Thread: Dust sensor measurements - post results here.

My initial post on a 'Household' PM2.5 5003, here.

Details of my workshop size and DC setup, in earlier post here

Second session - Day 2

I attached the sensor at head height near to where I stand at the lathe, as suggested by Bob. This is the reading after I first started sanding with DC running.

PM2.5 5003 sensor at nose height.JPG

Here is the relative humidity reading.

PM2.5 5003 sensor - RH reading.JPG

I've just noticed that the rating at the bottom of this first screen is now showing Severely 'Pollated'. As far as I can see this rating doesn't budge regardless of the actual readings displayed on the second screen. When I first got the sensor it seemed to be consistently rating the AQ as Good (ie green). I'm hoping this is just a software and not a sensor malfunction.

Here is a reading after 1 hour of turning and sanding.

PM2.5 5003 sensor - best reading at 1 hr runtime.JPG

Session 3 - Day 3


Baseline reading on arrival in workshop.

PM2.5 5003 sensor - Day 3-1 baseline.jpg

I then did something I haven't done in twenty years. I sanded a piece on the lathe without a DC running, then took a reading after doing that for 10 mins. Note: I did this wearing my positive pressure filtered air respirator setup + Willson P1 mask inside that to make doubly sure, just in case!

PM2.5 5003 sensor - Day 3-2 sanding without DC.JPG

No surprises there!

The next reading indicates the (relative) level of particulates after turning on the DC and continuing to sand for 10 minutes. I was pleased to see the rapid drop and the levels continued to drop below that over the next hour as I continues to work.

PM2.5 5003 sensor - Day 3-3 after DC 10mins on.JPG

For reference, here is the Relative Humidity reading.

PM2.5 5003 sensor - Day 3-4 RH.JPG

Then I turned off the DC to re-grind some gouges. Turning the DC off while grinding is a carry over from when I used to have Alox wheels on my grinder and there was a risk of a fire in the DC ignited by the shower of sparks. Not so relevant with diamond and CBN wheels, but old practices are persistent. Anyway, I was most surprised to see the reading after grinding for 10 mins.

PM2.5 5003 sensor - Day 3-5 after grinding.JPG

I'm still digesting what to do about these high levels of metal dust in my workshop air. Running the DC while grinding would reduce this but I'm not keen to load up my DC filters with that anymore metal dust than I have already. More readings will be needed to sort this out. I'm more concerned about wood than metal dust. The higher metal dust levels are brief and infrequent

Last reading is of the air outside the workshop. Apologies for the camera shake, it was getting dark by then and the flash was of no use, it just bounced back off the glass screen.

PM2.5 5003 sensor - Day 3-6 outside.JPG

Thanks Neil.

Assuming we double the 58 ug/m3 values you obtained for sanding with no DC this give us 116 ug/m3 which exceeds the 100 ug/m3 level recommended for seniors, children and anyone with breathing related problems. And this was only after 10 minutes of sanding - now imagine doing this all day.

The issue for metal dust is interesting - I too have seen this many times - not just for sharpening but for sanding (especially Al), rust removal with a bench grinder mounted wire wheel, polishing with a Scotchbrite wheel, cutting metal with a thin kerf cutting wheel. Plasma cutting and stick welding also produce a lot of dust, TIG welding is not so bad but it does release large amounts of CO and NOx.

One positive thing about metal dust is it falls out of the air faster than wood dust in proportion to it's density. So steel falls out between about 8 and 16 times faster. Al about 6 times faster. The slowest is the resin and fibreglass bonding agents in thin kerf cutting wheels, grinding discs and sand paper. These are about twice as fast as wood dust.

What to do.
For welding, cutting and flap sanding I have a fume hood type welding bay that I try to do this work in.

For bench grinders I disconnect one of the nearby WW bandsaw 4" flexies and attach it to a metal drum chip catcher.
The Aluminise mylar ducting is heat resistant enough to cope with the sparks.
The chip and dust catcher seems to catch the prevents hot metal objects from being sucked into the DC system and sawdust bags.
I have been using it for some 20 months nows and it does not seem to clog the DC filters up.
It's not as effective as I would like - I need to do more testing to determine the optimum orientation of the collection port.

IMG_1615.jpg

IMG_1616.jpg

Going back to the pyrolytic cleaning oven,
Apparently this morning the cleaning cycle self aborted part way through the cycle so SWMBO ran it through another full cycle while I was out this afternoon. This time she did turn the Stove exhaust fan on but when I got back the PM10 was over 350 ug/m3 in the study (4 rooms away) and one hour later is down to 250.
The dust levels are dominated by the 0.3 to 1 micron dust with the particle counters indicate about 50,000,000 particles per cubic metre - this is classed as "Heavily polluted" air.
It seems like the exhaust fan could not cope with the rate of particle production once the fats and oils start to be burnt off in the oven. Cooking is a known produced of fine particles especially if any oils or fats are involved.

Originally Posted by BobL

Assuming we double the 58 ug/m3 values you obtained for sanding with no DC this give us 116 ug/m3 which exceeds the 100 ug/m3 level recommended for seniors, children and anyone with breathing related problems. And this was only after 10 minutes of sanding - now imagine doing this all day.

It would have been interesting to leave the DC off after sanding for 10 minutes and see how long it took for that high level of dust to remain airborne inside the workshop, but I just couldn't let that happen having been so diligent over the years at keeping the fine dust levels at a minimum. A 10 minute experiment was my limit!

It will be interesting to see what the residual levels are in the workshop when I go back in there after they have had two days to settle/re-levitate.

Originally Posted by BobL

One positive thing about metal dust is it falls out of the air faster than wood dust in proportion to its density. So steel falls out between about 8 and 16 times faster.

....

What to do.

For bench grinders I disconnect one of the nearby WW bandsaw 4" flexies and attach it to a metal drum chip catcher.

Yes, the levels dropped quite rapidly after I stopped grinding and now that I have the sensor I can check to see when to turn the DC back on to avoid the metal dust clogging my DC filter.

~~~~

I've thought about something like what you have on your grinder setup, Bob.

Do you have water as a quencher in the bottom of your drum?

~~~~

As I understand it, my biggest risk from the metal dust exposure from grinding is the vanadium in some of my turning tool steels. From what I can work out, given the brevity of my grinding sessions and the fact that I also wear a filtered air respirator when I'm in the workshop, I would be well below the recommended exposure levels (see here).

Loading my DC filter with metal dust is more of a concern.

Originally Posted by NeilS

It would have been interesting to leave the DC off after sanding for 10 minutes and see how long it took for that high level of dust to remain airborne inside the workshop, but I just couldn't let that happen having been so diligent over the years at keeping the fine dust levels at a minimum. A 10 minute experiment was my limit!
It will be interesting to see what the residual levels are in the workshop when I go back in there after they have had two days to settle/re-levitate.

I'd say you won't see anything after that length of time.

I have done many dust settling experiments mainly of labs but in 2012 I did some in my shed. In one test I got the dust levels up to >10,000 ug/m^3 just by sweeping the floor (Particle Size Distributions 101 (warning - only invisible dust discussed)). Then I walked out and logged the dust levels over time. I posted the results here but the pictures have gone so I will post it again.
Sorry its such a technical graph
Screen Shot 2018-07-06 at 10.05.21 am.png
The results of this can be summarised as follows using a term called the "Half residence time (HRT) in air". This is the time required for the dust concentration to drop to half its original concentration.
The finest dust (0.3 to 0.5 microns ) has a HRT of about 25 minutes whereas the 5 micron dust has and HRT of about 12 minutes.
I have also done it for metal dusts and steel has an HRT of between i/8 and 1/16 of the wood dust, Al is a bit longer.
Using the right had side axis you can see the starting contraption was about 10600 ug/m3 and it took about an hour to reach 100 ug/m3.
Overnight is usually ore than sufficient to settle out any dust remaining in the air but f course its still in your shed and can get fluffed up again by various recesses within a shed. Just drop a piece or sheet of wood is usually enough.

Yes, the levels dropped quite rapidly after I stopped grinding and now that I have the sensor I can check to see when to turn the DC back on to avoid the metal dust clogging my DC filter. I've thought about something like what you have on your grinder setup, Bob.
Do you have water as a quencher in the bottom of your drum? .

I though about that and the resultant rusty mess that would ensue. When I first tried it out sanding a large piece of Al I periodically stopped to feel the sides of the metal drum but could not feel and change in the temperature fo teh drum probably because it has such a large mass and surface temperature and the large air flow rapidly cools the metal dust.

Under my thin kerf cutting wheel bench grinder attachment I collect the waste coming off the workpiece and wheel using a baked bean can suspended directly under the cutting point. This really reduces the scatter of grit and dust around the shed. Without the DC running that can gets so hot you cannot touch it for long but as soon as DC airflow is brought into proximity you can easily touch the can.

As I said I do collect the residual metal dust after the chip collector and have not noticed any drop off in the performance of the DC filter.

As I understand it, my biggest risk from the metal dust exposure from grinding is the vanadium in some of my turning tool steels. From what I can work out, given the brevity of my grinding sessions and the fact that I also wear a filtered air respirator when I'm in the workshop, I would be well below the recommended exposure levels (see here).
Loading my DC filter with metal dust is more of a concern.

Vanadium is one of a number of metals but probably the main one from tool steels. Tungsten carbide and cobalt bearing alloys would be others but noticeable effects has only been noticed in factories where these are made. The short term exposure resulting from sharpening only processes is unlikely to be significant to woodworkers.

Originally Posted by BobL

I'd say you won't see anything after that length of time.
...

The finest dust (0.3 to 0.5 microns ) has a HRT of about 25 minutes whereas the 5 micron dust has and HRT of about 12 minutes.

Thanks, Bob.

That is good information to have.

Sent from my ZTE T84 using Tapatalk

Originally Posted by BobL

I'd say you won't see anything after that length of time.

So, I went off to the workshop expecting to get some very low readings after being out of the workshop for several days, but got some most unexpected results.

The initial readings were up around 600 for >0.3um. Confusing!

I then turned on the DC and the numbers were all over the place, but trending up and this was before I turned on the lathe or picked up a tool.

When the >0.3um got as high as the following inside the workshop, still with nothing running other than the DC, I was very puzzled.

PM2.5 5003 sensor - unexpected inside WS.JPG

Fortunately I decided to take an outside reading to see if the outside air might be contributing to the unexplained high and erratic readings inside the workshop.

The readings were bouncing about wildly outside and going up as high as the following alarming level.

PM2.5 5003 sensor - outside WS.JPG

Then I picked up a whiff of smoke that came and went depending on the wind direction and strength. Here in the Adelaide Hills a lot of people run wood heaters in winter and there must have been someone up wind with one going, albeit some distance away as I couldn't see where it was coming from.

Puzzle solved!

Also, a lesson learned. Always take an outside reference reading before monitoring the air inside. Despite my relatively sealed workshop (the inside readings were only 1/6th the outside readings) the outside air was skewing the inside readings to the point where they had no relation to what was happening inside the workshop.

PS - My 'Household' PM2.5 5003 has gone back to giving me a 'Good' air rating. I didn't think to check what it was reporting when it got above the 50ug/m³ outside in that smoke filled air.

All good info Neil - keep up the good work.

Neil maybe a subject for another thread but many industrial cartridges are used in metal grinding/polishing/finishing operations and work the same as for wood. As long as no sparks get to the filter it doesn't know the difference. As yours and Bob's will likely have a wood dust layer first it will come off with reverse flow, leaf blower or compressed air. The filters I'm going to use are all sourced from work when they were too clogged for the air pulse cleaner. Took them to a filter cleaning company that cleans them to within 2% of new. There were a few fires in our downdraft tables from sparks but it was just as likely the dust on them started to burn from the shower of sparks and not the filters. For those operations we got a downdraft system that drew the air through water and then through water impinging filters before returning the air to the shop. The little dust generated from tool grinding, if cold, won't hurt the filters and be better for your health.

Pete

Originally Posted by QC Inspector

Neil maybe a subject for another thread but many industrial cartridges are used in metal grinding/polishing/finishing operations and work the same as for wood. As long as no sparks get to the filter it doesn't know the difference.

In my old shed where for a couple of years I had a 1HP DC in an enclosure outside a shed and 100mm ducting, I had a Makita 100mm sander turned on its back attached directly to the ducting using about 3m of 50mm polyurethane translucent flexy. I sanded a lot of steel with that sander so it produced a lot of sparks. To test how far the sparks went into the Dc system I sanded some steel at night with the shed lights off so the sparks were more visible inside the flexy and never saw a spark go further than about a metre down the flexy. My theory is that the (albeit limited) air flow was sufficient to cool the sparks within that distance so that they no longer glowed - of course that does not mean the metal particle would not have been hot - just not visible.

Some months later I had to move things around in the shed and noticed the flexy contained a lot of metal dust that had settled out in the bottom of flexy. The deepest layer was about 10 mm deep and that was close to the sander with ever decreasing depths out to about 1.5 meters which was consistent with how far the sparks went. Beyond the 1.5 meter mark there was only some very fine metal dust caught in the corrugations of the flexy.

My theory is that because of the cooling effect of the air flow only the larger metal dust particles could remain hot enough to produce spark light but they too were quickly cooled down and dropped out of the air flow.

Now greater air flow will may mean the metal dust travels further but it also means they will be more rapidly cooled so these two should cancel each other out. My main concern is not sparks but that a hot small metal object might be sucked all the way into a dust collection bag and start a fire. This has been reported on several occasion and is a known cause of DC fires. This is why metal dust collectors often use a heat proof chip catcher between the machine and the DC ducting.

Originally Posted by QC Inspector

The little dust generated from tool grinding, if cold, won't hurt the filters ...

Useful to know, Pete.

Thanks

Originally Posted by BobL

My main concern is ... that a hot small metal object might be sucked all the way into a dust collection bag and start a fire. This has been reported on several occasions and is a known cause of DC fires.

Mine too, Bob.

Also, although less likely, the possibility of an explosion inside the DC system. They do happen.

If I do extend the ducting to my grinder I will implement some form of hot swarf capture/quench.

Cross posting my results from here

In summary: small shed (12sqm) with only an 8 inch extraction fan rated at 1000m3/h.




This is the first reading from the shed:




I let it settle for a few minutes, it didn't change much from that.

Then I put my mask on and did my worst

I put a few pieces of MDF and hardwood through pretty much every powertool I own, stopping every couple of minutes to take a reading.

Then I blew all surfaces with compressed air and vacuumed the floor, as I'd normally do.

At that point it was pretty much a gas chamber in there, I could literally see dust suspended in the air.

I left the shed for half an hour to have dinner, and then came back and took a couple more readings.

Then I cracked the window open and started the fan.

This is what the readings looked like:



Basically according to this device it took the fan about 5 minutes to bring the dust content back to normal.

Which makes sense because the shed is really small, and (if the cfm rating is correct) this fan should need less than 2 minutes to replace all the air and it's contents with fresh air.

One of the things I do when I open up my shed in the morning before making dust (not that I'm doing much of that these days) is look at the dust counter and it's usually showing <10 ug/m^3 for the PM10.

This morning it showed the following.
The top figure is for PM1, the first number on the second row is for PM2.5 and the other is PM10 - all in ug/m^3
Smoke23.jpg

Invariably this is caused by prescribed burning off in forests. this time from as far away as 300+km from where I live.
The ratio of the PM2.5 to PM10 being almost one also indicates it is smoke.
These values are about double what I saw last time there was a major burn off and the smoke came down from the Perth hills and blanketed the city.
Here are a few pics about this on the ABC website https://www.abc.net.au/news/2018-11-...burns/10507566
Above 100 ug/m^3, the recommendations for kids, seniors and anyone with respiratory problems is to stay indoors.

Inside my house or shed I cannot see any evidence of dust - perhaps a faint haziness in one room with the best lighting.
Inside the stillest most air tight room of the house the values are around 110 ug/m^3 for PM2.5.
The rest of the house is between 160 and 180 ug/m^3

Only outside over distances of about 1km could one see the smoke was obvious - this photo from the abc website is taken just down the road from my place
10507598-3x2-700x467.jpg

Again this demonstrates that you can have very high levels of fine dust in a shed and not see a thing.

It's smoky here too. These are indoor readings:
Indoor Particle.jpg

And outdoors:
Outdoor Particle.jpg

Of course it's leaf burning season.
Smoke.jpg