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Establishing Minimum Ventilation Rates for Control
of Health Hazards in Laboratories Using Chemicals
John L. Peterson, P.E.,
the University of Texas System
Laboratory design professionals include dilution ventilation
in their designs to control the buildup of fugitive emissions in
laboratories using chemicals. However, providing this standard duty
of care is fraught with legal liability because the appropriate
dilution rate, often referred to as air exchange rate, depends upon
the physical properties, toxicity, and quantity of the fugitive
chemical emissions released.
Unfortunately, the ventilation rates recommended in ASHRAE Standard
62, "Ventilation for Acceptable Indoor Air Quality," are
not useful in limiting occupant exposure to the potential health
hazards resulting from such chronic releases. Furthermore, calculating
an acceptable air exchange rate using the approach presented in
Annex A to NFPA 45, "Fire Protection for Laboratories Using
Chemicals," is not advisable because this approach assumes
that the same rate of vapor emission regardless of chemical volatility.
The approach presented herein is offered as guidance to the design
community as it pursues the establishment of recommended air exchange
rates for such laboratories.
Labs21 Connection:
A calculation approach for determining occupant exposure to hazardous
chemicals resulting from fugitive emissions is presented. A specific
liquid volume representing a release is postulated, the rate of
the resulting vapor emission calculated, and the time-dependent
chemical concentration determined. The resulting short-term and
long-term concentration averages are compared to the Threshold Limit
Values for Chemical Substances in The Work Environment adopted by
the American Conference of Governmental Industrial Hygienists. Finally,
the air exchange rates limiting occupant exposure to these thresholds
is tabulated.
In demonstrating a commitment to the principles of the Labs21 Approach
to laboratory design, the energy cost implication of applying various
air exchange rates within a typical laboratory is determined. The
eQuest building energy analysis computer program is applied in this
determination using Dallas, Texas, weather data and results are
presented in graphical form showing annual utility bill savings
as functions of miscellaneous equipment loads and minimum air exchange
rates.
Biography:
John L. Peterson, P.E., holds 25 years of experience in
the design and analysis of building energy systems. He is author
or co-author of 35 technical publications and two United States
patents related to energy use in building and associated equipment.
He served on a nationally-recognized committee supporting Texas'
efforts to develop energy efficient design standards for state residential
buildings, and he performed research in renewable energy programs
at the Los Alamos National Laboratory. John has conducted training
and testing programs for lighting, refrigeration, space-conditioning,
ventilation, water heating, and electrical system equipment and
has applied models to define energy use and conservation opportunities
in numerous structures. Currently, John serves the University of
Texas System as a Mechanical Engineer in review of mechanical, electrical
and plumbing (MEP) designs submitted by consultants for new construction
and major renovations at University of Texas System campuses. He
holds a bachelor's degree and a master's degree in mechanical engineering
from San Jose State University and New Mexico State University,
respectively. John has served in committee leadership posts for
the American Society of Heating, Refrigerating, and Air Conditioning
Engineers, and was recently recommended for membership on the Environmental
Health Committee by ASHRAE's President-Elect.
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