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Literature Review of Health Effects of Humidity-Influenced Indoor Pollutants

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Literature Review of Health Effects of Humidity-Influenced Indoor Pollutants UC Berkeley Indoor Environmental Quality (IEQ) Title Indoor Humidity and Human Health--Part I: Literature Review of Health Effects of Humidity- Influenced Indoor Pollutants Permalink https://escholarship.org/uc/item/5kz1z9cg Authors Baughman, A. Arens, Edward A Publication Date 1996 Peer reviewed eScholarship.org Powered by the California Digital Library University of California 3951 lndeer Humidity and HumanHealth Part Literature Reviewof Health Effects Anne V. Baughman Edward A. Arens, Ph.D. Student MemberASHRAE Member ASHRAE ABSTRACT under elevated humidities, although humidityinteractions with nonbiotic pollutants, such as formaldehyde, mayalso cause Standards for indoor thermal conclitions and ventilation include upper limits for relative humidio,(RH) that O~pically adverse effects. Existing limits appear to be based on engi- are hz the range of 60%to 80%RH. Although the reasons for neering experience with such humidityproblems in buildings. the limits are often not explicitly stated, it is generallyknown The position of any upper humidity limit has great that they were set out of concernfor the health effects that economicsignificance, particularly in hot and arid parts of the might occur shouMthe humidio, becometoo high. The pri- country, where evaporative cooling is an energy-conserving mal3, health effects o~ high humidio, are caused by the g~vwth option. In the West,it affects the needfor billions of dollars of and spread of biotic agents, although humidiO, interactions newpeak electrical generatingcapacity that could be offset by with nonbiotic pollutants, such as formaldehyde, may also noncompressor-based cooling. It also directly affects a causeadverse ~ffects. This literature review ident~’es the most substantial fraction of the cooling load in hot, humidclimates. important health issues associated with high humidities and Undersuch economicimperatives, it is desirable to carefully presents humidio, requirements, ~,pical contamination sites examinethe position of any upper humiditylimit. Ideally, one within buiMings, and remediation measures for each pollut- wouldbe able to assess the health risks against the economic ant. Part ~vo of the paper addresses the physical causes of benefits for any given humiditylimit. At present, there is not moisture-relatedptvblems in buildings. enoughinformation on this subject to even begin such an anal- ysis. INTRODUCTION Standards for indoor thermal conditions and for ventila- This reviewof the literature identifies a numberof health- tion have traditionally put upper limits on the amount of related agents that are affected by indoor humidity.All of them humiditypermissible in interior spaces becauseof concernfor affect humanhealth primarily throughtheir inhalation fiom the the health effects that mightoccur should the humiditybecome air, althoughsome of themhave lesser effects throughthe skin. too high. Such limits are found in past versions of ASHRAE Biological agents require appropriate conditions in the building Standards 55-1992 (ASHRAE1992) and 62-1989 (ASHRAE lbr their germination,growth, release to the air’, andtransport to 1989)and in most international standards. The values set for the humanhost. Airborne levels of nonbiological pollutants, the upper limits have typically ranged from 60%to 80%RH, such as formaldehyde and ozone, may also be affected by although boundaries of absolute humidityhave also been used. humiditythrough influences on offgassing and surface reaction To date, the relationship of high humidityto the full spectrum rates. Finally, the occupants’susceptibility to these agents may of air quality issues and to the relevant characteristics of also be a function of humidity, although this appears to be a building envelopes and conditioning systems has not yet been problem primarily at low humidities, when respiratory addressed in a comprehensivemanner’. This situation affects ailments result from dry mucousmembranes (Green 1985). our ability to set rational standardsand buildingspecifications. The health implications of low humidities are not addressed in Humanhealth is not affected by high levels of humidity this paper. Part two of this paper addressesthe relationships of per sen Knownhealth effects related to high humidity are the environmentswithin buildings and conditioning systems to primarily caused by the growth and spread of biotic agents the growthof biological pollutants. AnneV. Baughmanis a graduatestudent researcherand EdwardA. Arensis a professorin the Departmentof Architectureat the University of California,Berkeley~ ASHRAETransactions: Research 193 OVERVIEW OF HUMIDITY-RELATED Nonallergic immunologicresponses, characterized by HEALTH CONCERNS recurrent flu-like symptoms(e.g., hypersensitivity pneu- The primary influences of humidityon health are through monitis, farmer’s lung, and humidifierfever), seemto be unre- biological pollutants. The following outline describes the lated to the IgE antibody. Theyoccur as a result of repeated health issues most commonlyassociated with biological pollutant exposures that trigger other antibody-dependent pollutants. mechanismsas well as cellular immuneresponses. Although there seemsto be no genetic predisposition, only a fraction of Infectious disease (pathogens) those exposed develop overt symptoms(Burge 1988). bacteria (e.g., Streptococcus,Legionella) viruses (e.g., commoncold, flu) Mycotoxinsare producedby fungi and can lead to respira- fungi (e.g., Aspergillusfumigatus) tory irritation, interference with pulmonarymacrophage cells, and/or higher risks of cancer (Flanniganand Miller n.d.). Many Allergic reactions(e.g., asthma,rhinitis) fungi also produce volatile organic compounds(VOCs) that dust mites (dried bodyparts and fecal excreta) maybe respiratory irritants and have been suggested as a fungi contributing factor to sick-building-type symptomsin microbi- Nonallergic immunologicreactions (e.g., hypersensitivity ally contaminated buildings (Bjurman1993; Sorenson1989). pneumonitis) Nonbiological pollutants, such as formaldehyde,ozone, fungi oxides of nitrogen, and sulfur, affect humansprimarily through bacteria chemicalirritation of the mucousmembranes. Formaldehyde is Myctoxicosis released into the indoorair frombuilding materials in waysthat fungi are dependenton atmospherichumidity. Surface reactions, and Infectious disease can occur when viable pathogenic consequently the amountand toxicity of ozone and nitrogen organismsenter (usually through inhalation) and colonize oxides (NOx)and sulfur oxides (SOx) in the air, maybe influ- the body of a susceptible host. The most commonlyfound enced by humidity levels. The extent to which humidity pathogensare bacteria or viruses, although fungal pathogens, increases or’ decreases the health impactsof these pollutants, such as Aspergillus fimffgatus, also exist (Flannigan 1992). however’,is relatively small comparedto other environmental Most pathogens are transmitted through human-to-human factors, such as air changerates and outdoorpollutant levels. contact whendroplet nuclei form as a result of sneezing or For exarnple, the use of direct evaporative cooling leads to a coughingand are subsequently inhaled by a humanreceptor: A rise in indoor humidity levels, which mayreduce ozone by few pathogens, most notably the bacterium Legionella, can increasing surface reactions. However,this effect is relatively colonize abundantly within moist environments outside the insignificant comparedto the increased influx of outdoorair; humanbody and becomeairborne given proper conditions. whichtends to increase indoor ozone concentrations to levels Noninfectioushealth conditionsrelated to biological pollut- near those of the outdoor’air’ (Stocket aL 1993). ants include allergic, immunologic,and toxic responses, The primarysources of these adversehealth effects are the byproducts DUST MITES of organismsrather than the viable organismitself. The term Introduc~ion allergyis usedspecifically to refer to illnesses that take placeas a result of the formationof IgEantibodies in affectedpersons. All Mites are considered one of the most important allergens humanbeings have someIgE antibodies, but only a fraction of the in housedust, particularly in regions with high humiditiesand population respondsreadily to allergen exposureand produces temperate climates. The most commongenus of mites found in enoughIgE antibodies to cause an allergic reaction. Oncethe house dust in North America and Europe is Dermatopha- antibodies form, the person becomessensitized and re-exposure goides, of whichthere are two species, D. pteronyssinusand D. to the allergencan then trigger larger’ immunereactions resulting farinae. It is estimatedthat 10%of the populationin the U.S. is in allergic symptoms.This IgE-mediatedreaction develops in allergic to housedust and 70%of these people are specifically 20%to 30%of the peoplein the UnitedStates (Seltzer 1995). The allergic to mite allergens (Bates et al. 1993). The actual allergic diseases with well-documentedlinks to indoorair quality allergen is not the mites themselves, whichare approximately (IAQ)include allergic rhinitis (rhino conjunctivitis), primarily 1/3mmin length at maturity, but the dried fragmentsof their affecting the nasal area, and allergic asthmaand bronchopulmo- bodyparts and fecal excreta. Theseby-products are initially 10 nary aspergillosis (ABPA),both of whichaffect the lowerairways to .50/.tm in diameter but break downinto smaller fragments and alveolL The majority of patients suffering fromasthma are that becomeairborne whendust
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