Engineering Manual o.. - HVAC.Amickracing

INDOOR AIR QUALITY FUNDAMENTALSGas And Vapor ContaminantsThe terms gas and vapor are often used to describe a commonstate of a substance. Gas normally describes any mixture, exceptatmospheric air, that exists in the gaseous state at normalatmospheric conditions. Examples are oxygen, helium, andnitrogen, all naturally occurring useful gases, and ozone, anunstable ion of oxygen which is a contaminant.Vapor describes a substance in the gaseous state that can alsoexist as a liquid or solid at normal atmospheric conditions.Examples include contaminants such as gasoline, benzene,carbon tetrachloride, and life sustaining water.Radionuclide ContaminantsRadioactive contaminants can be particulate or gaseous andemit 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 anexternal hazard. The penetrating ability of gamma rays dependson their energy, which varies with the type of radioactiveelement or isotope.Radioactive materials present problems that make themdistinctive. The contaminants can generate enough heat todamage filtration equipment or ignite materials spontaneously.The concentrations at which most radioactive materials arehazardous are much lower than those of ordinary materials.INDOOR AIR CONTAMINANT INDICATORSHUMAN RESPONSES TO CONTAMINANTSHumans respond to contaminated and uncomfortableenvironments in predictable and known ways. Responses tocontaminants in the air can be coughing, sneezing, nausea,breathlessness, drowsiness, headaches, depression, and eye,throat, and skin irritation. All of these lead to annoyance andloss of productivity if not illness. Odors are more easily detectedwhen relative humidity is high. These symptoms often lead tocomplaints or cases of sick building syndrome, building relatedillness, or multiple chemical sensitivity, all of which haveeconomic costs.Sick Building Syndrome is the term applied to buildingswith no specific, identifiable contaminants, but with at least20 percent of the occupants complaining of a problem thatsubsides after exiting the building. Complaints often resultfrom discomfort from temperature or humidity rather thanIAQ problems.Building Related Illness is the term applied to a specificidentifiable medical condition of know etiology that isdocumented by physical signs and laboratory tests.Multiple Chemical Sensitivity is the term applied to an illnessresulting from exposure to multiple chemicals, none of whichby itself would cause a problem in most people.BUILDING RESPONSES TO CONTAMINANTSBuilding responses to indoor air contamination include visualsigns of fungus, mold, mildew, dirt buildup, corrosion, anddiscoloration The growth of fungus, mold, and mildew is foundin showers, duct work, local humidifiers and dehumidifiers,mechanical spaces, cooling towers, and also on walls andwindows.Dirt buildup occurs around supply air diffusers, in filter banks,on coils, and in duct work.Corrosion, embrittlement, and discoloration result fromgaseous contaminants causing chemical reactions, usually withmoisture, in high relative humidity conditions.DESIGN CONSIDERATIONS.GENERALThe generally accepted rules for improving IAQ are:1. Eliminate the source.2. Eliminate the path.3. Remediate the level of contaminants that cannototherwise be eliminated.These rules are discussed in the following as well as theeffects of temperature and humidity on the occupants..ELIMINATING CONTAMINANT SOURCESControlling the source of contaminants requires identifyingand categorizing contaminants into those that can and thosethat cannot be eliminated. Sources that can be eliminated bygood design principals are selection of building materials andfurnishings that eliminate VOCs. Building occupants and theirprocess items are sources that cannot be eliminated. Wheresources cannot be eliminated they must be controlled tominimize their prevalence and removed or reduced toacceptable levels. An example is applying a fume hood to astove or other process.ELIMINATING CONTAMINANT PATHSPathways for airborne contamination are categorized as activeor passive. Active pathways are those where a mechanicaldevice aids movement of the contaminant. Passive pathwaysare those where gravity or pressure differential provide themotive force.ENGINEERING MANUAL OF AUTOMATIC CONTROL147