Honeywell AUTOMATIC CONTROL, Engineering Manual

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INDOOR AIR QUALITY FUNDAMENTALS
158 ENGINEERING MANUAL OF AUTOMATION CONTROL
Gas And Vapor Contaminants
The terms gas and vapor are often used to describe a common
state of a substance. Gas normally describes any mixture, except
atmospheric air, that exists in the gaseous state at normal
atmospheric conditions. Examples are oxygen, helium, and
nitrogen, all naturally occurring useful gases, and ozone, an
unstable ion of oxygen which is a contaminant.
Vapor describes a substance in the gaseous state that can also
exist as a liquid or solid at normal atmospheric conditions.
Examples include contaminants such as gasoline, benzene,
carbon tetrachloride, and life sustaining water.
Radionuclide Contaminants
Radioactive contaminants can be particulate or gaseous and
emit alpha, beta, or gamma rays. Alpha rays present no hazard,
except when the material is deposited inside or on the body.
Beta rays are more penetrating and are both an internal and an
external hazard. The penetrating ability of gamma rays depends
on their energy, which varies with the type of radioactive
element or isotope.
Radioactive materials present problems that make them
distinctive. The contaminants can generate enough heat to
damage filtration equipment or ignite materials spontaneously.
The concentrations at which most radioactive materials are
hazardous are much lower than those of ordinary materials.
INDOOR AIR CONTAMINANT INDICATORS
HUMAN RESPONSES TO CONTAMINANTS
Humans respond to contaminated and uncomfortable
environments in predictable and known ways. Responses to
contaminants in the air can be coughing, sneezing, nausea,
breathlessness, drowsiness, headaches, depression, and eye,
throat, and skin irritation. All of these lead to annoyance and
loss of productivity if not illness. Odors are more easily detected
when relative humidity is high. These symptoms often lead to
complaints or cases of sick building syndrome, building related
illness, or multiple chemical sensitivity, all of which have
economic costs.
Sick Building Syndrome is the term applied to buildings
with no specific, identifiable contaminants, but with at least
20 percent of the occupants complaining of a problem that
subsides after exiting the building. Complaints often result
from discomfort from temperature or humidity rather than
IAQ problems.
Building Related Illness is the term applied to a specific
identifiable medical condition of know etiology that is
documented by physical signs and laboratory tests.
Multiple Chemical Sensitivity is the term applied to an illness
resulting from exposure to multiple chemicals, none of which
by itself would cause a problem in most people.
BUILDING RESPONSES TO CONTAMINANTS
Building responses to indoor air contamination include visual
signs of fungus, mold, mildew, dirt buildup, corrosion, and
discoloration The growth of fungus, mold, and mildew is found
in showers, duct work, local humidifiers and dehumidifiers,
mechanical spaces, cooling towers, and also on walls and
windows.
Dirt buildup occurs around supply air diffusers, in filter banks,
on coils, and in duct work.
Corrosion, embrittlement, and discoloration result from
gaseous contaminants causing chemical reactions, usually with
moisture, in high relative humidity conditions.
DESIGN CONSIDERATIONS.
GENERAL
The generally accepted rules for improving IAQ are:
1. Eliminate the source.
2. Eliminate the path.
3. Remediate the level of contaminants that cannot otherwise
be eliminated.
These rules are discussed in the following as well as the effects
of temperature and humidity on the occupants.
ELIMINATING CONTAMINANT SOURCES
Controlling the source of contaminants requires identifying
and categorizing contaminants into those that can and those
that cannot be eliminated. Sources that can be eliminated by
good design principals are selection of building materials and
furnishings that eliminate VOCs. Building occupants and their
process items are sources that cannot be eliminated. Where
sources cannot be eliminated they must be controlled to
minimize their prevalence and removed or reduced to
acceptable levels. An example is applying a fume hood to a
stove or other process. Another example is substituting for the
process chemical.
ELIMINATING CONTAMINANT PATHS
Pathways for airborne contamination are categorized as active
or passive. Active pathways are those where a mechanical device
aids movement of the contaminant. Passive pathways are those
where gravity or pressure differential provide the motive force.