Thread: Interesting video from UK Govt re wood dust control

Oh dear, the usual misconceptions appearing again.

The idea that am incandescent lamp will provide any measure of fine dust is foolish as the really fine dust will be invisible to such a lamp .
Something like a laser is needed to see the reflections from fine dust.

The concept of increasing the ducting size alone, without increasing the size of the dust port, is plain wrong.

Overheadguard.jpg


Overheadguard2.jpg
There will be next to no increase in flow because of the bottleneck on the saw guard.
This is demonstrated by the poor air flow rates obtained below.

The next one is this hood
The claim is the second hood is better.
There's nothing wrong with the design of the old hood - the flared design is far superior to the second one but is is somewhat poorly fitted as it should go right underneath the blade
Dustcollection.jpg

It is totally beyond me why they claim this is better
Firstly it uses a much smaller port (it looks like a 4"port) and the grille over the top will be struggling for it to draw 400 CFM
DustcollectionBox.jpg


Now here are the flow rates after the modifications.
It would have been interesting to know the flow rates before the modifications
Dustlevels.jpg
130 m3/hr is about 75 cfm , and If the air flow was done using industry standards which are incorrect, the real rates would be less again, and consistent with the throttled overhead guard.
The 800 m3/hr under the table = 466 cfm, which will also be incorrect so expect something like 300 cfm which is again consistent with the chocked down enclosure.
I would expect a lot more givem the 6" ducting in use in that workshop.

The 5mg/m3 level is the old UK Standard for softwoods.
Aussie hardwoods require and OHS level of 1 mg/m3 and even this is not based on any sort of medical research (we just copy the UK standards).
The mg/m3 dust levels are only a rough guide to the problem as they take ZERO consideration of particle sizes into account.

If the fine dust is taken into account much greater air flows are needed to reduce the fine dust.
I recommend a real 800 CFM on the cabinet and at least a real 200 CFM on the overhead guard.

So Bob how do we get the regulators to get it right? If they can't, then the advice they give misleads a lot of people.

I am struggling to find better solutions for my small Woodfast TS250. I have improved it over what was supplied but I'm far from satisfied with the dust collection. A lot of my cuts on the TS are cross cuts of small work so I have been trialing an inverted U shaped perspex guard that attaches to the off side of the fence, covers the blade and a substantial area of the table and is about 280 mm wide by approx 90 mm high with a standard 4" dust chute (Carbatec M134) on the out feed side of the blade. I draws a large volume of air from the in feed side and vastly improves dust collection but it is only suitable for that particular task.

Next step is to improve under table collection because the standard setup is woeful. I'm actually considering discarding the current setup, making the whole cabinet the collection box and attempting to introduce cross flow across the blade, i.e. inlet one side, preferably the in feed side, with a central outlet to the DE centered and below the cl of the saw blade to take advantage of the down draft the saw itself creates.

Calm down Bob and have a think about what this video is trying to achieve.

The UK HSE exposure limit advice is

Both hardwood and softwood dusts have a Workplace Exposure Limit (WEL) of 5mg/m3 which 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’.

This video is about demonstrating what is "reasonably practicable" it's not about demonstrating what is "possible" or what is "possible at reasonable expense". There is a world of difference between the two, and I believe Australian standards are based on "possible at reasonable expense".


in that light ...

1. The "dust" light is not about detecting all the fine dust particles, it's about demonstrating that a saw generates a cloud of dust in front of the blade guard. The emphasis in the video is on the dust lamp being a "simple" "cheap" "readily available" "powerful tool" which I'm sure is intended to encourage the audience to go out and buy one to "illuminate" the dust cloud generated by the saw in their own workshop.

2. Increasing the size of the hose connected to the blade guard should, at least in theory, reduce the internal friction (and hence pressure loss) and thus lead to increased ability to collect dust through the guard. Remember the video makers are trying to get the dust exposure level for the operator below 5mg/cu.m. This they achieve. The fact that the 2mg/cu.m achieved following the mods is twice the 1mg/cu.m standard for Aussie hardwoods is not relevant in the UK HSE context.

3. The intended take home message is: buy a dust lamp and use it to see the cloud of dust your saw produces; modify the saw's dust collection till the dust cloud either disappears, or is greatly reduced. Doing these things constitutes adopting a "reasonably practicable" approach to dust control.


However, I too have doubts about the dust hood -- apart from the grill, there appears to be no consideration of supplying "cleanish" ambient air to the motor to keep it cool.

Originally Posted by Lappa

Found this link from a UK Govt site on wood dust control.

Interesting.

How to improve dust control at circular saw benches - YouTube

what I found interesting was the cloud of dust in front of the blade, which seems to be associated with the gap in the blade guard in line with the blade.
I wonder if closing that gap and opening up the rear of the guard would provide improved collection -- all else with the guard remaining unchanged.

the protocol with the panel saws at Tech was to leave a 10mm gap between the overhead guard and the work piece, providing a space for make-up air to enter the guard.

http://www.hse.gov.uk/lev/common-processes.htmHow to improve dust control at circular saw benches - YouTube

Looking at this from both sides I can see exactly where Bob and Ian are coming from. Anything simple, like the light, that can make people think about dust for even once in their life has to be a good starting point.

My reason for replying though is another annoyance with that Bench saw Video.

When the first "before" readings of dust levels are taken through the operators dust mask, he is very close to the blade, bends slightly forward and leans slightly into the line of the blade to maximize the dust pickup readings.

In the "after" readings, a different timber is used and is orientated differently, therefore the operator is now some distance from the blade, stays very upright and leans slightly away from the blade as he completes the cut. I may appear to be nit picking, but that type of inconstancy (intentional or otherwise) always annoys me.

EDIT

This is also of interest as it shows a few things that BobL and others have mentioned before about dust on clothing, bad cleaning out practices, etc.

Local exhaust ventilation systems (LEV) - Common processes and sources


Forgot to thank Lappa for posting the Link.

Originally Posted by Mobyturns

So Bob how do we get the regulators to get it right? If they can't, then the advice they give misleads a lot of people.

Once a law or reg is set regulators will hide behind it until sufficient people are affected. Unfortunately I don't reckon there will ever be sufficient people affected by wood dust as so many cancers and wood dust related illnesses are masked by other problems. My main concern is not cancers but allergies preventing people continuing to work with wood and this the regulators don't give a cuss about.

The 1 and 5mg/m3 levels are not backed by any sort of comprehensive health related study or research, especially for Australian timbers on which nothing has been done. All the authorities know is that less wood dust means less health related trouble, but the dust levels themselves are set at what they are because that is all established dust control practices and dust extraction equipment could achieve in the 1980s when the Australian Standard was set.

What is disturbing to me the difference between the exposure limit set for ORDINARY dust for members of the public and what woodworkers are allowed to be exposed to.

BP sent me the following info for ordinary dust , and BTW ppm ~ mg/m^3.
European Standard is 0.1 ppm for fine (PM10 particles less than 10 microns) airborne dust
Environment Canada's acceptable air quality has a limit of fine particulate matter of 0.03 ppm (PM10 - particles less than 10 microns)
The US EPA is 0.15 ppm (PM10) ,0.035 ppm (PM2.5) [24 hours] and 0.01 ppm across 1 year.

These levels reflect the coverage needed for young, and (more importantly for us) older persons with reduced lung capacity.
However, if wood dust is supposed to lead to more problems than ordinary dust then wood dust levels should be lower and not higher than ordinary dust.
Anyway enough ranting about this as I prefer to finding practical solutions and improvements that are backed by measurements.

I am struggling to find better solutions for my small Woodfast TS250. I have improved it over what was supplied but I'm far from satisfied with the dust collection. A lot of my cuts on the TS are cross cuts of small work so I have been trialing an inverted U shaped perspex guard that attaches to the off side of the fence, covers the blade and a substantial area of the table and is about 280 mm wide by approx 90 mm high with a standard 4" dust chute (Carbatec M134) on the out feed side of the blade. I draws a large volume of air from the in feed side and vastly improves dust collection but it is only suitable for that particular task.

There are many good examples of overhead guards in this forum. Also take a look at what I way above about dust guards.

Next step is to improve under table collection because the standard setup is woeful. I'm actually considering discarding the current setup, making the whole cabinet the collection box and attempting to introduce cross flow across the blade, i.e. inlet one side, preferably the in feed side, with a central outlet to the DE centered and below the cl of the saw blade to take advantage of the down draft the saw itself creates.

Yep that's the way to go and is sort of what I did on my TS

Dust levels are measured through a device strapped to his chest, not his mask.

Originally Posted by BobL

Oh dear, the usual misconceptions appearing again.

The idea that am incandescent lamp will provide any measure of fine dust is foolish as the really fine dust will be invisible to such a lamp .
Something like a laser is needed to see the reflections from fine dust.
.

This article would appear to dispute this statement.

http://www.hse.gov.uk/pubns/mdhs/pdfs/mdhs82-2.pdf

Originally Posted by Lappa

Dust levels are measured through a device strapped to his chest, not his mask.

True, but it does not make any difference to my concerns about the results. I wanted to get a rough idea of the difference the added DE or DE modification made to the indicated air quality, to me the video is invalid on that count as the conditions are not the same and therefore not showing the true result, they are distorted by the completely different operator position.


This is not an attack on what is being presented here, it just annoys me that this happens all too often in many videos on many important subjects.


Perhaps it's just me, others may not be as interested in what actual near identical measuring conditions may have shown.

I see your point. In the first instance he is sawing a narrow board and is closer to the blade line and in the second instance he is sawing a wide board and is standing away from the blade line. His vertical stand In both instances is similar.
Good pick-up

Originally Posted by Lappa

This article would appear to dispute this statement.

http://www.hse.gov.uk/pubns/mdhs/pdfs/mdhs82-2.pdf

The dust lamp will indeed indicate if there is some dust there that would otherwise be difficult to see but no information about numbers, or sizes, of the particles can be extracted from such a setup.
The ambient light must be minimised, direct light from the lamp blocked out, and an optimised angle between light and dust source be maintained.
The recommended angle strongly preferences the bigger particles because they also produce the most intense twinkling or light output.
Comparative results can be obtained using a sensitive photometer (light intensity meter) but all this will measure is mainly large dust particles

However, the angle recommend for viewing the bigger particles is not the best angle to see the smaller particles - in fact it is the worst angle because the reflections from the bigger particles dominates the view.
To see the smaller particles the reflections from the bigger particles have to be blocked by baffles and sensors placed at different angles away from the angle used to view the bigger particles.
The further away from that angle the lower will be the scattered light intensity, so much so that it may drop below the ability of the human eye and even basic photometers to see but that does not mean there is nothing there. The fine dust tends to make more of a dull fog than definitive twinkles which is harder for the eye to see.

Lots of what Ive said above is mentioned in some form or other in that article.

A multichannel particle detector passes a small stream of dusty air into a small chamber illuminated by an intense light so that the air and dust passes by an array of baffled small photo sensors placed at different angles around the light beam.
The different angles correspond to a particle size range.
Because the light intensity drops off as a function of angle (and particle size) and distance a very intense non-divergent light source like a laser is used.
A laser will make even fine dust twinkle to register as a pulse by a sensor while minimising the effect of ambient light
The photosensors also have to be very sensitive and their outputs still have to have to be amplified and filtered.
When thousands or tens of thousands of twinkles are being detected per second the electronics has to be very fast to count the pulses.
Before use the sensors have to be carefully calibrated with known particle sizes.
That's why multichannel particle detectors cost so much.

The dust lamp is better than nothing but just because you can see anything with such a lamp does not mean there is no fine dust present.

The most accurate personal dust monitors use an ultrafine fine teflon filter and small waist mounted battery powered pump with an silicone air line inlet opening clipped to a shoulder or collar. The monitors use a pump that approximately runs at normal breathing rates that traps the fine dust on the filter. Built in sensors measures the volume of air through the filter and by removing the filter and weighing it (before and after) the mg of dust is measure divided by the volume of air take gives the mg/m^3. Of course this only gives an integrated measurement e.g. across minutes, hours, days etc. Instantaneous exposure has to be done with multichannel particle counters which are not as accurate.

The dust can also be looked at under an electron microscope, placed under radiation detectors or dissolved up for chemical analysis.

I used some of these monitors in Canada to collect dust iin the the air after forest fires. The aim of the project was to see how much uranium was kicked into the air with the smoke - it not much but we could easily measure it.

Have any studies, including measurements with the particle detectors etc. that you mention, been carried out in woodworking shops in Australia?

Originally Posted by BobL

The most accurate personal dust monitors use an ultrafine fine teflon filter and small waist mounted battery powered pump with an silicone air line inlet opening clipped to a shoulder or collar. The monitors use a pump that approximately runs at normal breathing rates that traps the fine dust on the filter. Built in sensors measures the volume of air through the filter and by removing the filter and weighing it (before and after) the mg of dust is measure divided by the volume of air take gives the mg/m^3. Of course this only gives an integrated measurement e.g. across minutes, hours, days etc. Instantaneous exposure has to be done with multichannel particle counters which are not as accurate.

The dust can also be looked at under an electron microscope, placed under radiation detectors or dissolved up for chemical analysis.

I used some of these monitors in Canada to collect dust iin the the air after forest fires. The aim of the project was to see how much uranium was kicked into the air with the smoke - it not much but we could easily measure it.

Thats my job... I work in asbestos now, but for about the last four or five years Ive been working in Occupational Hygiene, HAZMAT and air quality roles. My daily job is to deploy dust monitoring at various locations around Sydney.

Without going into too much detail, there are many may ways to measure dust. The filter method is one of the cheapest. There are many different filters you can use depending on the dust and the way you want to measure it.. A tapered element Oscillating Microbalance is one of the most expensive (25000ish to purchase last time I checked, plus ongoing monthly costs for maintence/filter changing etc). Suffice it so say, that you want to avoid respirable dust as much as possible. Particle sizes of 10 microns and 2.5 microns will settle in your lungs. they dint get caught by mucous in the airways and they dont get expelled easily.
The modifications mentioned in the video are probably worthwhile just to minimise the exposure. If I were cutting masses of timber I can assure you I would be wearing my half face P3 asbestos dust mask (and hearing protection) as well as wanting the best extraction you can get. Emphysema is a terrible slow death and cancer... well. it can go right to hell.