Thread: Metal dust measurements1

I posted something about this in another forum but since then I have expanded this and here are the results.

The experiment is to see what sorts of numbers and sizes of dust particles are made by using a thin (1 mm) kerf cut off wheel in an angel grinder and using the same wheel in a much lower revving setup (i.e. a table saw)
the test cuts were of the same piece of steel, cut was 114 mm long so basic geometry and density of steel says that at least 5.7g of steel needs to be removed to make these cuts.

On the angle grinder the amount of metal cut was 7.51 g with a net loss in the weight of the wheel of 1.4 g.
On the table saw the amount of metal lost was 6.55 g while the amount of wheel used up was 3.5 g so more than twice as much wheel is used up to make the same size cut (you guessed right Karl )
The thin wheel in the table saw removes 14% less metal in making the cut which is probably an indication of how unsteady it is to hold an angle grinder versus working the metal against a fixed wheel.

Now lets look at the numbers and distribution of particles.
Before I started I took some background readings (these are the readings at zero time) and then performed the cut and then took readings over the next 48 minutes to see how the dust levels changed with time
Remember, the small particles are invisible and are the ones that penetrate further into airways AND stay suspended for much longer that the heavier ones.

Here is the angle grinder results.The numbers of particles for a range of dust parcels sizes is shown.

The heaviest particles (>5 microns, probably metal) fall out of the air very quickly having 1/2 residence time (time taken to reach half of previous value) of about 1.5 minutes
The smallest particles (0.3 - 0.5 microns, probably mostly from the wheel) stay in the air much longer. 1/2 residence time of ~17 minutes.
Whether the # of particles represents a danger I still have to do the maths but this represent about twice the amount of dust generated by sanding wood on a lathe for 2 minutes. (Wood turning is one of the worst dust making activities for woodworkers)

Here is the same thing for the same wheel in a much lower revving situation of a table saw
1/2 Residence time in air for the finest dust is now 40 minutes (i.e. stays suspended in air much longer) while for the heaviest particles it's now around 10 minutes.

To assist you in comparing the first 2 graphs I show a 3rd one which plots the % difference between the two setups.
Values >0 represent more dust from the angle grinder and VV


The angle grinder clearly produces more fine dust than the table saw during the grinding but the dust from the table saw cutting setup hangs around much setuplonger.
The table saw produces more heavy dust that also hangs around longer.
The table saw produced a blue smoke during cutting which, because its visible, represents the 2-5 and >5 micron dust.
Because this takes so long to settle I suspect it's wheel material and not so much metal.

All in all it does not look good for either setup and because the 1/2 residence time is long for the finest particles (even for the angle grinder) it's no good enough to just wear a mask or respirator for the period of cutting - they will need to be worn for hours after the last cut. If you do this regularly you are much better off install dust extraction that removes this dust from the shed.
Like I said I now need to do some homework i.e. look up the composition of wheels, the OHS limits of their contents, and then calculate the milligrams/m3 of the dust in air and make some assumptions about the mix of metal V wheel in the dust.
FWIW I do all my cutting either under or adjacent to my fume hood. If I run the fume hood the dust levels drop to near background, in fact they never rise much above background - I just need to remind myself to turn it on!!!!

Luckily we have lost most of our manufacturing to overseas before our workers have dropped dead.

Hopefully you have contacted comparethemeercat for insurance advices.

Hi there,

An interesting study, one that would have taken some time to think through and conduct. I'm interested to know how you collected the dust and measured the volume from which it came?

Edit: Oh, also how did you measure the particle size or distribution of? AND,
I notice that after time 0s, there is a steady decline in all dust particles but then between 5 and 10 seconds there is an increase before once again a steady decay or decline in particle numbers. What would cause that? Is that a statistical anomaly or a result of your counting or filter system?

Simon

Im not.

Originally Posted by pipeclay

Im not.

You're not what?

Grumpy tonight? I would disagree!

Simon

Thanks Bob for taking the time to set up and run your experiment, and then to collect and analyse the data, and finally thanks for writing up your conclusions and explanations. Although I like to think of myself that I'm logical and can think most things through, I just don't have the fire power to get through something like this, with the masses of variables, and the ramifications of same, both individually and in combination. While many of us won't have dust or fume extraction, often we can choose to do the cutting and grinding outside the main workshop, which also keeps grinding residues from our machine tools, as well as our lungs. The residues can dissipate to a large extent instead of recirculating time and time again, only to catch us when we least expect it, after all, who masks up every time we sweep up around our work bench, or even if we set out to sweep the whole workshop. There would be other simple to implement procedures which could substantially improve the situation I'm sure, as few have the resources to set up a workshop along the lines of a University prototyping centre, with all the good gear, all the right accessories and the correct infrastructure to handle risks, almost without regard to the cost. Thanks again,
Rob.

Originally Posted by simonl

Hi there,
An interesting study, one that would have taken some time to think through and conduct.

The experiment is very similar to many experiments I have done at work, and also for woodworking activities, so it took me about 1 minute to work it out for metal dust and about 50 minutes to conduct.
These experiments are a PITA to perform because I should not really do any other work in the shed while I'm measuring the dust level changes - I can't even clean up or put things away.
Even me just walking too quickly past the dust detector will fluff enough dust off my clothes and upset the measurements.
Gusts of strong wind blowing past a building can be enough to pulse the dust inside a shed.
The fluctuations you refer to below are most likely due to these effect

I'm interested to know how you collected the dust and measured the volume from which it came?
Oh, also how did you measure the particle size or distribution of?

I'm using an detector/instrument called a particle counter that does it all.
Some pictures of instrument and a heap of measurements on household and shed dust are in this thread http://www.woodworkforums.com/showthread.php?t=158090
Post #10 in that thread show just how much dust is stirred up by just sweeping a floor, not that vacuum cleaners are any better - and most make things worse.

The detector has s little air pump that sucks in a known amount of air over a set time - the air stream is passed through a small chamber in which there is a laser and a set of photodiodes. As the air with the dust passes through the chamber the dust twinkles and the photodiodes pick up the reflections. The bigger the particle the bigger the twinkles. It's a pretty expensive instrument and costs about $5k. The more particle size ranges and the more sensitive the detector the more they cost. A research grade instruments can cost around $25k.

I notice that after time 0s,

The time scale is in "minutes" not seconds.

there is a steady decline in all dust particles but then between 5 and 10 seconds there is an increase before once again a steady decay or decline in particle numbers. What would cause that? Is that a statistical anomaly or a result of your counting or filter system?

see above

Hi Bob,

*edited* Simon stole all the good questions while I was stuffing about lol

You wouldnt have the same sort of numbers for say standing on the corner of "pick two streets in your favorite capital city"?

Stuart

Originally Posted by Ropetangler

Thanks Bob for taking the time to set up and run your experiment, and then to collect and analyse the data, and finally thanks for writing up your conclusions and explanations. Although I like to think of myself that I'm logical and can think most things through, I just don't have the fire power to get through something like this, with the masses of variables, and the ramifications of same, both individually and in combination. While many of us won't have dust or fume extraction, often we can choose to do the cutting and grinding outside the main workshop, which also keeps grinding residues from our machine tools, as well as our lungs.The residues can dissipate to a large extent instead of recirculating time and time again, only to catch us when we least expect it, after all, who masks up every time we sweep up around our work bench, or even if we set out to sweep the whole workshop. There would be other simple to implement procedures which could substantially improve the situation I'm sure, as few have the resources to set up a workshop along the lines of a University prototyping centre, with all the good gear, all the right accessories and the correct infrastructure to handle risks, almost without regard to the cost. Thanks again,Rob.

No worries Rob. I understand your line of thinking, especially the raft of variables/issues. And holding it all in your head to make some sort of a judgement call is indeed a minefield. I tried to keep the experiment simple and provide just one major variable, slow speed versus high speed cutting. I did this because I do both, well mainly slow speed and wanted to know the ramifications. Even though it loots complicated it's not a rigorous experiment. What I'm really targeting here is general principles which is most cases are common sense but some are not. Like using a mask or respirator just while cutting is not going to reduce exposure by very much.

There are a few straightforward things people can do. Like you say cutting outside is better than inside but not everyone has a vice etc outside that they might use for angle grinding/cutting small stuff. If cutting has to be done inside and you have an externally venting dust extractor (increasing number of forum members have these after all the hop-haa that has gone on in the dust forum) then use it. Likewise when sweeping up. Even opening a all doors and windows will be worth doing. For folks who are in the process of designing and building a new shed setting up a dedicated fume hood is not difficult in fact its easier than wood dust extraction. Mine is made out of corrugated iron over an angle iron frame, and uses a 30 year old squirrel cage fan with a half HP motor. I have WIP of its construction in my shed thread. Provided they are unrestricted, squirrel case fans move a lot of air and are ideal for this sort of thing.

You wouldnt have the same sort of numbers for say standing on the corner of "pick two streets in your favorite capital city"?

I have more distributions than probably I have had hot dinners but not many for city air. I posted an inner suburban distribution for a carpark alongside Canning Highway in Perth in post 2 of this thread http://www.woodworkforums.com/showthread.php?t=158090
Canning Highway is a major road that links Perth and Fremantle south of the river.
The readings were made around mid afternoon and would have been high if it was peak traffic time.

City air can have similar particle counts to those posted in this thread. It's a mix of combustion products (Carbon) from motor vehicles, car tyre rubber and car tyre mold release agent (Zinc Sterate), building and construction dust, pollen and vegetation fibres, paper and fabric fibres, etc. As well as the sheer numbers of particles it's what is in them that also needs to be considered and it's pretty easy to look these up for grinding wheels and then I need to do a few more sums with the data I collected and see if it comes anywhere near to the OHS limits for the material in the wheels.

Interesting. Just another one of many reasons why it is commonly said that :there are no old boilermakers".

Just a note to say I haven't forgotten about this. I have been trying to chase down the manufacturers MSDS for the thin kerf cut off wheels to find out exactly what is in these wheels. Emails sent to the manufacturers website have gone nowhere and eventually I found the website was "under construction". I finally called and asked about them and after a bit of running around they got back to me to say they are still chasing them and to give them a week to track them down.

Exposure time is probably the most important thing...

I hope I do not start causing mass suicides and rampant hysteria by my next statement but truth of the matter is for airbourne particles that have the potential for causing disease like asbestos does, all of us have sucked in asbestos particles.... We all have asbestos particles in our lungs... But the more exposure increases the risk of developing the asbestos related disease..

In theory one asbestos particle could cause asbestosis, in reality the risk is small...

Next question is does metal cutting wheel dust cause nasty diseases in humans?

I would say people need to take precautions, but a full moon suit is probably not needed, so long as you take the correct precautions to minimise exposure... dust mask and do it outside upwind from the neighbours you do not like

Although after seeing the old old senile people that lost their marbles years ago I wonder if I would prefer to take a few more risks and die just as I reach senility rather then go on and on as a dribbling vegetable..

Originally Posted by .RC.

Exposure time is probably the most important thing...
I hope I do not start causing mass suicides and rampant hysteria by my next statement but truth of the matter is for airbourne particles that have the potential for causing disease like asbestos does, all of us have sucked in asbestos particles.... We all have asbestos particles in our lungs... But the more exposure increases the risk of developing the asbestos related disease..
In theory one asbestos particle could cause asbestosis, in reality the risk is small...
Next question is does metal cutting wheel dust cause nasty diseases in humans?
I would say people need to take precautions, but a full moon suit is probably not needed, so long as you take the correct precautions to minimise exposure... dust mask and do it outside upwind from the neighbours you do not like
Although after seeing the old old senile people that lost their marbles years ago I wonder if I would prefer to take a few more risks and die just as I reach senility rather then go on and on as a dribbling vegetable..

RE: What is in Cutting wheel dangers.
All we can go on at the moment is based on what is in the cutting wheels and that's what I'm trying to find out. It took 40 years to determine that workers in TC factories and factories where TC tools are made and tips are bonded onto tools were at greater risk of contracting cancer from the cobalt bonding agents used. Now that we know something can be done about it, but what about the poor sods that got caught in the meantime? The same applies to workers in Chrome plating facilities. No one is going to do the research on possible cause and effect on grinding and cutting wheels until a problem stares them in the face and by then who knows how many people will have been affected.

Exposure is definitely a factor and that's what I was targeting. My experiments seems to demonstrate thatwearing a mask just while cutting is not going to do much to reduce exposure because the whole workplace becomes contaminated so workers will need to wear a make basically for hours after the last cut in that shed. My experiment suggest that ventilation is needed while cutting and for some time after.