Environmental Engineering Reference
In-Depth Information
gated and an additional 27 substances regulated under occupational safety
and health rules. ASHRAE guideline values for HCHO proved to be very
controversial. Due to threatened lawsuits by HCHO producers and users,
ASHRAE, in its revision of 62-1981, deleted HCHO from its IAQ guidelines
and relegated other guideline values to the document's appendix.
In response to residential exposure concerns, a committee of the National
Research Council developed and published interim exposure guidelines for
pesticides used to control termites. These included guideline values of 5
µ
chlorpyrifos; values that
were one tenth of the permissible limits used to protect occupationally
exposed persons.
g/m
chlordane, 2
µ
g/m
heptaclor, and 10
µ
g/m
3
3
3
B.
Ventilation guidelines
Ventilation guidelines for mechanically ventilated buildings have a long
history of use in the U.S. and other developed countries. Historically, these
have been developed through a consensus process by ASHRAE. Ventilation
guidelines (or standards, as they are called) are recommended values. They
have the force of law only when incorporated into building codes (as they
often are). ASHRAE guidelines are considered to be good practice design
values; therefore they are used by architectural firms whether or not they
are included in state and local building codes. They usually specify some
minimum ventilation rate that will provide occupants with a reasonably
comfortable environment at design capacity, with minimum sensory percep-
tion of human odor and discomfort.
Guideline values for ventilation in mechanically ventilated buildings
have changed over the past four decades. In 1973, ASHRAE, in response to
energy conservation concerns, reduced its ventilation guideline for office
environments from 10 CFM (4.76 L/sec) per person to 5 CFM (2.37 L/sec)
per person. This was contained in ASHRAE Standards 62-73 and 62-81, and
used by building design engineers for approximately 15 years. In Standard
62-89, ASHRAE, recognizing that a 5 CFM per person ventilation standard
was not adequate, increased the ventilation guideline to 20 CFM (9.52 L/s)
per person for office buildings and 15 CFM (7.14 L/sec) per person for
schools. A building designed for a 5 CFM per person ventilation rate at
design capacity would be expected to have maximum CO
levels of 2500
2
ppmv; one for 20 CFM would have 800 ppmv.
Guideline values are used by design engineers to determine air flow
capacity required in new buildings at design occupancy. It is expected that
facility managers can then operate ventilation systems to achieve and main-
tain adequate ventilation during occupancy. Unfortunately, in many cases
ventilation systems are not operated to conform to guideline values, as
evidenced in complaint investigations. This has been due to management
concerns associated with ventilation air energy costs, malfunctioning equip-
ment, and poor technical and operational understanding of HVAC system
operation by facility staff.
