Theatre Design & Technology - Summer 2017 - 40

Figure 4 - Custom cabinet and venting solutions can be fabricated after
consultation with appropriate experts.

per hour, sometimes called the air change rate, which
is the measure of how often the air in a room is replaced.
The phrase "10 air changes per hour" is a common recommendation in darkroom photography ventilation, which
can be similar to air change rates for theatres and classrooms. The big distinction for darkroom photography is
that the air vented out is sent outside the building and not
recirculated. Recirculating air typically adds 5 to 30 percent
of fresh outside air, while the same amount of inside air
is exhausted out, so the majority of the air is just reused.
This recirculation is common in comfort HVAC systems
because they are primarily looking at controlling the CO2
levels. For workspaces that introduce chemicals, replacing
exhausted air is recommended.
One option for dealing with air contaminant exposure
is to leave the room while the printer is in use, although
this is unlikely to be a viable solution for most users. If a
printer is specified for unsupervised operation, then it may
be possible to print unattended and only enter the room
hours after the print is finished; however, most low-cost
consumer models are not designed for this type of operation. In practice, clearing the work area is a very impractical
solution due to its inefficient use of resources.
Two more practical and common methods of mitigating particulates in the air include diluting the amount
of particulates in the area and exhausting the fumes out
of the workspace entirely. OSHA explains the options like
this: "General exhaust ventilation, also called dilution ventilation, is different from local exhaust ventilation because
instead of capturing emissions at their source and removing them from the air, general exhaust ventilation allows
the contaminant to be emitted into the workplace air and
then dilutes the concentration of the contaminant to an
acceptable level (e.g., to the PEL or below). Dilution systems are often used to control evaporated liquids." General
exhaust ventilation is usually considered appropriate when
the hazards are diluted in the air and are a 'relatively low
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hazard' like most airborne dusts. Whereas a local exhaust is
required for larger particles (like sawdust) or more hazardous particles emitted from a single point like spray booth
or 3D printer. A detailed explanation can be found on OSHA's website (https://tinyurl.com/osha3D). While having
general exhaust can help with air quality, it is not effective for fumes with very low PELs or TLVs. (Remember,
the lower the value the higher the toxicity.) To understand
what may be required to reduce the airborne chemicals
from 3D printers and to address operator exposure, it is
helpful to look at the SDSs for the materials again. The
sometimes innocuous phrasing used by manufacturers can
have some deeper implications.
SDS Sheets: While the information on Safety Data
Sheets for 3D printers is incredibly varied and sometimes
conflicting, most do specify local ventilation. Users will see
general advisories about the need for ventilation because
of the fumes produced through 3D printing. For instance,
Makerbot's SDS for their brands of ABS and PLA plastic
specifies: "Provide local exhaust ventilation system. Ventilation should be sufficient to effectively remove and prevent buildup of any dusts or fumes that may be generated
during handling or thermal processing" (Makerbot ABS
SDS).
However, the focus on ventilation can obscure other
risks, particularly for casual users and readers. For example,
Ultimaker specifies for their brand of ABS: "Good general
ventilation (typically 10 air changes per hour) is recommended." They also recommend "process enclosures, local exhaust ventilation, or other engineering controls that
maintain airborne levels below recommended exposure
limits." But there are no PELs or TLVs mentioned on
their data sheet to guide users with assessing those exposure limits. In fact, in the hazards identification section it
notes: "No risk exists to the health of users if the product
is handled and processed properly" (Ultimaker ABS SDS).
The latter could be seen as downplaying the potential risks,
given that we are unsure about the PELs and TLVs.
As discussed earlier, the lack of discussion of PELs
does not mean that no hazardous fumes are emitted during printing. Consider the Safety Data Sheet for Formlabs resin, which suggests: "Ventilation Controls: Ensure
adequate ventilation." The same Formlabs SDS states that
there are no OSHA PELs for the components in the resin.
All that means is that the components listed are not among
the tiny percentage of chemicals that have been tested by
OSHA. But if we look at other chemicals common in resins, they all have a very low value. Butadiene, one of the byproducts of ABS plastic, has a PEL of one part per million.
Some resins, like the ones by FormLabs, use methacrylic
acid esters mixed with other chemicals. Methacrylic acid
has a PEL of 20 parts per million. In comparison, carbon
dioxide has a PEL of 5,000 parts per million. That should

https://www.tinyurl.com/osha3D

Table of Contents for the Digital Edition of Theatre Design & Technology - Summer 2017