ASHRAE Journal - September 2023 - 14

COLUMN ENGINEER'S NOTEBOOK
diffusers should be located so as not
to create a cross draft. Standard Z9.5
states that " Supply air distribution
shall be designed to keep air jet
velocities less than half, preferably
less than one-third of the capture
velocity or the face velocity of the
laboratory chemical hoods at their
face opening. "
Some activities, such as small
dissections, may benefit from a
point of use exhaust device, such
as a snorkel in lieu of a fume hood.
Snorkels have an articulating arm and
can be positioned directly behind the
operation to pull contaminants away
from the student's breathing zone.
Science Laboratory Exhaust
The International Mechanical
Code (IMC) (2021 and previous
versions) requires that science laboratories in education
occupancies be mechanically exhausted at the rate
of 1 cfm/ft2 (5 L/s·m2). This air is not allowed to be
recirculated to other spaces. In limited situations,
recirculation of some air from laboratories is allowed,
but this would only be allowed if the supply air to the
space exceeds 1 cfm/ft2 (5 L/s·m2) (see Note g in Table
403.3.1.1 of the 2018 IMC). If a science laboratory will
not have any materials present that are hazardous
to humans, it may be prudent to label it a " science
classroom " to avoid the IMC exhaust requirement for
science laboratories.
The Ventilation Rate Procedure in ANSI/ASHRAE
Standard 62.1-2022 requires educational science
laboratories to be exhausted at 1 cfm/ft2 (5 L/s·m2) and
designates the air as Class 2. Per the standard, Class 2
air may only be recirculated within the space of origin
or to Class 2 or Class 3 spaces that are used for the same
or similar purpose and involve the same or similar
pollutant sources. The standard also states that exhaust
from laboratory hoods shall be " air Class 4 unless
determined otherwise by the EHS [environmental
health and safety] professional responsible to the
owner or to the owner's designee. " The standard
prohibits recirculation or transfer of Class 4 air. This
appears to prohibit the use of any energy recovery
14
ASHRAE JOURNAL ashrae.org S E PTEM B ER 2023
FIGURE 4 Laboratory hazards.
device that has leakage or carryover
from the exhaust to the supply side.
If fume hoods are present in the
lab and their combined exhaust flow
equals or exceeds 1 cfm/ft2 (5 L/s·m2),
they are allowed to count toward the
code or ASHRAE Standard 62.1-2022
required exhaust. If the combined
hood airflow is less than or will be
reduced below 1 cfm/ft2 (5 L/s·m2),
additional general exhaust would be
required to make up the difference.
Most higher education science
laboratories are business (B)
occupancy per the International
Building Code; therefore, the science
lab exhaust requirement in the IMC
technically doesn't apply since it only
addresses education (E) occupancies.
ASHRAE Standard 62.1-2022 uses the
term " Occupancy Category " when
defining exhaust requirements for educational science
laboratories. It does not differentiate between code
occupancy classifications, so the exhaust requirements
in the standard would apply.
The IMC also lists requirements for location and
termination point for exhaust ducts carrying flammable
vapors, fumes or dusts. This may require the fan have
a stack. Proximity to operable openings, exterior walls
and roofs, and adjoining grade are all addressed.
An adequate supply of makeup air should be supplied
to the lab either via supply or transfer air. Since
Standard Z9.5 states that " airflow shall be from areas of
low hazard to higher hazard, " airflow from the adjacent
corridor should flow into the lab to minimize the risk of
hazardous fumes migrating into the corridor or other
adjacent spaces.
It may be prudent to check with the fire marshal
associated with the authority having jurisdiction to
confirm whether they have additional requirements that
need to be addressed.
Eyewash and Shower
Where a person's eyes or body may be exposed to
injurious corrosive materials, such as a science lab,
an emergency eyewash and shower is needed3 and
should be installed. ANSI/ISEA Z358.1-2014, Standard
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ASHRAE Journal - September 2023

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