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I am soldering using lead-free solder for about 1 hour a day with a solder fume extractor that has a carbon filter that looks like the image below. The place of soldering is in a building with commercial-grade ventilation, but without the ability to open windows.

This source claims solder fumes to consist of 95% particulates and 5% gases, while this other source claims 99.5% particulates and 0.5% gases.

Considering the effectiveness of the carbon filter, the possible composition of the fumes, and location, would this setup be considered safe?

enter image description here

plu
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    You should be aware that solder fumes, even those from leaded solder, don't contain any lead. The fumes are entirely from the flux. That said, they're still not great stuff to breathe--it's just not lead as many people seem to think. – Hearth Feb 02 '21 at 03:42
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    If you are at a company then I would recommend it. Workers comp is way more than some silly air filter. When I'm soldering at home I use the tried and true breath out while its smokey. On the plus side blowing on the joints cools it slightly faster as well! – Parker Feb 02 '21 at 03:49
  • Well, me poor hobbyist's life does not matter that much, so all these years I do high lead soldering without any filter: What type of solder is safest for home (hobbyist) use? - @Russell McMahon, EE SE, Asked 9 years, 5 months ago Active 1 year ago Viewed 69k times https://electronics.stackexchange.com/questions/19077/what-type-of-solder-is-safest-for-home-hobbyist-use. BTW, I always appreciate Keynes saying: "In the Long Run We Are All Dead: https://www.ftadviser.com/european/2019/09/25/in-the-long-run-we-are-all-dead-keynesianism-political-economy-and-revolution-by-geoff-mann/. Cheers. – tlfong01 Feb 02 '21 at 04:24
  • @Hearth The flux in lead free solder (SAC types at least) is far more aggressive than that in leaded solder which makes the use of an extraction fan even more desirable. – Peter Smith Feb 02 '21 at 12:23

4 Answers4

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That "filter" doesn't really do anything. The fan however disperses the fumes, which are then ideally vented out by the HVAC system without reaching harmful levels. How safe that is depends on how much air exchange you have and the volume of fumes you're generating.

Edit: I'm surprised this is controversial, but those "charcoal filters" are worthless at removing particulates, which are the primary component in solder fumes. Take a look at the particle size that will fit through them:

enter image description here

Those millimeter-wide gaps are literally thousands of times too large to remove the sub-micron particulates generated by soldering. Activated carbon is more helpful at removing gases, but again, the surface area is negligible and most gases will pass through without ever encountering any surface at all because the filter is simply too thin. If you have one of these, you are depending on the HVAC system to exchange fumes for fresh air. There is a whole EEVBlog episode going over this: https://www.youtube.com/watch?v=ffaiKZMU0Lw

This isn't just my opinion either. Here is a quote from a study evaluating activated carbon foam filters for solder fume extraction:

Activated carbon filters in the form of foams, used with the simpler type of cleaner, had negligible filtration efficiency against either particulates or vapours and would, therefore, offer no protection against any hazardous component of the fume.

Measurement of the Performance of Air Cleaners Against the Particulate Element of Rosin-based Solder Flux Fume

If you can't get access to that ventilation and are going to be generating any serious fumes, then you need a HEPA filter. Otherwise you're just blowing the same particulates in a circle and then breathing them in.

Those generic HEPA filters Dave Jones talks about in the EEVblog videos are relatively inexpensive and they're generally effective (will remove smoke and the order of burning flux from a room), can actually remove particulates, and the filters are interchangeable if you want to buy a name-brand or certified replacement filter rather then trust the generic parts. If you can't work in a well ventilated space, they (at a minimum if not something better) are worthwhile.

user1850479
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    Have you ever used one of these? The filters may not be perfect but they're extremely effective. It's definitely not just dispersing the fumes. – pericynthion Feb 02 '21 at 03:39
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    @pericynthion Yes, I use one regularly. And no, they provide negligible filtration. Check the EEVblog video I linked, or just look at one. They have very little surface area and almost no ability to trap particulates, unlike a HEPA filter. – user1850479 Feb 02 '21 at 03:44
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    @pericynthion See edits. – user1850479 Feb 02 '21 at 04:37
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    @user1850479 Does the visible smoke contain most of these particulates? From what I observe, white smoke comes in from the intake side, and no visible smoke goes out the outtake side. Would that mean the filter had actually captured most of the particulates? – plu Feb 02 '21 at 05:04
  • @user1850479 thanks for the additional info and references. I'm still confused though, for the same reason as plu. – pericynthion Feb 02 '21 at 06:47
  • I am also confused for the same reason as plu. Additionally, I can tell you that if you use one of these for a while, you will clearly see a buildup of gunk on the input side of the filter. – user253751 Feb 02 '21 at 12:31
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    @user253751 If you look at the linked paper, the "filter" lets through most particles but not 100%. The few percent (probably large, heavy particles) that are actually absorbed will gradually build up on the surface, same way dust builds up on a computer case fan/filter. That doesn't really help you though since you're still breathing in the vast majority, and probably nearly all of the smaller particles that would land deep in your lungs. – user1850479 Feb 02 '21 at 14:25
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    @plu Wavelength scale and smaller particles are not directly visible, no. Dense aggregations of them will form a visible smoke, but just blowing air through them with disperse that smoke. The fan is pretty effective at preventing you from breathing in particles so long as you have enough air volume or air exchange around you that the smoke can actually disperse to safe levels. I actually think those devices are fine for light use or even heavier use in a well ventilated space (I use one regularly for quick soldering at work in a large, well ventilated space). – user1850479 Feb 02 '21 at 14:34
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    @user1850479 Your own linked study says: "Although some deposit was seen on the filters, a penetration of over 80% was obtained for filter A and over 50% for filter B"

    "The data on monodisperse aerosols in Table 2 are consistent with 50-100% of particulates [...] penetrating through filters A and B"

    That still means that say for every 8 hours of soldering you will breathe only 6 hours worth of fumes. I wouldn't call it worthless, but certainly less then ideal.

     – SilentAxe Feb 02 '21 at 14:39
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    I just find it funny that people consider say 20% negligible when it reduces danger, but the same percantage would suddenly be huge if it reduced for example your salary. – SilentAxe Feb 02 '21 at 14:45
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    @SilentAxe The risk from particulate matter is not uniform, so that reasoning is not correct. The paper shows 100% penetration of particles smaller than 1.5 microns, while filtration above 10 microns (which would pose much less risk) is better. That paper is saying that no filtration at all occurs of the most harmful particles, while some small amount of filtration happens on the least dangerous. A good analogy would be that you get a 20% raise, but only on the days you don't work. – user1850479 Feb 02 '21 at 14:57
  • @user1850479 I thought that primary danger of solder fumes was heavy metal absorption instead of mechanical particulate damage, which should be independent of particle size. I might be horribly wrong though. My cursory search didn't yield any scientific articles that explain the exact mechanism, so if you have any I would gladly read them. – SilentAxe Feb 02 '21 at 16:06
  • @user1850479 I did find an article that might be relevant but I don't have access to it. There the figure 3 shows that the peak size of tin particle distribution is slightly above 10μm which should mostly be blocked by these filters. Although without reading the article I lack context of how applicable that is. – SilentAxe Feb 02 '21 at 16:06
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I use one of those, and the ONLY benefit is that it keeps the fumes and resin plume from rising up into my nose & mouth whilst soldering.

I realize the OP doesn't have this option, but for other readers: I run a 4-inch PVC flexible dust/woodworking tube from the vent to the closest window.

enter image description here

(Image from Amazon, "Ultra-Flex-Clear-Vue-PVC-Hose")

P2000
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That solder fume extractor not only does not perform any filtering of particulates, but it also doesn't perform any filtering of dangerous VOC. It is not possible to compare particulate & gas pollutants by mass, as their mechanism of toxicity is different.

In order to capture any significant amount of dangerous gasses, you need a significant mass of activated charcoal to adsorb the chemicals, as well as to change the filter as it becomes saturated.

Disclaimer: I'm not an occupational health specialist or a chemist. I expect my calculations to be correct within about an order of magnitude, and no more.

To calculate exactly how dangerous the gases are, here is one of my soldering sessions. I'm indoors, and I have a HEPA filter but no significant VOC filtration, and my readings are from a SGP30 VOC sensor and a PMS7003 particle sensor:

graph showing a sharp increase in VOCs to 40ppm before dropping to ~0ppm

I start my soldering session at 8:35 PM, and finish up and open a window at 8:52 PM. Ambient air quality was pretty crummy to start with, but my soldering caused the VOCs in the air to climb from 12ppm to 38ppm.

It's unclear what exactly the chemical compounds that make up soldering fumes are, and it depends heavily on the exact type of flux. An Investigation Into The Composition of Solder Fume suggests that about 26% of fumes are some sort of aldehyde. These aldehydes are split about 50:50 between formaldehyde and acetaldehyde. With these rough numbers, and the (IMO, likely too permissive) occupational limits:

┌──────────────┬────────────────────┬────────────┬──────────────────┐
│   compound   │ est. concentration │ 8-hr limit │ short-term limit │
├──────────────┼────────────────────┼────────────┼──────────────────┤
│ formaldehyde │ 3 ppm              │ 0.75 ppm   │ 2 ppm            │
│ acetaldehyde │ 3 ppm              │ 25 ppm     │ 25 ppm           │
└──────────────┴────────────────────┴────────────┴──────────────────┘

My soldering task exposed me to unsafe amounts of formaldehyde. My exposure was likely dramatically higher because I was next to the work while the sensor was in the middle of the room.

I was also exposed to a wide variety of other chemicals, but the health effects of these chemicals are not well studied or regulated.

flaviut
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In this case, "Safe" is speculative. If you want an absolute level of safety, you want a fume hood or extractor(Could be built into a window with PC fans I would note similar to a drop in air conditioning unit). Carbon filter units like that are the next best option for when a proper extractor is not an option. You would have to specifically analyse the unit in question(how often carbon sheets are changed, quality, total thickness, air flow rate per area) to know exactly what made it through the filter.

As far as different distributions of particulate and gas, there are different alloys of solder and types of flux and soldering temperatures that could account for the distribution, so both of your sources are probably right. If an extractor isn't an option for you and you don't fully trust your engineered unit, it's a very simple device that would be very easy to overbuild. Add a hepa filter, increase carbon filter quality/thickness, make it easy to change and use high static pressure fans to compensate for the additional restriction. How much there was to gain from this would depend on the original engineering, but it's an easy and cheap project.

K H
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