder that connects from the stand alone or portable unit to the particular machining plant through with the dust particles and shavings pass through into the collection bags.

Hood

A plastic or metal funnel shaped insert that sits near the machine tools work area and connects to the collection hose stiffening dust and shavings into the extraction system. Some machines already have a dust hood mounted on the side in which to connect the hose. Also known as a ‘dust collector’.

Dust and Fume Extraction SOURCES Department of Industrial Affairs (SA), SAFEGUARDS GS13,1997 Furnishing Training Australia, THE MANAGEMENT OF SAFETY AT WOODWORKING MACHINES, 1997 Government of New South Wales, SECONDARY SCHOOL CODE HS 580.29. TECHNOLOGY AND APPLIED STUDIES EDUCATIONAL SPECIFICATION,1994 Stanford University, TOOL AND MACHINERY SAFETY,1995 Standards Association of Australia, AUSTRALIAN STANDARD 2001 AS1473.4-2001 SAFETY AND HEALTH IN WORKROOMS OF EDUCATIONAL ESTABLISHMENTS. Department of Education and Training, EQUIPMENT SAFETY IN SCHOOLS, 2003 South Australian Government Schools Website SOUTH AUSTRALIAN DEPARTMENT OF EDUCATION AND CHILDREN’S SERVICES

www.desc.sa.gov.au

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