mitigating iaq problems (pdf)

Mitigating IAQ Problems 81

7Mitigating IAQ Problems

Over the years many types of mitigation(correction) strategies have been imple-mented to solve indoor air quality prob-lems. The purpose of this section is toprovide an understanding of basic ap-proaches to mitigation and the varioussolutions that can be effective in treatingcommonly-encountered IAQ problems. Itis not intended to provide detailed instruc-tions for using each type of mitigationapproach but rather to give guidance inselecting a mitigation strategy and injudging proposals from in-house staff oroutside consultants.

Mitigation of indoor air quality prob-lems may require the involvement ofbuilding management and staff represent-ing such areas of responsibility as:

■ facility operation and maintenance■ housekeeping■ shipping and receiving■ purchasing■ policymaking■ staff training

Successful mitigation of IAQ problemsalso requires the cooperation of otherbuilding occupants, including the employ-ees of building tenants. Occupants must beeducated about the cause(s) of the IAQproblems and about actions that must betaken or avoided to prevent a recurrence ofthe problems.

BACKGROUND: CONTROLLINGINDOOR AIR PROBLEMS

Section 2 introduced the idea that indoorair quality problems result from interac-tions between contaminant source,building site, building structure, activitieswithin the building, mechanical equipment,climate, and occupants. Efforts to control

indoor air contaminants change therelationships between these factors. Thereare many ways that people can intervene inthese relationships to prevent or controlindoor air contaminant problems. Controlstrategies can be categorized as:

■ source control■ ventilation■ air cleaning■ exposure control

Successful mitigation often involves acombination of these strategies. Possibleremedies for the other environmentalstressors discussed in Section 6 arediscussed briefly below.

Source Control

All efforts to prevent or correct IAQproblems should include an effort toidentify and control pollutant sources.Source control is generally the most costeffective approach to mitigating IAQproblems in which point sources ofcontaminants can be identified. In the caseof a strong source, source control may bethe only solution that will work.

The following are categories andexamples of source control:

Remove or reduce the source■ prohibit smoking indoors or limit

smoking to areas from which air isexhausted, not recirculated (NIOSHregards smoking areas as an interimsolution)

■ relocate contaminant-producing equip-ment to an unoccupied, better ventilated,or exhaust-only ventilated space

■ select products which produce fewer orless potent contaminants while maintain-ing adequate safety and efficacy

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■ modify other occupant activities

Seal or cover the source■ improve storage of materials that

produce contaminants■ seal surfaces of building materials that

emit VOCs such as formaldehyde

Modify the environment■ after cleaning and disinfecting an area

that is contaminated by fungal orbacterial growth, control humidity tomake conditions inhospitable forregrowth

Source removal or reduction cansometimes be accomplished by a one-timeeffort such as thorough cleaning of a spill.In other cases, it requires an ongoingprocess, such as establishing and enforcinga non-smoking policy.

Sealing or covering the source can be asolution in some cases; application of abarrier over formaldehyde-emittingbuilding materials is an example. Sealingmay also involve educating staff orbuilding occupants about the contaminant-producing features of materials andsupplies and inspecting storage areas toensure that containers are properlycovered.

In some cases, modification of theenvironment is necessary for effectivemitigation. If the indoor air problemarises from microbiological contaminants,for example, disinfection of the affectedarea may not eliminate the problem.Regrowth of microbiologicals couldoccur unless humidity control or othersteps, such as adding insulation to preventsurface condensation, are taken to makethe environment inhospitable to micro-biologicals.

Ventilation

Ventilation modification is often used tocorrect or prevent indoor air qualityproblems. This approach can be effectiveeither where buildings are underventilatedor where a specific contaminant source

cannot be identified. Ventilation can beused to control indoor air contaminants by:

Diluting contaminants with outdoor air■ increase the total quantity of supply air

(including outdoor air)■ increase the proportion of outdoor air to

total air■ improve air distribution

Isolating or removing contaminants bycontrolling air pressure relationships■ install effective local exhaust at the

location of the source■ avoid recirculation of air that contains

contaminants■ locate occupants near supply diffusers

and sources near exhaust registers■ use air-tightening techniques to maintain

pressure differentials and eliminatepollutant pathways

■ make sure that doors are closed wherenecessary to separate zones

Diluting contaminants by increasingthe flow of outdoor air can be accom-plished by increasing the total supplyairflow in the complaint area (e.g., openingsupply diffusers, adjusting dampers) or atthe air handling unit, (e.g., cleaning thefilter on the supply fan). An alternative isto increase the proportion of outdoor air(e.g., adjusting the outdoor air intakedamper, installing minimum stops onvariable air volume (VAV) boxes so thatthey satisfy the outdoor air requirements ofASHRAE 62-1989).

Studies have shown that increasingventilation rates to meet ASHRAEStandard 62-1989 (e.g., from 5 to 15 or 20cfm/person) does not necessarily signifi-cantly increase the total annual energyconsumption. The increase appears to beless than 5% in typical commercialbuildings. The cost of ventilation isgenerally overshadowed by other operatingcosts, such as lighting. Further, improvedmaintenance can produce energy savingsto balance the costs that might otherwiseresult from increased ventilation.


The cost of modifying an existingHVAC system to condition additionaloutdoor air can vary widely dependingupon the specific situation. In somebuildings, HVAC equipment may not havesufficient capacity to allow successfulmitigation using this approach. Originalequipment is often oversized so that it canbe adjusted to handle the increased load,but in some cases additional capacity isrequired.

Most ventilation deficiencies appear tobe linked to inadequate quantities ofoutdoor air. However, inadequate distribu-tion of ventilation air can also produceIAQ problems. Diffusers should beproperly selected, located, installed, andmaintained so that supply air is evenlydistributed and blends thoroughly withroom air in the breathing zone. Short-circuiting occurs when clean supply air isdrawn into the return air plenum before ithas mixed with the dirtier room air andtherefore fails to dilute contaminants.Mixing problems can be aggravated bytemperature stratification. Stratificationcan occur, for example, in a space withhigh ceilings in which ceiling-mountedsupply diffusers distribute heated air.

Note the side effects of increasedventilation:■ mitigation by increasing the circulation

of outdoor air requires good outdoor airquality

■ increased supply air at the problemlocation might mean less supply air inother areas

■ increased total air in the system andincreased outdoor air will both tend toincrease energy consumption and mayrequire increased equipment capacity

■ any approach which affects airflow inthe building can change pressuredifferences between rooms (or zones)and between indoors and outdoors, andmight lead to increased infiltration ofunconditioned outdoor air

■ increasing air in a VAV system mayovercool an area to the extent thatterminal reheat units are needed

Ventilation equipment can be used toisolate or contain contaminants bycontrolling pressure relationships. If thecontaminant source has been identified,this strategy can be more effective thandilution. Techniques for controlling airpressure relationships range from adjust-ment of dampers to installation of localexhaust.

Using local exhaust confines the spreadof contaminants by capturing them near thesource and exhausting them to the out-doors. It also dilutes the contaminant bydrawing cleaner air from surrounding areasinto the exhaust airstream. If there arereturn grilles in a room equipped with localexhaust, the local exhaust should exertenough suction to prevent recirculation ofcontaminants. Properly designed andinstalled local exhaust results in far lowercontaminant levels in the building thancould be accomplished by a generalincrease in dilution ventilation, with theadded benefit of costing less.

Note that replacement air must be ableto flow freely into the area from which theexhaust air is being drawn. It may benecessary to add door or wall louvers inorder to provide a path for the make-up air.(Make sure that this action does not violatefire codes.)

Correct identification of the pollutantsource and installation of the local exhaustis critically important. For example, animproperly designed local exhaust candraw other contaminants through theoccupied space and make the problemworse.

The physical layout of grilles anddiffusers relative to room occupants andpollutant sources can be important. Ifsupply diffusers are all at one end of aroom and returns are all at the other end,the people located near the supplies maybe provided with relatively clean air whilethose located near the returns breathe airthat has already picked up contaminantsfrom all the sources in the room that arenot served by local exhaust.

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Elimination of pollutant pathways by airsealing (e.g., caulking cracks, closingholes) is an approach that can increase theeffectiveness of other control techniques.It can be a difficult technique to implementbecause of hidden pathways (e.g., abovedrop ceilings, under raised flooringagainst brick or block walls). However, itcan have other benefits such as energysavings and more effective pest control (byeliminating paths used by vermin).

Air Cleaning

The third IAQ control strategy is to cleanthe air. Air cleaning is usually most effec-tive when used in conjunction with eithersource control or ventilation; however, itmay be the only approach when the sourceof pollution is outside of the building.Most air cleaning in large buildings isaimed primarily at preventing contaminantbuildup in HVAC equipment and enhanc-ing equipment efficiency.

Air cleaning equipment intended toprovide better indoor air quality for occu-pants must be properly selected and de-signed for the particular pollutants of inter-est (for example, gaseous contaminants canbe removed only by gas sorption). Onceinstalled, the equipment requires regularmaintenance in order to ensure good per-formance; otherwise it may become amajor pollutant source in itself. This main-tenance requirement should be borne inmind if an air cleaning system involving alarge number of units is under consider-ation for a large building. If room units areused, the installation should be designedfor proper air recirculation.

There are four technologies that removecontaminants from the air:

■ particulate filtration■ electrostatic precipitation■ negative ion generation■ gas sorption

The first three approaches are designedto remove particulates, while the fourth isdesigned to remove gases.

Particulate filtration removes sus-pended liquid or solid materials whosesize, shape and mass allow them to remainairborne for the air velocity conditionspresent. Filters are available in a range ofefficiencies, with higher efficiency indicat-ing removal of a greater proportion ofparticles and of smaller particles. Movingto medium efficiency pleated filters isadvisable to improve IAQ and increaseprotection for equipment. However, thehigher the efficiency of the filter, the moreit will increase the pressure drop within theair distribution system and reduce totalairflow (unless other adjustments are madeto compensate). It is important to select anappropriate filter for the specificapplication and to make sure that theHVAC system will continue to perform asdesigned. Filters are rated by differentstandards (e.g., arrestance and dust spot)which measure different aspects ofperformance.

Electrostatic precipitation is anothertype of particulate control. It uses theattraction of charged particles to oppo-sitely charged surfaces to collect airbornepar-ticulates. In this process, the particlesare charged by ionizing the air with anelectric field. The charged particles arethen col-lected by a strong electric fieldgenerated between oppositely-chargedelectrodes. This provides relatively highefficiency filtration of small respirableparticles at low air pressure losses.

Electrostatic precipitators may be in-stalled in air distribution equipment or inspecific usage areas. As with other filters,they must be serviced regularly. Note,however, that electrostatic precipitatorsproduce some ozone. Because ozone isharmful at elevated levels, EPA has setstandards for ozone concentrations in out-door air, and NIOSH and OSHA have


established guidelines and standards, re-spectively, for ozone in indoor air. Theamount of ozone emitted from electrostaticprecipitators varies from model to model.

Negative ion generators use staticcharges to remove particles from the indoorair. When the particles become charged,they are attracted to surfaces such as walls,floors, table tops, draperies, and occupants.Some designs include collectors to attractthe charged particles back to the unit.Negative ion generators are not availablefor installation in ductwork, but are sold asportable or ceiling-mounted units. As withelectrostatic precipitators, negative iongenerators may produce ozone, eitherinten-tionally or as a by-product of use.

Gas sorption is used to control com-pounds that behave as gases rather than asparticles (e.g., gaseous contaminants suchas formaldehyde, sulfur dioxide, ozone, andoxides of nitrogen). Gas sorption involvesone or more of the following processeswith the sorption material (e.g., activatedcarbon, chemically treated active clays): achemical reaction between the pollutantand the sorbent, a binding of the pollutantand the sorbent, or diffusion of the con-taminant from areas of higher concentrationto areas of lower concentration. Gas sorp-tion units are installed as part of the airdistribution system. Each type of sorptionmaterial performs differently with differentgases. Gas sorption is not effective forremoving carbon monoxide. There are nostandards for rating the performance ofgaseous air cleaners, making the design andevaluation of such systems problematic.Operating expenses of these units can bequite high, and the units may not be effec-tive if there is a strong source nearby.

Exposure Control

Exposure control is an administrative ap-proach to mitigation that uses behavioralmethods, such as:

Scheduling contaminant-producing acti-vities to avoid complaints■ schedule contaminant-producing activi-

ties to occur during unoccupied periods■ notify susceptible individuals about up-

coming events (e.g., roofing, pesticideapplication) so that they can avoid contactwith the contaminants

Scheduling contaminant-producing ac-tivities for unoccupied periods wheneverpossible is simple common sense. It maybe the best way to limit complaints aboutactivities (such as roofing or demolition)which unavoidably produce odors or dust.

Relocating susceptible individuals■ move susceptible individuals away from

the area where they experience symptoms

Controlling exposure by relocating sus-ceptible individuals may be the only practi-cal approach in a limited number of cases,but it is probably the least desirable optionand should be used only when all otherstrategies are ineffective in resolving com-plaints.

Remedies for Complaints NotAttributed to Poor Air Quality

Specific lighting deficiencies or localizedsources of noise or vibration can sometimesbe readily identified, and remedial actionmay be fairly straightforward (more orfewer lights on, adjustments for glare; relo-cating, replacing or acoustically insulating anoise or vibration source). Similarly, fla-grant ergonomic stress or blatant psycho-social stress may be apparent even toan untrained observer.

In other cases, however, problems maybe more subtle or solutions more complex.Since specialized knowledge, skills, andinstrumentation are usually needed toevaluate lighting, noise, vibration, ergo-nomic stress, or psychosocial stress, suchevaluations are generally best done by aqualified professional in that particularfield.

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Remedial actions for lighting, noise,and vibration problems might range frommodifications of equipment or furnishingsto renovation of the building. Ergonomicdeficiencies may require furniture orequipment changes or different workpractices. The solution to psychosocialproblems may involve new managementpractices, job redesign, or resolution ofunderlying labor-management problems.

SAMPLE PROBLEMS ANDSOLUTIONSIn the investigation section you wereintroduced to a variety of problems that areoften found in buildings. This sectionpresents fifteen categories of IAQ prob-lems. Specific problem “examples” aregiven, followed by solutions” that havebeen used for that category of problem.Most of the problems presented here arecommon and do not have serious, life-threatening consequences. At the end ofthe section is a brief description ofproblems that can have severe healthimpacts. The basic correction principlesthat apply to these serious problems aresimilar to those used in less criticalsituations.

Reading these examples may help youto think about the best way to solve yourindoor air quality problems. Rememberthat these are brief sketches, and apparentparallels to your building could be mis-leading. It is better to carry out a buildinginvestigation and learn the specific facts inyour own case, rather than adopt a mitiga-tion approach that might not be appropri-ate. Attempting to correct IAQ problemswithout understanding the cause of thoseproblems can be both ineffective andexpensive.

You will note that some solutions aresimple and low-cost, while others arecomplex and expensive. Do not assume

that each solution listed would be aneffective treatment for all of the problemsin its category.

The example problems and solutions arepresented in the following sequence:

Problem #1: Outdoor air ventilation rateis too low

Problem #2: Overall ventilation rate ishigh enough, but poorlydistributed and not sufficientin some areas

Problem #3: Contaminant enters buildingfrom outdoors

Problem #4: Occupant activities contrib-ute to air contaminants or tocomfort problems

Problem #5: HVAC system is a source ofbiological contaminants

Problem #6: HVAC system distributescontaminants

Problem #7: Non-HVAC equipment is asource or distribution mecha-nism for contaminants

Problem #8: Surface contamination due topoor sanitation or accidents

Problem #9: Mold and mildew growthdue to moisture from con-densation

Problem #10: Building materials andfurnishings producecontaminants

Problem #11: Housekeeping or mainte-nance activities contribute toproblems

Problem #12: Specialized use areas assources of contaminants

Problem #13: Remodeling or repair activi-ties produce problems

Problem #14: Combustion gases

Problem #15: Serious building-relatedillness


Problem #1:Outdoor Air VentilationRate is Too Low

Examples

Routine odors from occupants andnormal office activities result in problems(e.g., drowsiness, headaches, discomfort)

Measured outdoor air ventilation rates donot meet guidelines for outdoor air supply(e.g., design specifications, applicablecodes, or ASHRAE 62-1989)

Peak CO2 concentrations above 1000ppm indicate inadequate ventilation

Corrosion of fan casing causes airbypassing and reduces airflow in system

Solutions

Open, adjust or repair air distributionsystem

■ outdoor air intakes■ mixing and relief dampers■ supply diffusers■ fan casings

Increase outdoor air within the designcapacity of

■ air handler■ heating and air conditioning equipment■ distribution system

Modify components of the HVAC systemas needed to allow increased outdoor air

(e.g., increase capacity of heating andcooling coils)

Design and install an updated ventilationsystem

Reduce the pollutant and/or thermal loadon the HVAC system

■ reduce the occupant density: relocatesome occupants to other spaces toredistribute the load on the ventilationsystem

■ relocate or reduce usage of heat-generating equipment

Malfunctioning controls such as this brokendamper linkage can virtually eliminateintake of outdoor air. Such problems maygo undetected for years without a carefulinvestigation of the HVAC systemcomponents.

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Problem #2:Overall Ventilation Rate IsHigh Enough, But PoorlyDistributed and NotSufficient in Some Areas

Examples

Measured outdoor air meets guidelines atbuilding air inlet, but there are zoneswhere heat, routine odors from occu-pants, and normal office activities resultin complaints(e.g., drowsiness, headaches, comfortcomplaints)

Solutions

Open, adjust, or repair air distributionsystem

■ supply diffusers■ return registers

Ensure proper air distribution

■ balance the air handling system■ make sure that there is an air gap at tops

and bottoms of partitions to prevent deadair space

■ relocate supply and/or return diffusers toimprove air distribution

Seal leaky ductwork

Remove obstructions from return airplenum

Control pressure relationships

■ install local exhaust in problem areasand adjust HVAC system to provideadequate make-up air

■ move occupants so that they are closer tosupply diffusers

■ relocate identified contaminant sourcescloser to exhaust intakes

Reduce source by limiting activities orequipment use that produce heat, odors,or contaminants

Design and install an appropriateventilation system

Complaining of discomfort, buildingoccupants blocked air supply diffusers intheir work areas. The HVAC system in thisbuilding was in poor condition and was notbalanced.


Problem #3:Contaminant EnteringBuilding From Outdoors

Examples

Soil gases(e.g., radon, gasoline from tanks, methanefrom landfills)

Contaminants from nearby activities(e.g., roofing, dumpster, construction)

Outdoor air intake near source(e.g., parking, loading dock, buildingexhaust)

Outdoor air contains pollutants or excessmoisture(e.g., cooling tower mist entrained inoutdoor air intake)

Solutions

Remove the source, if it can be movedeasily

■ remove debris around outdoor air intake■ relocate dumpster

Reduce source (for example, shift time ofactivity to avoid occupied periods)

■ painting, roofing, demolition■ housekeeping, pest control

Relocate elements of the ventilationsystem that contribute to entry of outdoorair contaminants

■ separate outdoor air intakes from sourcesof odors, contaminants

■ separate exhaust fan outlets fromoperable windows, doors, air intakes

■ make rooftop exhaust outlets taller thanintakes

Change air pressure relationships tocontrol pollutant pathways

■ install subslab depressurization toprevent entry of soil gas contaminants(radon, gases from landfills and under-ground tanks)

■ pressurize the building interior relative tooutdoors (this will not prevent contami-nant entry at outdoor air intakes)

■ close pollutant pathways (e.g., sealcracks and holes)

Add special equipment to HVAC system

■ filtration equipment to remove pollutants(select to fit the situation)

For cosmetic reasons, airintakes are frequently locatedon rooftops or near theground. This air intake couldbecome a means of drawinglawn cuttings, vehicleexhaust, and pesticides intothe building.

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Problem #4:Occupant ActivitiesContribute to AirContaminants or toComfort Problems

Personal equipment such as humidifiersbrought in by building occupants canbecome a source of contaminants if notproperly maintained. An effectivecommunication strategy can helpoccupants to understand their role incausing indoor air quality problems and incorrecting those problems.

Examples

Smoking

Special activities such as print shops,laboratories, kitchens

Interference with HVAC systemoperation:

■ blockage of supply diffusers to eliminatedrafts

■ turning off exhaust fans to eliminatenoise

■ use of space heaters, desktop humidifiersto remedy local discomfort

(Note: While such interference can causeIAQ problems, it is often initiated inresponse to unresolved ventilation ortemperature control problems.)

Solutions

Remove the source by eliminating theactivity(Note: This may require a combination ofpolicy-setting and educational outreach.)

■ smoking■ use of desktop humidifiers and other

personal HVAC equipment■ unsupervised manipulation of HVAC

system

Reduce the source■ select materials and processes which

minimize release of contaminants whilemaintaining adequate safety and efficacy(e.g., solvents, art materials)

Install new or improved local exhaust toaccommodate the activity, adjust HVACsystem to ensure adequate make-up air,and verify effectiveness

■ smoking lounge, storage areas whichcontain contaminant sources

■ laboratory hoods, kitchen range hoods(venting to outdoors, not recirculating)


Problem #5:HVAC System is a Source ofBiological Contaminants

The HVAC system can act as a source ofcontaminants by providing a hospitableenvironment for the growth of microorgan-isms and by then distributing biologically-contaminated air within the building.

Examples

Surface contamination by molds (fungi),bacteria■ drain pans■ interior of ductwork■ air filters and filter media (collected

debris).

Solutions

Remove source by improving mainte-nance procedures■ inspect equipment for signs of corrosion,

high humidity■ replace corroded parts■ clean drip pans, outdoor air intakes,

other affected locations■ use biocides, disinfectants, and sanitizers

with extreme caution and ensure thatoccupant exposure is minimized

(Note: See discussion of duct cleaning inAppendix B.)

Provide access to all the items thatmust be cleaned, drained, or replacedperiodically

This blackish deposit was scraped from apoorly-maintained air handling unit drainpan. The pan contained nutrients causedby poor upstream filtration and stagnantwater that fostered the growth ofmicrobiological contaminants.

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Problem #6:HVAC System DistributesContaminants

Standing water on a roof can cause waterdamage and potential mold growth sitesinside the building as well as providing abreeding area for insects andmicrobiologicals such as Legionella. Theoutside air intake (near the far left of thisphotograph) is located close to thestanding water and could be drawing ininsects and microbiological contaminants.

Examples

Unfiltered air bypasses filters due toproblems

■ filter tracks are loose■ poorly-maintained filters sag when they

become overloaded with dirt■ filters are the wrong size

Recirculation of air that contains dust orother contaminants

■ system recirculates air from roomscontaining pollutant sources

■ return air plenum draws air from roomsthat should be exhausted (e.g. janitor’sclosets)

■ return air plenums draw soil gases frominteriors of block corridor walls thatterminate above ceilings

Solutions

Modify air distribution system tominimize recirculation of contaminants

■ provide local exhaust at point sources ofcontaminants, adjust HVAC system toprovide adequate make-up air, and test toverify performance

■ increase proportion of outdoor air■ seal unplanned openings into return air

plenums and provide alternative localventilation (adjust HVAC system toprovide adequate make-up air and test toverify performance)

Improve housekeeping, pest control,occupant activities, and equipment use tominimize release of contaminants fromall sources

Install improved filtration equipment toremove contaminants

Check filter tracks for any gaps


Problem #7:Non-HVAC Equipment isa Source or DistributionMechanism for Contaminants

This discussion pertains to medium- tolarge-scale pieces of equipment.

Examples

Non-HVAC equipment can producecontaminants, as in the case of:

■ wet process copiers■ large dry process copiers■ engineering drawing reproduction

machines

It can also distribute contaminants, as inthe case of:

■ elevators, which can act as pistons anddraw contaminants from one floor toanother

Solutions

Install local exhaust near machines(Note: Adjust HVAC system to provideadequate make-up air, and test to verifyperformance.)

Reschedule use to occur during periods oflow occupancy

Remove source

■ relocate occupants out of roomsthat contain contaminant-generatingequipment

■ relocate equipment into special useareas equipped with effective exhaustventilation (test to verify control of airpressure relationships)

Change air pressure relationships toprevent contaminants from enteringelevator shaft

Sometimes there are unusual sources ofindoor air quality problems. An inspectionof the HVAC system revealed air filterscovered with a graphite dust deposit from abroken elevator motor generator. Themotor generator was repaired andcorrections were made to prevent thecrossover of ventilation air from the motorgenerator into the HVAC mechanical room.

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Problem #8:Surface ContaminationDue to Poor Sanitation orAccidents

The carpet on this floor was floodedand an outbreak of humidifier feveroccurred. To eliminate microbiologicals,the contaminated carpet was removed andnew carpet was installed.

Examples

Biological contaminants result in aller-gies or other diseases

■ fungal, viral, bacterial (whole organismsor spores)

■ bird, insect, or rodent parts or droppings,hair, dander (in HVAC, crawlspace,building shell, or near outdoor airintakes)

Accidents

■ spills of water, beverages, cleansers,paints, varnishes, mastics or specializedproducts (printing, chemical art supplies)

■ fire damage: soot, odors, chemicals

Solutions

Clean

■ HVAC system components■ some materials and furnishings (others

may have to be discarded)(Note: Use biocides, disinfectants, andsanitizers with caution and ensure thatoccupant exposure is minimized.)

Remove sources of microbiologicalcontamination

■ water-damaged carpet, furnishings, orbuilding materials

Modify environment to prevent recur-rence of microbiological growth

■ improve HVAC system maintenance■ control humidity or surface temperatures

to prevent condensation

Provide access to all items that requireperiodic maintenance

Use local exhaust where corrosivematerials are stored

Adjust HVAC system to provide adequatemake-up air, and test to verify perfor-mance


Problem #9:Mold and Mildew GrowthDue to Moisture fromCondensation

Examples

Interior surfaces of walls near thermalbridges(e.g., uninsulated locations around struc-tural members)

Carpeting on cold floors

Locations where high surface humiditypromotes condensation

Solutions

Clean and disinfect to remove mold andmildew.(Note: Follow up by taking actions toprevent recurrence of microbiologicalcontamination. Use biocides, disinfec-tants, and sanitizers with caution andensure that occupant exposure is mini-mized.)

Increase surface temperatures to treatlocations that are subject to condensation

■ insulate thermal bridges■ improve air distribution

Reduce moisture levels in locations thatare subject to condensation

■ repair leaks■ increase ventilation (in cases where

outdoor air is cold and dry)■ dehumidify (in cases where outdoor air

is warm and humid)

Dry carpet or other textiles promptly aftersteam cleaning(Note: Increase ventilation to acceleratedrying.)

Discard contaminated materials

This is a school crawlspace in whichmoisture should be controlled. The fungusis Fusarium, some species of which aretoxigenic and should not be inside. Thespores were distributed by the air handlerbecause the return plenum was open to thecrawlspace.

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Low levels of contaminants are emittedfrom many of the building materialsand furnishings in an office. Dust canaccumulate on stacks of papers andopen shelves. Depending on howthey are cared for, plants potentiallyadd moisture, soil microbiologicals,and pesticides.

Examples

Odors from newly installed carpets,furniture, wall coverings

Newly drycleaned drapes or other textiles

Solutions

Remove source with appropriate cleaningmethods

■ steam clean carpeting and upholstery,then dry quickly, ventilating to acceler-ate the drying process

■ accept only fully dried, odorlessdrycleaned products

Encapsulate source

■ seal surfaces of building materials thatemit formaldehyde

Reduce source

■ schedule installation of carpet, furniture,and wall coverings to occur duringperiods when the building is unoccupied

■ have supplier store new furnishings in aclean, dry, well-ventilated area untilVOC outgassing has diminished

Increase outdoor air ventilation

■ total air supplied■ proportion of fresh air

Remove the materials that are producingthe emissions and replace with loweremission alternatives(Note: Only limited information onemissions from materials is available atthis time. Purchasers can request thatsuppliers provide emissions test data, butshould use caution in interpreting the testresults.)

Problem #10:Building Materials andFurnishings ProduceContaminants


Problem #11:Housekeeping or MaintenanceActivities Contribute toProblems

Examples

Cleaning products emit chemicals, odors

Particulates become airborne duringcleaning (e.g., sweeping, vacuuming)

Contaminants are released from painting,caulking, lubricating

Frequency of maintenance is insufficientto eliminate contaminants

Solutions

Remove source by modifying standardprocedures or frequency of maintenance(Note: Changing procedures may require acombination of policy-setting and trainingin IAQ impacts of staff activities.)

■ improve storage practices■ shift time of painting, cleaning, pest

control, other contaminant-producingactivities to avoid occupied periods

■ make maintenance easier by improvingaccess to filters, coils, and other compo-nents

Reduce source

■ select materials to minimize emissions ofcontaminants while maintaining ad-equate safety and efficacy

■ use portable HEPA (high efficiencyparticulate arrestance”) vacuums vs. low-efficiency paper-bag collectors

Use local exhaust

■ on a temporary basis to remove contami-nants from work areas

■ as a permanent installation wherecontaminants are stored

Indoor air quality problems can be causedby lack of adequate house-keepingpractices. On the other hand, deodorizers,cleansers and other products can alsoproduce odors and contaminants.

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Problem #12:Specialized Use Areas asSources of Contaminants

This chemical storage room should bemaintained under negative pressure.Properly designed and maintained localexhaust will achieve the proper air pressurerelationship with surrounding areas.Otherwise, such storage areas can be asource of occupant exposure to manyairborne contaminants.

Examples

Food preparationArt or print roomsLaboratories

Solutions

Change pollutant pathway relationships

■ run specialized use area under negativepressure relative to surrounding areas

■ install local exhaust, adjust HVACsystem to provide make-up air, and testto verify performance

Remove source by ceasing, relocating, orrescheduling incompatible activities

Reduce source by selecting materials tominimize emissions of contaminantswhile maintaining adequate safety andefficacy

Reduce source by using proper sealingand storage for materials that emitcontaminants


Problem #13:Remodeling or RepairActivities Produce Problems

Examples

Temporary activities produce odors andcontaminants

■ installation of new particleboard,partitions, carpet, or furnishings

■ painting■ reroofing■ demolition

Existing HVAC system does not provideadequate ventilation for new occupancyor arrangement of space

Solutions

Modify ventilation to prevent recircula-tion of contaminants

■ install temporary local exhaust inwork area, adjust HVAC system toprovide make-up air, and test toverify performance

■ seal off returns in work area■ close outdoor air damper during

re-roofing

Reduce source by scheduling work forunoccupied periods and keeping ventila-tion system in operation to remove odorsand contaminants

Reduce source by careful materialsselection and installation

■ select materials to minimize emissionsof contaminants while maintainingadequate safety and efficacy

■ have supplier store new furnishings in aclean, dry, well-ventilated area untilVOC outgassing has diminished

■ request installation procedures (e.g.,adhesives) that limit emissions ofcontaminants

Remodeling may involvemany activities that cancause IAQ problems.Ventilation modifications canbe used to isolate the workarea and prevent pollutantbuild-up in occupied spaces.Proper storage practices canminimize the release ofcontaminants.

Modify HVAC or wall partition layout ifnecessary

■ partitions should not interrupt airflow■ relocate supply and return diffusers■ adjust supply and return air quantities■ adjust total air and/or outdoor air supply

to serve new occupancy

100 Section 7

Problem #14:Combustion Gases

Combustion odors can indicate theexistence of a serious problem. Onecombustion product, carbon monoxide, isan odorless gas. Carbon monoxidepoisoning can be life-threatening.

Examples

Vehicle exhaust

■ offices above (or connected to) anunderground parking garage

■ rooms near (or connected by pathwaysto) a loading dock or service garage

Combustion gases from equipment(e.g., spillage from inadequately ventedappliances, cracked heat exchanger, re-entrainment because local chimney is toolow)

■ areas near a mechanical room■ distributed throughout zone or entire

building

Solutions

Seal to remove pollutant pathway

■ close openings between the contaminantsource and the occupied space

■ install well-sealed doors with automaticclosers between the contaminant sourceand the occupied space

Remove source

■ improve maintenance of combustionequipment

■ modify venting or HVAC system toprevent backdrafting

■ relocate holding area for vehicles atloading dock, parking area

■ turn off engines of vehicles that arewaiting to be unloaded

Modify ventilation system

■ install local exhaust in undergroundparking garage (adjust HVAC system toprovide make-up air and test to verifyperformance)

■ relocate fresh air intake (move awayfrom source of contaminants

Modify pressure relationships

■ pressurize spaces around area containingsource of combustion gases

Air intakes are frequently located near theloading dock for aesthetic reasons.Unfortunately, this air intake placement candraw car and truck exhaust into thebuilding, causing a variety of indoor airquality complaints.


Problem #15:Serious Building-RelatedIllness

Some building-related illnesses can be life-threatening. Even a single confirmeddiagnosis (which involves results fromspecific medical tests) should provoke animmediate and vigorous response.

Examples

Legionnaire’s disease(Note: If you suspect Legionnaire’sdisease, call the local public healthdepartment, check for obvious problemsites, and take corrective action. There isno way to be certain that a single case ofthis disease is associated with buildingoccupancy; therefore, public healthagencies usually do not investigate singlecases. Watch for new cases.)

Hypersensitivity pneumonitis(Note: Affected occupant(s) should beremoved and may not be able to returnunless the causative agent is removed fromthe affected person’s environment.)

Solutions

Work with public health authorities

■ evacuation may be recommended orrequired

Remove source

■ drain, clean, and decontaminate drippans, cooling towers, room unit airconditioners, humidifiers, dehumidifiers,and other habitats of Legionella, fungi,and other organisms using appropriateprotective equipment

■ install drip pans that drain properly■ provide access to all the items that must

be cleaned, drained, or replaced periodi-cally

■ modify schedule and procedures forimproved maintenance

Discontinue processes that depositpotentially contaminated moisture in airdistribution system

■ air washing■ humidification■ cease nighttime shutdown of air handlers

This air intake is locatedbetween the cooling towers.If the water in the coolingtowers becomescontaminated with Legionella,there is potential forLegionnaire’s disease in thebuilding.

102 Section 7

JUDGING PROPOSEDMITIGATION DESIGNSAND THEIR SUCESS

Mitigation efforts should be evaluated atthe planning stage by considering thefollowing criteria:

■ permanence■ operating principle■ degree to which the strategy fits the job■ ability to institutionalize the solution■ durability■ installation and operating costs■ conformity with codes

Permanence

Mitigation efforts that create permanentsolutions to indoor air problems are clearlysuperior to those that provide temporarysolutions (unless the problems are alsotemporary). Opening windows or runningair handlers on full outdoor air may besuitable mitigation strategies for a tempo-rary problem such as outgassing of volatilecompounds from new furnishings, butwould not be good ways to deal withemissions from a print shop. A permanentsolution to microbiological contaminationinvolves not only cleaning and disinfec-tion, but also modification of the environ-ment to prevent regrowth.

Operating Principle

The most economical and successfulsolutions to IAQ problems are those inwhich the operating principle of thecorrection strategy makes sense and issuited to the problem. If a specific pointsource of contaminants has been identified,treatment at the source (e.g., by removal,sealing, or local exhaust) is almost alwaysa more appropriate correction strategy thandilution of the contaminant by increasedgeneral ventilation. If the IAQ problem iscaused by the introduction of outdoor airthat contains contaminants, increasedgeneral ventilation will only make the

situation worse (unless the outdoor air iscleaned).

Degree to Which the StrategyFits the Job

It is important to make sure that youunderstand the IAQ problem well enoughto select a correction strategy whose sizeand scope fit the job. If odors from aspecial use area such as a kitchen arecausing complaints in a nearby office,increasing the ventilation rate in the officemay not be a successful approach. Themitigation strategy should address theentire area affected.

If mechanical equipment is needed tocorrect the IAQ problem, it must bepowerful enough to accomplish the task.For example, a local exhaust systemshould be strong enough and close enoughto the source so that none of the contami-nant is drawn into nearby returns andrecirculated.

Ability to Institutionalizethe Solution

A mitigation strategy will be most success-ful when it is institutionalized as part ofnormal building operations. Solutions thatdo not require exotic equipment are morelikely to be successful in the long run thanapproaches that involve unfamiliarconcepts or delicately maintained systems.If maintenance or housekeeping proce-dures or supplies must change as part ofthe mitigation, it may be necessary to planfor additional staff training, new inspectionchecklists, or modified purchasing prac-tices. Operating schedules for HVACequipment may also require modification.

Durability

IAQ mitigation strategies that are durableand low-maintenance are more attractive toowners and building staff than approachesthat require frequent adjustment or

The most economicaland successfulsolutions to IAQproblems are thosein which the operat-ing principle of thecorrection strategymakes sense and issuited to the prob-lem.


specialized maintenance skills. New itemsof equipment should be quiet, energy-efficient, and durable, so that the operatorsare encouraged to keep them running.

Installation and OperatingCosts

The approach with the lowest initial costmay not be the least expensive over thelong run. Other economic considerationsinclude: energy costs for equipment opera-tion, increased staff time for maintenance;differential cost of alternative materialsand supplies; and higher hourly rates ifodor-producing activities (e.g., cleaning)must be scheduled for unoccupied periods.Although these costs will almost certainlybe less than the cost of letting the problemcontinue, they are more readily identifi-able, so an appropriate presentation tomanagement may be required.

Conformity with Codes

Any modification to building componentsor mechanical systems should be designedand installed in keeping with applicablefire, electrical, and other building codes.

Judging the Success of aMitigation Effort

Two kinds of criteria can be used to judgethe success of an effort to correct an indoorair problem:

■ reduced complaints■ measurement of properties of the indoor

air (often only of limited usefulness)

Reduction or elimination of complaintsappears to be a clear indication of success,but that is not necessarily the case.Occupants who see that their concerns arebeing heard may temporarily stop report-ing discomfort or health symptoms, even ifthe actual cause of their complaints has notbeen addressed. Lingering complaints mayalso continue after successful mitigation ifpeople have become upset over the

MANAGING MITIGATION PROJECTSINVOLVING SEVERE CONTAMINATION

Cautions

Locating the original source of a chemi-cal release or microbiological growthmay only be the tip of the iceberg.Pollutants often tend to migrate througha building and collect in “sinks”, fromwhich they can be resuspended into theair. For example, particles accumulateon horizontal surfaces that are notsubject to regular housekeeping; odorsmay adsorb (stick) to porous materials.Detailed surface and/or bulk samplingmay be needed to locate such “second-ary” sources in order to solve an airquality problem.

Depending on the problem, a detailedknowledge of chemistry, microbiology,building science, and health and safetymay be required.

Include air sampling along with regularinspections if needed. Decontaminationof areas within an occupied building isespecially critical.

In the event of severe contamination,representative air samples should becollected to ensure that key indicatorshave returned to background levels andthat the space can be safely reoccupied.

Elements

Identify the extent of contami-nation

Develop a precise scope ofwork specifying exactly howremediation will be performed

Monitor remediation to ensurework practices are followed

Conduct clearancesampling

Many routine IAQ problems can becorrected by a common sense approachnot requiring special expertise. However,when complex exposure or contaminationissues are involved, more detailed techni-cal assistance may be needed for success-ful remediation. Efforts such as thoseoutlined above are sometimes needed todeal with severe contamination.

104 Section 7

handling of the problem. Ongoing (butreduced) complaints could also indicatethat there were multiple IAQ problems andthat one or more problems are still unre-solved.

However, it can be very difficult to usemeasurements of contaminant levels as ameans of determining whether air qualityhas improved. Concentrations of indoorair pollutants typically vary greatly overtime; further, the specific contaminantmeasured may not be causing the problem.If air samples are taken, readings takenbefore and after mitigation should beinterpreted cautiously. It is important tokeep the “before” and “after” conditions asidentical as possible, except for theoperation of the control strategy. Forexample, the same HVAC operation,building occupancy and climatic condi-tions should apply during both measure-ment periods. “Worst-case” conditionsidentified during the investigation shouldbe used.

Measurements of airflows, ventilationrates, and air distribution patterns are themore reliable methods of assessing theresults of control efforts. Airflow mea-surements taken during the buildinginvestigation can identify areas with poorventilation; later they can be used toevaluate attempts to improve the ventila-tion rate, distribution, or direction of flow.Studying air distribution patterns will showwhether a mitigation strategy has success-fully prevented a contaminant from beingtransported by airflow.

Persistent Problems

Solving an indoor air quality problem is acyclical process of data collection and

hypothesis testing. Deeper and moredetailed investigation is needed to suggestnew hypotheses after any unsuccessful orpartially-successful control attempt.

Even the best-planned investigationsand mitigation actions may not produce aresolution to the problem. You may havemade a careful investigation, found one ormore apparent causes for the problem, andimplemented a control system. Nonethe-less, your correction strategy may not havecaused a noticeable reduction in theconcentration of the contaminant orimprovement in ventilation rates orefficiency. Worse, the complaints maypersist even though you have beensuccessful at improving ventilation andcontrolling all of the contaminants youcould identify. When you have pursuedsource control options and have increasedventilation rates and efficiency to the limitsof your expertise, you must decide howimportant it is to pursue the problemfurther.

If you have made several unsuccessfulefforts to control a problem, then it may beadvisable to seek outside assistance. Theproblem is probably fairly complex, and itmay occur only intermittently or cross theborders that divide traditional fields ofknowledge. It is even possible that poorindoor air quality is not the actual cause ofthe complaints. Bringing in a newperspective at this point can be veryeffective.

The next section provides guidance onhiring professional indoor air qualityassistance. An interdisciplinary team (suchas people with engineering and medical orhealth backgrounds) may be needed tosolve particularly difficult problems.

If you have madeseveral unsuccessfulefforts to control aproblem, then it maybe advisable to seekoutside assistance.

mitigating iaq problems (pdf)

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