One of the primary concerns associated with occupant wellness in a laboratory building is the ability to maintain acceptable indoor air quality
levels. This can be challenging as these facilities are
designed for activities that use, and often result in the
release of, emissions from various types of hazardous
and odorous chemical compounds. This creates a risk
that indoor air quality will be compromised within the
laboratory space, potentially exposing occupants to
unsafe or uncomfortable emission levels.
This aspect of risk can be addressed during the
design stage through the use of detailed modeling
and optimization of the ventilation system. Internally,
this process involves the use of computational fluid
dynamics (CFD) modeling to evaluate and optimize
performance of the ventilation system to maintain
indoor air quality and comfort.
CFD modeling has the ability to consider several
internal variables; such as diffuser/exhaust locations,
heat from windows and equipment and chemical spills
outside of fume hoods, or other containment devices.
Externally, dispersion modeling of the exhaust (using
numerical or physical wind tunnel techniques) is used to
optimize the exhaust ventilation rate and stack design.
Through evaluation of parameters such as exhaust
and air intake locations, stack height and stack exit
velocity, the minimum exhaust ventilation rates
required to maintain acceptable air quality levels at
the building air intakes can be determined. Thus,
any air entering the laboratory space would not
compromise the indoor quality of air provided by the
internal ventilation system.
This whole building approach is an effective means
of balancing a laboratory design that is energy efficient
and sustainable, while providing a safe and effective
environment for the occupants.
Optimizing internal ventilation
The term or metric that is most often used as an
indicator of the internal ventilation effectiveness for
laboratory design is the air change rate—or more
specifically, the number of air changes per hour
There is a common misconception in the industry
that a higher ACH provides a safer laboratory. In
many cases, the ventilation systems may be over-
designed, and there is reluctance to reduce ventilation
rates due to the perceived risk involved. Part of the
risk is associated with the potential to compromise the
safety within the laboratory when a chemical spill or
leak occurs outside of a fume hood. In these cases, the
hope is that the ventilation rate will provide enough
air changes to recover from the spill and provide some
protection to the occupants of the laboratory.
However, even for minor chemical releases within
the room itself, a ventilation rate between 6 and
12 ACH (which may be considered high by today’s
standards) is not nearly enough to maintain safety.
As an example, considering a database of commonly
used liquid laboratory chemicals, Figure 1 illustrates
the percentage of chemicals adequately ventilated in
the case of a spill by a given air change rate (this data
involves several assumptions including complete mixing
of chemicals within the room).
Two spill sizes are represented in Figure 1—500 mL
and 5 mL. The latter size is representative of a very
minor spill, and would also be indicative of normal
operating conditions within a laboratory where some
analyses and procedures may take place on the bench
itself, rather than within a fume hood.
As an example, considering a spill ranging from 5 mL
to 500 mL, the ACH required to address the majority
(~80 percent) of commonly used chemicals can range
from 40 to over 1000. Based on this, it is not possible
to maintain safety by simply relying on the ACH.
The design of the laboratory to recover from a spill
Lab Design Optimized for Occupant Health
By Aimée Smith, M.Eng., P.Eng., RWDI
Figure 1: Percentage of chemicals reduced to acceptable
concentrations for a given ACH. Image: RDWI