Honeywell AUTOMATIC CONTROL SI Edition, Engineering Manual

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ENGINEERING MANUAL OF AUTOMATIC CONTROL
INDOOR AIR QUALITY FUNDAMENTALS
158
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 other-
wise 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.
Passive pathways include vertical elevator and mechanical shafts
which permit gravity flow of airborne contaminants, and drop
ceilings, tunnels, and partition walls where mold, mildew and
fungus may be growing, spreading, and generating spores.
Frequently, exterior walls are found to permit entry of water,
moisture, and contaminated outdoor air. In large spaces such as
manufacturing areas and atriums, pressure differentials cause the
movement of contaminants.