New study on UFP and VOC emissions

[pubs.acs.org]

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

The conspiracy 'nut' in me just reads it as just another example of organizations trying to stop people doing anything fun...


Its like everything else... use in moderation.

If your going to setup a print farm then like all commercial ventures you need to look at the health and safety issues.

UFPs, particles have been know about for a long time... eg [www.sciencedirect.com] from 2013

Hence the interest in building filters. Especially for abs.

The high voc emissions from nylon are interesting - I had a vague impression that my nylon prints were a bit on the smelly side. The styrene from abs remains the biggest annoyance, but I guess the UFPs would have long term exposure issues rather than acute symptoms. Interesting from the 'implications" section at the end of the paper that they place more concern on the VOCs than the UFPs.

Overall, some sort of filter seems to be a good idea. A well ventilated room is not very practical during the Canadian winter!

There is something I don't understand about this. They say the emission of particles is on the order of >10^8/min. My machine has roughly 1/6 m^3 volume in the enclosure. If I run a 20 hour print, I should have >1.2x10^12 particles in that 1/6 m^3 volume. That's a density of >7.2x10^12 particles/m^3 = >7.2 x10^6 particles/cm^3. I would think that with that sort of density I should be able to see something like smoke inside the enclosure, yet I do not. I shine a green laser through the enclosure and it doesn't light up anything that I can see, and a green laser can cause air molecules to light up even in a particle free environment.

What is the physical mechanism of particle production? Is it VOCs boiling off and ejecting unreacted monomers into the air? What is the composition of the particles? Why does the particle emission rate (and VOC emission rate) depend more on the bed temperature which is lower than the nozzle temperature (3 orders of magnitude variation), more than it does the nozzle temperature (about 1 order of magnitude variation) (refer to figure 5)? All I can figure is that the plastic is in contact with the bed throughout the print and only in contact with the nozzle for the time it takes the plastic to melt and resolidify on the print, then once again as the next layer is being deposited and the hot nozzle touches it again, briefly. Why would prolonged contact with the bed at low temperatures create a lot of particle emissions? Are the particles coming from the melted plastic or from the bed itself or the coating on the bed? Are they coming from the silicone heater? Hmmmm.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Lots of good questions. I haven't seen much of an explanation of how the UFPs are formed, but I would have expected it to be more of a physical process involving the nozzle than a chemical one involving the bed, so that doesn't fit with their observations.

Your comment about the laser has me a little confused, if you could actually see scatter off air molecules then you would be able to see the beam all the time, including when you shine it through the enclosure - unless you're printing in a vacuum these days

James

Edited 1 time(s). Last edit at 01/30/2016 11:45AM by JamesK.

Based on that article we've had a proposal at my local Hackspace to ban ABS printing until a fume extraction system is put into place.

Quote
JamesK
Your comment about the laser has me a little confused, if you could actually see scatter off air molecules then you would be able to see the beam all the time, including when you shine it through the enclosure - unless you're printing in a vacuum these days

James

The brightness of the scattered beam should be a function of the both the air molecules and the particles the air. Even with no particles, air molecules will cause visible scattering (Rayleigh scattering off N2 molecules makes the sky look blue). I'm looking through a box that is only about 0.5 m wide, so there's not a lot of scattering due to air molecules- i.e. the scattered beam will be relatively dim because of the short distance involved (also why the air in the box doesn't look blue). But, over that distance I have a particle concentration of 7 x10^6 particles/cm^3 (after a 20 hour print, if I interpret the original study correctly), so though I may not see any scattering due to air molecules inside the box, I expect to see scattering due to the UFPs, but maybe the magnitude is just too small to be visible, even with such a particle concentration.

[en.wikipedia.org]

much deeper and even more juicy math:
[www.princeton.edu]

Edited 1 time(s). Last edit at 01/30/2016 01:02PM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Hmm, I suspect that invoking effects at a planetary scale may be stretching things, although with a sufficiently powerful laser...

Your question remains as to why you're not seeing the particles in the chamber. Two possibilities come to mind, one is that they are just too small for significant optical effects at the volumes considered, and the other is that the things don't just build up indefinitely in the chamber but have some mechanism for removal.

On the first front, I tried to find out how UFP detectors work and found this link that contains

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Due to the lack of significant scattering or absorption by particles in the nanometre size range, particles are counted in commercially available, condensation nucleus counters (CPC or CNC), in which the particles are activated to droplets in a supersaturated atmosphere of alcohol, which can then be detected optically

So that would seem to support the idea that the particles themselves are too small to interact with light in a useful way.

From an older paper, this graph shows that concentrations decay at the room level after printing stops, and presumably some of the same mechanisms will also be happening inside the build chamber during the print.



Any mechanism that removes UFPs from the environment will reduce the concentration available for you to observe at the end of the print. So I guess both factors are probably involved, making it difficult to assess our exposure without access to some serious equipment.

The study indicates that Styrene is the primary product from ABS.
This link has all the info needed about styrene exposure, see page 2 on the right. [www.atsdr.cdc.gov]

This indicates exposure should be less than between 0.2ppm and 5ppm depending on duration.

[Edit: is it possible to convert the particle emission info from the study to PPM? I guess it would also depend on the size of the enclosed space, extrusion rate, temperature. Makes one wonder if un-enclosed printers are a good idea. Thanks for posting the study, it confirms others we've been watching.]

Health Effects
 The most sensitive target of toxicity is
the nervous system. Effects observed
in workers include decreased color
discrimination, vestibular effects,
hearing impairment, symptoms of
neurotoxicity (particularly “feeling
drunk” and tiredness), delays in
reaction time, impaired performance
on tests measuring attention and
memory, impaired nerve conduction
velocity, and EEG alterations.
 Nasal olfactory epithelial damage and
liver necrosis have been observed in
animals. However, humans are likely
to be less sensitive to these effects due
to species difference in styrene
metabolism.
 DHHS has classified styrene as
reasonably anticipated to be a human
carcinogen. IARC has assigned
styrene to Group 2B, possibly
carcinogenic to humans.

Edited 1 time(s). Last edit at 01/30/2016 01:56PM by Paul Wanamaker.

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My printer: Raptosaur - Large Format Delta - [www.paulwanamaker.wordpress.com]
Can you answer questions about Calibration, Printing issues, Mechanics? Write it up and improve the Wiki!

Quote
JamesK
... So I guess both factors are probably involved, making it difficult to assess our exposure without access to some serious equipment.

I believe you are right.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

According to this from the EPA "The odor threshold for styrene is 0.32 parts per million (ppm)."