ASHRAE FUNDAMENTALS SI CH 11-2017 Air Contaminants.pdf

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1、11.1CHAPTER 11AIR CONTAMINANTSCLASSES OF AIR CONTAMINANTS 11.1PARTICULATE CONTAMINANTS . 11.2Particulate Matter 11.2GASEOUS CONTAMINANTS . 11.8Volatile Organic Compounds 11.13Semivolatile Organic Compounds . 11.15Inorganic Gases. 11.15AIR CONTAMINANTS BY SOURCE. 11.16Outdoor Air Contaminants. 11.16I

2、ndustrial Air Contaminants 11.17Commercial, Institutional, and Residential Indoor Air Contaminants . 11.18Flammable Gases and Vapors . 11.20Combustible Dusts . 11.20Radioactive Air Contaminants . 11.21Soil Gases. 11.22IR contamination is a concern for ventilation engineers whenA it causes problems f

3、or building occupants. Engineers need tounderstand the vocabulary used by the air sampling and building aircleaning industry. This chapter focuses on the types and levels of aircontaminants that might enter ventilation systems or be found asindoor contaminants. Industrial contaminants are included o

4、nly forspecial cases. Because it is not a building air concern, the effects ofrefrigerants on the atmosphere are not included in this chapter; seeChapter 29 for discussion of this topic.Air is composed mainly of gases. The major gaseous componentsof clean, dry air near sea level are approximately 21

5、% oxygen, 78%nitrogen, 1% argon, and 0.04% carbon dioxide. Normal outdoor aircontains varying amounts of other materials (permanent atmosphericimpurities) from natural processes such as wind erosion, sea sprayevaporation, volcanic eruption, and metabolism or decay of organicmatter. The concentration

6、 of permanent atmospheric impurities var-ies, but is usually lower than that of anthropogenic (i.e., caused byhuman activities) air contaminants.Anthropogenic outdoor air contaminants are many and varied,originating from numerous types of human activity. Electric-power-generating plants, various mod

7、es of transportation, industrial pro-cesses, mining and smelting, construction, and agriculture generatelarge amounts of contaminants. These outdoor air contaminants canalso be transmitted to the indoor environment. In addition, the indoorenvironment can exhibit a wide variety of local contaminants,

8、 bothnatural and anthropogenic.Contaminants that present particular problems in the indoor en-vironment include allergens (e.g., dust mite or cat antigen), tobaccosmoke, radon, and formaldehyde.Air composition may be changed accidentally or deliberately. Insewers, sewage treatment plants, agricultur

9、al silos, sealed storagevaults, tunnels, and mines, the oxygen content of air can become solow that people cannot remain conscious or survive. Concentrationsof people in confined spaces (theaters, survival shelters, submarines)require that carbon dioxide given off by normal respiratory functionsbe r

10、emoved and replaced with oxygen. Pilots of high-altitude air-craft, breathing at greatly reduced pressure, require systems thatincrease oxygen concentration. Conversely, for divers working atextreme depths, it is common to increase the percentage of helium inthe atmosphere and reduce nitrogen and so

11、metimes oxygen concen-trations.At atmospheric pressure, oxygen concentrations less than 12% orcarbon dioxide concentrations greater than 5% are dangerous, evenfor short periods. Lesser deviations from normal composition can behazardous under prolonged exposures. Chapter 10 further detailsenvironment

12、al health issues.Although lack of oxygen can be a danger in confined spaces, it isunlikely ever to be a problem in naturally and mechanically venti-lated buildings. Although the amount of oxygen consumed approx-imates the amount of carbon dioxide produced by respiration, thelevel of oxygen in the ai

13、r is so much greater than that of carbon diox-ide to start with that there is effectively no change in oxygen contentbetween air intake and exhaust.1. CLASSES OF AIR CONTAMINANTSAir contaminants are generally classified as either particles orgases. Particles dispersed in air are also known as aeroso

14、ls. In com-mon usage, the terms aerosol, airborne particle, and particulate aircontaminant are interchangeable. The distinction between particlesand gases is important when determining removal strategies andequipment. Although the motion of particles is described using thesame equations used to desc

15、ribe gas movement, even the smallestparticles are much larger and more massive than individual gas mol-ecules, and have a much lower diffusion rate. Conversely, particlesare typically present in much fewer numbers than even trace levels ofcontaminant gases.The particulate class covers a vast range o

16、f particle sizes, fromdust large enough to be visible to the eye to submicroscopic particlesthat elude most filters. Particles may be liquid, solid, or have a solidcore surrounded by liquid. The following traditional particulate con-taminant classifications arise in various situations, and overlap.

17、Theyare all still in common use. Dusts, fumes, and smokes are mostly solid particulate matter,although smoke often contains liquid particles.Mists, fogs, and smogs are mostly suspended liquid particlessmaller than those in dusts, fumes, and smokes.Bioaerosols include primarily intact and fragmentary

18、 viruses,bacteria, fungal spores, and plant and animal allergens; their pri-mary effect is related to their biological origin. Common indoorparticulate allergens (dust mite allergen, cat dander, house dust,etc.) and endotoxins are included in the bioaerosol class.Particulate contaminants may be defi

19、ned by their size, such ascoarse, fine, or ultrafine; visible or invisible; or macroscopic,microscopic, or submicroscopic.Particles may be described using terms that relate to their interac-tion with the human respiratory system, such as inhalable andrespirableThe gaseous class covers chemical conta

20、minants that can exist asfree molecules or atoms in air. Molecules and atoms are smaller thanparticles and may behave differently as a result. This class coverstwo important subclasses:The preparation of this chapter is assigned to TC 2.3, Gaseous Air Con-taminants and Gas Contaminant Removal Equipm

21、ent, in conjunction withTC 2.4, Particulate Air Contaminants and Particulate Contaminant RemovalEquipment.11.2 2017 ASHRAE HandbookFundamentals (SI)Gases, which are naturally gaseous under ambient indoor or out-door conditions (i.e., their boiling point is less than ambient tem-perature at ambient p

22、ressure)Vapors, which are normally solid or liquid under ambient indooror outdoor conditions (i.e., their boiling point is greater than ambi-ent temperature at ambient pressure), but which evaporate readilyThrough evaporation, liquids change into vapors and mix with thesurrounding atmosphere. Like g

23、ases, they are formless fluids thatexpand to occupy the space or enclosure in which they are confined.Air contaminants can also be classified according to their sources;properties; or the health, safety, and engineering issues faced by peo-ple exposed to them. Any of these can form a convenient clas

24、sifica-tion system because they allow grouping of applicable standards,guidelines, and control strategies. Most such special classes includeboth particulate and gaseous contaminants.This chapter also covers background information for selectedspecial air contaminant classes (Chapter 10 deals with app

25、licableindoor health and comfort regulations).Outdoor air contaminantsIndustrial air contaminantsNonindustrial indoor air contaminants and indoor air qualityFlammable gases and vaporsCombustible dustsRadioactive contaminantsSoil gasesIn the 2016 ASHRAE HandbookHVAC Systems and Equip-ment, Chapter 29

26、 discusses particulate air contaminant removal, andChapter 30 covers industrial air cleaning. Chapter 46 in the 2015ASHRAE HandbookHVAC Applications deals with gaseous con-taminant removal.2. PARTICULATE CONTAMINANTS2.1 PARTICULATE MATTERAirborne particulate contamination ranges from dense clouds of

27、desert dust storms to completely invisible and dilute cleanroomparticles. It may be anthropogenic or completely natural. It is oftena mixture of many different components from several differentsources. A much more extensive discussion of particulate contam-ination is available from the U.S. Environm

28、ental ProtectionAgency (EPA 2016a).Particles occur in a variety of different shapes, including spheri-cal, irregular, and fibers, which are defined as particles with aspectratio (length-to-width ratio) greater than 3. In describing particlesize ranges, size is the diameter of an assumed spherical pa

29、rticle.Solid ParticlesDusts are solid particles projected into the air by natural forcessuch as wind, volcanic eruption, or earthquakes, or by mechanicalprocesses such as crushing, grinding, demolition, blasting, drilling,shoveling, screening, and sweeping. Some of these forces producedusts by reduc

30、ing larger masses, whereas others disperse materialsthat have already been reduced. Particles are not considered to bedust unless they are smaller than about 100 m. Dusts can be min-eral, such as rock, metal, or clay; vegetable, such as grain, flour,wood, cotton, or pollen; or animal, including wool

31、, hair, silk, feath-ers, and leather. Dust is also used as a catch-all term (house dust, forexample) that can have broad meaning.Fumes are solid particles formed by condensation of vapors ofsolid materials. Metallic fumes are generated from molten metalsand usually occur as oxides because of the hig

32、hly reactive natureof finely divided matter. Fumes can also be formed by subli-mation, distillation, or chemical reaction. Such processes createsubmicrometre airborne primary particles that may agglomerateinto larger particle (1 to 2 m) clusters if aged at high concentration.Bioaerosols are airborne

33、 biological materials, including virusesand intact and fragmentary bacteria, pollen, fungi, and bacterial andfungal spores. Individual viruses (virions) typically range in sizefrom 0.02 to 0.4 m, although filioviruses (e.g., ebola) may be lon-ger than 1 m. Viruses usually occur as aggregates (drople

34、t nuclei)and are associated with sputum or saliva. Therefore, in air theygenerally appear to be much larger than their true size. Most indi-vidual bacteria range between 0.4 and 5 m and may be found sin-gly or as aggregates. Intact individual fungal and bacterial sporesare usually 2 to 10 m, whereas

35、 pollen grains are 10 to 100 m,with many common varieties in the 20 to 40 m range. The sizerange of allergens varies widely: the allergenic molecule is verysmall, but the source of the allergen (mite feces or cat dander) maybe quite large. See the section on Bioaerosols for more detailed dis-cussion

36、.Liquid ParticlesMists are aggregations of small airborne droplets of materialsthat are ordinarily liquid at normal temperatures and pressure. Theycan be formed by atomizing, spraying, mixing, violent chemicalreactions, evolution of gas from liquid, or dissolved gas escapingwhen pressure is released

37、.Fogs are clouds of fine airborne droplets, usually formed by con-densation of vapor, which remain airborne longer than mists. Fognozzles are named for their ability to produce extra-fine droplets, ascompared with mists from ordinary spray devices. Many droplets infogs or clouds are microscopic and

38、submicroscopic and serve as atransition stage between larger mists and vapors. The volatile natureof most liquids reduces the size of their airborne droplets from themist to the fog range and eventually to the vapor phase, until the airbecomes saturated with that liquid. If solid material is suspend

39、ed ordissolved in the liquid droplet, it remains in the air as particulatecontamination. For example, sea spray evaporates fairly rapidly,generating a large number of fine salt particles that remain sus-pended in the atmosphere.Complex ParticlesSmokes are small solid and/or liquid particles produced

40、 by in-complete combustion of organic substances such as tobacco, wood,coal, oil, and other carbonaceous materials. The term smoke is ap-plied to a mixture of solid, liquid, and gaseous products, althoughtechnical literature distinguishes between such components as sootor carbon particles, fly ash,

41、cinders, tarry matter, unburned gases,and gaseous combustion products. Smoke particles vary in size, thesmallest being much less than 1 m in diameter. The average is oftenin the range of 0.1 to 0.3 m.Environmental tobacco smoke (ETS) consists of a suspensionof 0.01 to 1.0 m (mass median diameter of

42、0.3 m) solid and liquidparticles that form as the superheated vapors leaving burning tobaccocondense, agglomerate into larger particles, and age. Numerous gas-eous contaminants are also produced, including carbon monoxide.Smog commonly refers to air pollution; it implies an airborne mix-ture of smok

43、e particles, mists, and fog droplets of such concentrationand composition as to impair visibility, in addition to being irritatingor harmful. The composition varies among different locations and atdifferent times. The term is often applied to haze caused by a sunlight-induced photochemical reaction

44、involving materials in automobileexhausts. Smog is often associated with temperature inversions in theatmosphere that prevent normal dispersion of contaminants.Sizes of Airborne ParticlesParticle size can be defined in several different ways. Thesedepend, for example, on the source or method of gene

45、ration, visi-bility, effects, or measurement instrument. Ambient atmosphericAir Contaminants 11.3particulate contamination is classified by aerosol scientists and theEPA by source mode, with common usage now recognizing threeprimary modes: coarse, fine, and ultrafine.Coarse-mode aerosol particles ar

46、e largest, and are generallyformed by mechanical breaking up of solids. They generally have aminimum size of 1 to 3 m (EPA 2009a). Coarse particles also in-clude bioaerosols such as mold spores, pollen, animal dander, anddust mite particles that can affect the immune system. Coarse-modeparticles are

47、 predominantly primary, natural, and chemically inert.Road dust is a good example. Chemically, coarse particles tend tocontain crustal material components such as silicon compounds,iron, aluminum, sea salt, and vegetative particles.Fine-mode particles are generally secondary particles formedfrom che

48、mical reactions or condensing gases. They have a maxi-mum size of about 1 to 3 m. Fine particles are usually more chem-ically complex than coarse-mode particles and result from humanactivity, particularly combustion. Smoke is a good example. Chem-ically, fine aerosols typically include sulfates, org

49、anics, ammonium,nitrates, carbon, lead, and some trace constituents. The modes over-lap, and their definitions are not precise.Recently, there has been increased interest in even smaller con-taminants, known as ultrafine-mode particles. Ultrafines have amaximum size of 0.1 m (100 nm) (EPA 2009a). They are complexparticles for which the biggest source is reaction of gases with otherparticles. They also form as a result of degradation of larger particles.Natural sources include volcanic eruptions, ocean spray, and smokefrom wildfires. Sources involving human activity include