DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

NIOSH Manual of Analytical Methods (NMAM), 5th Edition

Quantification of Airborne 

Dusts From Powders 

by Douglas E. Evans, PhD, NIOSH

1 Introduction.............................................................................................................................................. AD-2

2 Powders and dusts in the workplace.................................................................................................. AD-5

3 Dustiness test methods........................................................................................................................AD-13

4 Key considerations for dustiness.......................................................................................................AD-38

5 Criteria for current, improved, or new dustiness test configurations ......................................AD-43

6 Summary .................................................................................................................................................AD-44

7 Acknowledgements...............................................................................................................................AD-45

8 References...............................................................................................................................................AD-46
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Quantification of Airborne Dusts From Powders 

1 Introduction

If powders become airborne as a dust within the workplace, they may pose significant 

health or safety implications. The relative ease or propensity with which a powder 

becomes airborne from an external stimulus may be quantified or measured. This 

attribute may be defined by the term dustiness.

This chapter can serve as a helpful guide for industrial and occupational hygienists,

safety professionals, environmental health and safety (EHS) managers, EHS

investigators, product manufacturers, process engineers, and scientific instrument or 

equipment manufacturers. This guidance may also be useful to labs focusing on

analytical, powder characterization, and process safety. Professionals may find this 

information helpful both in exploring the value of dustiness testing and in selecting the 

most appropriate test method for their application.

This chapter briefly discusses how dustiness information may be used to develop lowdust products, inform exposure estimation, and execute risk mitigation, for example, 

through control banding. The content covers the development of test systems for 

quantifying dust release from bulk-powdered solids. The various test configurations are 

categorized according to their underlying dust generation mechanisms: gravity-induced, 

rotating, fluidization, and aerodynamic. The historical development of the more widely 

used and standardized test systems is also covered. This information highlights the 

multiple steps (in some instances) taken to develop and standardize test methods, 

making this information more readily accessible to the reader. Finally, criteria that need 

to be considered to evaluate or improve existing test methods or to develop new 

methods are described, particularly with respect to workplace inhalation exposures.

a. Powders, dusts, and aerosols

Powders, granules, flakes, chips, and pellets are either divided solids, finely divided 

solids, or particulate solids. These types of divided solids may be created or used across 

many different industrial sectors. Some are naturally occurring, such as those derived 

from agriculture, forestry, or through minerals extraction, for example. Others are 

synthetically manufactured or processed, such as pigments, pharmaceuticals, polymers, 

resins, or additive manufacturing feedstocks. Powders are the most finely divided solid 

form. The term “powders” is used more consistently throughout this discussion, but 

granules, flakes, and pellets may also apply in certain situations. A powder may be 

defined as finely divided matter or a preparation in the form of fine particles. Powders 

may therefore be considered as prepared or manufactured (i.e., deliberate or 

intentional). Conversely, dusts may be considered as waste or having less value. 

Airborne dust generation is typically unintentional. 

The International Standards Organization [ISO 2020] defines dust as “small solid 

particles, conventionally taken as those particles below 75 μm [micrometer] in diameter, 

which settle out under their own weight, but which may remain suspended for some 

time.” The International Union of Pure and Applied Chemistry [IUPAC 1990] defines dust

as “small, dry, solid particles projected into the air by natural forces... and by mechanical 

or man-made processes. Dust particles are usually in the size range from about 1 to 100 
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μm in diameter and settle slowly under the influence of gravity.” The World Health 

Organization [WHO 1999] defines dusts as “solid particles, ranging in size from below 1 

μm up to at least 100 μm, which may be airborne or become airborne.” Dust particles 

with dimensions below 1 μm are often encountered and particles greater than 100 μm 

may also become airborne [WHO 1999]. The U.S. National Fire Protection Association 

(NFPA) defines dust as any finely divided combustible solid, less than 500 μm (0.5 mm, 

or those particles passing a 35 U.S.-mesh sieve), as a potential combustible hazard 

[NFPA 2022]. Therefore, from the broad occupational health and safety perspective, dust

may span a particle size range from below 1 μm through 500 μm.

The scientific and universal term “aerosol” may be defined as a disperse system of liquid 

or solid particles suspended in a gas, usually air [ACGIH 1999; Hinds 1999; Vincent 

1995, 2007]. Aerosol may describe dispersed liquid particles, such as mists or sprays 

[Vincent 1995]. This can include newly condensed particles from a gas or vapor, more 

commonly referred to as fumes [Hinds 1999]. We will not consider mists, sprays, and 

fumes any further in this discussion. 

When a powder or dust becomes airborne, the resulting suspension is an aerosol. 

Aerosol is the correct scientific term, but we use the terms dusts or airborne dusts more 

consistently in this chapter as they are in wider general usage outside of the scientific 

research community.

b. Dust generation from powders

A powder will remain at rest or at a stable equilibrium until some external stimulus is 

applied. This situation differs from an analogy sometimes made with vapors that result 

from volatile liquids, for example, where vaporization is a spontaneous process. Within a 

liquid at rest, sufficient internal energy exists to facilitate vapor release from the liquid 

surface into air. For a finely divided solid at stable equilibrium, the energy required to 

release particles into air, and overcome interparticle attractive forces, must come 

externally.

For powder to become an airborne dust, there needs to be a coupling of at least two 

phases. At a minimum, this involves the mixing of powder and air. In further instances, 

the interaction of a powder, air, and a solid surface (a bench or floor for example) 

contributes to generating airborne dust. The stimuli can be applied in many ways. 

Gravity acting on the powder can result in some portion of the powder becoming 

airborne if the powder is set in motion. For example, an unstable powder pile (at 

unstable equilibrium), initially at rest, may cascade down, a portion of which may be 

entrained within the resulting displaced air. In another example, a poured powder can 

produce turbulent air currents as it displaces air, entraining and dispersing particles as 

it does. The impact of a bolus of falling powder with a solid surface can also result in 

some fraction of the powder being entrained. The dry sweeping of a spilled powder, 

perhaps with a brush or broom, would also likely result in some fraction of the powder 

becoming airborne. As the bristles move, they stir and agitate both the powder and air. 

These examples would generally be considered mechanical stimuli.
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One further noteworthy scenario is the induced movement of air over a finely divided 

solid or powder. This may be the result of wind (i.e., an Aeolian process) [Bagnold 1941; 

Cowherd 1981; Gillette et al. 1974; Visser 1992] or forced mechanical ventilation. Air 

movement might also result from fast-moving and energetic compressed air used during 

industrial processes, materials conveyance, cleaning operations, or pneumatically 

powered equipment operations, for example. These examples are considered 

aerodynamic stimuli, resulting from some fraction of the powder breaking away from 

the bulk and becoming entrained within the induced airflow.

Other airborne dust-generation mechanisms exist that are not discussed further in this 

chapter but may be the result of direct comminution (size reduction) from bulk solids. 

Comminution of parent bulk materials may include, for example, crushing, machining, 

grinding, drilling, sanding, scraping, etc. From the perspective of this discussion, 

airborne dust generation is the conversion of some fraction of the powder into an 

airborne dust.

c. Dustiness

The physical properties of a powder may influence the quantity of airborne dust 

liberated and can be considered a source strength factor [Lidén 2006]. The term 

“dustiness,” first used by Powell and Russell [1933] to describe the dust-generating 

ability of coal and coke, was undefined. The term dustability was used briefly [Bransby 

1977; Schofield et al. 1978], but dustiness has seen far wider usage, both historically and

geographically. We continue here with the dustiness terminology. 

An early definition of dustiness was “the tendency of dry materials to liberate dust into 

the air when handled under specified conditions” [BOHS 1985]. This definition referred 

to materials transfer and processing operations, but notably did not include the (direct) 

generation of particles during deliberate comminution [BOHS 1985], noted in the 

previous section. A further step could be added to this definition that addressed 

handling the collected dust generated from comminution.

Chung and Burdett [1994] argued that there was no unique definition of dustiness, as all 

dustiness measures were empirical and method dependent. Lyons and Mark [1994]

defined dustiness as the “propensity of materials to form airborne dust,” and Lidén 

[2006] defined it as the “propensity of a material to generate airborne dust during its 

handling.”

Boundy et al. [2006] defined dustiness as the “tendency of a powder to form an aerosol 

after it receives a given energy input.” The finely divided solid or powder, as discussed 

earlier, requires an external mechanical or aerodynamic stimulus to produce the 

airborne dust, and at least two (or even possibly three) phases are required. An inclusive 

definition of dustiness, therefore, may be the following: the propensity of a finely 

divided solid to form an airborne dust (aerosol) by a mechanical or aerodynamic 

stimulus.

Chung and Burdett [1994] and Lidén [2006] noted that dustiness is not an intrinsic 

powder property but is influenced by the selected test method. While not an intrinsic 
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material property, dustiness is a property of a given powder that should be quantifiable

and reproducible under a given controlled testing protocol [Evans et al. 2013]. With the 

many dustiness techniques developed, one simple approach to comparing results is 

through standardization, as noted by Chung and Burdett [1994]. 

Standardization from an occupational inhalation exposure perspective was proposed as 

early as 1980 [Hammond 1980]. The British Occupational Hygiene Society (BOHS) 

formed a technical working group in 1980 to review available test methods and 

recommend a standard dustiness approach [BOHS 1985]. It is now well recognized that 

different test configurations (i.e., different underlying dust generation mechanisms with 

varying particle sampling arrangements) will provide different dustiness results. For 

example, of the two standardized test configurations described in the European 

Standard EN15051, “Workplace atmospheres—Measurement of the dustiness of bulk 

materials” [CEN 2013b,c], powders tested under each configuration do not consistently 

rank in a similar manner [e.g., Pensis et al. 2010].

1) Primary particles, aggregates, and agglomerates

Powders are comprised of primary particles, which in some instances may be further 

aggregated, fused, or sintered together very strongly. These strongly bonded particle 

assemblies are sometimes referred to as aggregates or hard agglomerates [Friedlander 

2000]. Primary particles (or aggregates, if present) may be further held together by 

relatively weak adhesive particle interactions (e.g., van der Waals, electrostatic, 

capillary, and morphological interlocking). These latter loosely held structures are 

generally referred to as agglomerates [Nichols et al. 2002]. 

Although it is relatively easy to break up the loose agglomerates, breaking up aggregates 

into their primary particles often requires considerable mechanical action (ball-milling,

for example). The fracture or further comminution of primary particle size can only be 

achieved with extreme difficulty. In dustiness testing, the energy supplied is insufficient 

to divide primary particles or break up strongly bound aggregates/hard agglomerates

made up of primary particles [Evans et al. 2013]. However, the energy supplied may be 

enough to overcome interagglomerate adhesion and separate some fraction of the 

agglomerates from the bulk powder. The deagglomeration of a fraction of the loosely 

held agglomerates, which constitutes the bulk powder, is responsible for airborne dust 

generation.

2 Powders and dusts in the workplace

If powders, dusts, or finely divided solids are permitted to become airborne, forming an 

aerosol, they may potentially pose a health hazard or a safety hazard or both in 

workplaces across multiple industrial sectors.

a. Relevance of airborne dusts to occupational health

Airborne dusts or aerosols in a broader context, can be inhaled and enter the respiratory 

system as an inhalation exposure. Particle penetration and deposition within the 

respiratory system are largely influenced by particle size or aerodynamic particle 
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diameter. The particle health-based size fractions, inhalable, thoracic, and respirable, 

provide information on where particles are capable of penetrating and further 

depositing within the respiratory system [ACGIH 1999]. 

Inhalable (~PM100) particles are those that may enter the mouth or nose; thoracic 

(~PM10) particles pass the larynx and into the conducting airways; and respirable 

(~PM4) particles may penetrate the unciliated or gas-exchange regions of the 

respiratory system [ACGIH 1999; CEN 1993; ISO 1995]. The health-based particle 

penetration curves and their mathematical approximations are discussed in ACGIH 

[1999], Hinds [1999], and Vincent [2007]. They are also shown in Figure 1. The U.S. 

Environmental Protection Agency (EPA) ambient air quality particulate matter fractions 

for PM10 and PM2.5, which were developed independently of ACGIH [1999], CEN 

[1993], and ISO [1995], are included for comparison [Hinds 1999]. 

Figure 1. The inhalable, thoracic, respirable, PM10, and PM2.5 particle 

penetration curves [Hinds 1999; Vincent 2007]. 

Inhalation exposure is of particular concern when considering the potential health 

hazards of airborne dusts. Occupational lung disease has declined globally from 2000 

through 2016, but inhalation exposure to silica, asbestos, and particulate matter are still 

responsible for more than 700,000 deaths and 16 million disability-adjusted life years in 

2016 [WHO/ILO 2021]. Airborne particles may also enter the mouth (ingestion), the 

eyes (ocular), or deposit on the skin (dermal). 
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The adult human respiratory system offers about 70 square meters (m2) of surface area 

[Hasleton 1972]. By some estimates, the respiratory system is twice the surface area of 

the digestive system, thirty times the surface area of the skin, and arguably more 

susceptible to the outside environment [Combs and Dickson 2020]. Depending on size, 

chemical composition, morphology (shape), and concentration, dusts resulting from 

powders may be characterized as nuisance, irritant, toxic, or carcinogenic. In 

pharmaceutical manufacturing or dispensary environments, airborne dusts may be 

highly pharmacologically potent [Champmartin and Clerc 2014; Fent et al. 2014; Gold et 

al. 1973].

b. Relevance of airborne dusts to occupational safety

Airborne dust generation from a process, activity, or spill can result in an increased risk 

of slips and falls. Some materials can reduce the friction between a worker’s footwear 

and that of the floor, stairs, ladders, for example. Powders that are used for their 

lubricant or glidant properties are particularly noteworthy, even in small quantities. 

Excessive dust generation (a nuisance dust, for example) can result in decreased 

visibility within the workplace, potentially causing other accidents. Materials that are 

electrically conducting can lead to electrical short circuiting [OSHA 2005]. Short

circuiting can damage equipment or electrical infrastructure, and become a source of 

ignition, causing a fire [NFPA 2021, 2022].

Materials that are capable of being oxidized in air, themselves a potential fuel, can pose a 

fire and explosion risk. These materials are commonly referred to as combustible dusts

and can be a considerable hazard within the workplace [NFPA 2019]. An ignition source, 

the powder (fuel), combined with oxygen in the air, may be capable of supporting 

combustion as a powder fire. By further dispersing the powder in air, either as part of a 

process or inadvertently, a sufficiently strong ignition source (hot surface, flame, spark, 

electrical arc, etc.) can result in a flash fire. When coupled with confinement, 

combustible dusts can lead to dust explosions [Cashdollar 2000; CSB 2006, 2018; 

Eckhoff 2003]. Confinement can result from containing process equipment, pneumatic 

conveyance systems, or dust control or collection systems. On a larger scale, it can be the 

walls of a structure or the entries within a mine.

These risks and their potential consequences are well documented in coal mining, 

manufacturing, agriculture, food processing, and other industrial environments. The 

reader is encouraged to seek expert guidance in analyzing the risks and adopting 

appropriate mitigation measures [CSB 2006, 2018; Eckhoff 2003; HSE 2003; NFPA 2019, 

2020; OSHA 2005, 2020].

c. Economic considerations resulting from airborne dusts

During materials manufacturing and processing, potential loss of product or degradation 

in product quality creates a potential loss in revenue. Preventing or controlling dust 

emissions is therefore economically prudent. Where multiple product lines are situated 

close together, the potential exists for cross contamination of both equipment and 

product. Therefore, a decrease in product quality could occur with airborne dust from 

one source possibly contaminating another. Cross contamination may also have 
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consumer health or regulatory implications, particularly in food processing or 

pharmaceutical manufacturing [e.g., Gold et al. 1973]. Equipment contamination can 

lead to premature wearing and failure of critical moving parts. In addition, there are 

costs associated with dust cleanup (housekeeping). 

One further aspect is using potentially costly engineering dust-controls. The system size, 

possibly amplifying the capital investment and operating costs, must be considered. 

Often, manufacturers desire a process, product, or intermediate that does not require 

the use of ventilation, dust capture, containment, or filtration systems, or perhaps 

requires scaled-down versions of these systems.

d. Factors influencing exposure

Many factors can influence whether workers will be exposed to aerosolized particles 

from powders and to what extent. Possible factors include the following:

• Type of operation or task (from low to high energy processes or activities, for 

example)

• Quantities of materials (mass or volume)

• Proximity of the worker to the emission source

• Ventilation in general (dilution)

• Presence of any engineered exposure controls (enclosures, local exhaust ventilation, 

etc.)

• Leaks in process equipment

• Worker technique with respect to manual handing scenarios

• Physical properties of the powders themselves

From an occupational or industrial hygiene perspective, when material flow is followed 

within the workplace, transfer points stand out as emission sources. These transfer 

points have the potential for elevating worker exposures. Examples might include 

removing lids, emptying containers or bags of feedstocks, scooping manually, weighing

out, pouring, dumping, conveying, transferring from conveyor, stockpiling, reducing 

aggregate size, classifying size (e.g., sieving), bagging and packing of product, harvesting 

product from reactors, unmolding, maintaining systems, spilling accidents, cleaning

equipment, disposing of bags, etc. [e.g., Cheng 1973; Dahm et al. 2012; Dennis and 

Bubenick 1983; Evans et al. 2008; Evans et al. 2010; Hammond 1980; Heitbrink et al. 

1992; Heitbrink et al. 1989; HSE 2013; Lundgren 1986; NIOSH 2014a, 2018b; Petavratzi 

et al. 2007; Ribalta et al. 2019a; Sutter et al. 1982; Visser 1992].

Task-based, short-term, or direct-reading sampling [NIOSH 2021b] in these situations

may be particularly useful for identifying and quantifying these exposure-prone 

activities. The use of video exposure monitoring (VEM), whereby video footage of tasks 

or operations are overlayed with aerosol concentration data from a direct reading 

instrument, can be used to identify key events that contribute to a worker’s exposure 

[e.g., NIOSH 2014b]. VEM can also be a powerful tool in the subsequent training of 

workers [Rosén et al. 2005]. A fine dust cloud can be visualized directly and coupled 

with photography or video footage. 
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The “dust lamp” is another dust visualization tool that uses a strong, carefully positioned 

light to exploit the Tyndall effect, which is the scattering of light by particles [HSE 2015]. 

Exposure-prone activities, even for short durations (i.e., less than 15 minutes), can also 

be drivers of time-weighted exposure concentrations when averaged over an entire 

working shift of 8 to 10 hours.

e. Relating dustiness to inhalation exposure

The best available worker inhalation exposure information is through exposure 

assessment, where air sampling is conducted within the personal breathing zone of the 

worker [Vincent 2007]. This can be done on a short-term, task-based, or long-term (full 

shift) basis. However, where inhalation exposure information is incomplete, dustiness 

information may be used to fill knowledge gaps based on potential source strength (dust 

yield). For example, it may not be feasible to concurrently sample for all particle size 

fractions (inhalable, thoracic, and respirable) on a worker. Dustiness information could 

potentially be used in historical worker exposure reconstruction if existing exposure 

information was rudimentary, incomplete, or lacking.

Cowherd et al. [1989b] studied the dust emissions from 3.8 liter (L) (1-gallon) volumes 

of finely divided powders transferred to 23 L (6-gallon) containers within an 

experimental room. Test powders consisted of talc, sodium chloride, Portland cement, 

and a Direct Yellow 4 dyestuff. Emission factors, especially those at a 25-centimeter (cm) 

drop height, compared well with dustiness indices resulting from the Midwest Research 

Institute (MRI) dustiness test configuration described later (see Section 3.b.2). Emission 

factors for scooping and dumping were the same as the emission factors for pouring at a 

given drop height. Therefore, drop height was determined as an important experimental 

variable.

Heitbrink et al. [1989] found a significant correlation between dustiness tests and 

worker exposure during the bagging of powdered acrylic resins at an industrial facility. 

Investigators used the Heubach (Type I) rotating drum (see Section 3.c) and the MRI 

dustiness test configurations (see Section 3.b.2) to assess workers for total dust 

exposure. They noted that addressing material dustiness is important for predicting and 

controlling worker dust exposure. 

In later work, Heitbrink et al. [1990] compared MRI test results with that of task-based 

worker exposure measurements (total dust) from four work sites while workers 

performed bag dumping, bag packing, or tank charging with acrylic resins, crystalline 

silica, titanium dioxide, talc, and lead chromate. Dust controls were described as 

“minimally effective.” At two of the sites, dustiness measurements provided the relative 

exposure potential of the materials used. However, at two other sites, an inconsistent 

relationship was found, presumably with other exposure factors playing a more 

significant role.

Brouwer et al. [2006] compared the dustiness of magnesium stearate, aluminum oxide, 

and calcium carbonate obtained in the EN15051-2 rotating drum [CEN 2013b] with 

operator exposures from semi-controlled dust-handling experiments within a room. 

Ventilation and environmental variables were controlled during scooping, weighing, 
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adding, and dry clean-up tasks (brushing, scooping, discarding waste) from both bench 

and floor surfaces. Dustiness was found to be the major exposure determinant, 

contributing to ~70% of the exposure variance. Furthermore, the ratios of respirable 

and inhalable fractions, as determined by dustiness tests, were comparable with the 

ratios observed for the exposure measurements. The results emphasized the relevance 

of dustiness as a parameter for exposure potential.

Ribalta et al. [2019b] found a high degree of correlation (R2 = 0.77–0.97) between 

dustiness indices from the EN15051-2 rotating drum and EN15051-3 continuous drop 

test configurations [CEN 2013b,c] and inhalable exposure concentrations measured 

during high- and low-energy materials-handling experiments. Five ceramic test 

powders, which included silica sand, three quartz powders, and kaolin, were handled in 

2-kg batches. Researchers suggested that dustiness could be considered a relevant 

predictor for workplace exposure.

Dustiness is a major determining factor in the concentration of worker inhalation 

exposures. Therefore, dustiness may be used to provide inhalation exposure estimates 

based on the quantities of materials used in the workplace. For example, considering the 

milligrams of dust generated per kilograms of material used or “dust yield.” Tests that

provide the inhalable, thoracic, and respirable particle size fractions are best suited for 

this purpose. Particle size fractions of exposure need to be measured within the worker 

breathing zone and compared with that measured during dustiness testing if the 

relationship between exposure and dustiness is being investigated. Improved control of 

external variables (humidity, air flow, etc.) in the experimental design may result in a 

stronger relationship between dustiness and worker exposure when future dustinessexposure studies are conducted. The relative anticipated ratios of the particle size 

fractions may also be estimated from dustiness experiments. 

f. Controlling exposures through the hierarchy of controls

The first and most basic step in the control of hazards is recognizing them [WHO 1999]. 

Traditionally, a hierarchy of controls has been used as a way to implement feasible and 

effective controls [NIOSH 2023]. Following the hierarchy normally leads to 

implementing inherently safer systems, ones where the risk of illness or injury has been 

substantially reduced. In order from the most effective to the least effective control is

elimination, substitution, engineering controls, administrative controls, and personal 

protective equipment. 

Elimination would be an example of removing a hazard in its entirety from the 

workplace. This may be difficult to achieve if the hazardous product has unique and 

desirable physical properties that are required for the product/process. Substitution 

might be possible through replacing a hazardous product with one that was less 

hazardous or possibly the same material in a less hazardous form. For example, a form

that produces much less airborne dust. Bakeries used this approach where they 

increased vegetable oil content from 2% to 4% within an improver mix. This reduced 

airborne dust allergen content and the potential for worker exposure by 77% [HSE 

2010].
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Engineering controls remove hazardous conditions (e.g., local exhaust ventilation that 

captures and removes airborne emissions) or place a barrier between the worker and 

the hazard (e.g., containment). Well-designed and implemented engineering controls can 

be highly effective in protecting workers. These actions should be passive, that is,

independent of worker interactions [NIOSH 2014a]. Engineering controls should not 

hinder workers’ productivity or make work more difficult to do. NIOSH provides 

strategies and guidance on applying engineering controls to the processes and 

downstream handling of nanoscale materials [NIOSH 2014a, 2018b]. These strategies 

may also apply to other industrial scenarios besides nanoscale manufacturing.

Administrative controls could involve training of employees, perhaps in applying 

techniques that generate less airborne dust. It may involve restricting access or limiting 

shifts to a dust-generating area or process to only those workers who need to be 

present. A last resort would be using personal protective equipment, such as a 

respirator [NIOSH 2018a], to address the potential for worker exposure.

In the United States, workers are required to be trained, fit-tested, and medically cleared 

for certain types of respirators as part of a formal Respiratory Protection Program (CFR 

1910.134) [OSHA 1998]. Similar requirements can apply in other countries. For a 

comprehensive discussion of the use of ventilation, enclosures, and other approaches in 

controlling dust exposures, readers are encouraged to consult AIChE [2005], ACGIH 

[2020, 2023], and HSE [2013, 2017a, 2022]. For specific guidance and examples for 

mining or minerals processing, see the NIOSH Dust Control Handbook for industrial 

minerals mining and processing [NIOSH 2019] or the NIOSH Best Practices for Dust 

Control in Coal Mining [NIOSH 2021a]. For pharmaceutical containment, look to the 

International Society for Pharmaceutical Engineering [ISPE 2012] for good practice 

guidance.

g. Control banding

The traditional approach to protecting worker health is to measure worker exposures to 

potentially hazardous agents, compare them with occupational exposure limits (OELs), 

and then determine if existing control measures provide adequate protection [NIOSH 

2009]. However, relying on this approach has become increasingly difficult due to the 

growing number of potentially hazardous materials in the workplace that do not have 

OELs [Garrod and Rajan-Sithamparanadarajah 2003]. The EPA reports that the Toxic 

Substances Control Act Chemical Substance Inventory contains over 86,000 chemical 

substances [EPA 2023], yet only about 1,000 chemical substances have been assigned at 

least one authoritative (government, consensus, or peer reviewed) OEL. In addition, 

small- and medium-sized enterprises may employ a large proportion of the workforce 

yet may not possess occupational safety and health expertise [HSE 2017b; Zalk and 

Nelson 2008]. 

Consequently, control banding (CB) strategies have been proposed to make engineering 

control decisions for general chemical substances without OELs or perhaps without 

expert guidance [NIOSH 2009; Zalk and Nelson 2008]. Typically, CB strategies consist of 

two main components: (1) hazard bands and (2) exposure (or emission potential) 
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bands. These qualitative bands rank substances based on their hazardous properties 

and their production/use, which range from low to high levels of hazard and/or 

exposure potential. The combination of the hazard and exposure bands is used to derive 

the exposure control band and associated engineering control options for a given 

task/process. 

CB takes a pragmatic approach in that many previous worker-exposure problems have 

solutions, and only limited control options are generally applied in practice. Risks can 

therefore be grouped or banded. In ascending order, control measures could include, at 

a minimum, good industrial hygiene practice coupled with general ventilation (dilution), 

the use of fume hoods or local exhaust ventilation, containment, enclosure, isolation, and 

last, expert guidance [Brouwer 2012; Maynard 2007; Paik et al. 2008; Zalk and Nelson 

2008].

Exposure or emission potential bands are qualitative descriptors of potential exposure 

levels, given the factors that may influence exposure such as dustiness, type of process 

or task performed, and the amount of material being handled (ISO 12901-2) [ISO 2014]. 

The standardized dustiness test configurations (i.e., continuous drop and rotating 

drum), described in EN15051 [CEN 2013a–c] and discussed later in Sections 3.b.2.A and 

3.c.2, provide threshold dustiness values to which a tested product may be compared. 

Values can ultimately be designated for each of the health-based particle size fractions, 

such as very low, low, medium, or high dustiness (exposure potential). Those products 

with higher dustiness, and therefore exposure potential (depending on hazard), may 

require more stringent control measures. Dustiness values, as we will see later, may 

range by several orders of magnitude. A dustiness parameter, where available, is a 

useful input into CB tools. Further guidance on control banding may be found in NIOSH 

[2009], ISO [2014], and HSE [2017b].

h. How dustiness testing may be used

A major reason for work-related ill health and disease is airborne dust that results from 

the dustiness of a powder [Burdett et al. 2000]. Dustiness testing data may be used in a 

myriad of ways. In this chapter, we will not cover all ways in which data can be used. We 

will provide the reader with some perspective on the possibilities with respect to 

occupational safety and health. The strong correlations generally observed between 

dustiness and inhalation exposure, and which are used as an exposure potential input in 

control banding, are discussed in Sections 2.e and 2.g.

In product and process engineering, dustiness information may inform the development 

of less dusty products or forms of the same material. Efficacy of dust suppression 

additives, such as moisture or oil, for example, may inform a substitution control. Less 

dusty (reduced dustiness) products can greatly benefit downstream users. The selection 

of appropriate surrogate powders (e.g., lactose, mannitol, and naproxen sodium) for 

assessing exposure control performance in pharmaceutical manufacturing can be based 

off dustiness performance data of the active pharmaceutical ingredient (API) or 

formulations containing the API. The use of dustiness information (with reference to the 

method used) can be included with safety data in communicating hazards (health or 
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safety) to downstream users about the potential for dust generation through handling of 

a product. Data derived from experimental test systems, which emulate the dispersion 

characteristics of propagating coal dust explosions, may be used in selecting effective 

mitigating products [Perera et al. 2016].

The dustiness of a new or unknown powder may be compared with that of a more 

familiar powder. This could be done through laboratory dustiness tests of both powders 

and through workplace inhalation exposure measurements, typically conducted in the 

worker breathing zone. The effect on inhalation exposure measurements in the 

workplace may then be directly related back to the differences in powder properties. 

One may also compare a new or previously unknown powder to the threshold dustiness 

values included in EN15051-2 and EN15051-3 [CEN 2013b,c] (and see Sections 3.b.2.A 

and 3.c.2), if these test configurations are used. Dustiness comparisons can help identify 

improvements needed in manufacturing equipment design and exposure controls before 

the new powder goes into full scale production. These are examples of exposure 

prevention through design [ANSI/ASSP 2021].

A further use of dustiness test systems is to compare aerosol sampler or instrument 

performance [e.g., Dahm et al. 2019; Evans et al. 2010] from a well-mixed contaminant 

atmosphere or perhaps to further method development and validation [e.g., Baron et al. 

2008; Neu-Baker et al. 2019]. In this application, dustiness test systems provide a 

realistic source of contaminant dust, one that might be encountered in the workplace, 

for example.

3 Dustiness test methods

a. Classification of methods

It is useful to classify the various dustiness test systems by the mechanism used to 

generate airborne dust. Lyons and Mark [1992] noted that one must consider the way 

dust is dispersed and sampled when designing a dustiness test method. A number of

dustiness test configurations have been described in the past. When initially classifying 

different dust generation testing methods, BOHS and others categorized them into three 

main methods: gravity (drop methods), mechanical dispersion (including rotating 

drums in this case), and gas dispersion (aerated fluidization) [BOHS 1985; Chung and 

Burdett 1994].

The goal of all dustiness methods is to produce results that relate the mass of airborne 

dust produced to the mass of the original powder [Boundy et al. 2006; Burdett et al. 

2000]. The more widely used examples are discussed here, however, readers can find 

less notable examples in other sources [e.g., BOHS 1985; Hamelmann and Schmidt 2003,

2004]. 

For a historic view, BOHS [1985] reviewed 18 dustiness test devices that existed at the 

time, and Hamelmann and Schmidt [2004] documented more than 65 devices. Over the 

intervening years, as of 2023, many more devices have been developed. In further 

sections, test configurations described are categorized into gravity-induced methods, 
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rotating methods (closely affiliated with gravity-induced methods), fluidization 

methods, and aerodynamic methods. These categories are used because they more 

appropriately describe the underlying material-dispersion processes.

b. Gravity-induced test configurations

A falling powder within the workplace is a very common mechanism of airborne dust 

generation, whether part of a materials transfer processes, activity, or an accidental 

spill. It is no coincidence that many historical dustiness test configurations are within 

this category. Falling powder test systems can use one of three different methods: a

single drop type, where a powder sample is dropped as a single bolus and impacts with a 

solid surface; multiple drop types (such as rotating test configurations discussed in 

Section 3.c); or continuous falling types, where a continuous stream of powder winnows 

down a test chamber. 

Some test configurations include the contribution from the powder impacting the solid 

surface, yet others do not [e.g., Heitbrink et al. 1992]. As noted by BOHS [1988], when 

comparing dustiness devices, continuous falling methods generally provide more 

consistent results than single drop methods. Although with notable exceptions, the 

majority of falling powder configurations have been of the single drop type.

1) Single drop configurations

An early test device to quantify dust release from coal and coke was developed in 1928 

[Powell and Russell 1933]. This device was the first reported quantitative dustiness test 

configuration and used the single drop method. The investigators were motivated as 

dustless or low-dust domestic solid fuel products became commercialized. They realized 

that an empirical method was needed to quantify dust release so the effectiveness of 

dust suppression (laying) additives could be assessed. 

A metallic dust-tight enclosure, which was 1,520-millimeters (mm) or 5-feet (ft) high

and 457-mm or 18-inches (in) wide and deep, incorporated three horizontal slides and a 

305-mm (12 in) deep drawer. A large upper slide inserted 305 mm (12 in) below the top 

of the cabinet formed the base of the initial test powder compartment. In here, a massive 

25 kilogram (kg) or 55 pounds (lb) of the dried test sample was loaded. Two polished,

passive settling slides (one situated above the other), inserted 610 mm (24 in) above the 

base of the sample receiving drawer, were used to collect the settled dust. The dried test 

powder was loaded with the upper sample compartment slide inserted, whereas the 

lower settling slides were initially withdrawn. 

The test began by a rapid withdrawal of the upper slide, t = 0 second (s), allowing the 

25-kg test sample to fall into the receiving drawer at the base of the enclosure. The 

resulting dust cloud, presumably generated during both the powder fall and the impact 

with the receiving drawer, was allowed to settle under gravity. At t = 5 s, the two settling 

slides were inserted into the enclosure. Following 2 minutes of settling (t = 125 s), the 

upper (coarse dust) sampling slide was withdrawn, and the lower (fine dust) slide 

remained. After another 8 minutes of settling (t = 605 s), the fine dust slide was 

withdrawn. The two dustiness indices (coarse dust and fine dust) were collected by
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carefully brushing off and weighing the dust on the two slides. The results were 

reported in gram/ton of dust to fuel product.

ASTM D547-41 [1980], a test method for determining the dustiness of coal and coke, 

was directly derived from Powell and Russell [1933] above. The method, first 

standardized in 1939 (ASTM D547-39T), was revised in 1941 (ASTM D547-41), last 

reapproved in 1980, and finally withdrawn in 1986. Only minor changes were 

incorporated into the ASTM D547-41 [1980] test configuration over the earlier Powell 

and Russell [1933] device. The receiving drawer was enlarged to 356-mm (14 in) deep, 

minimum sheet metal gauges were suggested to ensure containment integrity, and an 

optional automated slide insertion was used. The test sample mass was standardized to 

22.7 kg (50 lb), and samples could be tested either as received or dried over 1 to 3 days. 

Duplicate tests were anticipated to have a reproducibility of within 20% of the mean 

average. If this was not initially attained, additional testing was recommended. 

The fine coal or coke dust was denoted as “float” dust. This long-established terminology

[e.g., BoM 1927] continues today within mining environments to describe airborne coal 

dust particles that remain airborne and may be transported on air currents. These 

particles are defined as those with a diameter less than 75 μm or that pass through a U.S. 

200-mesh sieve [NIOSH 2006].

There was also a scaled down version of ASTM D547-41 [1980]. It required a 200-g test 

sample, a pivoting hopper, and a fall of about 400 mm [BOHS 1985]. Active particle 

samplers were used to measure total dust and the thoracic particle size fraction (using a 

horizontal elutriator).

Andreasen et al. [1939] performed a classical study of the dust-generating capacity of 24 

fine materials. Lycopodium powder (Lykopodium), which contains the spores from the 

Lycopodium clubmoss plant, were used as a reference material and assigned a 

dispersibility of 100. Twenty-three other test powders were then compared. The test 

system comprised a single drop of a 2-milliliter (mL) bolus of powder down a vertical 

chamber with a 145-mm diameter and 2500-mm height. Collection plates at the base of 

the apparatus were used to determine the quantity of dispersed dust by Stokes’ 

gravitational settling.

A European dyestuff industry consortium developed another single drop configuration 

called the Roaches Dust Particle Apparatus (Roaches Engineering Ltd., UK). It was 

reported in Berger-Schuun et al. [1989] and evaluated by Lyons and Mark [1992]. A 

single 10 g of test powder was dropped from an open funnel at a fall height of 800 mm. 

The powder went through a vertical enclosure and into a cylindrical and initially 

quiescent chamber. Here, the falling powder impacted with the base. Five seconds 

following the test sample drop, a pre-weighed filter positioned at the top of the 

collection chamber (200 mm above the base) started sampling the total dust for 2 

minutes at 15 liter per minute (L/min).

Another single powder drop device, the Dustview II, developed by BASF and the 

University of Wuppertal (Wuppertal, Germany), is remarkably similar to the Roaches 

Dust Particle Apparatus configuration [Berger-Schuun et al. 1989]. The 30-g powder 
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sample was dropped 750 mm as a single bolus into a chamber where the resulting 

aerosol is optically monitored with an aerosol photometer. A combination of the initial 

dust cloud (maximum concentration) and dust concentration at 30 s provide for a 

dustiness number between 0 and 100. 

Further inspired by the Dustview II configuration, O’Shaughnessy et al. [2012] described 

a single drop low-mass dustiness test system. The powder sample (15 mg) was dropped

from a height of 610 mm within a metal tube with an inner diameter of 9.5 mm. 

Substituting an aerosol photometer with an aerodynamic particle sizer, O’Shaughnessy 

et al. [2012] estimated the respirable aerosol fraction from the test powder.

A further single drop test configuration conforms to DIN 55992-2 [1999] and was briefly 

assessed by Burdett et al. [2000]. It consisted of a single drop column, required a 2-g 

dust sample, and used optical extinction to estimate the mass concentration of airborne 

dust. A sliding plate arrangement allowed for several repeat tests. An output of between 

0 and 1 indicated the total dust light-extinction. As with any optically based method, a 

relationship between gravimetric mass and optically derived mass for a given test 

powder needs to be established.

Burdett et al. [2000] described a novel single/multiple drop test configuration. It used a 

test drop column above a stationary, cylindrical drum. In the drop configuration, a 600-

mm high column held the test powder in a hopper with a trap door, in a similar 

arrangement to the Roaches test configuration previously described. As the experiment 

began, the test powder was allowed to fall the 600-mm length down the column, which 

was fixed atop a 300-mm diameter drum. An impaction plate 200 × 250 mm at the base 

of the drum received the falling test sample. A gentle cross flow of air (38 L/min) 

through the drum transported dust containing air to size-selective foam substrates. A 

final filter allowed for the health-based inhalable, thoracic, and respirable size fractions 

to be determined [ACGIH 1999; CEN 1993; ISO 1995]. In initial testing, the falling test 

powder splashed from the impaction plate to the collection foams, adding considerable 

variability between experiments. This phenomenon was directly observed by removing

the drum inlet. Later tests incorporated an impaction plate lip to reduce the potential 

sideways splash of the test powder impact. Although this drop test configuration is not 

currently used, the drum received further development, as later discussed in Section 3.c.

A contemporary drop method, which measures dispersed powder, is the ASTM D6393 

[2021] Carr dispersibility test. It is a single drop configuration described as one of 

several powder tests measured by the PT-X Powder Characteristics Tester. In this test, 

10 g of test powder falls 170 mm unconfined. It then falls through a cylindrical tube with 

100-mm diameter and 340-mm height. The test powder falls another 102 mm, 

unconfined, onto a pre-weighed concave watch glass (with 100-mm diameter). The total 

height of the powder fall is about 612 mm. The dispersed powder is the mass of the 

powder that does not deposit on the watch glass, i.e., is not recovered from the 

experiment. Dispersed powder is usually expressed as a percentage of the original mass 

(10 g) of the powder test sample. This test configuration is focused more on 

manufacturing product performance than from a worker health or a safety perspective. 
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The open nature of portions of the apparatus and the subsequent external loss of some 

fraction of the test powder may preclude the handling of some powders.

2) Pour or continuous drop configurations

A pour configuration was described by Wells and Alexander [1978] at Unilever 

(Sharnbrook, UK). This Unilever dust-yield test-configuration was notable as it was one 

of first to consider health-related particle size fractions. During the test, the 100 to 300 g 

test powder was loaded into a wide stainless-steel funnel with a 20-mm stem bore 

diameter and 20-mm length with a closed slide. The slide was opened, allowing the test 

sample to pour a height of about 310 mm into the sample chamber below (within a few 

seconds). Air drawn horizontally across the falling powder at 50 L/min entered a Hexlet 

elutriator and provided the respirable particle size fraction. A similar flow rate across 

the powder and with a simple filter arrangement provided for total dust in a repeat 

experiment. 

To study fugitive dust emissions, a pouring device was described by Lundgren [1986]

and Lundgren and Rangaraj [1986] at the University of Florida (Gainesville, FL, USA). 

The device simulated pouring and dumping of relatively coarse industrial aggregates,

such as phosphate rock. The test was similar to the Powell and Russell [1933] and ASTM 

D547 [1980] devices, but it used active instead of passive sampling. Over a 1-min period, 

5 kg of test material was poured down a 1,524-mm (5 ft) column into a rectangular test 

chamber. As the material fell down the column, air was sampled at 1.9 m3/min using a 

standard high-volume (Hi-Vol) sampling configuration located 914 mm (3 ft) above the 

chamber base. 

Cowherd et al. [1989a] at the Midwest Research Institute (MRI; Kansas City, MO, USA) 

described the MRI pouring/drop device. The device had a powder drop height of 250 

mm and fell onto a solid receiving surface. The MRI device was inspired by the earlier 

Lundgren [1986] configuration. A vibrating stainless-steel sample cup of 270 mL, filled 

with 250 g of test powder, was slowly rotated at 0.8 rotations per minute (rpm). This 

resulted in a more continuous stream of powder. The airborne generated dust was 

sampled from the top of the containment chamber with a 47-mm filter at 8.3 L/min for 

10 minutes, resulting in about 4.2 air exchanges within the device.

A. EN15051-3 [CEN 2013c] continuous powder drop test

Falling powders are common mechanisms of dust generation within the workplace, 

whether intentional or unintentional. As noted earlier by BOHS [1988], continuous 

falling test methods generally provide more consistent results when compared with 

single drop test methods. The EN15051-3 continuous falling powder test derives from 

an early prototype [Burdett et al. 2000; Dahmann et al. 1997]. A former DIN method, 

DIN 33897-2 [2002], was withdrawn and superseded by EN15051 in 2006. A schematic 

is provided in Figure 2.
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Figure 2: Schematic drawing of the EN15051-3 [CEN 2013c] continuous powder 

drop test configuration: continuous powder (P), main flow (F), inhalable 

sampler location (S1), and respirable sampler location (S2). Dimensions are in 

millimeters.

In the contemporary EN15051-3 [CEN 2013c] drop test, the powder is continuously fed 

at between (6 g/min to 10 g/min) by a metering device, such as a vibrating chute with 

adjustable feed-rate. The powder moves down a cylindrical feed tube of 400-mm length 

and 15-mm diameter within a larger backflow tube of 150-mm diameter. An earlier 

screw feed metering device could not deliver all test powder types, and in general, 

metering of the powder limits testing to dry powders [Burdett et al. 2000]. The powder 

falls a total height of 1,100 mm within the backflow tube, with the lower end of the feed 

tube positioned 700 mm above the base of the backflow tube and 400 mm below the top. 

The experiment is performed against a slow countercurrent of upward moving air 

controlled at 0.05 m/s (53 L/min). A maximum particle size of about 38 μm can be 

carried by the upward countercurrent and be sampled [Burdett et al. 2000]. Test 

materials with a substantial particle fraction larger than 38 μm may result in a 

significant underestimation of the inhalable particle size fraction [Burdett et al. 2000]. 

The falling powder is collected into pre-weighed filter cups at the base of the apparatus. 

The falling powder is sampled by air samplers conforming to the inhalable (BIA GSP 

conical sampling head at 3.5 L/min) and respirable (BIA FSP cyclone sampling head at 

2.0 L/min) size fractions. This occurs at a height of 300 mm below the top of the 

backflow chamber and 100 mm above the base of the feed tube, typically for about 10 

minutes. The thoracic particle fraction is not quantified in this test configuration. 
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The mass collected by the inhalable and respirable samplers is then compared with the 

mass of powder delivered into the filter cup. A 500-g test sample mass is usually 

required for multiple tests to be performed (a minimum of four repeat tests). 

Threshold values for the continuous drop method have been established from results of 

over 500 test samples (EN15051-3) [CEN 2013c]. The thresholds compare the amount 

of dust released (mg) to the parent powder fed into the test device (kg). For the 

inhalable fraction, less than 1,000 mg/kg is considered very low dustiness; between 

1,000 and 4,000 mg/kg, low dustiness; between 4,000 and 10,000 mg/kg, moderate 

dustiness; and greater than 10,000 mg/kg, high dustiness. For the respirable size 

fraction, less than 20 mg/kg is very low dustiness; between 20 and 70 mg/kg, low 

dustiness; between 70 and 300 mg/kg, moderate dustiness; and greater than 300 

mg/kg, high dustiness. These threshold values and their corresponding exposure 

potential bands for each of the particle size fractions (very low, low, medium, and high

dustiness) allow for the exposure risk assessment of new and unknown powders. 

EN15051-3 [CEN 2013c] has special application to certain workplace operations where 

the powder is poured a distance through air (perhaps 1 meter or more). Such operations 

might include the filling of containers or bags from a hopper, the filling of silos, or 

transferring powder from a conveyor, where the powder is permitted to fall 

continuously in a stream from a height. The EN15051-3 [CEN 2013c] continuous drop 

method has been further adopted for nanoscale materials and is described in EN17199-

3 [CEN 2019c]. The dust generation portion of the test method remains unchanged, but 

different sampling arrangements may be employed.

c. Rotating test configurations

In rotating test configurations, a test powder is rotated within a cylindrical containment 

vessel fitted with internal lifters. As the substrate angle periodically increases, the test 

powder exceeds its angle of repose, and a local avalanche ensues; this aerosolizes a 

fraction of the falling test powder [Evans et al. 2013]. This multiple drop process repeats 

continuously throughout the test as the cylinder is rotated. A falling powder within the 

workplace is a common mechanism of airborne dust generation, as noted earlier. 

Earlier classification of rotating, tumbling, or rolling drum/cylinder configurations 

considered the attrition (break up of larger particles or granules) aspect of these devices

[BOHS 1985; Lyons and Mark 1994]. For example, in the first known description of a 

rotating test configuration [Cocke et al. 1978], attrition certainly contributed to the dust 

generation from agricultural grains. An attrition element may be present, particularly 

for larger materials such as grains, granules, or pellets, etc. However, the energy 

imparted to the test material that forms the airborne dust comes from the repeated fall 

of the material under gravity—where material is repeatedly scooped up by the internal 

protrusions, fins, lifters, or flights within the drum. So, we could say that rolling, 

tumbling, or rotating drum configurations are an important set of test configurations 

closely affiliated with gravity-induced falling powder methods, particularly those 

configurations operated at lower rotating speeds. 
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The finely divided solid, the internal surfaces of the drum, and air moving through the 

drum interact to generate and transport airborne dust. This dust moves out of the 

working dust-generation section to the sampling section for collection. Drum 

configurations more generally are capable of not only testing powders, but also flakes, 

granules, and pellets, or even larger forms of materials. For larger test materials, dust 

abraded or released from the surface is useful performance information. These larger 

forms are generally considered low-dust alternatives to fine powders.

Contemporary methods include the EN15051-2 rotating drum [CEN 2013b], discussed 

in later sections; the National Research Centre for the Working Environment (NRCWE, 

Copenhagen, Denmark) small rotating drum (Schneider and Jensen [2008] and 

EN17199-4 [CEN 2019]); Types I and II of the Heubach rotating drum (DIN 55992–1)

[DIN 2006]; and an Australian coal dust device (AS 4156.6) [AS 2000]. All rotating test 

configurations tumble the same test powder continuously for the duration of the 

experiment. It is feasible that the particle size distribution of the dust released from the 

test powder may potentially change over time. This effect may be most marked over 

longer duration experiments.

The NRCWE drum [Schneider and Jensen 2008] includes aspects of both the Warren 

Spring Laboratory (WSL; Stevenage, Hertfordshire, UK) and later EN15051 [CEN 2013a–

c] drum configurations, described in Section 3.c.2. A 6-g test sample mass is rotated 

within the NRCWE drum with 163-mm diameter, 5.93-L volume, and 20-mm diameter 

outlet. Three internal vanes, 20-mm deep, lift the test sample no more than 163-mm 

high at a rotation rate of 11 rpm for 1 minute. A 90-mm filter collects the generated dust 

and can be substituted for other particle samplers or by aerosol instruments (e.g., 

EN17199-4) [CEN 2019d]. 

Heubach drum configurations were originally developed in formulating dust-reduced 

pigments, potentially those containing toxic lead [Gawol and Adrian 1983]. Stauber and 

Beutel [1984] used a modified Heubach drum device to reduce the dusting potential of 

growth promoters in porcine feed premixes. Heubach drum configurations have seen 

considerable industrial use including chemicals, pharmaceuticals, food processing, and 

construction materials. The original Type I uses a dust-generating drum (140-mm 

diameter, 180-mm length, and three internal vanes) attached to a horizontal glass bottle 

as a sedimentation chamber, prior to collection on a filter cassette. 

The Type II also employs the drum, glass sedimentation bottle, and filter cassette, but it 

is configured with the sedimentation bottle at an angle between horizontal and vertical,

connected through an intermediate throat. The Type II configuration is typically used for 

dusty materials requiring greater sedimentation, as not to overload the filter. Rotation 

speeds can vary from 0 to 60 rpm and air flow rates from 0 to 40 L/min. These 

parameters are fixed and specified to conform to the DIN 55992-1 standard [DIN 2006]. 

One major drawback to Heubach Types I and II test configurations is that they do not 

provide for the health-based particle size fractions (inhalable, thoracic, and respirable).

The AS 4156.6 [2000] Australian Standard (AS) drum of 300-mm diameter was 

developed specifically for determining the dust and moisture relationship for coals. As 

moisture content of a coal increases, the dust-generating ability of the coal decreases
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below the Dust Extinction Moisture (DEM) threshold, corresponding to a dust number of 

10. The dust number is gravimetrically derived from the mass of dust collected within a

filter bag to the initial test material of 1 kg. The AS 4156.6 [2000] standard was derived 

from the work of Farrugia et al. [1989]. The coal moisture content required to reduce 

coal dust generation below the DEM threshold is informative, as it can be applied to 

reduce dust hazards (health and safety) in transportation, transfer, and further 

processing of the coal. See Section 4.a on moisture content, humidity, and liquid 

additives. One possible shortcoming of this approach is that the moisture content of the 

coal may change over longer time periods, resulting in an increased ability to generate

dust once the moisture is reduced.

Heubach and AS 4156.6 [2000] drum configurations operate at higher rotation rates (30 

to 45 rpm, and 29 rpm, respectively) than the EN15051-2 and NRCWE versions (4 rpm 

and 11 rpm, respectively). At higher rotation speeds, air mixing, dust transport, and flow 

regimes appear to differ from configurations that operate at lower rotation speeds [Chen 

et al. 2021; Chen et al. 2023]. Drum configurations that convey inhalable, thoracic, and 

respirable particle size fraction information (e.g., EN15051 [CEN 2013]; EN17199 [CEN 

2019a–e]), discussed in Sections 3.b.2.A and 3.c.2, are generally better suited to address 

worker inhalation exposure concerns. Those from worker health/worker exposure 

backgrounds may be more familiar with these devices. Test configurations that do not 

separate the airborne dust into the health-related size fractions can serve the needs of 

industry for product, process, and batch control, but provide limited information on the 

health hazards [Lyons and Mark 1992].

1) Evolution and development of the USDA, WSL, HSE, and CEN rotating tests

From the original U.S. Department of Agriculture (USDA) rolling device to the Comité de 

Européen Normalisation (CEN) rotating drum, this family of rotating test configurations 

received multiple iterative refinements in dust generation, particle sampling, and in 

general usability. The USDA rolling cylinder [Cocke et al. 1978] was refined by WSL for 

general material handling scenarios [Higman et al. 1984; Taylor 1984]. 

Several other investigators [e.g., Goodfellow and Smith 1988; Janhunan et al. 1988; 

O’Farrell and Vaughan 1986] used WSL drum configurations, but also suggested 

incremental improvements. The WSL rolling drum was selected as a promising method 

for further development[Lyons and Mark 1994]. Following a round-robin study by 

multiple laboratories [Lyons et al. 1996], the rotating drum was first adopted as a UK 

standard method (MDHS-81) [HSE 1996]. The rotating drum saw further development 

and refinement [Burdett et al. 2000] and, as a result, was subsequently adopted by CEN 

as one of two European dustiness methods described in EN15051 [CEN 2006]. The 

current EN15051-2 version [CEN 2013b] remains unchanged from the 2006 iteration. 

The EN15051-2 [CEN 2013b] rotating drum is arguably the most developed of the 

dustiness test configurations described in this guidance chapter, and one that has been 

most widely adopted worldwide.

An agricultural test device, described by Cocke et al. [1978] at the USDA (Clemson, SC, 

USA), consisted of a rolling cylinder, with a 430-mm (17 in) diameter and 680-mm (27

in) total length, that rotated on a hollow, fixed axle. Three internal angle-iron lifters
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(dimensions not specified) lifted the test material as the cylinder rotated at 38 rpm. For 

a single test, 1.81 kg (~4 lb) of test material (wheat, soybean, and shelled corn grains)

were used. Dust-suppressing oil of varying quantities was added as a spray. Following 2

minutes of rotation, the airborne dust within the upper section of the cylinder was 

actively sampled at 1.5 L/min for varying periods of further rotation (1–10 min), using a 

37-mm, three-section (closed-face) cassette sampling for total dust. The cassette was 

positioned mid-length, with the inlet downward facing. An external vacuum pump, with 

flexible tube routed through the axle, provided the air flow. Grain (wheat) dust levels 

were reduced by more than 92% with an oil content of 0.07% [Cocke et al. 1978]. A 

dust-reduction approach using a mineral-oil additive was earlier applied to cotton 

textiles [Cocke et al. 1977].

Inspired by the earlier USDA rolling cylinder, the UK WSL established a rotating test 

system, among other tests, to study dust release, suppression, and prevention from a 

general material-handling perspective [Bransby 1977; Lyons and Mark 1994]. The 40-L

WSL rolling drum configuration came with detachable conical ends, 110 mm in length, a 

dust generation section 460 mm in length, and a 300-mm diameter. It had a narrow 30-

mm inlet and 20-mm exit [Higman et al. 1984; Taylor 1984] and eight equally spaced 

longitudinal internal lifting vanes (25-mm deep). The rolling drum sat upon two rollers, 

driven by an enclosed motor within the chassis, which rotated the drum assembly at 30 

rpm. An air pump and flow control were housed within the lower chassis. 

The chassis approach, with rollers, motor, pump, and flow control all housed below, was 

retained through the development of these rotating tests. The chassis remains in use 

with the current EN15051-2 standard [CEN 2013b]. The exit consisted of a rotating 

coupling, a pipe, and finally a static, modified, three-stage Anderson cascade impactor 

assembly with a 10-μm preselector, 9-μm impactor stage (coarse), and a final filter (< 9 

μm, fine). The 10-μm preselector minimized overloading of the subsequent 9-μm 

impactor stage. A 100-g test sample was used. A flow rate of 23.8 L/min (1 ft3/min), the 

nominal flowrate required by the Andersen cascade impactor, passed through the drum 

transporting dust laden air to the impactor. The drum rotated initially for 5 seconds. The 

sampling flow commenced, and the drum continued rotation for the next minute. Three 

dustiness values were gravimetrically obtained: coarse (> 9 μm), fine (< 9 μm), and the 

sum of the coarse and fine fractions. The drum and collection substrates were cleaned. 

Two repeat experiments were further completed, for a total of three replicates.

In 1981, the BOHS Technical Committee and the UK Health and Safety Executive (HSE)

established a longstanding goal in the selection, development, and standardization of a 

dustiness test method. Lyons and Mark [1994] selected the WSL rolling drum, from 

many test methods available in the early 1990s, as a candidate method for 

standardization. With a 300-mm dust generation diameter, the WSL drum was larger 

than the Heubach drum described in Section 3.c, providing flexibility in the type of 

materials that could be studied (e.g., powders, granules, pellets, lumps of materials, 

damp materials, etc.) Its construction was modular. It was the most versatile of 

dustiness test configurations, replicating dust generation by industrial rotating mixers, 

rotating feeders, or rotating conveyance systems. The WSL drum had been previously 

used to generate a large body of test material data for reference [Higman et al. 1984; 
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Quantification of Airborne Dusts From Powders 

Lyons and Mark 1994]. The detachable end cones were very amenable to subsequent 

design changes.

Lyons and Mark [1992, 1994] suggested that the narrow 30-mm drum inlet and 20-mm 

exit potentially resulted in a central air jet forming. This air jet would not necessarily 

interact and mix sufficiently with dust generation toward the outer walls. Particle losses 

between the dust-generating section and the sampling section (within the pipe and a 90°

radius in some setups) were thought to be significant, as well as the potential 

misclassification of dust because of impactor stage overloading for very dusty materials. 

Cleaning between experiments could often be laborious and time consuming.

Test powder initially positioned closest to the WSL drum exit was preferentially 

collected as airborne dust [Lyons and Mark 1994]. Quantitative measurements, with an 

aim of increasing the dust yield, favored a shorter drum length [Lyons et al. 1992]. The 

dust generation section length was shortened from 460 mm to 230 mm, which continues 

in the current EN15051-2 configuration [CEN 2013b]. Lyons and Mark [1994] also 

studied variables, such as test powder mass (25 to 400 g), air flow rate (20 to 40 L/min), 

and test run length (5 seconds to 4 minutes) to maximize the quantity of dust entering 

the sampling section at a drum rotation of 30 rpm. Following initial testing, an air 

flowrate of 40 L/min (initially), dust dispersion time of 1 minute, and a test mass loading 

of 200 g were further selected for the anticipated large range of materials that would 

ultimately be tested. 

The sampling system required a significant redesign considering the newly defined (at 

that time) inhalable, thoracic, and respirable particle size fractions [CEN 1993; Chung 

and Burdett 1994; Lyons et al. 1992]. To achieve these particle size fractions, 

experiments were done to validate the use of porous polyester foams as particle sizeselective collection media for the drum, based on long-established prior research and 

practice [Aitken et al. 1993; Brown 1980; Gibson and Vincent 1981; Roesler 1966; 

Whitby et al. 1961; Vincent et al. 1993].

Porous polyester foams of 30 pores per inch (ppi) and 90 ppi were selected; these were 

25-mm thick and, nominally, 150-mm in diameter. Glass fiber filters of initially 70-mm 

diameter (prototype), and later 140-mm diameter (final version), were installed at both 

the inlet and dust collection ends of the drum. The central 130-mm diameter of the open 

foams collected the generated dust within a slightly larger (150 mm) aluminum carrying 

frame. A spacing insert placed between the drum and the first foam was found to have 

an insignificant effect on the resulting sampled dust. The flow rate through the drum 

was reduced slightly from 40 L/min to 38 L/min to provide a closer agreement between 

measured foam penetration to that of the thoracic and respirable particle size fractions 

within an acceptable 10% error. The 38 L/min flow rate remains in the current 

EN15051-2 standard [CEN 2013b]. 

Incidentally, and at least not initially by design, the combination of conical geometry and 

flow rate through the drum exit closely followed the inhalable particle size fraction.

Lyons and Mark [1994] assessed particle penetration experimentally with sodium 

fluorescein and aloxite particles fed axially into the entry. Good agreement was observed 

with the inhalable size fraction for particles up to 30-μm aerodynamic diameter. As 
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Quantification of Airborne Dusts From Powders 

particle diameter further increased to 46 μm, particle penetration tailed off. Only those 

particles that were carried by the gentle lateral airflow and escaped the dust generation 

section could ultimately be quantified. The foams and filters rotated with the drum 

assembly. The foam and filter diameters made gravimetric weighing challenging. Only 

gravimetric balances (with four decimal places) capable of accommodating large media 

diameters could be used. Weighing/carrying frames held collection media in a vertical 

position during weighing.

For larger test sample masses (e.g., 200 g), there was some initial concern over the dust 

loading capacity of the porous foam media [Breum 2000]. Lyons and Mark [1994] 

reported that sample masses as high as 20 g could be reliably collected on porous foam 

media. With higher mass loadings, care in handling was needed to minimize dislodging 

collected material. A significant limitation was that polyester foams were subject to 

weight variations due to the uptake of atmospheric water vapor. Therefore, creating the 

need for two foam sets, one set in the entry to the drum (as controls) and another at the 

exit as collection media. An alternate method, using five sets of control foams set aside, 

was also feasible, but required many more gravimetric measurements to be made. The 

potential weight instability of the foams led to a measurement limit of about 6 mg on 

each foam, that is, dust loadings over 6 mg could conceivably be quantified. Lyons and 

Mark [1994] reported a range of dustiness values spread over five orders of magnitude 

was possible with the new prototype drum configuration, using 23 test materials from 

across different industrial sectors.

A round-robin study of the HSE/WSL prototype drum was eventually done by five 

laboratories using ten industrially relevant materials [Lyons et al. 1996]. A minimum 

four decimal place balance was stipulated. Results from low to high dustiness test 

materials spanned about four orders of magnitude (from ~1 to 10,000 mg). Respirable 

fractions below ~4 mg represented values below the test resolution limit. At least five 

dustiness measurements were recommended for each test material. A standardized 

version of the HSE/WSL drum was adopted as a UK method (MDHS-81) [HSE 1996]. 

The MDHS-81 [HSE 1996] rotating drum underwent further development and 

refinement by Burdett et al. [2000] and was recommended for further CEN technical 

workgroup consideration as a European standard. Much of the Burdett et al. [2000]

study focused on optimizing the foam collection media and test variables that potentially 

influenced dustiness measurement. The adoption of metalized (nickel) porous foams

largely mitigated the moisture (weight) variation issue of the earlier polyester foams. A 

control set of foams was no longer required, simplifying the configuration and the effort 

needed to perform a single test. Weighing weight-stable collection media improved 

precision and accuracy. This was particularly important for the quantification of lowdustiness materials. As a result of smaller foam diameters (150 mm reduced to 80 mm), 

a larger potential pool of analytical balances could be employed in the quantification of 

the collected dust.

Smaller foam diameters meant the drum had to have a smaller conical exit geometry, 

going from a 150-mm to 80-mm diameter. The 150-mm inlet and 80-mm exit remained 

in the current EN15051-2 standard [CEN 2013b]. The porosity (reduced from 30 to 20 
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Quantification of Airborne Dusts From Powders 

ppi, and from 90 to 80 ppi) and dimensions of the foams (reduced from 150-mm to 80-

mm diameter and from 25-mm deep, reduced to 20-mm and 12-mm deep) also changed 

to ensure the particle penetration of the foams continued to closely match the thoracic 

and respirable particle size fractions [CEN 1993]. The larger foam porosities (smaller 

ppi numbers) also improved dust loading capacities. The later nickel foams with 80-mm 

diameters (20-ppi and 20-mm deep; 80-ppi and 12-mm deep) are retained in the 

current EN15051-2 standard [CEN 2013b].

The latter 80-mm conical exit geometry was tested with four aloxite test dusts, fed 

axially into the drum entry at particle sizes up to about 60 μm [Burdett et al. 2000]. A 

generally good agreement with the inhalable particle size fraction was observed. An 

improvement was seen, particularly at larger particle sizes, over earlier iterations 

[Lyons and Mark 1994]. Standard conditions that further maximized dust release 

consisted of an electrically grounded (earthed) rotating drum, operated over a period of 

one minute, and used a low moisture content dust, at a relative humidity of 50% 

[Burdett et al. 2000]. These parameters were also further adopted. A summary of test 

variables for these rotating test configurations is provided in Table 1. Test 

configurations are typically fabricated from stainless steel.

Table 1. Parameters for notable, commonly used, or standardized rotating 

dustiness test configurations. Values in bold denote the most frequently used 

or standardized variable when several values were reported. 

Drum Drum

Diameter 

(mm)

Drum

Length 

(mm)

Vanes & 

Rotation 

Rate

Flow 

Rate 

(L/min)

Dust 

Collection 

Method

Test 

Powder 

Quantity

Test 

Duration

Cocke et al. 

[1978] USDA 

Agricultural 

Dust Cylinder

430 680 3 vanes, 38 

rpm

1.5 37-mm threepiece (closedface) cassette

within upper 

cylinder

1,810 g 1 to 10 

min

Heubach (DIN 

55992-1) [DIN 

2006]

140 180 3 vanes* 30 

to 45 rpm

20 Settling 

chamber and 

filter

100 g 5 min

WSL Drum 

[Higman et al. 

1984; Taylor 

1984]

300

(30 inlet and 

20 outlet)

460 with 

detachable 

110-conical 

ends

8 vanes, 30 

rpm

28.3 (1 

cfm)

Stationary 

three-stage 

Anderson 

Impactor, 10 

μm, 9 μm, and 

filter

100 g 

evenly 

along 

drum

1 min

Prototype WSL 

Drum [Lyons 

and Mark 

1994]

300

(30 inlet and 

20 outlet) 

initially then 

modified to 

150 to 

accommodate 

foams at inlet 

and exit

460 

Shortened 

to 230

8 internal 

vanes, 25-

mm deep, 2-

mm width, 

30 rpm

20, 28.3, 

35, 40, 

and

38

Three-stage 

Anderson 

impactor, then 

150-mm 

diameter 

polyester 

foams (30 ppi 

and 90 ppi)

and filter at 

inlet and 

outlet (130-

25 g, 100 

g, 200 g, 

400 g

5 s, 20 s, 1 

min, 2 

min, 4 min
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Quantification of Airborne Dusts From Powders 

Drum Drum

Diameter 

(mm)

Drum

Length 

(mm)

Vanes & 

Rotation 

Rate

Flow 

Rate 

(L/min)

Dust 

Collection 

Method

Test 

Powder 

Quantity

Test 

Duration

mm effective 

foam 

diameter)

HSE MDHS 81 

[1996] 

HSE/WSL drum

300

(150, foams, 

in carrier 

frames) and 

filters at both 

inlet and exit)

230 8 internal 

vanes, 30 

rpm

38 150-mm 

diameter 

polyester 

foams (30 ppi 

and 90 ppi)

and filter at 

inlet and 

outlet (130-

mm effective 

diameter)

200 g 1 min

Burdett et al. 

[2000] 

modified 

HSE/WSL MkII 

drum

300

(150 inlet, 80 

exit)

230 8 internal 

vanes, 25-

mm deep, 4 

rpm

38 Proposed 

nickel foams 

of 80-mm 

diameter with 

larger pores 

(20 ppi and 80 

ppi) to negate 

overloading

Standard 

volume 

(35 mL) 

but also 

weighed

1 min

AS 4156.6 [AS 

2000] 

Determination 

for dust 

moisture 

relationship for 

coal

300 (40 inlet, 

40 exit)

300 with 

100 conical 

exit

8 lifters, 7-

mm wide 

and 6-mm 

deep, 29 rpm

170 Vacuum bag 1,000 g 10 min

Small-rotating 

drum NRCWE 

(Denmark)

[Schneider and 

Jensen 2008]†

163, 20 exit, 

5.93-L total 

volume 

230 dust 

generation 

section, 63 

conical ends

3 internal 

vanes, 20-

mm deep, 11 

rpm

11 90-mm filter 

plus aerosol 

instruments

6 (and 2) g 1 min

EN15051-2 

[CEN 2013b]

300

(150 inlet, 80 

exit)

230 dust 

generation 

section, 

130-mm 

conical 

inlet, 80-

mm conical 

exit

8 vanes 25-

mm deep, 2-

mm width, 4 

rpm

38 80-mm 

diameter, 

nickel foam 

(20 ppi and 80 

ppi) and filter 

(60-mm 

effective

diameter)

35 mL 

weighed

1 min

*

Internal vanes do not point radially toward the center of the drum, as in most other drum test

configurations. †The NRCWE (Denmark) small rotating drum is the only configuration to specify

internally polished surfaces (450+/–50 gloss units). In the EN17199-4 Standard [CEN 2019d], the

inner surfaces of the small rotating drum are polished to a mean roughness profile of 0.19 μm, which

may be obtained by vibratory polishing.

2) The CEN [2013] EN15051-2 rotating drum

The contemporary EN15051-2 [CEN 2013b] drum is arguably one of the most widely

used test methods worldwide for determining the dustiness of bulk powders. It has been
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Quantification of Airborne Dusts From Powders 

employed to quantitatively assess a large range of industrially relevant test materials, as 

well as those commercially used. As noted in the previous section, the test configuration 

received significant attention by multiple laboratories while being developed, resulting 

in several iterative performance and usability improvements. The EN15051-2 drum has 

been adopted globally by many research institutions and is used routinely within 

industry and commercial laboratories. 

A falling material height of less than 300 mm within the drum closely approximates

gentle to moderate manual (seated or standing) benchtop procedures involving 

powders within the workplace. These procedures might include scooping, weighing, 

transferring, and preparing powder subsamples for quality control, for example. The 

drum also approximates well the dust generated from using industrial mixers and bulk 

rotational conveyance methods. 

The apparatus consists of a stainless-steel drum with a 300-mm internal diameter on a 

lower rotating roller assembly with pump and air flow control. The drum is electrically 

bonded and grounded to the equipment electrical power supply. The ultimate fall height 

of less than 300 mm is influenced by the angle of repose for the powder (an indication of 

how cohesively the powder behaves). This determines how far the powder travels into 

the upper portion of the drum before cascading down under gravity. The pre-weighed 

test powder (35 mL) is loaded evenly along the base of the dust-generating section of 

the drum, prior to final assembly of the 150-mm inlet with filter. The drum rotates at 4 

rpm for a total 1-min test cycle. Air is drawn through the drum at 38 L/min for the entire 

test period, passing through the 150-mm diameter inlet filter, the 300-mm diameter 

dust generation section, and, finally, the 80-mm diameter dust sampling system. A 

schematic of the rotating drum is shown in Figure 3. Within the dust generation section, 

a winnowing air current with a mean velocity of 0.9 centimeter per second (cm/s) is 

generated [Burdett et al. 2000]. The Reynolds number for the air flow within the central 

dust generation section of the drum is Re~570 and indicates the flow is gentle and 

laminar [Chen et al. 2021]. The Reynolds number at the drum inlet is Re~1140 and at 

the exit is Re~2140 [Chen et al. 2021].

The sampling section of the drum is next to the dust generation section. It consists of 

two porous, metallic (nickel) foams (20-ppi or 800 ppm, 20-mm depth; and 80-ppi or 

3,200 ppm, 12-mm depth). The 80-mm diameter foams are followed by an 80-mm 

diameter quartz-fiber final filter. The conical geometry that transitions between the dust 

generation section of the drum to the sampling section of the drum, at the 38 L/min

flow, provides for the inhalable particle size fraction. The two foams and filter in the 

sampling section are each separated by 2-mm thick annular gaskets, with 80-mm outer 

diameter and 60-mm inner diameter. The effective sampling area of the foams and filter 

used for dust collection is therefore the central 60-mm portion. The combined weight 

change of the metallic foams and the quartz filter provides the inhalable, thoracic, and 

respirable particle size fractions simultaneously from a single experiment. A minimum 

of three replicate experiments are usually performed. If the relative standard deviations 

of the results are not within 10%, further replicates may be required. Results are 

typically expressed in mg/kg for each of the particle size fractions. Dustiness values for 

materials tested within the drum can span about four orders of magnitude [e.g., Chung 
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Quantification of Airborne Dusts From Powders 

and Burdett 1994; Lyons et al. 1996]. Potential suppliers of the rotating drum apparatus 

are included in the EN15051-2 standard [CEN 2013b].

Figure 3. Schematic of the CEN [2013b] EN15051-2 rotating drum with 

dimensions in millimeters. Air flow at 38 L/min enters from the 150-mm 

filtered inlet (left) and goes through the 300-mm diameter dust generation 

section. It then enters the 80-mm dust collection section (right), consisting of 

three annular gaskets, two porous foams, and a final quartz filter. 

Figure 4 shows a photograph of the porous cylindrical foams and filter. The air flow 

finally passes through a radial rotating union to flexible tubing, a pump, and flow 

controller. The whole drum assembly sits upon a chassis and is rotated by two external 

rollers (not shown) at 4 rpm.

A minimum five decimal place analytical balance (i.e., from 1-g, readability to 0.01 mg) is 

required for quantifying the dusts collected on the size-selective foams and filter 

(EN15051-2) [CEN 2013b]. Clean metallic foams typically weigh ~40 to 60 g. Clean 80-

mm quartz-fiber filters typically weigh 270 to 285 mg. The draft shield of the analytical 

balance needs to be large enough to hold the 80-mm filter without the filter contacting 

the walls. An analytical balance with a minimum resolution of 0.1 g is required for 

weighing the 35-mL bulk test samples (EN15051-2) [CEN 2013b].

The EN15051-2 [CEN 2013b] drum has been used in characterizing nanoscale materials 

in EN17199-2 [CEN 2019b]. Gravimetric measurements are first performed by following 

EN15051-2 [CEN 2013b] and provide for the conventional inhalable, thoracic, and 

respirable dustiness fractions reported in mg/kg. In the EN17199-2 [2019b]

configuration, the two porous foams and filter are replaced with an annular spacer (80-

mm outer diameter and 60-mm inner diameter). An axial rotating union replaces the 

more typical radial rotating union that connects the drum to the system flow control and 

vacuum pump. The spacer and axial union allow for further external measurements to 

be made by aerosol instruments. The tubing needs to be kept short and sharp bends
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Quantification of Airborne Dusts From Powders 

should be avoided to minimize particle transport losses. The total flow through the 

drum needs to be maintained at 38 L/min.

Figure 4. The two porous nickel foams (20 ppi top left and 80 ppi middle) and 

final quartz filter (base) used to collect the generated dust within the rotating 

drum (photo provided by D.E. Evans, NIOSH). The foams and filter have 80-mm

diameters. The sample collection media are typically separated by 2-mm thick 

annular gaskets (80-mm outer diameter and 60-mm inner diameter, not 

shown). 

Threshold values for the rotating drum method have been established from over 220 

test samples (EN15051-2) [CEN 2013b]. The thresholds are based on the amount of dust 

released (mg) compared with the parent powder initially added to the test device (kg). 

For the inhalable fraction, less than 300 mg/kg is considered very low dustiness; 

between 300 and 650 mg/kg, low dustiness; between 650 and 3,000 mg/kg, moderate 

dustiness; and greater than 3,000 mg/kg, high dustiness. For the thoracic fraction, less 

than 80 mg/kg is considered very low dustiness; between 80 and 300 mg/kg, low 

dustiness; between 300 and 1,000 mg/kg, moderate dustiness; and greater than 1,000 

mg/kg, high dustiness. For the respirable size fraction, less than 10 mg/kg is very low 

dustiness; between 10 and 60 mg/kg, low dustiness; between 60 and 210 mg/kg, 

moderate dustiness; and greater than 210 mg/kg, high dustiness. These threshold values 

and their corresponding exposure potential bands for each of the particle size fractions 

(very low, low, medium, and high dustiness) allow for the exposure risk assessment of 

new and unknown powders.

Burdett et al. [2000] noted that surface adhesion was an important test system variable, 

yet a polish or roughness value was not later specified in the EN15051 [CEN 2006] or 

later [CEN 2013a–c] standards. In contrast, the Schneider and Jensen [2008] NRCWE 

small rotating drum specified a surface polish or roughness value of 450+/–50 gloss 

units. In the EN17199-4 standard [CEN 2019d], the inner surfaces of the small rotating 
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drum are polished to a mean roughness profile of 0.19 μm, which as noted, may be 

obtained by vibratory finishing.

The coupling of the test powder, the internal surfaces of the test apparatus, and the 

cross airflow are important aspects of all rotating drum dustiness test configurations. 

The internal surface plays a larger role in drum test configurations than in others, such 

as falling powders. Intuitively, the roughness of the inner surfaces within the drum may 

influence wall adherence of the powder; but how much of that powder takes part in the 

experiment and what particles can escape the drum and be quantified. Different 

manufacturers of the standard test equipment may source different construction 

materials, so the internal surface roughness or polish quality may vary. We anticipate 

that a more polished finish would likely reduce inner wall adherence and maximize dust 

generation. Conducting multiple experiments in a series may help negate walladherence, with test material from the first experiment potentially pre-coating the 

internal surfaces. In practice, between experiments of the same powder, the excess 

powder is removed, but the internal surfaces may remain coated.

d. Fluidized test configurations

Fluidization may result in some fraction of powdered test materials being entrained 

within air. Fluidized methods may be further grouped into aerated or aero-fluidization

and vibrating or vibro-fluidization. Fluidized methods are generally limited to dry test 

materials [Burdett et al. 2000]. Broßell et al. [2019] provide a summary of different 

fluidization modes for further reading.

Schofield et al. [1979] at WSL described an aero-fluidized device consisting of a vertical 

glass tube, 2,050-mm long with 70-mm inner diameter, and a porous base where a 400-g 

test sample was placed. The sample, consisting of no less than 10% test material (40 g) 

and no more than 90% (360 g) 350–500 μm sand, was pulvated (fluidized) by air at a 71 

L/min flow rate through the medium. This was a two-component test sample and test 

configuration. A proportion of the aerosol was drawn iso-kinetically into an Andersen 

cascade impactor (size range ~1–10 μm). The remainder of the aerosol was vented to 

the atmosphere. Dust was collected over a 1-min sampling period. The dustability

(dustiness) of the test sample was determined as a cumulative emission rate in mg/min 

of “fines.”

An additional method was ASTM D4331-84 [1984], withdrawn in 1988, that assessed 

the effectiveness of dedusting agents mixed with powdered chemicals. ASTM D4331 

could be classified as a combined aero- and vibro-fluidized testing configuration. A 

vertical, butyrate-plastic tube, with a 73-mm (2 7/8 in) internal diameter and 457-mm

(18 in) height, acted as the vibrating housing where an initial 200-g test sample was 

placed. A pneumatic vibrating device, operating at 29 kilohertz, was clamped to the 

housing. An aeration flow of 15 L/min provided a face velocity of 6 cm/s up through the 

tube. Fluidized powder was applied from a polyester fabric-covered base. The vibrating 

housing prevented defined air channels from forming within the test powder column. A 

fraction of the dust-laden air was collected on a two-piece (open-face) 37-mm filter 

cassette for 20 minutes. Excess dust-laden air was vented to the atmosphere through an 
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Quantification of Airborne Dusts From Powders 

optional 73-mm filter. The gravimetric mass of material collected on the filter provided 

the dustiness measurement.

Both fluidized methods described above suffered from electrostatic charge buildup, with 

particles adhering to the glass and butyrate walls of the devices [Cowherd et al. 1989a].

Fluidized methods are known for triboelectrification within the powder bed, and these 

charges subsequently carried on aerosolized particles. A further fluidized test 

configuration [Sethi and Schneider 1996] was assessed by Burdett et al. [2000] but not 

considered for further standardization.

The BOHS Technology Committee Working Party on Dustiness Estimation [BOHS 1985]

reviewed six aerated or aero-fluidizing (gas dispersion) methods, including the WSL 

fluidized method [Schofield et al. 1979]; however, they did not recommend a fluidized 

method as practical for dustiness standardization. A primary factor was limited 

relevance to workplace operations that would result in worker exposures [BOHS 1985]. 

All fluidized methods agitate the same test powder sample over and over. The particle 

size distribution of the dust liberated from the test sample at the beginning of the test 

may differ from that liberated toward the end. The longer the test duration, the more 

marked this difference may be. 

Contemporary fluidizer-based dustiness methods include the EN17199-5 [2013e] vortex 

shaker and a vibro-fluidization method specifically developed for dispersing fibrous 

materials [Broßell et al. 2019]. Vibro-fluidization contributes to aerosol generation in 

both test configurations. In the Broßell et al. [2019] combined aero- and vibro-fluidizer 

device, an upright aluminum sample tube (with 25-mm inner diameter, tapering to 16

mm at the top) was oscillated vertically at frequencies between 10 and 60 Hz and 

amplitudes between 0.05 and 1.5 mm. An air flow between 0.1 to 1.0 L/min was passed 

up through the vibrating powder column. A 300-mg test sample mass sat on a stainlesssteel mesh at the base of the column. A variety of aerosol sampling and collection 

configurations could be connected to the device through a small (0.5 L) mixing chamber. 

A 75-min sampling time was noted. One of the major drivers for developing this device 

was the fiber analysis and counting according to the WHO phase-contrast method [WHO 

1997].

1) Vortex shaker

The vortex shaker was first described as an approach to qualitatively aerosolize and 

study the properties of airborne single-walled carbon-nanotube particles [Maynard et al. 

2004]. The device released particles from a 100-mg bulk powder sample. This work was 

conducted in parallel with some of the first reported nanomanufacturing workplace 

studies, also described by Maynard et al. [2004]. An initial attempt to use a conventional 

two-component fluidized aerosol generator, with the air flow fluidizing the medium 

(aero fluidization), was insufficient in aerosolizing the test powder for further analysis.

A more aggressive agitation with the vortex shaker (vibro-fluidization) was then 

attempted in both single- and two-component configurations. In the two-component 

mode, an aerosol contribution from the 70-μm bronze beads was detected. As further 

remarked by Maynard et al. [2004], “...it should not be assumed that the laboratory-
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based method of aerosol generation provides a definitive characterization of workplacerelated processes.” The authors recognized potential limitations with the vortex shaker 

approach.

Relevance to the workplace is a cornerstone of dustiness test methods from a worker 

inhalation exposure perspective. The close match between workplace operations or 

activities to dustiness test methods has historically been well understood [e.g., BOHS 

1985; Lidén et al. 2006; Lyons and Mark 1992]. A subtle but very important distinction 

exists between laboratory aerosol generation techniques and quantitative dustiness test 

methods: the latter being those test configurations that tell us something about the test 

powder from a workplace health or safety perspective [e.g., Boundy et al. 2006; Evans et 

al. 2013; Lidén 2006].

In the EN17199-5 [CEN 2019e] approach, a small volume (0.5 mL) of the test powder is 

held within a vertical tube (31-mm internal diameter and 110-mm length) with a conical 

base. The test sample tube is vigorously shaken in an orbital motion (4-mm amplitude 

and 1,850 rpm at the base). An airflow (4.2 L/min) is introduced at the top fixed portion 

of the vertical tube and directed toward the powder sample with a smaller internal tube. 

The air does not pass through the test powder column as in aero-fluidization 

configurations. A small fraction of the fluidized particles from the top of the powder 

sample is transported by the airflow that ultimately exits in the opposite direction to the 

inflow. The vortex shaker is coupled to a cyclone to provide the respirable aerosol 

fraction. Ku et al. [2013] reported that small configuration or operational changes can 

have a potentially sizeable effect on the aerosol output from the vortex shaker. Ku et al. 

[2013] also reported the temporal evolution of the particle-size distribution of the 

aerosol generated by this method. This implies significant kinetic redistribution within 

the heterogeneous powder. While these effects are not completely understood, they 

underscore the challenges with this approach.

e. Aerodynamic test configurations

Aerodynamic dust dispersal mechanisms are observed in nature (i.e., Aeolian processes)

[e.g., Bagnold 1941; Cowherd 1981; Gillette et al. 1974; Visser 1992]. These are highly 

relevant to the workplace, though perhaps not encountered as often as the gravityinduced mechanical dispersion experienced by falling powders. Aerodynamic dispersion 

involves the movement of air over a powder, in contrast to the movement of powder 

through air (mechanical dispersion). Aerodynamic dust dispersion can be differentiated 

from air moving through a test powder column (such as aero fluidization discussed 

earlier or gas dispersion described by [BOHS 1985]). Airborne dust generation and 

subsequent worker inhalation exposure from certain industrial processes or activities 

might be better simulated by aerodynamic dustiness test configurations. 

Pneumatic conveyance systems (where air flow is used to transfer powders or other 

bulk solids within enclosed equipment) are common industrial transfer applications that 

have been available since the late 1960s [Bransby 1977]. Though not initially in powder 

form, another aerodynamic process example involves the removal of surface-grown or 

adhered products from substrates with a focused air jet. Products may then be collected 
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as a fine powder downstream for further processing. Using an air jet or air knife to clean 

contamination from a surface, or for drying or cooling manufactured parts, is also an

aerodynamic process. A resulting aerosol is a finely divided solid suspended within the 

airflow.

The uncontrolled cleaning of contaminated clothing, surfaces, or process equipment 

using compressed air, although not recommended either from an exposure or safety 

perspective, is nevertheless observed in the workplace [Evans et al. 2013]. The closing 

and cinching of bags during product filling, and the removal of air from bags prior to 

disposal [e.g., Evans et al. 2010; Hammond 1980], can also be responsible for 

aerodynamic airborne dust generation. In general, these are vigorous dispersal 

mechanisms where moving air imparts kinetic energy to the powder. The underlying 

dust dispersion mechanism is by aerodynamic shear, consistent with a steep air velocity 

gradient. The result is typically highly turbulent air flows characterized by high 

Reynolds numbers. The aerodynamic reentrainment and dispersion of combustible dust 

from surfaces are responsible for the transmission of dust explosions [e.g., Cashdollar 

2000; Eckhoff 2003; Perera et al. 2016].

An overview of aerodynamic dispersion mechanisms and available approaches for 

aerodynamically dispersing powders is provided by Calvert et al. [2009]. One of the 

underlying aerodynamic phenomena common to many dispersal devices is the Venturi 

effect. The Venturi effect is a reduction in fluid (air) pressure, resulting from a 

constriction within a pipe or tube. This reduced pressure region can be used to draw 

powder, aerosol, liquids, or other materials, and introduce them into a fast-moving 

airflow. The acceleration (or deceleration) of powder particles within the airflow 

provides enough aerodynamic shear to break up agglomerates that are held together by 

the relatively weak interactive forces (such as van der Waals). Multiple commercial 

dust/aerosol generators rely on the Venturi principle to combine powders/dusts and 

rapid air flows into airborne dusts/aerosols. 

1) UNC Venturi

Boundy et al. [2006] at the University of North Carolina (UNC; Chapel Hill, NC, USA) 

introduced a novel dustiness testing device for pharmaceutical application. It allowed

small (mg) quantities of pharmacologically active powder to be safely dispersed within a 

fully enclosed device. The device used a small stainless-steel funnel/nozzle arrangement 

where 5 mg of a test powder sample was initially placed. Figure 5 shows the nozzle with 

the lid removed. When activated, the device dispersed the test powder sample (under 

reduced pressure) into a 5.7-L glass chamber. In the chamber, metallic versions of two

common industrial hygiene samplers (37-mm closed-face Slaton cassette and BGI 

GK2.69 cyclone fitted with a 37-mm filter cassette) were placed to sample the resulting 

dispersed dust.
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Figure 5. The UNC Venturi dispersion nozzle with lid removed (photo provided 

by D.E. Evans, NIOSH). The nozzle is fabricated from stainless steel. The O-ring 

seal for the lid (removed) is visible at the funnel. The length of the nozzle (from 

left to right) is 72 mm. The left portion of the nozzle is inserted into the glass 

containment chamber through a rubber grommet.

Closed-face and opened-face 37-mm cassette configurations performed comparably for 

five test powders [Boundy et al. 2005]. The closed-face configuration was chosen for 

improved sample integrity. Both metallic samplers were electrically bonded to the 

metallic chamber lid and the lid electrically grounded to the power supply. Figure 6 

shows the two samplers fixed to the underside of the containment chamber lid. A 

microbalance of at least 6 decimal places (i.e., 1 μg readability from 1 g) is recommended 

for quantifying the collected airborne dust on the polytetrafluorethylene (PTFE) or PVC 

37-mm diameter filters [Boundy et al. 2005; Evans et al. 2013]. See the later section 

(Section 4.d) on gravimetric weighing.

A single dustiness test involved two consecutive 5-mg dispersions for a total of 10 mg of 

dispersed test powder. This increased the quantity of material ultimately collected, 

improving sensitivity twofold. For each dispersion, the sampling period lasted 4 minutes 

and the dispersion phase lasted 1.5 s. The 4-minute sampling period provided for more 

than four air exchanges within the chamber: an air exchange approach similar to 

Cowherd et al. [1989b]. The aerosol samplers provided for total aerosol, approximating

the inhalable size fraction [Dahm et al. 2019] and respirable aerosol [Kenny and 

Gussman 1997] at flow rates of 2.0 L/min and 4.2 L/min, respectively. As with many

other dustiness devices, the mass collected on the filters (determined gravimetrically) 

was compared with the initial mass of the test material. Due to the narrow geometry 

within the Venturi nozzle, in practice, this dustiness method applies to testing powders 
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and small granules only. Flakes and pellets are not suitable as with many other test 

configurations.

Figure 6. Metallic aerosol samplers attached to the underside of the UNC 

Venturi containment chamber lid (photo provided by D.E. Evans, NIOSH). The 

respirable GK2.69 cyclone sampler is on the left and the total dust closed-face 

Slaton cassette is on the right. Both samplers are in contact with the center 

grounding clip.

Motivated by the need to disperse small (less than 1 g) quantities for expensive, difficult 

to obtain, or toxic test powders, Evans et al. [2013] applied the UNC Venturi to 27 fineand nanoscale-powdered test materials. Authors reported results that spanned about

two orders of magnitude for both total and respirable dustiness. They also observed an 

exponential particle concentration decay following dispersion of the test sample within 

the containment chamber. Within the ISO [2021] TS 12025 technical specification, this 

test configuration is described as a dynamic method of the release and measurement of 

nano objects from powders.

The UNC device is more commonly referred to as the Venturi method, as it is best 

understood that the Venturi effect is used in both drawing and aspirating the test 

powder into the containment chamber [Evans et al. 2013; Evans et al. 2014]. 

Aerodynamic shear within the nozzle, and for some cohesive test powders, perhaps into 

the containment chamber, appear to be the underlying mechanisms by which the 

powder is dispersed. Numerical or computational fluid dynamic modeling of the 

sampling chamber with airflows and particle trajectories (1-μm aerodynamic diameter) 

has also been studied once injected from the nozzle [Dubey et al. 2017]. 
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The airflow, at the point of exiting the nozzle and entering the chamber, is highly 

turbulent and characterized by a Reynolds number of Re~20,000 [Dubey et al. 2017].

Test powder aerosolization within the dispersion nozzle is only partially understood 

[Palakurthi et al. 2017, 2022; Sharma et al. 2020a,b]. The UNC device appears to be 

robust to inhomogeneous test powder injection or injection being delayed. The test 

powder is also well mixed at the conclusion of the injection phase: an important 

consideration when sampling from within the chamber.

The Venturi method offers an energetic and efficient powder dispersal, making best use 

of small (mg) quantities of available test powder. It has been used to disperse many

carbon nanotube and carbon nanofiber test samples [Bishop et al. 2017; Dahm et al. 

2019; Fraser et al. 2020]. Particularly when minimizing test powder quantities and 

generating less waste (a substitution exposure control) are desired and good laboratory 

practice. The method has been described as possibly representing a worst-case 

exposure scenario [Evans et al. 2013]. Therefore, when exposure controls are selected to 

mitigate potential exposures through dustiness information gained from the Venturi 

dustiness configuration, they are likely to be the most protective and capable of 

mitigating the full spectrum of worker exposure scenarios, from gentle handling through 

to worst-case energetic dispersions. Materials with a greater dustiness, and therefore 

exposure potential, may require more stringent exposure controls. Several Venturi 

dustiness testing devices are located at research institutes and pharmaceutical 

manufacturing sites worldwide.

2) Rock dust dispersion chamber

Coal dust explosions are a serious safety hazard in underground coal mines [Cashdollar

2000]. Rock (stone) dusting in coal mines goes back over 100 years in the United States

[BoM 1927]. The practice originated in the United Kingdom and France following

multiple mining disasters and prevents propagating coal-dust explosions. Unlike most

occupational dust release scenarios, an increase in the relative dispersibility of rock dust

is beneficial because only rock dusts that disperse and become airborne can effectively

mitigate the risks from combustible coal dust. An incombustible content of 80% or more

is required when mixed with coal dust to prevent propagating coal dust explosions

[NIOSH 2010]. An aerodynamic test configuration was developed to quantify the

dispersion of pulverized rock dusts. Perera et al. [2016] describe the device, which uses

a carefully controlled pulse of compressed air (40 psi, 276 kPa, 2.76 bar) though a

narrow (1.4-mm internal diameter or nominal 1/8 in) nozzle, placed upstream at the

upper surface of the test sample tray. During the 0.3 s air pulse, a channel of rock dust is

scoured from the upper test sample surface. The mass of initial test sample may range

from ~45 to 260 g (directly related to the bulk density of the test dust) within the

constant volume (225 mL) sample tray. The resulting airborne dust cloud is carried

downstream at 1.5 m/s within a 152 × 152 mm (6 × 6 in) × 1,524 mm (5 ft) length

containment chamber, where it is detected optically. Figure 7 shows the rock dust

dispersion chamber with a more detailed view of the test sample tray and nozzle

arrangement in Figure 8. The loss of test powder from the tray and the relative optical

density (obscuration) measured downstream within the chamber quantifies how

effectively the rock dust is dispersed in each experiment.
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Figure 7. The rock dust dispersion chamber (photo provided by D.E. Evans, NIOSH). The 

transparent acrylic containment chamber is 1,524 mm (5 ft) in length. The chamber sits 

within a nominal ~1,800 mm (6 ft) width laminar-flow ventilation hood for easier cleaning 

between experiments. The dust sample tray and nozzle are to the left and the optical 

detection probe, pressure monitoring port, and flow control valve are to the right. The front 

hinged lid of the chamber is opened for clarity. The lid is closed during an experiment. 

Water in underground mining can cake rock dust, making dispersion much less effective. 

Coal dust retains some dispersibility when wet. Rock dusts with anti-caking properties 

have therefore been developed to address this problem [Perera at al. 2016]. 

Figure 8. Dispersion nozzle, test sample tray (pre-loaded with mineral dust), and ballast 

weight to prevent the tray shifting during an experiment (photo provided by D.E. Evans, 

NIOSH). A series of five holes in the chamber, situated above the nozzle, introduce 

laboratory air for dust transport. The front hinged lid of the chamber is opened for clarity. 

The dust sample tray is 190 mm long. 
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4 Key considerations for dustiness 

There are test powder measurements that typically accompany dustiness testing 

(moisture content and bulk unconsolidated density determinations) and are required 

according to EN15051-1 [CEN 2013a]. Moisture content (or the presence of other 

liquids) is perhaps the most important variable in the release of dust from powders, 

both within the workplace and during testing. There are important considerations for 

taking representative test samples from a bulk powder and in the gravimetric weighing

of test powders and dust collection media when quantifying dustiness. Finally, we 

discuss further factors that may influence dust release in the workplace and through 

laboratory dustiness testing. Though these factors may influence some powders, i.e., are 

material specific, they often exhibit a complex relationship with dustiness and so are not

reliable predictors in dustiness behavior. The role of multiple interparticle forces acting 

within a bulk powder is extremely complex [e.g., Castellanos 2005; Munroe 2020]. 

a. Moisture content, humidity, and liquid additives

One of the more widely recognized variables influencing dustiness is moisture content 

[e.g., Burdett et al. 2000; Farrugia et al. 1989; Levin et al. 2015; López-Lilao et al. 2017b; 

Plinke et al. 1995; Pujara 1997; Visser 1992]. Burdett et al. [2000] described moisture 

content as the most important variable in dustiness testing, potentially capable of 

producing order-of-magnitude variations. In the workplace, aqueous slurries or pastes 

are simple, low-dust alternatives to dry powders. These could conceivably be considered 

a substitution exposure control (see Controlling Exposures in Section 2.f) if slurries or 

pastes are amenable to downstream manufacturing processes. Oils, or other liquid 

additives, might also be considered in reducing dust generation [e.g., Cocke et al 1977, 

1978; HSE 2010]. Water or oils can potentially reduce the dustiness of a powder by

increasing interparticle or interagglomerate capillary adhesion. At the microscopic level, 

the formation of menisci or bridging between particles occurs, although the behavior is

exceedingly complex [e.g., Cleaver and Tyrrell 2004; Rabinovich et al. 2002]. 

Low moisture content for powders, perhaps coupled with low ambient humidity, can 

potentially cause problems with electrical charge accumulation and static electricity. 

This, in turn, can make the handling and transfer of materials considerably more 

challenging [Bailey 1984]. The dissipation of charge within dustiness test systems can 

also influence dustiness by a factor of two [Burdett et al. 2000]. So it is generally best 

practice that quantitative test systems be electrically grounded. Moisture content of the 

powder and the accumulation of electrical charge can at times be interrelated [Visser 

1976]. 
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The moisture content history of the powder may also influence dustiness. If a soluble or 

partially soluble component is present, water vapor may be adsorbed, forming solutions 

at higher humidities. Even if the powder is returned to a reduced relative-humidity 

environment (and moisture content), solute bridges at interparticle contact points may 

persist [Plinke et al. 1995], significantly influencing powder properties and dustiness. In 

one extreme example, fine granulated sugar (sucrose), when subjected to 50% or 

greater relative humidity, deliquesced, forming a liquid solution [Evans et al. 2013]. 

Once dried, a single solid pellet remained, and fine sugar granules were not recoverable. 

Powders can cake and sometimes plug equipment as their humidity or moisture content 

increases. This is a well-known problem in process engineering, bulk solids handling,

and bulk powder conveying and storing [AIChE 2005]. The caking of rock dusts caused 

by moisture, which are used to mitigate potentially explosive coal dusts in underground 

mining operations, can render rock dusts ineffective [Perera et al. 2016].

The effect on powders of water uptake or loss to the ambient atmosphere, therefore, has 

implications for both workplace risk assessment and for laboratory testing. In the first 

instance, worker exposure concentrations during powder processing and handling could

be influenced by season (dry winters, humid summers, for example), that is, if powders 

are permitted to equilibrate their moisture content with the atmosphere. If permitted,

humid summers may decrease the dust-generating potential of some powdered 

products. Conversely, drier winters might also result in an increase in the dustgenerating potential. In the laboratory, quantitative dustiness testing is significantly 

impacted by powder moisture content. For example, using the NRCWE small rotating 

drum and the same TiO2 test powder, dustiness decreased by three orders of magnitude 

(1000x) with a relative humidity increase from 30% to 50% during the preconditioning 

of test powders [Levin et al. 2015]. This underlines the importance of careful control of 

this variable.

1) Determining moisture content

There are generally two acceptable approaches in accounting for the moisture content of

test powders. The first approach is the testing of powders as received: the moisture

content of the test sample is determined and reported together with the dustiness

information. This approach is currently recommended in EN15051-1 [CEN 2013a, Annex

A], and the dustiness experiment conducted at 50 ± 10% relative humidity (RH). It may

be useful to determine the dustiness of a powder as produced or perhaps as an

intermediate product within a multistep manufacturing process. Commercial testing

laboratories routinely use the as received approach.

A second approach, and the one adopted more recently in EN17199 [CEN 2019a–e], is 

the careful preconditioning of the test powder at 50 ± 5% RH. Note that in this latter 

standard, the acceptable humidity range under which materials may be preconditioned 

and dispersion experiments performed is more carefully controlled (i.e., 50 ± 5% RH 

versus 50 ± 10% RH). The preconditioning period could span several hours to 48 hours,

depending on the size of the test powder sample. Generally, larger sample sizes require 

longer equilibration periods. For tight control of humidity (and ambient temperature), 

the test apparatus may need to be modified to supply acceptable conditioned air while 
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testing. This is required if ambient laboratory conditions do not meet test requirements. 

It can be achieved by supplying excess conditioned air to the test apparatus, for example,

through an antechamber arrangement or similar [Evans et al. 2013].

Determining the moisture content of test powder may be done in at least two ways. One 

of the simplest is the oven-dry method. For this, about 10 g of pre-weighed powder (as 

received or conditioned) are heated in an oven at 120°C for several hours or overnight 

(EN17199-1) [CEN 2019a]. The powder is briefly allowed to cool before post-weighing. 

Best practice is cooling the powder within a desiccator containing an active desiccant.

The mass loss is reported as the moisture content (typically in %). 

When both as received and conditioned moisture content are required, three sequential 

gravimetric measurements can provide this information efficiently, particularly if test 

sample quantities are scarce. In this approach, between 1 and 10 g of the as received 

powder are pre-weighed (into a small glass petri dish or similar). This powder sample 

may be conditioned (50 ± 5% RH, 21 ± 3°C) for at least several hours. The sample is then 

re-weighed. The sample can then be heated within the oven at 120°C overnight, briefly 

allowed to cool (within a desiccator, if available), and then post-weighed. Thus, the 

moisture content as received and conditioned at 50% RH may be deduced by 

subtracting the final oven-dried mass. Clean, dry petri dishes can also be conditioned in 

parallel to the test samples (and pre- and post-weighed) to provide for substrate control. 

In addition to the oven method, using a dedicated moisture analysis instrument is also 

acceptable (EN15051-1) [CEN 2013a].

b. Bulk density

A test material parameter commonly reported with dustiness information is the bulk 

density (EN15051-1) [CEN 2013a, Annex B]. More specifically, this is the unconsolidated

or untapped bulk density of the test powder. In the EN15051-1 [CEN 2013a] standard, 

10 g of test powder are gently placed into a volumetric cylinder, and the volume is 

recorded. Only very light tapping or knocking is acceptable in filling the cylinder, as 

further compression or consolidation of the test powder can erroneously influence the 

density measurement. A minimum of three separate determinations are typically made,

and the mean average reported. If dustiness measurements are made by the EN15051-2 

rotating drum [CEN 2013b], the required 35 mL of test powder is pre-weighed within a 

volumetric vessel before carefully loading into the drum. If the vessel is further postweighed, not only is the mass of the test material loaded in the dustiness experiment 

determined, but also the untapped bulk density (density = mass/volume). Each rotating 

drum dustiness experiment will provide an independent bulk density determination,

and no further measurements are required.

c. Representative powder samples

During testing it is important to take a representative test sample from a larger bulk 

powder. During transport, it is possible for particles to partially segregate within the 

bulk powder, particularly with a wide mix of particle sizes. Consider the Brazil nut effect 

where we often find the larger Brazil nuts migrate toward the top of a container of

mixed nuts [Gajjar et al. 2021]. A similar process occurs for heterogeneous powder 
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samples. Powder taken from the top of the sample may not possess the same size 

distribution as that at the base, or even be representative of the powder sample taken as 

a whole. 

To counter this effect, some approaches, such as using rotary sample dividers or rifflers,

or quartering the test material, can be done. Such approaches are often used when 

sending out test materials from a much larger master batch for interlaboratory 

comparisons [e.g., Lyons et al. 1996; Pensis et al. 2010; Totaro et al. 2016]. A simple 

method described in EN15051-1 [CEN 2013a] is inverting the bulk powder sample 

several times before taking a subsample from the top of the powder column. This should 

be done just before a subsample is removed for testing and ensures adequate mixing of 

the test powder. General guidance on sample preparation for powders can be found in 

ISO 14488 [2007].

d. Gravimetric weighing

Dustiness test configurations typically rely on the gravimetric measurement of airborne 

dust on collection substrates and may be directly compared with the quantity of the 

original test material (e.g., g/ton, %, mg/kg, etc.). Irrespective of balance type, 

manufacturer, or model, good weighing practices need to be followed when quantifying

the initial test material and the collected airborne dust. In general, balances are set up 

according to manufacturer specifications. A balance should be situated in a low draft 

environment and on a heavy weighing table, to minimize movement and vibrations. A 

draft shield, if supplied with the instrument, should be used. 

While using a balance, a stable temperature (21 ± 3°C) and RH (50 ± 5 %) are 

recommended (e.g., EN17199) [CEN 2019a–e]. Test powders and collection media 

(filters or foams) may need to be adequately conditioned prior to weighing. Depending 

on application, a balance with a readability from three to seven decimal places (from 1 

g) may be required (i.e., 1 mg to 0.1 μg readability). Masses ranging from milligrams to

tens of kilograms may need to be quantified. Two (or more) balances may be required to

cover an exceptionally large range of values. Electrostatic effects can be minimized by

using static dissipative devices (ionizers). Standardized weights and media blanks

should be used to regularly assess that the balance is operating correctly, to ensure

there is no drift, and to provide confidence in weighing results. There are several

sources of information on good weighing practices and minimizing the uncertainties in

weighing [e.g., ACS 2021; EURAMET 2015; ISO 2009; Mettler-Toledo 2015].

e. Compression

The compression of powders may be intentional or perhaps a consequence of 

processing, conveyance, or storage. For example, compressing formulations into tablets 

can provide effective, low-dust, and convenient forms of pharmaceuticals for storage, 

transport, and dispensing to consumers [e.g., Davies 1992]. Tableting, pelletizing, or 

granulating products could be considered a substitution exposure control (see 

Controlling Exposures, Section 2.f) if these forms are amenable to downstream use. Like 

moisture-induced effects, the physical effects resulting from powder compression may 
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not be completely reversible once the powder load is removed. This suggests that 

powder compression history is an important factor in testing. 

The storage of powders in industrial bulk quantities can generate compression loads on 

the powder. Levin et al. [2015], for example, reported 160 kilogram per square meter 

(kg/m2) corresponded to a pressure experienced at the base of a single European pallet 

holding of five layers of bagged product. In the same study, Levin et al. [2015] subjected 

five nanoscale test powders to 160 kg/m2 uniaxial pressure, followed by dustiness 

testing in the NRCWE small rotating drum [Schneider and Jensen, 2008]. Compaction 

increased, decreased, or had no effect on dustiness depending on the test powder, so the 

results were highly material specific. Much smaller changes in dustiness were observed 

than those by moisture content [Levin et al. 2015]. Following low pressure compaction 

(3.5 kg/cm2), a granulated organoclay increased in dustiness whereas the dustiness of a 

loose bentonite was reduced [Jensen et al. 2009]. These effects are material specific. 

f. Surface modifications and coating

Using the EN15051-2 rotating drum [CEN 2013b], Burdett et al. [2013] observed that 

when nanoscale calcium carbonate powders were surface coated, dustiness increased

45 times for the inhalable, 90 times for the thoracic, and 331 times for the respirable 

dustiness fractions. Although organic (carbon containing) additives, the coatings were 

not specified. Perera et al. [2016] noted an increase in dustiness (quantified by airborne 

optical extinction) of treated limestone dusts when compared with untreated examples. 

A 1% (by mass) coating of calcium stearate was sufficient in generating about a fourfold 

increase in dustiness of the treated dusts when compared with their parent limestone 

constituents [Perera et al. 2016]. 

As noted previously, surface-treated limestone dusts are more effective in mitigating

propagating coal dust explosions in wet, underground mining environments. Polymer 

coatings added to multiwalled carbon nanotube powders resulted in both observed 

increases and decreases in the dustiness measured by the UNC Venturi device [Bishop et 

al. 2017]. Authors observed a tenfold decrease and elevenfold increase in total dustiness 

and a corresponding elevenfold decrease and fivefold increase for the respirable 

dustiness fractions. This suggests a more complex and material specific relationship 

between dustiness and surface coating.

g. Particle size

In their study of powders, Plinke et al. [1995] assessed four parent test materials:

limestone, TiO2, glass beads, and lactose. These were further classified into three 

aerodynamic size fractions prior to testing: less than 5 μm, between 5 and 25 μm, and 

greater than 25 μm. Other factors, such as powder cohesion and impaction (height) 

during powder dispersion, were found to play a more prominent role in dustiness 

behavior than particle size for these four materials [Plinke et al. 1995].

Primary particle size, indicated through BET specific surface area measurements

[Brunauer et al. 1938; ISO 2022], did not correlate with either total or respirable 

dustiness measured with the UNC Venturi for 27 fine and nanoscale powders [Evans et 
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al. 2013]. Counter intuitively, smaller particles do not necessarily result in increased 

dustiness. Respirable dustiness made up about one third of the total dustiness for the 

fine and nanoscale powders studied, but this relationship is not expected to hold for 

coarse test materials [Evans et al. 2013]. Given a sufficiently energetic aerodynamic 

stimulus (such as provided by the UNC Venturi), many of the nanoscale test powders 

tested could exhibit a relatively high respirable content.

López-Lilao et al. [2017a] studied 20 commercial materials (all minerals), including 

quartzes, feldspars, nephelines, carbonates, dolomites, sands, zircons, and alumina, with

particle sizes collectively ranging from about 1 to 300 μm. Authors did not initially 

observe a clear relationship between mean particle size (d50) and dustiness as measured 

by the continuous drop method (EN15051-3) [CEN 2013c]. However, when the 

inhalable and respirable dustiness results were compared with the relative emission 

potential of the parent mineral, a stronger relationship was observed between dustiness 

and particle size. Particle size of the parent powder may influence dustiness and the 

particle size fractions observed in the resulting airborne dust, but there is not a 

consistent relationship.

5 Criteria for current, improved, or new dustiness 

test configurations

What constitutes a good quantitative dustiness test configuration from the variety of 

tests described here is worth considering. This consideration may apply to current test 

configurations, to improvements or redesigns of existing tests, or to the development of 

new quantitative dustiness test methods. From a workplace inhalation exposure 

perspective, the tests may incorporate most, if not all, of the following attributes:

1. Direct relevance to workplace inhalation exposure scenarios.

2. Enclosed during operation for the health and safety of the technician.

3. Direct gravimetric determination of the health-based particle size fractions:

inhalable, thoracic, and respirable [ACGIH 1999; CEN 1993; ISO 1995].

4. Particle transport losses between dust generation and collection either eliminated

or minimized. If particle losses do occur, it should be shown that losses closely

result in the particle health size fractions stated above.

5. Discriminate test materials over a wide dustiness range (i.e., orders of

magnitude).

6. Ideally quantifies a range of test material forms (powders, granules, pellets, damp

samples, etc.).

7. Well characterized.

8. Threshold dustiness values or exposure potential bands (i.e., very low, low,

medium, and high dustiness, for example) are established for the comparison of

new or unknown test powders.

Of the various contemporary test configurations discussed in this chapter, the EN15051-

2 rotating drum [CEN 2013b] meets all these criteria from an inhalation exposure 

perspective. Most of these attributes may apply to other (non-inhalation exposure) test 
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configurations, including dust dispersion systems designed for studying the mitigation 

of dust explosion transmission.

6 Summary

The propensity with which a powder/dust becomes airborne is a major contributing 

factor in worker inhalation exposures [Brouwer et al. 2006; Heitbrink et al. 1989; 

Ribalta et al. 2019b] and can result in work-related illness and disease [Burdett et al. 

2000]. This attribute may be defined by the term dustiness, and although not an intrinsic 

powder or dust property, is quantifiable, repeatable, and may be assessed independently 

of the workplace by well-prescribed test configurations [Evans et al. 2013]. Once 

airborne, powders and dusts may also pose significant safety hazards [Cashdollar 2000; 

Eckhoff 2003].

Quantifying the dustiness of powders and dusts can contribute to closing exposureknowledge gaps. This would help in estimating the approximate airborne concentrations 

of worker inhalation exposures and improving understanding of the nature of those 

exposures. Testing potentially provides information on the particle size fractions that 

may be generated from an inhalation exposure perspective. This can help in selecting

appropriate exposure or safety mitigation measures (control banding) and developing

reduced or non-dust producing alternative products. The efficacy of dust reducing 

additives may also be assessed. Product packaging could then provide information 

warning potential employers and employees, particularly those who infrequently handle 

products, of possible hazards, so mitigation measures (controls) may be adopted.

Quantitative test configurations that provide the three health-based particle size 

fractions (inhalable, thoracic, and respirable) are preferred, particularly when 

considering worker inhalation exposures. Dustiness test configurations that possess 

dust generation mechanisms with direct relevance to the workplace, i.e., gravity-induced 

falling powders through air, and perhaps aerodynamic based methods, where air moves 

over the test powder, provide for more realistic exposure characteristics and exposure 

scenarios.

Results from new or unknown test powders may be compared with threshold dustiness 

values. In this way, we can determine the exposure potential (very low, low, medium, and 

high dustiness) that new test powders may have for each of the three health-based 

particle size fractions [CEN 2013]. Exposure mitigation (controls) selection can be based 

of these exposure potential categories. Both test configurations described in EN-15051 

[CEN 2013a,b] provide these thresholds; the rotating drum (EN15051-2) [CEN 2013b]

provides all three size fractions, and the continuous drop (EN15051-3) [CEN 2013c] 

offers two of the three. It is recommended that potential users choose the test method 

that best simulates their materials and handling processes as stipulated in EN15051-1 

[CEN 2013a].

The rotating drum test system (EN15051-2) [CEN 2013b] received substantial 

development and improvements in both performance and usability (see Section 3.c.2). It 

is the most widely adopted test method worldwide and closely replicates the dust 

generation mechanisms from moderate to gentle benchtop manual transfer/handling,
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Quantification of Airborne Dusts From Powders 

rotational mixers, or rotational bulk conveyance. Powder is permitted to fall no more 

than 30 cm (12 in). This test configuration also meets all criteria (Section 5) for current, 

improved, or new quantitative dustiness tests. The rotating drum may also be used to

characterize nanoscale test powders as described by both EN15051-2 [CEN 2013b] and 

EN17199-2 [CEN 2019b]. Each experiment requires 35 mL of test powder, and 

experiments are conducted in replicate. 

To simulate the continuous pouring of powder from a height (more than 1 m for 

example), the EN15051-3 continuous drop test [CEN 2013c] is an effective test system. 

Nanoscale materials may be charactered using the same dust generation configuration, 

but with other particle sampling options (EN17199-3) [CEN 2019c). This test 

configuration does not incorporate the thoracic aerosol fraction. Further, not all test 

materials may be continuously fed with the powder feed mechanism, limiting test 

materials mostly to fine dry powders. The test may also underestimate the inhalable 

particle size fraction for test materials with a substantial fraction of particles greater 

than ~38 μm [Burdett et al. 2000]. About 100-g of test powder is required per 

experiment, and experiments are conducted in replicate.

One possible shortcoming to the rotating drum, continuous drop test, and several other 

test systems described here are the quantities of test material required for testing. 

Experiments are typically repeated in replicate to assess variability. These quantities 

can be problematic when test materials are in limited quantities, cost prohibitive, or 

potentially toxic. The EN15051-2 [CEN 2013b] rotating drum and EN15051-3 [CEN 

2013c] continuous drop are relatively gentle dust-generating test configurations. They 

may underestimate airborne particle concentrations and their size fractions from more 

energetic dispersion processes observed in the workplace. A complimentary 

aerodynamic technique, such as the Venturi, may provide for a better simulation of more 

vigorous (worst case) dust-dispersion processes and requires orders of magnitude less 

test material (10 mg per experiment).

Disclaimers: Mention of any product or company name does not constitute 

endorsement by NIOSH. Citations to external websites do not constitute NIOSH 

endorsement of the sponsoring organizations or their programs or products. NIOSH is 

not responsible for the content of these websites. Web addresses referenced in this 

document were accessible at the time of publication.

Suggested Citation: NIOSH [2024]. Quantification of airborne dusts from powders.

Chapter AD. By Evans DE. In: Andrews RN, ed. NIOSH manual of analytical methods. 5th

ed. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease 

Control and Prevention, National Institute for Occupational Safety and Health, DHHS 

(NIOSH) Publication No. 2014-151, https://www.cdc.gov/niosh/nmam/.

7 Acknowledgements

Kevin H. Dunn (NIOSH/DFSE), Leonid A. Turkevich (NIOSH/DFSE), M. Christina Kander 

(NIOSH/DSI), David Mark (HSE, UK, Retired), David Leith (Professor Emeritus, 

University of North Carolina), and Patrick O’Shaughnessy (Professor, University of Iowa) 

reviewed this NMAM guidance chapter. The author appreciates their many helpful 
NIOSH Manual of Analytical Methods  5th Edition  Chapter AD January 2024 Page AD-46 of AD-61

Quantification of Airborne Dusts From Powders 

suggestions. The author is grateful for the longstanding support provided by the NIOSH 

Nanotechnology and Emerging Technologies programs.

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