I would like to buy a 3D printer, but I'm concerned about the health risks that are associated with its operation. Some groups of scientists say it can be harmful for humans.
What do I need to consider before buying a 3D printer if I care about my health? Are there any safe printers?
There is very little information about safety available, as home 3D printers are relatively new. However, plastics such as ABS have a long history in making plastic products, and a study found that at traditional manufacturing methods (such as injection molding and hot wire cutting) do not release dangerous levels of carcinogens and/or respiratory sensitizers in to the air.
Of course, 3D printers are not among the processes covered in the study. In home 3D printing circles, this study that looks at ultrafine particle (UFP) emissions, is often cited. It finds that printing ABS releases relatively high levels of UFP's and PLA releases significantly fewer (but still quite a large amount). However, it is unclear whether/how dangerous these UFP's are in the amounts emitted.
It is often suggested that PLA, partly because of the reduced UFP emissions is safer to print than ABS, partly because of its "natural" origins as it can be derived from materials such as cornstarch. I would caution against this line of reasoning since "natural" materials can still be poisonous (snake venom is natural, after all) and the cornstarch is heavily processed so it hardly resembles its original form. The lower UFP emissions may suggest it is safer, but the study is only quantitative, not qualitative.
That said, PLA does probably pose less of a risk (despite my earlier argumentation against "natural" materials, PLA does play quite nicely with the human body), but I contend the risk with ABS is not too large anyways, given that it has been safely used in factories for decades.
Another study is often miscited, supposedly saying that 3D printing ABS releases hydrogen cyanide. The study only looks at the thermal decomposition of ABS, which happens at significantly higher temperatures than are reached during printing (but a significantly malfunctioning printer might cause toxic gasses to be released, but I contend that at that point you should worry about your printer being on fire, rather than temporary exposure to some toxins).
There are no printers out there that are fundamentally safer than others. However, some printers have an enclosure (containing the fumes) and some even have a carbon filter and a fan for fume extraction. If you would like to err on the side of caution, this might be a good choice (but again, it is not clear if a carbon filter is totally effective).
Finally, as printers are generally quite noisy it tends to be preferrable to keep your printer in a separate room from where you usually work. In this case, fume exposure (during the few minutes that you go to check on your print) is minimal, and the potential advantages of a "safer" printers or using "safer" materials diminish.
Incidental exposure as a hobbyist is probably not a big deal; workers in factories are exposed to the fumes of melted plastic their entire lives and they don't seem to be dropping dead. On the other hand, if you are going to be printing structurally then it is probably preferable to move your printer to a separate room, if not because of health and safety because of the noise.
Almost all 3D printers have issues that could cause health problems.
FDM/FFF printers heat plastic to a temperature that may cause it to off-gas, and these byproducts may not be healthy.
SLA printers often use epoxies that may off-gas, or may be somewhat toxic prior to being cured.
Powder based printers can also off-gas, in addition to the powder itself presenting a possible hazard.
Many hobbyist and small companies dance around the problem, and suggest that the machines always be used in well ventillated areas. Professional machines often have filters and ventillation systems built in.
Rather than trying to find a "perfectly safe" 3D printer, spend some time deciding what you want to use one for, find printers suitable for your use, and expect that you'll need to provide reasonable ventilation for almost any printer. Plan your installation for that, and you should be able to make any printer safe for your required use.
If, however, you plan on setting up a printer farm with many printers, and plan to have yourself or others spend significant time operating them, I suggest you work with a health and safety professional and have them identify possible hazards and plan mitigation.
I am going to address the air issue as it is currently unresolved. the third dimension offers a great answer for common safety issues.
The short answer is that based on our limited knowledge at this point, there may be imperceptible health hazards related to FDM / FFF printers and therefore additional safety precautions are, in my opinion, necessary and not optional or secondary as suggested by some in the community.
In other words, if you can isolate your printer in a well-vented area where people rarely go, then of course it's not a health risk, but if people will be exposed to the air of the printer for any significant periods of time, you need to do something about it. This is my situation - where I live dedicated workshops and extra rooms are luxuries that most people do not have.
The key information at this point in time is the UFP (Ultra-Fine Particle) study that is linked in Tom's answer.
Leaving out the scary / detailed parts:
Therefore, results herein suggest that caution should be used when operating these 3D printing instruments inside unvented or unfiltered indoor environments due to their large emissions of UFPs.
One important limitation to this study is that we have no information about the chemical constituents of the UFPs emitted from either type of 3D printer [...]
[...] there may also be differences in toxicity because of differences in chemical composition.
This means that although many processes release UFPs (the authors of the paper compare to cooking), all UFPs are not created equal. Since the UFPs from 3D printing are still an unknown, the only real answer from a safety perspective is to treat them as dangerous.
I am not qualified to give an opinion on what should be done but I will share what I would do:
A note on positive vs negative pressure related to venting and filtering: if you produce positive pressure within the enclosure, you are going to be blowing all the UFPs out into your environment anyway. Negative pressure vented to a safe body of air or neutral pressure with good seals and recirculated filtering may avoid that.
A note on filters: Activated carbon filters will not remove UFPs. HEPA filters may remove 3D printing UFPs.
As long as the uncertainty exists, I predict that as the market matures, filtering and enclosures will become more standard. At this point in time, the only enclosed AND HEPA filtered consumer-grade FDM printers I am aware of are the Up! Box and the Zortrax Inventure. There are a number of enclosed printers without filtering.
As an alternative, at least one company has appeared with products targeted at those who are concerned about various safety aspects of 3d printing.
Apart from the inherent process itself and direct health hazards from that, many 3D printers also require some complementary technology to work.
fdm printers have a printing head that needs to move around in 3D space. Moving machinery parts can be a hazard. In a home/hobbyist environment with children for example, I would recommend to buy a printer with a housing.
"open" designs often feature bare electronics mounted directly to the printer structure. This rises the possibility of short circuits and electric shock.
The printers that heat material often do so at very high temperatures. Hot parts of the printer should not be touched.
