25 

WORKPLACE AEROSOL MEASUREMENT 

JON C. VOLKWEIN 

Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Pittsburgh, Pennsylvania 

ANDREW D. MAYNARD 

University of Michigan School of Public Health, Ann Arbor, Michigan 

MARTIN HARPER 

Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Morgantown, West Virginia 

25.1 Introduction 571 

25.2 Aerosol Exposure Measurement in the Workplace 572 

25.2.1 Health Relevant Sampling 572 

25.2.2 Deposition Regions 572 

25.3 Sampling Conventions 573 

25.3.1 Sampling Against Exposure Conventions 574 

25.3.2 Matching the Sampler to Sampling 

Requirements 575 

25.3.3 Filter and Substrate Selection 576 

25.3.4 Pump Selection 576 

25.4 Direct-Reading Instruments 579 

25.4.1 Light Scattering 579 

25.4.2 Tapered Element Oscillating Microbalance 580 

25.4.3 Other Direct-Reading Instruments and 

Methods 580 

25.1 INTRODUCTION 

Traditionally, workplace aerosols have been categorized as 

fumes (fine particles and agglomerates generated through 

combustion and vapor condensation), smokes (solid and 

liquid particles arising from incomplete combustion), dusts 

(solid particles generated through mechanical means), 

sprays (liquid aerosols with relatively large particle sizes, 

usually produced through mechanical means), and mists 

(liquid aerosols with finer particles, generally produced 

through condensation or atomization) (Vincent 1995). 

25.5 Particle Size Measurement 581 

25.5.1 Sampling Strategy 581 

25.5.1.1 Personal Monitoring 581 

25.5.1.2 Evaluation of Workplace Controls 583 

25.6 Current Trends 583 

25.6.1 Diesel Particulate in the Workplace 583 

25.6.2 Toxic Materials 583 

25.6.3 Engineered Nanomaterials 584 

25.6.4 Sampling Aerosol and Vapor 584 

25.6.5 Penetration versus Deposition 584 

25.7 List of Symbols 584 

25.8 References 585 

These definitions tend to be used as descriptors rather 

than discrete classifications, and when considering measurement and health effects their use can be somewhat misleading. For example, a size selective sampler will not 

differentiate between a fume, smoke, or mist, and the distinction between health effects arising from a fume and 

a submicrometer dust can be somewhat blurred. Workplace 

aerosols present potential health impacts through ingestion, 

inhalation, or dermal contact, although it is the inhalation 

route that is of prime importance when considering aerosol 

measurement. 

Aerosol Measurement: Principles, Techniques, and Applications, Third Edition. Edited by P. Kulkarni, P. A. Baron, and K. Willeke 

© 2011 John Wiley & Sons, Inc. Published 2011 by John Wiley & Sons, Inc. 

571 
572 WORKPLACE AEROSOL MEASUREMENT 

Early workplace measurement (Walton and Vincent 1998) 

relied on particle number as the dominant metric with devices 

such as the koniometer (Le Roux 1970; Hewson 1996), 

impinger (Greenburg and Smith 1922), and thermal precipitator (Green and Watson 1935; Hamilton 1956) being used 

to collect samples and optical microscopy used to count numbers of particles. Although exposure to fibers is still assessed 

on a particle number basis, current sampling and analysis 

methods are dominated by the use of aerodynamic sizing of 

the aerosol followed by collection on filters and mass analysis 

(gravimetric, or by chemical analysis for specific elements or 

compounds). Mass is a suitable metric for assessing the 

dosage of systemic poisons, for example metals or pesticides, 

but it may be less suitable for assessing dosage for other end 

points. The main reason that mass is used is simply that gravimetric or chemical analysis is more accurate and more amenable to automation and instrumental analysis. 

Workplace aerosol measurement, while similar to other 

areas of aerosol measurement, differs somewhat in application and circumstance. In most cases the bulk aerosol 

composition is known or can be deduced from the processes 

or products in use. The mass concentrations involved are 

typically an order of magnitude greater than those in the general environment. Finally, sampling is carried out specifically 

for assessing human exposure, rather than characterizing the 

aerosol itself or the physical or chemical processes associated 

with it. 

While philosophies and approaches may differ, there is a 

great deal of commonality between methods used in the 

workplace, and those used in other areas of aerosol measurement. Thus, techniques and applications described elsewhere 

in this book will frequently be directly relevant to workplace 

sampling. Chapters 6 to 10 and 14 are particularly pertinent, 

providing detailed information on approaches to aerosol 

monitoring, filter collection, inertial, gravitational, centrifugal and thermal sampling, and direct-reading techniques. 

Chapters 23, 24, 26, and 27 on nonspherical particle measurement, bioaerosol measurement, ambient aerosol sampling, 

and aerosol exposure measurement are all relevant to the 

workplace. In this chapter, the emphasis is on the basic 

sampling philosophies and methods used on a routine basis 

in the. workplace and the application of direct-reading monitors in workplace aerosol measurement. 

25.2 AEROSOL EXPOSURE MEASUREMENT 

IN THE WORKPLACE 

25.2.1 Health Relevant Sampling 

Workplace aerosol measurement involves the collection and 

analysis of samples, but ultimately concerns specific health 

effects caused by workers' exposure to aerosols. Thus, the 

method of sampling and metrics used aim to provide health 

relevant information. Aerosol particles can enter the body 

through the skin, eyes, and gastrointestinal system, but generally the most sensitive route of entry into the body is through 

the respiratory system. The health effects resulting from deposition of an aerosol in the respiratory tract will depend on the 

dose received, and the body's response to the deposited particles (see Chapter 38). Physiological response to an aerosol 

is dependent on the chemical and physical nature of the particles and the location of the interaction (i.e., deposition 

region). The ultimate goal of workplace aerosol measurement 

is therefore to ascertain the dose of aerosol delivered to the 

body and to evaluate whether the dose or potential dose is sufficient to cause adverse health effects. 

The respiratory system deposition region is primarily governed by particle size and shape. The health response may be 

a function of mass, chemical composition, or morphology, 

and possibly particle size, surface area, and surface chemistry. 

Ideally dose should be expressed in terms of the most appropriate metric. However, practical and economic restraints 

factor into the decision of appropriate aerosol measurement 

methods. In practice, it is simpler to measure penetration to 

the relevant areas of the respiratory system rather than dose, 

thus giving a measure of the potential dose. Mass and bulk 

chemical composition are easier to measure than parameters 

such as particle shape and surface area, and correlati

between health effects and particle number and mass conce

tration (e.g., Bedford and Warner 1943) indicates mass to be

suitable metric in many cases. Asbestiform fibers present 

exceptional case where dose is best represented by partic

number and shape, and accordingly a number a

morphology-based metric is used (Chapters 23). Recentl

there has been concern that the health impacts of inhal

nanometer-scale aerosol particles-particularly those assoc

ated with some classes of emerging nanotechnologies-a

not well-characterized by mass concentration measurement

but require exposure to be assessed in terms of alternative pa

ameters (Maynard and Kuempel2005; Maynard et al. 200

Fissan et al. 2007; Maynard and Aitken 2007; Oberd6st

et al. 2007). 

25.2.2 Deposition Regions 

The respiratory system is an effective size-selective aeros

sampler in its own right, and it is false to assume that all ai

borne particles will enter it. Large particles are excluded fro

entering the nose and mouth (the nasopharyngeal regio

through inertial separation. Aspiration is a function of

number of parameters, including particle size, external 

speed, orientation to the prevailing air movement directio

and breathing rate and volume. However, for external wi

speeds of a few m/ s and lower, the probability of a partic

entering the mouth or nose (termed inhalable particle

may be generalized as being around 100% for particl

with aerodynamic diameters of a few micrometers a
below, reducing to around 50% at 100-/-Lm aerodynamic 

diameter (Vincent et al. 1990). 

Aerosol deposition in the nasopharyngeal region is dominated by inertial impaction, although interception and diffusion (for particles in the nanometer size range) also 

contribute. Further inertial separation and interception 

occurs as the particles pass into the trachea and the upper 

lungs (tracheobronchial region). Although population variance is high (Lippmann 1977), penetration into the tracheobronchial region may be typified by particles smaller than 

approximately 10-/-Lm aerodynamic diameter (Lippmann 

1977; ISO 1995). As the airways bifurcate to ever finer 

branches towards the alveolar region, aerosol particles are 

predominantly removed from the flow through a combination 

of impaction, interception, charge effects, and diffusion. In 

the preceding regions, deposited particles are cleared primarily by the action of cilia transporting them along to the 

upper airways. Particles depositing in the alveolar, or gas 

exchange, region are typically cleared either through the 

action of alveolar macrophages engulfing them, or transporting them to ciliated airways (phagocytosis), or by dissolution 

in the lung fluid. Particle deposition is through impaction and 

diffusion, and penetration to the alveolar region is restricted 

to particles around 5-j-Lm and less aerodynamic diameter 

(Lippmann 1977; ISO 1995). The clearance mechanism 

employed in the alveolar region, together with the close 

proximity of the bloodstream, leads to a number of health 

effects specific to particle deposition within this region. Not 

all particles that enter the respiratory track are deposited; 

a portion, depending on size, are exhaled in the breath 

[International Commission on Radiological Protection 

(ICRP) 1995]. 

Aerosol characteristics such as size, morphology, surface 

area, and structure are also influential; however, current technology lacks the means to characterize workplace aerosols as 

completely as may be desirable. Fortunately, the specificity 

of many workplace aerosols enables successful exposure 

monitoring to be carried out by linking a related metric 

(such as mass concentration) to empirical dose-response 

data (Maynard and Aitken 2007). The extent to which this 

approach is tenable where toxicity data are sparse is questionable however. 

25.3 SAMPLING CONVENTIONS 

The measurement of aerosol exposure via inhalation requires 

sampling devices that match particle deposition to the relevant areas of the respiratory system. However, aerosol deposition is highly dependent on the individual (Lippmann 

1977), and not trivial to replicate in a sampling device. 

Broad standards have therefore been developed describing 

representative penetration characteristics of aerosol particles 

through the respiratory system as a function of aerodynamic 

25.3 SAMPLING CONVENTIONS 573 

diameter. More recently, similar standards have been proposed with modifications to take into account deposition 

as well as penetration (Vincent 2005), and these standards 

are under discussion within the International Organization 

for Standardization, but they have not been accepted at 

this time. The existing aerosol penetration standards provide 

a basis for estimating the aerosol concentration potentially 

available to cause harm within specific areas of the respiratory 

system, and underlie many industrial hygiene aerosol sampling methods. 

Early estimates of penetration into what was considered the most vulnerable part of the system-the alveolar 

region-were proposed in the 1950s and 1960s, resulting 

in the British Mines Research Council (BMRC) and the 

American Conference of Government Industrial Hygienists 

(ACGIH) conventions describing respirable aerosols 

(BMRC 1952; ACGIH 1968). More recently, the International Organization for Standardization (ISO 1995) and 

the ACGIH (ACGIH 1998) arrived at convergent conventions 

describing the probability of particles penetrating to the nasopharyngeal, tracheobronchial, and alveolar regions. However, 

it wasn't until the early 1990s that international consensus 

was reached on particle penetration standards among ISO, 

AC GIH , and the European Committee for Standardization 

(CEN). The resulting conventions describe penetration as a 

function of particle aerodynamic diameter into the respiratory 

system (inhalable aerosol), into the tracheobronchial region 

(thoracic aerosol), and into the alveolar region (respirable 

aerosol), with thoracic and respirable aerosol as subfractions 

of the inhalable aerosol. These particle size-dependent fractions shown in Figure 25-1 are now widely used as the standards to which industrial hygiene aerosol samplers should 

conform (ISO 1995). 

The inhalable convention is based on particle penetration 

through the mouth and nose of a breathing mannequin over a 

.... ••••••••• Respirable 

. 

...... - - Thoracic 

0.8 ~- --Totallnhalable 

\ \- - - PM2.S 

,- -- PM10 

r::: 0.6 \.. 0 

~ '\ Q) \ \', r::: 

CD 0.4 \ a. \ \ 

" 

0.2 \\ '1 

.... \. , . , 

0 ....... ..... 

1 10 100 

Date/11m 

Figure 25-1 International workplace sampling conventions (ISO 

1995). Environmental conventions are also shown for comparison 

(Chapter 26). 
574 WORKPLACE AEROSOL MEASUREMENT 

range of wind speeds and orientations with respect to the 

wind, and is defined as 

(Eq.25-1) 

for 0 < dae < 100 /Lm. SJ(dae) is the fraction of particle entering the system as a function of aerodynamic diameter dae. 

Both the thoracic and respirable conventions are expressed 

as subfractions of the inhalable convention, and are based 

on lung penetration measurements. The thoracic convention 

is given as 

ST(dae) = SJ(dae) x [1 - F(x)] 

In(daelf) 

x = In(E) 

(Eq.25-2) 

ST(dae) is the fraction of particles penetrating beyond 

the larynx as a function of aerodynamic diameter. F(x) is a 

cumulative lognormal distribution, with a mass median aerodynamic diameter (MMAD) f of 11.64 /Lm and a geometric 

standard deviation (GSD) E of 1.5. 

The respirable convention SR(dae) is similarly given as 

SR(dae ) = SJ(dae) x [1 - F(x)] 

In(daelf) 

x = In(E) 

(Eq.25-3) 

where the cumulative lognormal distribution has a MMAD 

f of 4.25 /Lm, and a GSD E of 1.5. A respirable convention 

for susceptible groups is also defined, with f = 2.5 /Lm, 

although this has not been implemented in any exposure standards as yet. Penetration to the tracheobronchial and extrathoracic regions can be defined by the difference between 

the respirable and thoracic conventions (tracheobronchial), 

and the thoracic and inhalable conventions (extrathoracic). 

Further information on particle size-selective sampling for 

workplace contaminants may be found in ACGIH (1998). 

The greatest impact of moving to particle size-selection for 

sampling is to be expected from adopting the inhalable convention, because of the potentially large difference in mass 

collection between samplers designed to meet the inhalable 

convention and those that were not. Werner et al. (1996), 

Liden et al. (2000a), and Sivulka et al. (2007) can be consulted for further discussion of this issue, which has yet to 

be definitively resolved. Recently, the inhalable convention 

has come under scrutiny for a number of reasons. Firstly, 

the upper limit of the size range of interest (100/Lm) is an 

arbitrary selection, and particles larger than this can be airborne and therefore are available for possible inhalation. In 

addition, when considering the appropriate fraction of these 

particles there is a further issue of a large difference in inhalation efficiency between breathing through the mouth and 

through the nose. Heavy exertions lead to mouth breathing, 

or a combination of mouth and nose breathing, and a certain 

proportion of people breathe naturally through the mouth as a 

result of constricted passage in the nose. Therefore, it might 

be argued that the standard should account for mouth breathing, which is the more conservative estimate. However, even 

if this is accepted, our understanding of the efficiency of 

mouth breathing may be based on historical observations or 

experiments with groups of workers whose physiology is 

different from that of modem workers due to changes in 

workforce age distribution, fitness, gender, ethnicity, and 

so on. (Liden and Harper 2006). All studies of the inhalability 

of very large particles indicate a maximum size of inhalability, whether for nasal or oral breathing, while studies of sampler performance have not indicated a similar minimum, and 

this leads to problems in the assessment of exposures to 

coarse dust, for example wood dust (Harper and Muller 

2002; Harper et al. 2004). Secondly, the convention was 

based upon inhalation from moving air. Although initial 

studies included more slowly moving air (0.5 m/s), more 

recently, it has been shown that air velocities in the majority 

of workplaces are less than 0.3 mis, averaging around 0.1 m 

s -1 (Baldwin and Maynard 1998; Liden et al. 2000b). Since 

that time there has been research on inhalability under calm 

air conditions (Aitken et al. 1999), as well as investigations 

of sampler performance under these conditions (Kenny 

et al. 1999a). However, calm air is not the same as slowly 

moving air, and experiments covering the latter situation 

are only now underway (Witschger et al. 2004; Schmees 

et al. 2008; Sleeth and Vincent 2009). 

With increasing concern over potential health impacts 

associated with inhaling nanometer-scale aerosols, there has 

been some discussion over the need for a nanoparticle (or 

ultrafine particle) sampling convention. The rationale is that 

there is increasing evidence for inhaled particles between 

approximately 1-100 nm in diameter being associated with 

impacts to the respiratory and cardiovascular systems 

(Chapter 38; Delfino et al. 2005; Mills et al. 2007; 

Oberd6rster et al. 2007). It can be argued that selectively 

sampling particles smaller than 100 nm may provide a 

better indicator of potential risk associated with exposure to 

nanometer-scale particles. However, as yet, no physiological 

basis for such a sampling convention exists-1 00 nm is an 

arbitrary upper size limit that has little bearing on differentiating between particles that exhibit different modes of action 

within the body, either through where they deposit, or how 

they behave having deposited in the respiratory system. 

25.3.1 Sampling Against Exposure Conventions 

The relevance of workplace aerosol measurement relies on 

selection of an appropriate sampling device. Filter selection, 

pump selection and use, sampling strategy, and sample handling play an important role in determining the accuracy and 
suitability of sampling devices. Useful sources of information 

include ACGIH (1995) and ACGIH (1998). 

25.3.2 Matching the Sampler to Sampling 

Requirements 

A number of the industrial hygiene aerosol samplers introduced to the market in recent years have been developed 

and tested against International sampling conventions 

(ISO 1995). However, many devices are still available that 

were brought into use prior to acceptance of the current 

conventions. Many such samplers continue to be in use as 

they are prescribed by national regulations, or their use is 

preferred to maintain traceability to historic measurement 

methods, whose results may have been used to develop 

risk assessments. Some agree reasonably well with the 

relevant convention and others have been brought into line 

by altering the sampling flow rate [e.g., the SIMPEDS respirable cyclone (Bartley et al. 1994; Maynard and Kenny 

1995)]. Performance tests of existing samplers have given 

mixed results in the laboratory (Kenny et al. 1997; Gomer 

et al. 2001). 

The development of inhalable samplers has been hampered by the complexities of how external conditions, such 

as wind speed and direction, affect aspiration, together with 

the difficulties of making penetration measurements with particles up to 100-f.Lm aerodynamic diameter or larger. The 

10M personal inhalable sampler was the first sampler built 

to match the inhalable convention, and was developed following aspiration measurements with a breathing mannequin 

(Mark and Vincent 1986). The 10M sampler has significant 

shortcomings. For instance the filter is very accessible to accidental or deliberate sample tampering, plastic cassettes have 

severe instability in weighing (Smith et al. 1998; Li and 

Lundgren 1999; Liden and Bergman 2001), there is evidence 

for significant projectile and large particle entry (Liden and 

Kenny 1994; Aitken and Donaldson 1996; Aizenberg et al. 

2001), and it can give extremely variable results when external winds are directional (Roger et al. 1998). It is included in 

the UK method for determining dust gravimetrically (Health 

and Safety Executive 1997), where the entire capsule is 

weighed, and, by reference, in the UK method for metals 

analysis (Health and Safety Executive 2006). However, in 

this latter method, no guidance is given on how to account 

for particulate that has collected on internal surfaces of the 

sampler other than on the filter. This is a problem where 

these "wall deposits" are a significant part of the sample, 

since, by design they are intended to be an integral part of 

the sample. The issue of wall deposits has come to the forefront as the 10M sampler is compared to the traditional 

closed-face 37-mm cassette used in the United States and 

some European countries as a result of changes in limit 

values to reflect sampling in accordance with the inhalable 

convention (Harper and Demange 2007). Field studies of 

25.3 SAMPLING CONVENTIONS 575 

the closed-face cassette sampler side by side with the 10M 

sampler show much better agreement when the filter deposits 

alone are compared (Harper et al. 2007) or the filter deposits 

and the wall deposits are compared for both (Demange et al. 

2002). The cheap and disposable closed-face cassette has 

many practical advantages over more expensive and necessarily re-usable samplers. Internal capsules such as the TM 1 TM Accucap from SKC or the Woodchek from MSA are 

available for use in the closed-face cassette to ensure all particles are included in gravimetric analysis, including those 

that might otherwise have deposited on the walls of the sampler. Otherwise, for chemical analysis where the filter is 

digested, it may be necessary to wipe the internal surfaces 

of the sampler with a small piece of filter or wipe material 

and add this to the digestion step (Harper 2006). 

More recent samplers such as the CIP10-1 (ARE) address 

some of the problems inherent in the 10M inhalable sampler, 

but still fall short of the ideal. Samplers such as the Button 

Aerosol Sampler (SKC) have been developed specifically to 

reduce inters ampler variability and wind speed-dependence 

common to a number of inhalable samplers (Aizenberg 

et al. 2000, 2001), but it is unclear if it samples in accordance 

with the inhalable convention in the field (Harper and Muller 

2002; Linnainmaa et al. 2008). Samplers following the thoracic and respirable conventions have been easier to engineer. 

The development of an empirical understanding of particle 

penetration through cyclones and polyurethane foams in 

particular has led to sampling devices that match the respirable and thoracic conventions reasonably well (Vincent 

et al. 1993; Kenny and Gussman 1997; Chen et al. 1998; 

Maynard 1999). 

In recognition that no sampler will agree with the current 

workplace sampling conventions at all times, performance 

criteria are under development to set acceptable bounds on 

how well a device performs (CEN 1998). These boundaries 

are in essence set by comparing the mass fraction of a lognormal aerosol-characterized by its MMAD and GSD-that 

would be sampled by a device, to the mass that would be 

sampled by an ideal sampler (i.e., one following the convention perfectly). The comparison gives the sampler's bias 

as a function of aerosol size distribution (Bartley and 

Breuer 1982; Liden and Kenny 1992; Maynard and Kenny 

1995). Incorporating errors inherent in sampler performance 

measurements and typical usage into calculations of bias 

allows the sampler's accuracy as a function of the aerosol 

size distribution to be estimated. When sampler accuracy 

and bias lie within acceptable bounds, a basis is provided 

for determining acceptable sampler performance. 

From the available samplers that lie within acceptable 

performance criteria, the choice of device will depend largely 

on the sampling requirements. Two general types of sampling 

1 Refer to Appendix I for complete manufacturers' addresses indexed to a 

three-letter code. 
576 WORKPLACE AEROSOL MEASUREMENT 

are used in the workplace: fixed location sampling (also 

called static or area sampling) or personal sampling, where 

the sampler is placed on the worker. Static and personal samplers should not be interchanged because poor correlation 

exists between the two types of sampling (Kissell and 

Sacks 2002; Rodes and Thornburg 2005). High flow-rate 

samplers should be used to increase the aerosol detection 

limit, for instance during short term sampling or when the 

sampled material has a low exposure limit (although the 

detection limit will also be dependent on the filter used and 

the analysis method). Where high air velocities are expected, 

samplers with a sampling efficiency that are not as prone to 

wind speed should be selected. Other considerations should 

include whether the aerosol charge is likely to affect sampling 

(e.g., Baron and Deye 1990; Puskaret al. 1991), whether projectiles are likely to enter the sampling orifice and be included 

in the sample, and whether there is a possibility of significant 

sample loss during transport (see Chapter 6). Table 25-1 

summarizes many of the workplace sampling devices currently available or in use, and gives some indication as to 

their application. 

Sampler selection, however, may be constrained when 

compliance type measurements are required. To simplify 

compliance type measurements, many governments mandate 

that a specific type or types of samplers operated at prescribed 

flow rates be used to collect samples for analysis. In the 

United States, for example, respirable particulates are collected using Dorr-Oliver cyclones at a flow rate of 1.7 L/ 

min or SIMPEDS-type cyclones at a flow rate of 2.2 L/min 

to estimate an ISO respirable-size fraction of particulates for 

analysis [NIOSH Manual of Analytical Methods (NMAM) 

2003]. Specific government regulations should be consulted 

before compliance sampling is conducted. 

25.3.3 Filter and Substrate Selection 

Industrial hygiene aerosol samples are generally collected 

onto a filter, within polyurethane foam, or onto an impenetrable impaction substrate such as Mylar® (which is usually 

coated with a layer of grease or oil to prevent particle 

bounce). Filters may be held in a cartridge within the sampler, 

as is the case with the 10M inhalable sampler, or may be 

mounted directly into the sampling head. Selection of a suitable collection substrate is governed by the sampling equipment used and the subsequent sample analysis. Low-power 

lightweight pumps require filters with relatively low pressure 

drops at the operating flow rate. Gravimetric analysis requires 

a high degree of weight stability in changing environmental 

conditions. Chemical analysis requires that the collected 

material can be released from the substrate and/or that background levels of the analyte are low. Sample analysis by 

microscopy requires deposited particles to lie on the surface 

of the substrate. Chapter 7 gives further details of filter properties and selection. Table 25-2 summarizes the properties 

of filters, collection substrates, and filter holders commonly 

used within the workplace. 

The accuracy of gravimetric samples may be affected by 

water adsorption onto substrates and filter holders, and by 

losses or gains in material during transit (see Chapter 7; 

van Tongeren et al. 1994; Awan and Burgess 1996). In particular, cellulose ester membrane filters, polyurethane 

foams and conducting plastic filter cassettes are particularly 

prone to weight changes following water uptake (Vaughan 

et al. 1989; Smith et al. 1998; Li and Lundgren 1999; 

Liden and Bergman 2001; Linnainmaa et al. 2008). To 

combat bias from such sources, it is common practice to 

-weigh a number of control, or blank, filters with each set of 

sample filters (typically one blank per 10 samples, with a 

minimum of three blanks). It is advisable to condition filters 

in the weighing area (preferably a temperature- and humiditycontrolled environment) for up to 24 h before weighing to 

allow them to reach an equilibrium weight. Where possible, 

blank filters should be transported with the sample substrates 

and exposed to the same conditions, to minimize bias resulting from handling, transport, and changes in environment. 

Other sources of bias during weighing of filters include 

electrostatic attraction, where substrates are highly charged, 

and buoyancy effects. Electrostatic charge buildup may be 

significant for substrate materials such as polyvinyl chloride 

(PVC) and polytetrafiuoroethylene (PTFE) , particularly 

when working at low relative humidity. In all instances, 

samples should be electrically neutralized using a source of 

bipolar ions. A common approach is to place samples close 

to a radioactive anti-static source prior to weighing. 

25.3.4 Pump Selection 

Present day personal sampling devices usually rely on either 

diaphragm or piston-type pumps to draw air through them. 

The pump is connected to a direct current (DC) motor, supplied by a battery pack of rechargeable batteries. The achievable flow rates of pumps varies among manufacturers, but 

most will provide flows of 1.67 x 10-5 to 5 X 10-5 m3

/s 

[1-3 L/min] against a pressure drop of 6.25 kPA [25 in 

H20] for periods of up to 8 h. Personal pumps are available 

that will achieve flow rates of up to 2.2 X 10-4 m3

/s [15 

L/min] , but there is always a trade-off between sampling 

flow rate, sampling time, sustainable pressure drop, battery 

capacity, and pump weight. Most currently available pumps 

regulate the selected flow to minimize the impact of changes 

in temperature, pressure, and filter-loading on the flow rate 

and the total volume of air sampled. Regulation is achieved 

in a number of ways, including using feedback from pressure 

drop across the filter, atmospheric temperature and pressure, 

pump rotational rate, and power usage. As the performance 

of some size-selective samplers is adversely affected by pulsations in the sampling flow (e.g., Bartley et al. 1984), most 

pumps incorporate pulsation dampers. Wood (1977) presents 
TABLE 25-1 Summary of Industrial Hygiene Aerosol Samplers 

Flow Rate Manufacturer or Agreement 

(l0-5m3 Is Distributor (see with 

Sampler [L/minD Deployment Appendix I) Convention Notes 

Inhalable Samplers 

10M Inhalable 3.3 [2] Personal SKC Good Uses filter cassette (plastic version is rep

to have weight stability issues). Suscep

to large projectiles. Wind speed depen

10M Inhalable Static 5 [3] Static CAS Good 

CIP-1OI 17 [10] Personal ARE Rotating porous foam acts as an air move

collection medium. 

I 

GSP Inhalable 5.8 [3.5] Personal STR Good Different sampling cones are available f

different flow rates. 

Conical Inhalable Sampler 5.8 [3.5] Personal CAS, RGI Good Based on the GSP sampler. 

Seven Hole 3.3 [2] Personal Various Fair Also known as the multi-orifice, or UKA

sampler. 

Single Hole 3.3 [2] Personal Various Poor Used for lead aerosol sampling in the U

PAS-6 Personal KOE Fair 

Button Sampler 6.7 [4] Personal SKC Good Perforated inlet reduces wind speed 

dependence and inter-sampler variabi

and leads to a uniform filter deposit. F

rate can be a problem to achieve or ma

over longer time periods, even with th

glass-fiber filters recommended by the 

manufacturer. 

Thoracic Samplers 

Elutriator 12.3 [7.4] Static GMW Poor Specific to cotton dust. 

CIP-lOT 12 [7] Personal ARE Fair CIP-1OI with a thoracic separation stage

CATHIA 12 [7] Static ARE Fair Static version of the CIP-lOT. 

10M Thoracic 3.3 [2] Personal 10M Fair Separation based on polyurethane foam. 

GK 2.69 Cyclone 2.7 [1.6] Personal RGI Good Can also be used as a respirable sample

below. 

Modified SIMPEDS 1.3 [0.8] Personal Not commercially Good Developmental modification to the SIMP

Cyclone available cyclone. 

10M Inhalable + Thoracic 3.3 [2] Personal Not commercially Fair 10M inhalable sampler with a size-selec

Foam available polyurethane foam insert. 

Respirable Samplers 

CIP-lOR 17 [10] Personal ARE Good CIP-1OI with a respirable separation stag

SIMPEDS Cyclone 3.7 [2.2] Personal Various Good Also known as the Higgins and Dewell 

Cyclone. 

til 

.....:t 

.....:t 
!.II TABLE 25-1 Continued -..l 

QC 

Flow Rate Manufacturer or Agreement 

(lO-5m3/s Distributor (see with 

Sampler [L/minD Deployment Appendix I) Convention Notes 

SKC Cyclone Personal SKC Good Variant of the SIMPEDS Cyclone. 

GK 2.69 Cyclone 7 [4.2] Personal BGI Good Can also be used as a thoracic sample

above. 

DOff-Oliver (lO mm) 2.8 [1.7] Personal Various Good Sampler constructed from non-conduct

Cyclone nylon. 

MRE 113A (Gravimetric 4.2 [2.5] Static CAS Fair Use limited to UK mines. 

Dust Sampler) 

10M 3.3 [2] Personal SKC Good 10M inhalable sampler with a size-sele

Inhalable + Respirable polyurethane foam insert. Foam has 

Foam stability issues. 

Foam Respirable Sampler 3.3 [2] Personal Not commercially Good Cowled sampler with size selective 

available polyurethane foam plugs. 

Virtual Cyclone Personal Not commercially Good Provides a good match with the respira

available convention slope. 

Spiral Sampler 4.2 [2.5] Personal Not commercially Uses centrifugal particle separation. 

available 

FSP-10 17 [10] Personal/ STR Good 

static 

Miscellaneous Samplers 

37-mm Cassette (Open) 3.3 [2] Personal/ Various Standard filter cassette, worn facing do

static 45° to the body, but facing forward 

give a better approximation to the in

convention. Wall deposits should be 

accounted for where necessary. Stat

dissipative versions available. 

37-mm Cassette (Closed) 3.3 [2] Personal/ Various Standard filter cassette as above with a 

static containing a 4-mm diameter inlet. In

capsules to account for wall deposit

available. 

Static Sampler for "Total" Variable Static CAS Open faced filter. Widely used in the U

Aerosol 

Passive Sampler Personal/ HSE, UK Electret-based sampler relying on aero

static charge and naturally occurring air 

movements. Correlation is good wit

size selective samplers. 

Cowled Sampler 3.3 [2] (Typical) Personal/ Various Used in the main for fiber sampling. S

static selectivity not quantified. 

Respicon 5.2 [3.1] Personal TSI Virtual impactor and filter measures al

sampling conventions. 
TABLE 25-2 Filter Selection for Industrial Hygiene 

Aerosol Sampling 

Weight Pressure 

Substrate or Cassette Typical Application Stabilitya Dropa 

Glass fiber filter General collection *** ** 

Gravimetric 

analysis 

Quartz-fiber filter Chemical analysis *** 

Cellulose ester Imaging, fiber *** 

membrane filter sampling, 

digestion for 

metals analysis 

PVC membrane filter General collection   ** * 

Gravimetric 

analysis 

Teflon membrane Gravimetric analysis **** ** 

filter Chemical analysis 

Poly carbonate filter Particle imaging   

Silver membrane Chemical analysis, ** ** 

filter X -ray diffraction 

analysis 

Polyurethane foam Various samplers   

Mylar impaction Impaction substrate **  N/A 

substrate 

Aluminum foil Impaction substrate ** N/A 

impaction 

substrate 

Conducting plastic 10M inhalable N/A 

cassette sampler, conical 

inhalable sampler 

Stainless steel 10M inhalable   N/A 

cassette sampler 

PVC Accucap TM Gravimetric analysis ** ** *** 

WoodchekTM (PVC Gravimetric analysis   ** * 

filter and 

aluminum cone) 

a A higher star rating indicates better weight stability or lower pressure drop. 

a useful review of personal sampling pumps carried out in 

1977, and apart from advances in flow control technology, 

basic pump mechanisms are the same. 

The volumetric flow rate of sampling pumps needs to be 

set under the same conditions of temperature and humidity 

as sampling will be carried out and with the sampling 

device attached (including filter). Although many pumps 

incorporate a visual indication of flow rate such as a rotameter 

or digital display, these should be used for indication purposes 

only, and the sampling flow measured or calibrated using a 

primary standard such as a bubble flow meter or newer electronic flow meters, traceable to national or international standards. Typically, the set flow rate is expected to be within 

5 % of the target flow rate, although the most recent guidelines 

on sampling in the UK specify flows to be set to ±1.67 x 

10-6 m3 / s [± 0.1 L/min] in all cases (HSE 1997). 

25.4 DIRECT-READING INSTRUMENTS 579 

25.4 DIRECT-READING INSTRUMENTS 

Perhaps the most recent changes in workplace aerosol 

measurement have been in the area of real-time measurement. 

A report of the United States Secretary of Labor's Advisory 

Committee on the Elimination of Pneumoconiosis Among 

Coal Mine Workers listed several recommendations dealing 

with the need for continuous respirable dust monitors 

to help protect workers' health (US Department of Labor 

1996). In addition, a National Institute for Occupational 

Safety and Health (NIOSH) Criteria Document lists improved 

sampling devices as a research need pertinent to coal miner 

respiratory health and prevention of disease (NIOSH 1995). 

Monitors giving a near-instantaneous, or rapid measure of 

aerosol properties (commonly referred to as real-time 

measurement instruments) are widely used in the workplace. 

Vincent (1995), Walton and Vincent (1998), and Maynard 

and Baron (2004), provide a broad summary of techniques 

commonly used in the workplace. However, many devices 

described in earlier chapters may be applied to the workplace 

if unique aspects of the workplace are taken into account. 

Several approaches have being taken to address these 

unique aspects. An early effort used impaction sampling and 

beta-attenuation analysis of the deposit to determine short 

term aerosol measurements (Volkwein and Behum 1978). 

More promising technologies emerged that included lightscattering dust monitors, (Lehocky and Williams 1996; Tsao 

et al. 1996) and lately a person-wearable tapered-element 

oscillating microbalance (Volkwein et al. 2004, 2006). The 

principal goal of each of these efforts has been to develop an 

instrument that will give short term or real-time measurements 

of worker aerosol exposure. A further unique requirement for 

some workplace sampling may require intrinsic safety design 

such that Underwriters Laboratory or MSHA certification for 

use in potentially explosive environments can be secured. 

Detailed descriptions of the operational principles of these 

techniques may be found in Chapters 12 and 13 of this book. 

25.4.1 Light Scattering 

The theory of these instruments based on light scattering from 

particles has been summarized in Chapter 13. Several of the 

monitors have been characterized in the laboratory for different dusts (Keeton 1979; Marple and Rubow 1981, 1984; 

Kuusisto 1983; Rubow and Marple 1983). The relationship 

of the instruments' response to dust concentration is not 

simple but depends on particle size, particle composition, 

and on instrument design and manufacturing differences. 

Significant changes in dust particle characteristics such as 

shape, size, surface properties, and density can affect the 

instrument's correlation with mass concentration and require 

calibration of the instrument for each type of dust measured 

(Williams and Timko 1984). These factors have limited the 

use of photometers to dust-source identification and control 
580 WORKPLACE AEROSOL MEASUREMENT 

technology evaluation. They are not useful for monitoring 

compliance with dust standards. 

For routine walk-through measurements, aerosol photometers are widely used, and available from an increasing 

number of manufacturers. Their use covers checking short 

term, task-specific, or instantaneous exposure levels in low 

to high aerosol loadings, and identifying exposure hot spots. 

The implementation of the measurement method has various 

guises, from passive instruments relying on convection to 

bring particles into the sensing zone (as with the MiniRAM, and the later Personal Data-RAM (TFS), to pumped 

devices such as the Microdust Pro (CAS), to instruments 

incorporating data loggers [e.g., the DustTrack (TSl) and 

Data-RAM (TFS)] or person-wearable SIDEPAK1M (TSl). 

Most devices are compact, with the majority being portable, 

and a number of them being suitable for personal sampling. 

Over a relatively narrow size range (approximating to the 

upper end of respirable size fraction or the Mie scattering 

regime) the light scattered from an aerosol is roughly 

proportional to the scattering volume (Chapter 14; Baron 

1994). Thus, after correcting for density, scattered light 

may be used as an indirect measure of mass concentration. 

The method is relatively good for measuring respirable aerosol concentration, but becomes tenuous when used for the 

thoracic subfraction, and potentially misleading when used 

to measure the inhalable aerosol mass concentration (the 

sensitivity to equivalent aerosol masses represented by 

20-/Lm particles is approximately a factor of 102 lower than 

the sensitivity to 2-/Lm particles). Instruments such as the 

Respicon TM (HUN) go some way to overcoming this size 

dependence of photometry by selectively concentrating 

larger particles through the use of virtual impaction (Koch 

et al. 1998, 2002; Rando et al. 2005). In some situations it 

is feasible to calibrate a photometer to the inhalable mass 

concentration, but only when the fine particles detected 

form a constant fraction of the inhalable aerosol. Optical 

single particle detection and sizing instruments such as the 

Grimm Work -Check (GRl) overcome some of the limitations 

of photometers, but their sensitivity is still restricted to a similar range of particle sizes. 

In all cases it is advisable to calibrate photometers before 

using them with different aerosols, as particle size distribution, shape, and refractive index will affect measurements. 

Calibration is usually performed by carrying out parallel 

gravimetric sampling, and applying an adjustment factor to 

the photometer to ensure results agree. Many photometers 

have the facility to collect aerosol passing through the sensing 

zone on a filter, thus simplifying calibration. Zero offset 

checks are also recommended before use by placing the 

photometer in a clean environment; deposits on the optics 

and surfaces of the sensing zone can lead to a change in the 

instrument calibration. Calibration accuracy will further 

depend on the uniformity of the aerosol characteristics over 

the sample collection interval. 

25.4.2 Tapered Element Oscillating Microbalance 

The theory of the Tapered Element Oscillating Microbalance 

(TEOM, R&P) is summarized in Chapter 12. Despite its 

currently limited application to the mining industry, this 

technology offers a notable advantage of direct, near-realtime measurement of dust mass in the field. Since dust 

exposure standards are based on dust mass, this attribute of 

the TEOM is significant. Interest in the development of a 

prototype TEOM personal dust monitor began 25 years ago 

(Patashnick and Rupprecht 1983) as a device configured for 

strictly an end-of-shift measurement. It was not a real-time 

monitor, but used the oscillating microbalance principle to 

"weigh" the collection filter before and after dust sampling. 

The Bureau of Mines (BOM) evaluated this prototype system in the laboratory for end-of-shift applications (Williams 

and Vinson 1986). The effective standard deviation of 

repeated measurements was 1.6 fLg. Tests at controlled temperature and humidity showed less than 20 fLg of drift during 

an 8-h shift. 

These early attempts to construct a person-wearable form 

of the TEOM required a substantial mass in the base of the 

tapered element to dampen the vibrations; this reduced the 

concepts "wearability." A proprietary development by R&P 

solved the need for a substantial base mass by electronically 

dampening the base vibration and enabling development of 

a person-wearable TEOM-based personal dust sampler. The 

PDM 3600 dust sampler for miners is now available from 

TFS (Volkwein et al. 2004, 2006). 

25.4.3 Other Direct-Reading Instruments 

and Methods 

While mass-based criteria are dominant for workplace 

aerosol measurements, there is growing recognition that 

other metrics may be more appropriate for nanometer-sized 

particulates such as surface area or number count. Recent 

developments in condensation particle counter (CPC) technology have led to a commercially available portable 

device with logging capabilities, suitable for semi-quantitative particle number measurements. The Model 3007 (TSl) 

is designed to provide near-instantaneous measurements of 

particle concentration between 10 nm and approximately 

1000 nm. Although it is primarily aimed at investigating 

aerosol number concentration levels and variations, and 

tracking contamination sources in indoor environments, it is 

also being applied to measuring real-time particle number 

concentration measurements in the workplace. Other metrics 

under consideration include measurement of particulate 

surface area (Litton 2002; Ku and Maynard 2005; Maynard 

and Aitken 2007) or specific surface area equivalent dose 

(Oberdorster 2001) as used in the Model 3550, TSI 

N anoparticle Surface Area Monitor (Shin et al. 2007; 

Asbach et al. 2009). 
-

25.5 PARTICLE SIZE MEASUREMENT 

Full characterization of the size distribution of an aerosol may 

be carried out during non-routine investigations using a range 

of available methods described in previous chapters (see 

Chapters 8, 11, and 13 to 17). Although many instrument 

types have been used in the workplace (Mark et al. 1984), cascade impactors (Chapter 8) are often the instrument of choice, 

giving an indication of the mass-weighted size distribution of 

an aerosol. Impactors are generally capable of giving the size 

distribution of an aerosol between around O.I-/-lm and 15-/-lm 

aerodynamic diameter and above. For area sampling, cascade 

impactors such as the Thermo Scientific Andersen impactor 

(TFS) and the Multi-Orifice Uniform Deposit Impactor 

(MOUDI; MSP) have found relatively widespread use in 

the workplace. The Andersen consists of eight multi-orifice 

stages with cutpoints between 10 /-lm and OA/-lm when operated at 4.72 x 10-4 m3 Is [28.3 L/min]. Collection is usually 

onto aluminum foils, although other substrates are available. 

The use of multi-orifices in the Andersen impactor allows 

deposits to be distributed with relative evenness onto substrates. This is taken further within the MOUDI, where 

many orifices per stage, together with rotating substrates, 

lead to uniform deposits. The MOUDI is available in an 8-

stage or 10-stage version, and is capable of making aerosol 

size distribution measurements down to 0.056 /-lm at 

5 x 10-4 m3 Is [30 L/min]. 

Aerosol size distributions within the breathing zone are 

generally of greater relevance to health than area samples, 

and small cascade-sty Ie impactors have been developed to 

enable personal aerosol size distribution measurements to 

be made. The Marple personal cascade impactor (TFS) 

(Rub ow et al. 1987) is configurable with up to eight stages, 

and will provide information on particle size distribution 

down to 0.5/-lm at a flow rate of 3.33 x 10-5 m3 Is [2 LI 

min]. The Personal Inhalable Dust Spectrometer (PIDS) is 

similar in concept to the Marple impactor, although the 

slot-shaped impactor jets of the Marple device are replaced 

by circular jets (Gibson et al. 1987). The PIDS is not currently 

commercially available. Cutpoints in the 8 stages of the PIDS 

range from 0.9 /-lm to 19 /-lm at 3.33 x 10-5 m3 Is [2 L/min]. 

The Sioutas personal cascade impactor (SKC) is a more 

recent development that provides 50% cutpoints at 2.5 /-lm, 

1.0 /-lm, 0.50 /-lm, and 0.25 /-lm, giving a versatile device 

capable of measuring exposure against a range of sampling 

conventions (Misra et al. 2002). In addition, a newer 

MiniMOUDITM (MSP) impactor offers a person-wearable 

instrument with size data down to O.OI/-lm. 

Cascade impactors are of limited use for measuring 

aerosol size distributions to the upper limit of the inhalable 

convention (lOO-/-lm aerodynamic diameter), due to the 

relatively low cutpoint of the upper stage in most cases. 

Extrapolation of measured size distributions above this cutpoint is dependent on assumptions about the sampled aerosol 

25.5 PARTICLE SIZE MEASUREMENT 581 

and the aspiration efficiency of the device, and is generally 

not reliable. However the PIDS was designed with an inlet 

designed to follow the inhalable convention (Gibson et -al. 

1987). It may be assumed that summing all deposits within 

the PIDS impactor gives a measure of the inhalable aerosol 

mass, and subsequent analysis of the deposits gives the size 

distribution as a function of the inhalable aerosol. Such an 

approach is advantageous to industrial hygiene measurements, where ultimately measurements need to be related to 

the mass of particles inhaled. 

In cases where the specific health-related fractions of the 

aerosol are of more concern than a detailed analysis of 

particle size distribution, a number of samplers allow simultaneous measurement of all three fractions. The 10M personal 

multi-fraction sampler uses aerosol separation within polyurethane foams to achieve this (Vincent et al. 1993; Kenny 

et al. 1999b). Aerosol is sampled through a 15-mm diameter 

inhalable inlet at 3.33 x 10-5 m3 Is [2 L/min]. In the original 

concept, two polyurethane foam selectors of different grades 

placed in series separate the thoracic and respirable subfractions. The sampler enables the inhalable fraction to be 

measured by weighing deposits in both foams and the 

backup filter. The combined deposits on the filter and adjacent foam give the thoracic fraction, and the filter alone 

gives the respirable aerosol fraction. However, a version 

with thoracic foam is currently unavailable. An alternative 

approach is used by the Personal Spectrometer (PERSPEC; 

Prodi et al. 1988, 1989). The inhalable aerosol fraction is 

introduced to a highly divergent flow of clean air, and deposited onto a 47-mm filter. Deposition position is dependent on 

particle size, thus by weighing the complete filter the inhalable fraction can be determined, or by weighing specific 

areas of the filter (after cutting them out) different subfractions can be measured (Kenny and Bradley 1994). The 

Respicon sampler (TSl) achieves separation of the three 

aerosol size fractions using a series of virtual impactors 

(Koch et al. 1998, 2002; Rando et al. 2005). A modified 

version has been developed (Respicon TM , HUN) that allows 

real-time monitoring of each fraction using light scattering 

(Koch et al. 1998). A very recent development is a novel 

coarse particle sampler that incorporates diffusive sampling 

of ultrafine or nano-scale particulate (Gorbunov et al. 2009). 

25.5.1 Sampling Strategy 

Workplace aerosol measurements fall broadly into personal 

exposure assessment or engineering evaluation of controls. 

While general measurement requirements may seem similar, 

specific strategies should be tailored to the needs of the 

sampling. 

25.5.1.1 Personal Monitoring While "static" or "area" 

sampling with fixed-point samplers is still used in many situations, it is now widely preferred that representative aerosol 
582 WORKPLACE AEROSOL MEASUREMENT 

sampling to monitor personal exposure should be carried out 

in the breathing zone-frequently defined as a region of the 

body not more than 0.3 m from the mouth and nose 

(Vincent 1995). Breathing zone measurements give a better 

representation of worker exposure. However, Vincent notes 

that placement of sampling devices in this region does not 

guarantee representative sampling, and large variations in 

sampled aerosol concentration can be seen across the front 

of the body, depending on worker orientation, placement of 

the aerosol source, and local air movements (Raynor et al. 

1975; Vinson et al. 2007). A novel approach to sampling 

is to place a small device at the end of a personal "handsfree" microphone headset so that it is located much 

more centrally within the breathing zone (Liden and 

Sourakka 2009). 

In mining, for example, personal exposure monitoring 

is preferable to area monitoring (Leidel et al. 1977). Dust 

concentrations have been shown to change dramatically 

over times of a few seconds and distances of just 0.6 m in 

underground coal mines (Kost and Saltsman 1977). 

Therefore, to meaningfully approximate a worker's dust 

exposure, personal monitoring is the preferred strategy 

(Kissell and Sacks 2002). 

As a matter of convention, personal exposure measurements for chronic hazards are usually taken for the duration 

of a single work shift. An 8-h Time Weighted Average 

(TWA) mass concentration (cm ) relates to the process 

whereby exposure occurring within a 24-h period is treated 

as being equivalent to a single uniform exposure over 8 h. 

A TWA mass concentration can be determined from a 

single full-shift sample, or it can be calculated from a series 

of consecutive samples (Leidel et al. 1977). Where sampling 

gaps occur over a shift, exposures during these periods should 

be estimated from adjacent measurements, or from additional 

information (see Example 25-1). The TWA for a given time 

period (e.g., 8 h or 15 min for a Short Term Exposure Limit 

(STEL)) is calculated by: 

n 

LCmi x fi 

i=l cm=--T--

n L fi = full shift duration (Eq. 25-4) 

i=l 

where T is the given reference period (in minutes), fi is the 

duration of sample i in minutes and Cmi is the mass concentration of sample i. 

EXAMPLE 25-1 

Calculation of an 8-h TWA exposure. Three consecutive air 

samples for lead are collected at 3.3 x 10-5 m3

/s [2 L/min] 

onto filters in the breathing zone of a worker in a brass foundry, 

with the results shown in Table 25-3. 

The shift started at 08:00, and finished at 18:00. Breaks were 

taken between 09:30 and 10:00, 12:00 and 12:30, and 15:00 and 

15:30. The work pattern was split into different tasks in the 

morning and the afternoon. Using equation 25-4, calculate the 

8-h TWA exposure level over the total duration of the shift 

(600 min). 

The assumption is made that during breaks, exposure is zero. 

During the afternoon period where no sampling was carried out, 

it is assumed that exposure is similar to that measured by Sample 

3. Table 25-4 therefore gives a complete account of the day's 

exposure. 

The 8-h TWA mass concentration is therefore given as 

_ [(111 x 90) + (0 x 30) + (104 x 120) + (0 x 30) 

em - 8 x 60 

+(17 x 150) + (0 x 30) + (17 x 150)] 

x 8 X 60 

= 57 f-Lg/m3 

using Equation 25-4. 

For purposes of determination of compliance with occupational exposure limits, it is generally desirable to sample 

the workers assumed to be at maximum risk. Where the 

maximum-risk employees cannot be ascertained; employees 

should be selected at random. Leidel et al. (1977) recommend 

calculating the 95% one-sided lower confidence limit (LCL) 

and the 95% one-sided upper confidence limit (VCL). These 

are calculated as follows: 

LCL(95%) = X - fa. x CVT 

VCL(95%) = X + fa. x CVT (Eq. 25-5) 

where fa. = 1.645 when a = 0.95, CVT is the coefficient of 

variation for the sampling/analytical method and OEL is 

the exposure limit. If LCL and X are above unity, then the 

exposure is classified as noncompliant. If VCL and X are 

TABLE 25-3 Example Gravimetric Sample Data for a Worker in a Brass Factory 

Flow Rate Sample Sample Mass Mass 

Time Time (10-5 m3/s Duration Volume Collected Concentration 

Sample On Off [L/min]) (min) (L) (ILg) (f-Lg/m3

) 

#1 08:00 09:30 3.3 [2] 90 20 

#2 10:00 12:00 3.3 [2] 120 25 

#3 12:30 15:00 3.3 [2] 150 5 
25.6 CURRENT TRENDS 583 

TABLE 25-4 Complete Account of a Worker's Exposure to Lead in a Brass Factory (from Table 25-3) 

Flow Rate 

Time Time (10-5 m3 /s 

Sample On Off [L/minD 

#1 08:00 09:30 3.3 [2] 

#la (Break) 09:30 10:00 

#2 10:00 12:00 3.3 [2] 

#2a (Break) 12:00 12:30 

#3 12:30 15:00 3.3 [2] 

#3a (Break) 15:00 15:30 

#4 (Est. from #3) 15:30 18:00 

Total 

below unity, then the exposure is classified as compliant. 

Finally, if unity lies between LCL and X' or between UCL 

and X' the exposure is classified as possible overexposure. 

25.5.1.2 Evaluation of Workplace Controls Use of 

personal compliance type sampling results to judge the 

effectiveness of a control intervention may be misleading 

(Kissell 2003). Area sampling may be most appropriate for 

characterization of a workplace aerosol or for the evaluation 

of an engineering control. The chief advantage of area 

sampling is the elimination of the human variable in interpretation of the results. Other benefits include the use of a larger 

variety of instruments, and shorter sampling time periods. 

Walk-through evaluations using real-time monitors are 

used to obtain an overview of environment and to target specific areas, operations, or personnel for monitoring. More 

detailed strategy should be used to measure or verify the 

effectiveness. This strategy should account for variables 

such as aerosol generation rate (production), transport, dilution, sampler location, and other factors (Kissell 2003). 

Sound statistical design and error analysis should also be a 

part of the evaluation (Robson et al. 2001). 

25.6 CURRENT TRENDS 

25.6.1 Diesel Particulate in the Workplace 

In 1988, NIOSH recommended that whole diesel exhaust be 

regarded as a potential occupational carcinogen and that 

reductions in workplace exposure would reduce cancer 

risks (NIOSH 1988). Exposure to elevated concentrations 

of diesel exhaust has also been linked to health effects such 

as eye and nose irritation, headaches, nausea, and asthma 

(Kahn 1988; Wade and Newman 1993). Considerable 

debate has recently taken place regarding what should be 

the appropriate metric for measurement of diesel particulate 

matter (DPM) in the workplace. 

In the mining workplaces, MSHA has chosen to regulate 

engine emissions in coal mines and to set a limit on ambient 

Sample Sample Mass Mass 

Duration Volume Collected Concentration 

(min) (L) (/-Lg) (/-Lg/m3

) 

90 180 20 111 

30 0 0 

120 240 25 104 

30 0 0 

150 300 5 17 

30 0 0 

150 5 (est.) 17 

600 75 

particulate carbon levels in all other mines (Stephenson 

2006). The OSHA has no workplace ambient occupational 

limits for diesel particulate matter in general industry. The 

US Environmental Protection Agency (US EPA) , however, 

regulates diesel engine emissions and includes diesel particulate as part of their particulate matter (PM) standards. 

Personal exposure to DPM in the workplace may be 

sampled using a personal sampling pump with an impactorclassified filter sample followed by NIOSH method 5040 

analysis of the carbon components of the filter (Noll 2005). 

This provides a TWA measurement of the total, organic, 

and elemental carbon present on the filter. 

The measurement challenge, from the point of view of 

health effects and regulation and control of particulate 

matter, lies in the ability to distinguish between particulates 

generated by the process and ambient diesel particulates. 

This becomes especially problematic if the process particulates contain carbon. The aerosol scientist must also deal 

with the changing particulate size and particulate speciation, 

which change with changes in control technologies and fuel 

blends. 

The development of handheld oscillating microbalance 

systems for respirable dust monitoring in mining has been 

successful. While inlet and classification of inhalable and 

thoracic fractions will require special consideration using 

this technology, there is some optimism that the handheld 

oscillating microbalance may be capable of sensing the submicrometer DPM fraction of mine aerosols (Wu and Gillies 

2008). This work involved placing a 0.8-micrometer cutpoint 

impactor on the inlet of a monitor and measuring only the 

mass of the submicrometer aerosol. When continuous sideby-side measurements of respirable and submicrometer aerosol were conducted, source apportionment between combustion and commutation aerosols was possible in near real time. 

25.6.2 Toxic Materials 

Workplace assessment of toxic aerosols such as beryllium, 

silica, and radioactive aerosols, is problematic when the 

toxic limit values approach the level of detection of the 
584 WORKPLACE AEROSOL MEASUREMENT 

substance. Chapter 28 provides specific information on monitoring radon and radioactive aerosols. The general solution of 

sampling a larger volume of air and concentrating the sample 

to provide sufficient quantity for quantitative analysis is 

limited in personal sampling because of equipment size constraints. Misra et al. (2002) describes the use of a 1.5 x 10-4 

m3/s [9 L/min] flow-rate pump and impactor manufactured 

by SKC to enable collection of larger samples from a 

person-wearable device. Maynard (1999) describes the use 

of GK 2.69 (BG/) respirable cyclone using a 7 x 10-5 m3/s 

[4.2 L/min] flowrate which also enables larger samples for 

analysis. A 1.67 x 10-4 m3

/s [10 L/min] cyclone is also 

available (BIA 2002). Such portable, higher flow-rate 

samplers improve the limits of detection for high toxicity 

aerosols. Alternatively, more sensitive analytical techniques 

are required to assess personal exposure of toxic materials 

in the workplace. 

25.6.3 Engineered Nanomaterials 

Toxicological information on responses to inhaled nanometer-scale low solubility particles is challenging the applicability of current sampling conventions and philosophies 

(Maynard and Aitken 2007). Recent toxicology on low 

toxicity insoluble materials such as titanium dioxide has indicated that a more appropriate dose metric for depositing in 

the alveolar region may be particle number, or surface area 

(see Chapter 38 for more details; Maynard and Kuempel 

2005; Oberdorster et al. 2005, 2007). These studies appear 

to support some epidemiology investigations of the general 

population, indicating correlation between inhalation of fine 

particles and health effects (Dockery et al. 1993; Wichmann 

and Peters 2000; Pekkanen and Kulmala 2004; Delfino et al. 

2005; Penttinen et al. 2006). The extent to which such findings 

are applicable to exposure within the workplace is not apparent at present, although there is increased concern that 

new nanoscale materials-specifically those associated with 

the emerging field of nanotechnology-could present new 

and unusual occupational hygiene risks (Maynard 2007). As 

yet, few data are available on occupational exposures to 

engineered nanomaterials. There is evidence that materials 

such as carbon nanotubes and carbon black are not readily 

aerosolized (Kuhlbusch et al. 2004; Maynard et al. 2004; 

Bello et aL 2009), although these data are not generalizeable, 

and may not apply to all situations where these materials are 

handled. Based on research in progress, a number of publications are anticipated over the next few years that provide 

a clearer picture of conditions under which exposure to airborne engineered nanomaterials might occur. 

Occupational health agencies such as NIOSH in the 

United States have begun to formulate guidelines for the 

safe handling of engineered nanomaterials (NIOSH 2006). 

Similar guidelines are becoming available from industrybased groups (e.g., the DuPont/Environmental Defense 

Fund Nano Risk Framework; Dupont 2007) and from consensus standards bodies (ISO 2006; ASTM 2007; ISO 2008). 

These begin to outline the challenges and possible solutions 

associated with measuring and controlling exposure to airborne engineered nanomaterials in the workplace. 

25.6.4 Sampling Aerosol and Vapor 

In some cases it is necessary to assess exposures to aerosol 

and vapor simultaneously. This situation can occur when a 

volatile liquid or a solid with significant vapor pressure is 

sprayed, or when a vapor can give rise to a condensation aerosol, or when a volatile substance is absorbed on other particulates. The most typical examples are the isocyanates used 

in spray-on finishes, or toluene di-isocyanate, which, while 

volatile, can be found attached to polyurethane aerosol in 

foam manufacture. In this particular case, it is important 

not only to collect both aerosol and vapor fractions simultaneously, but to also derivatize the isocyanate group quickly 

so that further reaction does not take place. Thus, an impinger 

filled with liquid reagent followed by a filter also coated with 

reagent is the standard sampling apparatus. Less reactive 

aerosol-vapor combinations can be sampled using a diffusion denuder, followed by a filter, although these are not 

common as personal samplers because of their generally 

large size. An improvement may be a novel design of dichotomous sampler (Kim and Raynor 2009). 

25.6.5 Penetration versus Deposition 

While penetration of particles to the airways system is a 

measure of exposure, it is not a good measure of dose for certain particle sizes. This is because of a deposition minimum 

that occurs at around 0.3 /-Lm AED at the intersection of the 

two major mechanisms of particle capture: diffusion for 

small particles and interception and impaction for larger particles. As long as mass is the preferred metric, then this deposition minimum likely has little effect on sampling to meet the 

inhalable convention, because the much larger particles are 

associated with very much larger masses. However, for smaller particles, the deposition minimum becomes important. 

Vincent (2005) discusses the impact of accounting for deposition on the current thoracic and respirable sampling conventions and how this would require the development of 

novel sampling techniques, and also discusses the potential 

impact on any proposed ultrafine or nanoparticle sampling 

convention. 

25.7 LIST OF SYMBOLS 

Sf inhalable penetration fraction 

ST thoracic penetration fraction 

SR respirable penetration fraction 
c 

d 

VCL 

LCL 

r 

2: 

1] 

X 

ae 

R 

T 

I 

25.8 

concentration 

diameter 

upper confidence limit 

lower confidence limit 

mass median aerodynamic diameter 

geometric standard deviation 

efficiency 

ratio of the concentration mean divided by the occupational exposure limit 

aerodynamic diameter 

respirable 

thoracic 

inhalable 

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