The most common filament is ABS, and a common question is whether it is safe to use indoors. There has never been a study directly linking ABS use to adverse effects, and it is commonly used in a wide range of household products. However, Acrylonitrile, Butadiene, and Styrene are all either classified as carcinogens or mutagens. In other words doing things like breathing them on a regular basis over a long period of time is known to give you cancer or alter your DNA. To be fair, that is true of a lot of other things as well.
The thing that in our opinion could make this dangerous is that much like trees; waves at the beach; a pan full of olive oil; or Graphene; 3D printers create small particles called UFPs or ultrafine particles.1, Especially relevant are this passage:
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, although condensation of synthetic organic vapors from the thermoplastic feedstocks are likely a large contributor (Morawska et al., 2009). In addition to large differences in emission rates observed between PLA- and ABS-based 3D printers, there may also be differences in toxicity because of differences in chemical composition. As mentioned, thermal decomposition products from ABS have been shown to have toxic effects (Zitting and Savolainen, 1980 and Schaper et al., 1994); however, PLA is known for its biocompatibility and PLA nanoparticles are widely used in drug delivery (Anderson and Shive, 1997 and Hans and Lowman, 2002).
And this one:
In this work, we present some of the first known measurements of which we are aware of UFP emissions from commercially available desktop 3D printers. Emission rates of total UFPs were approximately an order of magnitude higher for 3D printers utilizing an ABS thermoplastic feedstock relative to a PLA feedstock: ∼1.9 × 1011 # min−1 compared to ∼2.0 × 1010 # min−1. However, both can be characterized as “high emitters” of UFPs. These results suggests caution should be used when operating some commercially available 3D printers in unvented or inadequately filtered indoor environments. Additionally, more controlled experiments should be conducted to more fundamentally evaluate aerosol emissions from a wider range of desktop 3D printers and feedstocks.
The primary concern with ultrafine particles is not that they exist, but what they are made of. Any material that the human body is unable to metabolize properly could be dangerous if it becomes an ultrafine particle.
Also, it is relevant to note that printing ABS releases HCN (Hydrogen Cyanide) which is neurotoxic in humans when chronic exposure takes place.2 And:
The toxicity of ABS thermal degradation products has been evaluated by five methods … no apparent toxicological difference exists between the flaming mode and the non-flaming mode.3
Acute exposure to lower concentrations (6 to 49 mg/m3) of hydrogen cyanide will cause a variety of effects in humans, such as weakness, headache, nausea, increased rate of respiration, and eye and skin irritation. link
So if you get a headache when you print ABS, immediate changes are needed to ensure the safety of your air supply.
Some commercially available home air filters are effective in mitigating UFP and HCN exposure, but they are unlikely to eliminate exposure. 4,5
Since carcinogenic exposure appears to be more or less cumulative 6 we encourage everyone to examine this information and draw their own conclusions, but we highly recommend the use of outside ventilation, or a HEPA, FEF or ESP filter if outside ventilation is unavailable. We have not found any evidence suggesting that PLA is dangerous, though dyes and other additives in PLA filaments could put humans at risk.
If you use a 3D printer indoors vent the exhaust outside or get an air purifier.
It may be best to avoid non-biodegradable filaments.
These steps may not be necessary, but the health hazards involved could have severe repercussions for you and those around you decades from now.