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An interview with Dr Angela Southey on the Characteristics of ISO Fine Test Dust versus Real House Dust

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The testing of vacuum cleaners and similar domestic electrical appliances such as air cleaners involves the use of "test-dust"; Dr Angela Southeyinert particles consisting of silicon dioxide, aluminium, iron and sodium oxides. It is used to mimic typical household dust, which is composed of a mixture of fibres and particles of varying sizes and compositions. Sources of which include skin, mites, soil, heating emissions and pollen grains. In this blog post, we talk to Dr. Angela Southey, a lead researcher at airmid healthgroup, about a recent study she conducted and presented at the prestigious 13th International Conference on Indoor Air Quality and Climate in Austin, Texas comparing the characteristics of ISO fine test dust to real house dust.

This blog post follows an interview format with Angela Southey PhD at the test facility at airmid healthgroup and offers a very valuable insight on the subject.

Introduction to the Study
Domestic products, such as vacuum cleaners, are often tested using inert particle mixtures called 'test dust'. Depending on the standard's testing requirements, the test dust consists of a defined mixture of silicon dioxide, aluminium, iron and sodium oxides and other components such as talcum powder, wood flour and potassium chloride (ASTM. 2007, CEI IEC. 2004, ASTM. 2004). The test dusts are graded according to their particle size range. ISO 12103-1 A2 Fine Test Dust (or ISO Fine Dust) is a test dust with a particle size range from 1-80m. ISO Fine Dust is used in ASTM standard F2608-07 (ASTM. 2007) for determining the change in room air particulate counts as a result of test dust removal from floor coverings with the vacuum cleaner under test. Household dust is composed of a heterogeneous mixture of fibres and irregularly shaped particles of varying particle sizes and composition. Particle sources include skin, hair, mites, plant pollen, fibres, soil, road dust, cooking emissions, heating emissions and cigarette smoke (Edwards et al. 1998; Molhave et al. 2000). Comparison of the particle size distribution of the ISO Fine Dust with that of household dust by laser diffraction, demonstrated that ISO Fine Dust bears little resemblance to the 'real' dust that a vacuum cleaner would encounter in the home (nor does it purport to).

The aim of this study was to determine if a test dust, more representative of household dust, should be produced and standardized for domestic appliance testing.

Dr. Southey, what prompted you to conduct this study

It comes down to standardisation. We wanted to compare current standardised test dust to actual household dust. This type of information allows our product development team here at airmid healthgroup to ensure our testing is illustrative of real life settings. This ensures the provision of quality control and assurance in the testing and validation of our client's products.

How did you go about this study, how was the dust analysed?
It was quite an elegant study. The test dust consisted of household dust collected from vacuum bags and pooled from several homes, ensuring a broad representation of dust from household settings. The standard dust used in this study was an ISO Fine Dust, with a particle size range from 1-80 micron. We compared both dust types on the basis of particle size and the average results were reported as Particle Volume, % Volume Less Than and Particle Count Distribution. It was possible to define these parameters thanks to our Malvern Mastersizer 2000.

What was the outcome of this study, how did the test dust compare to the ISO Fine Dust?
Our analysis showed that although house dust is heterogeneous, the average particle distributions were similar for all dust samples tested. Interestingly, the particle distribution for the household dust was quite different to that of ISO Fine Dust. ISO fine dust was much finer than household dust in terms of particle size. Deviations were also apparent in the volumes of test dust particles, compared to ISO Fine Dust. Based on the results of this study, we conclude that ISO Fine dust is different to the dust a vacuum cleaner faces in household settings. This may affect the accuracy of validations performed using test dust. This study also highlights the economy and ease at which real test dust could be produced using pooled sieved dust from vacuum bags. Such dust could easily be standardised by particle size distribution analysis.

What conclusion can be made related to this study?
Standardisation of consumer product testing is necessary to assist in making informed decisions and test dusts will always have a place in vacuum cleaner testing. However, from this study we found that the particle size distribution of ISO Fine dust, which is used for F2608-07 (ASTM, 2007), is markedly different to the dust a vacuum cleaner would encounter in the home. Therefore, a test dust, more closely resembling 'real' household dust should be used in conjunction with the current test dusts, for vacuum cleaner testing. Although house dust is heterogeneous, the particle distributions were remarkably similar for all dust samples tested in this study. Based results of this study, production of 'real' test dust should be relatively straightforward and inexpensive, using pooled sieved dust from vacuum bags. Standardisation would involve particle size distribution analysis. There is little information in the literature on particle sizing of household dust. In this study, the particle volume distribution for household dust, is similar to that reported by Lewis et al. (1999), using % by weight. Hunt et al. (2008) reported that the coarser particles of house dust were preferentially removed from vinyl flooring during vacuum cleaning and 73% of finer particles. 

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About airmid healthgroup
airmid helps their clients across a number of sectors improve, add value and differentiate their customer offerings through a focus on bio-medical data, health impact claims and optimising indoor air quality. We have a uniquely integrated facility which combines standard microbiology testing, molecular biology and state-of-the-art air sampling with a highly developed climate controlled walk in environmental test chamber. This gives us a world class aerobiology research facility that allows us to follow airborne pathogens such as nominated viruses, bacteria, molds or other ultra-fine particles. As a world's leading bio-medical research facility our clients describe us as a specialised extension to their research capabilities, we capture, store and manage data and most importantly convert it into tangible market value.

About Angela Southey
Head of Virology & Environmental Testing Chambers
Angela has responsibility for the running of our Virology Laboratory and Environmental Testing Chambers. Angela qualified with a BSc. in Microbiology from UCC, before going on to complete a PhD in Lung Fibrosis in UCD. She then spent two years working in Japan on Ulcerative Colitis with Tanabe Seiyaku Ltd. Returning to Ireland she took up a senior research position in the Veterinary College, UCD followed by extensive industry experience in the diagnostic area with Wyeth Biopharma and Abbott Diagnostics. 

 

References
1) ASTM. 2004. F1977-04, Standard Test Method for Determining Initial, Fractional, Filtration Efficiency of a Vacuum Cleaner System. PA: American Society of Testing Materials International.

2) ASTM. 2007. F2608-07, Standard Test Method for Determining the Change in Room Air Particulate Counts as a Result of the Vacuum Cleaning Process. PA: American Society of Testing Materials International.

3) CEI IEC. 2004. CEI/IEC 60312, Vacuum Cleaners for household use – Methods of measuring performance. Geneva: International Electrochemical Commission. Edwards R,

4) Yurkow E and Lioy P. 1998. Seasonal Deposition of house dusts onto household surfaces. The Science of the Total Environment 224, 69-80.

5) Hunt A, Johnson DL, Brooks J and Griffith DA. 2008. Risk remaining from fine particle contaminants after vacuum cleaning of hard floor surfaces. Environ Geochem Health 30, 597-611.

6) Lewis R, Fortune C, Willis R, Camann D and Antley J. 1999. Distribution of Pesticides and Polycyclic Aromatic Hydrocarbons in House Dust as a function of Particle Size. Environmental Health Perspectives 107(9), 721-726.

To view the poster that was presented Click Here (pdf)

To view the paper that was published Click Here (pdf)

Tagged in: fine test dust