How high are the actual emissions, once all factors are taken into account and compared with normally accepted thresholds?
In the 3D printing community it’s common to hear warnings related to printing ABS at home and suggestions about venting the fumes outside with a direct hose, using active carbon filters to adsorb VOcs, and so on.
But how dangerous is it really, once we take everything into account?
ABS is known to release, among the other, styrene, which is linked to development of cancer. WHO reclassified it in 2018 from “possibly cancerogenic” to “probably cancerogenic”. Still, biology doesn’t work as “yes/no”, concentration levels matter, and likewise exposure time matters.
People like to publish videos in YouTube showing measurements from (usually) cheap VOC meters, but they are seldomly calibrated and they don’t provide a detailed picture. I’ll try a more scientific approach.
A worst case scenario
We should consider the following aspects:
- Styrene emissions from the material
- removal of Styrene from the environment
- permanence of the person in the contaminated environment
- duration of the emission
- limits for inhalation
The scientific article “Summary and derived Risk Assessment of 3D printing emission studies” (public access) describes the results of a meta-analysis of other scientific papers on the topic. It mentions damages in cells due to the emissions from 3D printers. Styrene is discussed, but it is also mentioned that according to some studies PLA emissions, due to their smaller size, actually cause more damage.
The article publishes this figure with typical Styrene emissions in the range between approximately 10 µg/min to 115 µg/min during printing:
No further information is provided about which filaments are usually high emitters and which ones are low emitters.
We will assume the highest scenario — 115 µg/min — because the article predates the rise of modern (fast) 3D printers (which became widespread one year later). Therefore, the emission values published should be realistically doubled to account for the lower throughput of the machines used for the testing.
If the printer is located in a 3x4x1.75 m room (a home office or bedroom), that’s a volume of 21 m³, leading to a concentration of 5.5 µg/min/m³.
The official UL recommendations about ventilation in domestic environments refer to 1 to 5 complete air exchanges per hour for similarly sized rooms. Assuming just 1 exhange per hour, the maximum concentration would be:
5.5 µg/min × 60 min = 330 µg/m³
How long would the exposure last? We can assume the worst (and by far very unrealistic) scenario, with a printer is running all the time and the resulting concentration of pollutants constant, and a person spends 8 hours per day in that room. This would be classified as occupational exposure, not acute/intermittent exposure. The exposure limits would be higher, but again we will stick to non-industrial (residential) exposure thresholds for this assessment.
The document Styrene – A Common Air Pollutant lists the recommended exposure thresholds (residential and occupational) as provided by various health and safery entities from US and Europe.
For residential, non-occupational exposure, nearly all thresholds are around 800-1000 µg/m³, roughly three times as high as our worst case, unrealistic scenario. Only one entity, the German “Ausschuss zur gesundheitlichen Bewertung von Bauprodukten”, sets the LCI limit to 250 µg/m³, but said limit is related to product emissions, not for indoor air quality. Even then, this is only 25% lower than our calculated value.
While we referred to indoor, non-occupational limits, it’s worth noting that someone exposed 8 hours a day to such emissions would fall under occupational exposure, typically measured in mg/m³, not µg/m³, 100-2500 times higher than what we calculated.
Summary
We used the worst case scenario: day and night printing in a relatively small room, with a person spending 8 hours a day inside.
Even under this highly unrealistic assumption, the styrene concentration is comparable to the strictest recommended limit which could be found, and remains well below the more common recommended limits for indoor, residential air quality (with industrial limits hundreds of times higher).
It is reasonable to conclude that emissions from ABS are not a significant health concern, especially considering the article linked refers to PLA potentially resulting in even worse damage to cells.
Some practical cases
An old i3-style printer such as old Ender 3’s, Prusa MK3, Prusa Mini: these printers are by today standards very slow, so they emit little. They also cannot use the ABS filaments which are the most temperature resistant but must use specific blends which reduce warping, so styrene content is also lower to begin with. For example, Polymaker ABS emits barela any smell (surely less than PLA) and since styrene has a typical smell, this also implies very low emissions. No real risk here.
A similar old printer but with an enclosure: a wider range of ABS filaments can be used, but the enclosure limits release in the room, so ventilating the room by opening windows at the end of the prints should be enough.
A modern and fast printer (easily recognised by a maximum speed above 500 mm/s or by the use of “Klipper” as firmware): if it’s not enclosed, the same limitations apply, so high-styrene content filaments cannot really be used. If enclosed, the emissions can be intense, but the enclosure still contains them a lot. This is my case, for example, and personally I don’t find the smell very significant since the air inside the enclosure is not vented until the end of the print. Even in this case, ventilating the room at the end should be enough.
Ventilating the room means 5-10 minutes of windows open.
Addendum: Energy loss by opening the windows
I find online people complaining about ABS smell and refusing to open windows because of the energy losses in winter, or the need for extra cooling in summer. But is this really making any difference? not really, and this is why.
First of all, opening windows for 5-10 minutes won’t cool or heat the furniture or walls significantly, their mass is simply too big. Only the air in the room will be replaced with the external one.
This calculation is copied and adapted from this post in Reddit.
Let’s say you replace in summer all the air inside the room (20 °C) with hot air (35 °C), how much energy will it cost to cool it down to 20 °C again?
An single bedroom has a surface (common European houses) of 16 m² and it’s 2.65 m tall, for a volume of 42 m³ empty. Mass density of air is approximately 1.225 kg/m^3 which multiplied by 42 gives a total mass of 51 kg.
So we have 51 kg of air and want to cool the air from 35 °C to 20 °C. Let’s start with the easiest calculation – how much energy would we need to heat the cold air to room temperature (the other way around, which would be the case of opening windows in winter)? We can use this formula (which can be used with a calculator):
ΔQ = m x ΔT x c
where ΔQ is the heat we need (the energy), m is the mass of the air, ∆T is the temperature change and c is the specific heat. The only thing we don’t have is the specific heat. A quick google search reveals that at constant pressure, the specific heat is 1.00 kJ/(kg*K). Plugging in the numbers gives an energy cost of
ΔQ = m x ΔT x c = 51 x 15 x 1.0 = 765 kJ (kilojoules) of energy.
So the heating of the air needs 765 kJ. How expensive would that be? 4.7 kJ is approximately 0.2 kilowatt hours, so with average electricity prices, 0.30 €/kWh, it costs 0.2 x 0.30 = 0.06 € to heat all that air.
So, for the case of opening windows in winter, and printing every day, it would be less than 2 € per month.
In summer it’s cheaper… the cooling process in airco’s can give a coefficient of performance of higher than 1. The theoretical limit for the temperatures we mentioned above is COP <= T_c / (T_h – T_c) = 17.3125 (T_c is cold temperature, T_h is hot, both measured in Kelvin). This means that for each Joule you put into the fridge, it can suck much more than 1 Joule out. So it would actually cost less to cool down the air than heating it up. A realistic COP is nowadays 3 or more, so in summer cooling the room would cost 0.02 € per print.
TL;DR: So no, it isn’t expensive to ventilate a room after a 3D print.
Edit: as /u/TellMeYourButtStory pointed out, the calculations above assumed dry air whereas moist air might be more correct. To include these effects, two things will change: the mass density and the specific heat. The mass density will actually be reduced (because some of the heavier air molecules like N_2 are replaced by water molecules that are less dense. The specific heat will increase, but not by much (maybe a factor 2, for sure less than a factor 4 which is dense water specific heat). TL;DR: So including these effects will not change the conclusion at all.