Application Note

IntroductionOver the past several years,indoor air quality (IAQ) has beena much debated and publicizedtopic, especially as it concernspublic health. The EPA estimatesthat we spend approximately90% of our time indoors, and further studies indicate thatindoor air in some commercialsettings is up to five times morepolluted than outdoor air.

Airborne particulates come ina variety of forms ranging fromanimal dander, plant pollen, andairborne bacteria, to fiberglass,asbestos, and combustion parti-cles. Motionless, human beingsalone shed up to 500,000 parti-cles (≥0.3µm) per minute. Whenactive, this level can reach up to45,000,000 particles per minute.Humidity and temperature play asignificant role in the generationrate of these pollutants. To prop-erly identify and troubleshoot IAQproblems, the technician needs atool that not only reads particleconcentrations, but also providesinsight into the environment thatcauses pollutants to grow.

Why Particle CountsMatterDifferent locations have varyinglevels of acceptable particulateconcentrations, driven primarilyby health and comfort concerns(i.e. homes, offices, paint booths)or contamination (i.e. hospitals,food and beverage plants, clean-rooms). Excessive levels canresult in medical conditions suchas Sick Building Syndrome, lowerproductivity, contaminated prod-uct, or all of the above.

F r o m t h e F l u k e D i g i t a l L i b r a r y @ w w w . f l u k e . c o m / l i b r a r y

Evaluating Indoor AirQuality with the Fluke983 Particle Counter

Maintaining acceptable air qualitylevels may not only lower thecosts associated with downtime,but also reduce or remove costsassociated with expensive fixesin the future. The first step inestablishing an IAQ maintenanceprogram is to determine if aproblem currently exists.

IAQ InvestigationAn IAQ investigation is the firststep in an ongoing maintenanceprogram or in responding to

complaints potentially associatedwith air quality. In either case,the methodology is similar:1. Conduct a survey of credible

staff at the facility. Who hasfiled complaints, and what arethe symptoms? Are those whocomplained centrally located,or dispersed throughout thefacility? The purpose is togauge the level of toxicity asevidenced by allergic reactionsor irritation.

2 Fluke Corporation Evaluating indoor air quality

Scenario 1: The particulate levelsdisplayed in Figure B are from anew residence (< 5 years), anddo not indicate any concentra-tions outside of the norm. In aresidential setting, particle levelsare sometimes higher than outsidereadings due to more potentialparticle sources (i.e. pet dander),smaller diffusion area, and oftenless sophisticated filtration.

Scenario 2: The particulate levelsdisplayed in Figure C are repre-sentative of an average officeworkspace, and do not indicateany concentrations outside of thenorm. In a commercial setting,particle levels should be signifi-cantly less than outside readingsdue to better filtration and betterdilution with outside air.

2. Research the building’s history.When was the building builtand/or remodeled? Have therebeen any instances of exces-sive damage, and how werethe repairs carried out? Whatare the maintenance practiceswithin the facility? For exam-ple, roof or plumbing leaksmay have been repaired, butthe underlying water damagemay not have been addressed.

3. Perform a physical inspection.Technicians need to be awareof their test environments byconsidering harmful particulatesources. Within a given loca-tion, areas containing exhaustvents, furnaces, cleaning sup-plies, as well as areas withfresh paint and/or carpetingmust be accounted for, espe-cially if present within acomplaint area. Are there any odors or visible sources(i.e. mold)?

4. Take air quality measurements.When conducting a completeIAQ investigation, temperature,humidity, CO and CO2 read-ings should also be taken toidentify problems related toinadequate and/or contami-nated ventilation, potentiallycreating a particulate problem.For example, temperature andhumidity readings play a keyrole in identifying mold andbacteria. A location with highrelative humidity and higherconcentrations of particles 3.0 µm or larger may indicatethe presence of mold spores,which should be remediatedonce identified.The most efficient procedure

for assessing indoor air quality isto obtain several outdoor airreadings as baselines, notingwhere the readings are taken inrelation to the facility. At least oneof the readings should be fromnear the building’s fresh air intakevent. Note, however, the locationof the intake vent to ensure base-line readings are not skewed bypollutant sources, for example,locations near a loading dock. Anindoor air particulate “target” isthen calculated by modifying thebaseline readings by the effi-ciency of indoor filtering.

Particles tend to diffuse veryquickly into the surrounding air,making source identification achallenging task. One method isto take multiple indoor readings,starting with the complaint areafirst, then moving outwards. Asdata is collected, take note of anyunusual increases in particulatequantity and size. Using the Fluke983’s integrated temperature andhumidity sensors, gauge thereadings against the acceptedparameters (see ASHRAEStandards 55 and 62) for temper-ature and relative humidity.Compare the particle readingsagainst the outdoor baseline toget a feel for the relative severityof the particulate concentration,and identify hotspots and path-ways that may lead to theparticulate source. Continue tofollow the path of higher concen-trations until the source isidentified. Once the source isremediated, the area isreassessed to ensure the correc-tive action addressed the problem.

Multiple tools are often used tocarry out such an investigation;however, the Fluke 983 includesboth temperature and humiditysensors in a device with a six-channel particle display. Armedwith this tool, the technician canconduct a basic IAQ investigationand take appropriate steps totreat the problem.

Interpreting the DataA correct interpretation of thedata requires an understanding ofthe test area. Is the area residen-tial or commercial? Is the locationexposed to tobacco smoke or ani-mals? Is there construction at ornear the location? A properassessment of the environmentcan help narrow down the list ofproblem particulates.

Concentration limits varywidely according to the size andtype of facility, among other variables. However, a high-levelassessment can provide directionon whether or not a problemexists. The following outside air

Figure A.

Figure B.

Figure C.

readings provide a high-levelpoint of reference for the technician:

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Scenario 3: The particulate levels in Figure D are from anolder residential location with visible mold. The readings are significantly higher, and stepsshould be taken to remediate the mold and address the rootcause of the problem.

A Cleanroom ExerciseCleanrooms are an excellent application for a particle counter. Forillustration purposes, let’s put the Fluke 983 to the test in evaluatingan ISO Class 5 (per ISO 14644-1:1999) cleanroom. To qualify as aClass 5 cleanroom, levels cannot exceed the limits for the class ineach particle size stated in the following table:

Figure E.

Class Particulate Limits

ISO Classification 0.1 µm 0.2 µm 0.3 µm 0.5 µm 1.0 µm 5.0 µm

m3 m3 m3 m3 m3 m3

1 10 2

2 100 24 10 4

3 1000 237 102 35 8

4 10000 2370 1020 352 83

5 100000 23700 10200 3520 832 29

6 1000000 237000 102000 35200 8320 293

7 352000 83200 2930

8 3520000 832000 29300

9 35200000 8320000 293000

Our test is concerned with the concentration of 0.3 µm particulates in the room. Several 2-liter samples are taken from six different locations inside the cleanroom, with the following results:

Ave. Concentration Concentrations (C1) (AC1)

Location (L) 1 2 3 4 5 6

A 750 560 655 730 674

B 1575 1250 750 950 1100 1300 1154

C 1300 850 980 1125 1350 975 1097

D 1150 775 450 825 845 1000 841

E 825 855 730 940 695 925 828

F 1700 1585 1135 900 1725 1210 1376

Scenario 4: If the particle sourcein Scenario 3 is not visible, useparticle size tables such as Figure E to identify possiblesources. Obtain a sample of theparticles and submit to a lab forfurther analysis.

Figure D.

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Making Sense of Particle Counter FeaturesUsing a particle counter is relatively simple; how-ever, understanding the features that distinguishcounters can sometimes be a challenge. The follow-ing terms are commonly used to describe theaccuracy, efficiency, and other attributes of an optical particle counter (OPC).Count Mode: The count mode defines how the par-ticle counter displays data to the user. Concentrationand Totalize are two typical counting modes, andthe Fluke 983 adds an Audio mode as well. Concen-tration mode samples a small volume of air thencalculates the value based upon the volume setting(cm3 or ft3) in the counter. Totalize mode allows theuser to view actual particle counts as they accumu-late until the end of the sample. Audio mode isuseful when searching for areas with particle levelsthat exceed predefined parameters. Once levels areexceeded, the counter audibly notifies the user.Zero Count: Zero count is a measure of the particlecounter’s accuracy, and should be taken prior to useand periodically thereafter, or when sampling erroris suspected. The zero count filter is attached to theparticle counter per the manufacturer’s instructions,then the counter is run for 15 minutes. The countershould not have detected more than one particlegreater than 0.3 µm in a five-minute period.Coincidence Loss: Coincidence loss occurs whentwo particles cross the counter’s light beam simulta-neously, creating a single pulse and resulting in asingle particle count. This type of error occurs morefrequently as the concentration of particles increaseswithin the sample. Per FED-STD-209E, coincidenceloss must be less than 10%.Counting Efficiency: The probability that the counterwill sense and count a particle passing through thesample volume. Counting efficiency is a function ofsize up to a minimum sensitivity threshold, abovewhich all particles are sensed and counted. A count-ing efficiency of 50% at the most sensitive thresholdis typically considered optimal, and facilitates con-sistent comparisons between counts from OPCs andthose of higher-resolution instruments.Sensitivity: A device’s ability to detect small particlesizes at a certain counting efficiency. The Fluke 983detects 0.3 µm at 50% counting efficiency.Resolution: A device’s ability to detect minute dif-ferences in particle sizes. Sensor resolution is affectedby the uniformity of illumination across the samplevolume, variations in flow rate, and the relativequality of the optical system. A misaligned sensor orfailing laser diode will contribute to poor resolution.Calibration: A set of operations or actions taken toestablish the relationship between the measuredvalues obtained through a device and the values ofthe corresponding parameters as defined in a stan-dard. The Fluke 983 is calibrated using PSL(polystyrene latex) spheres, widely used due to theiruniform size and light-refraction properties.NIST traceable: Traceability is a characteristic of ameasurement or standard and its relationship tostated references, which are often national or inter-national standards. The PSL spheres used in theFluke 983 calibration process can be traced to NIST(National Institute of Standards and Technology)standards.

The individual readings are well within the limitations for thecleanroom; however, we can take the following steps to determinethe statistical validity of the readings:

Step 1: Calculate the mean average particulate concentrationM = (AC1 + AC2 + AC3+ AC4+ AC5+ AC6) / L

995 = (674 + 1154 + 1097 + 841 + 828 + 1376) / 6

Step 2: Calculate the standard deviation of the averages

SD = ( (AC1-M)2 + … + (AC6-M)2) / (L-1)

116 = ( (674-995)2 +(1154-995)2 + (1097-995)2 + (841-995)2 +(828-995)2 +(1376-995)2) / (6-1)

Step 3: Calculate the standard error of the mean of the averagesSE = SD / ( L)

47.36 = 116 / ( 6)

Step 4: Establish the upper confidence limit (UCL)

Upper Control Limit (UCL) Factor for 95% confidence

# Locations 1 2 3 4 5 6 7 8 9+

95% UCL 6.31 2.92 2.35 2.13 2.02 1.94 1.9 1.86 NA

UCL = M + (UCL Factor * SE)1,087 = 995 + (1.94 * 47.36)

The resulting mean count for all locations is within the require-ments of a Class 5 cleanroom.

The Fluke 983 provides particulate data over six channels on asingle display, allowing the technician to view all readings at aglance. Though the cleanroom exercise focused on 0.3 µm particu-lates, the single display would immediately alert the technician toanomalies in other particle size concentrations.

Particle Counting in PerspectiveThe key to a successful IAQ investigation is to be aware of the envi-ronment as a whole. Location, building history, complaints, andmeasurable factors such as temperature and humidity, can play a keyrole in uncovering IAQ problems. When using a particle counter, beaware that a particle’s source may only be a symptom of a muchlarger issue looming under the surface. Remediation of the sourcemay not address core problems of poor filtration, ventilation, orexcessive moisture. Left unchecked, these conditions will cause thesame symptoms, or worse, to reoccur with certainty. The Fluke 983 isa powerful, rugged, and easy to use tool to assist the technician inidentifying particulate problems and authenticating the efforts toaddress their root causes.

Fluke CorporationPO Box 9090, Everett, WA USA 98206

Fluke Europe B.V.PO Box 1186, 5602 BD Eindhoven, The Netherlands

For more information call:In the U.S.A. (800) 443-5853 or Fax (425) 446-5116In Europe/M-East/Africa (31 40) 2 675 200 or Fax (31 40) 2 675 222In Canada (800) 36-FLUKE or Fax (905) 890-6866From other countries +1 (425) 446-5500 or Fax +1 (425) 446-5116Web access: http://www.fluke.com

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