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Aerosol Photometers: The Gold Standard in HEPA Filtration Testing

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Presentation on theme: "Aerosol Photometers: The Gold Standard in HEPA Filtration Testing"— Presentation transcript:

1 Aerosol Photometers: The Gold Standard in HEPA Filtration Testing
Presented by: Dave Crosby Tim McDiarmid Don Largent Air Techniques International

2 Introductions

3 Agenda History of Photometry Science of Photometry
Applications of Photometry

4 History of Photometers & HEPA Filters

5 History of Photometers & HEPA Filters
“You can’t have one without the other”

6 The photometer was first since there was a need
David Sinclair, Ph.D. (Nephelometer) (Not portable and had logarithmic display) A Nephelometer is a type of photometer identified by Dr. David Sinclair. The need was monitoring of air pollution, particularly in cities where steel was manufactured.

7 Air Pollution Research 1933
Cities such as Pittsburgh and Baltimore. This is a picture of the ship building located in Baltimore, MD during the 1930’s and the steel foundries in the background.

8 WW II generated a high priority need
It all started in 1942

9 Some Key Players Wendell Anderson, Humphrey Gilbert, Dr. Melvin First

10 Captured WW II German Gas Masks
The US had performed no gas mask development since WW 1 German masks used cellulose asbestos media patented by Dräger Werke in 1933 Wendell Anderson working with H&V developed media comparable to the German sample German masks were acquired by the US and found to have far superior filtration characteristics to those used anywhere else in the world. Given the chemical warfare agents at the time, this became a very high priority for the US Military.

11 M10A1 Canister The M10A1 respirator canister was the first high efficiency filter deployed by the US Military.

12 Tank & APC M-25 Mask

13 Smoke Penetrometer to test the gas mask paper & filters
Now that a high efficiency paper (media) and filter existed, there was a need to test them. The Q-127 was the product developed to do this. There are still Q-127 instruments utilized today in both military and commercial industries. ATI was the premier provider of this instrument since the early 1960’s and still services components of this instrument today. This instrument is no longer manufactured and has been replaced by the TDA-100P instrument.

14 First Linear Photometer

15 Space Filter US military needed filtration of room areas for people and used gas mask media for a pleated filter for larger air flow ( ) Know as “Collective Protection” Used cardboard spacers between pleats, which had high air flow resistance

16 Cardboard Pleat

17 Manhattan Project Humphrey Gilbert safety engineer at Los Alamos was sent to Oak Ridge Filters used in Manhattan Project were very thick with extremely high pressure drop Foresaw need for high efficiency air filters in HVAC systems

18 Absolute Air Filter Gilbert (now with AEC) unhappy with Army Space filter and its limitations AEC in 1948 gives Author D. Little a contract to redesign filter and find a supplier Walter Smith Ph.D. comes up with corrugated cardboard separator idea

19 Improved Pleated Filter Design

20

21 HEPA Filter Development
First Air Cleaning Seminar for AEC personnel held June 1951 at Harvard Air Cleaning Laboratory First Handbook on Air Cleaning distributed at meeting Fires at several weapons plants made need for high temperature and water resistance necessary

22 Second Air Cleaning Conference held in Ames, IA Melvin W. First Ph.D. Presented four research papers

23 Military develops procedures and
Apparatus to test High Efficiency filters and related products Penetrometers Q-127 Low Flow Q-76 Med. Flow Q-107 High Flow Rough Handling Water Repellency etc.

24 HEPA Development for Fire & Water Resistance (1953)

25 First HEPA Guide (1961)

26 Willis Whitfield (1961) Discovery of Laminar Flow at Sandia National Labs

27 SNL Demonstrates Clean Room Concept in Chicago for IES(T)
(1962)

28 First “In Place Filter Test”
The US Nuclear Navy created the first need for in place filter testing.

29 First Portable Linear Photometer TDA-2 (1962)
Wasn’t very portable by todays’ standards, but it got the job done.

30 JM-1000 Photometer (1964)

31 Next Portable Photometer TDA-2A (1964)
Cabinet covered in white Formica (White Rooms) First Scanning Probe The portable photometer migrated to testing in place filters in what was then known as “White Rooms”, the precursor to the clean room as we know it today. This also created a need for scanning the filter to find and repair defects, which resulted in the first scanning probe.

32 Next Portable Photometer TDA-2B (1965-66)
Ergonomic front panel design

33 First Commercial Standards (1967)
Up until now, the commercial world knew nothing of high efficiency (HEPA) filters, how they were tested for efficiency or tested in place. This migrated into the Pharmaceutical and life sciences, aerospace, and semi-con/micro-electronics industries we are familiar with today.

34 First Commercial Standards (1967)

35 Discussion

36 What is a Filter

37 Before Photometry… What is a Filter? How to Test a Filter
Filtration Mechanics MPPS How to Test a Filter Efficiency Leak (Integrity)

38 What is a Filter? Separation of one phase from another
Solids or liquids in Air (Home Furnace) Solids in liquid (Auto Oil/Gas) Liquid in Air (Air oil separators) Liquid in liquid (RO) Gas in Gas (Activated Carbon)

39 What is a Filter? A Controlled Leak! Filtration controls the amount of impurity that is allowed to pass. There is no such thing as a ‘perfect’ filter (no resistance and 100% efficiency)

40 Filtration Types Materials Performance Fibers Fibrous Structures
Micropores Performance High Efficiency Low Efficiency Filters can be classified by many other means: applications, other properties such as temperature limitations, etc.

41 What are we dealing with?
Solids or liquids in Air & Fibrous Filters Other structures are more common in ultra filtration and special applications

42 Fibrous Filters Typically Depth Filters Fibrous Filter Construction
Filtration throughout media depth Very low to very high particle removal Fibrous Filter Construction Filter Disks/Pads Pleated Cartridges Bags/Pockets Membranes are usually considered surface filter as opposed to depth filters. Due to low loading requirements, this is less relevant in high purity applications found in Clean manufacturing. Filter cartridges can be cylindrical or flat panels In practice, multi stage filter or media used to get desired loading/performance effect.

43 Filtration Mechanics Pressure Drop Single Filter Efficiency
Collection Mechanisms

44 Darcy’s Law As systems require maximum resistance ratings, filter manufacturers must design around this parameter ΔP

45 Darcy’s Law The greater the flow rate through the filter the greater the resistance. Not rocket science, but what is that relationship?

46 Filter Pressure Drop CLEANROOM HVAC Pressure Drop
Manufacturers can design filters for specific applications i.e. known flow rate and pressure drop requirements. But what about the filtration characteristics? Linear Pressure Drop Inertial Velocity (Darcy Law) Regime Regime

47 Filtration Assumptions
Fibers are in cross flow Particles are ‘collected’ upon contact with fiber Uniform fiber diameter Uniform particle size

48 Single Fiber Efficiency
Air Volume swept out by fiber Single Fiber Efficiency ηs = Particles collected by fiber Particles in volume of air geometrically swept out by fiber

49 Fiber Structure - HEPA Image of a typical fibrous media. There are many fibers and many layers of fibers. There is variation of fiber to fiber thickness and thickness within fibers. The basic filter model uses the particle capture by one fiber and does not consider interference from additional fibers or additional fiber layers.

50 Particle Collection Mechanics
Sieving Inertial Impaction Diffusion Interception

51 Particle Collection: Sieving
Filtration: Theory, Design & Practice I 21 Feb 2002 Particle Collection: Sieving Fibers Particle Flow Sieving is the most intuitive collection method. However, this mechanism usually happens by pre-filters not HEPA filters. ATI Technical School

52 Particle Collection: Interception
Filtration: Theory, Design & Practice I 21 Feb 2002 Particle Collection: Interception Interception is simply a collision. The particle impinges upon the fiber and is collected. Interception is greater for larger particles simply because of the geometries involved and reduced diffusion effects. ATI Technical School

53 Particle Collection: Inertial Impaction
Filtration: Theory, Design & Practice I 21 Feb 2002 Particle Collection: Inertial Impaction Larger particles, due to their greater mass and, thus, greater inertia, separate from the air stream, as the air stream bends around a fiber, and impacts upon the fiber. Inertial effects are greater for larger particles and at higher flow rates. ATI Technical School

54 Particle Collection: Diffusion
Filtration: Theory, Design & Practice I 21 Feb 2002 Particle Collection: Diffusion Diffusion occurs due to the intrinsic natural random movement of small particles. Diffusion is much more significant for small particles, their random motion brings them in contact with the fiber and are collected. Diffusion effect reduces with larger sizes. ATI Technical School

55 Particle Collection Mechanisms
Van der Wall’s Law is what holds a particle to the fiber once contact is made. These are the small electrical bonds at a molecular level and is how a gecko is able to climb vertical and upside down without suction or adhesion properties. Electrostatic Deposition can also happen when a fiber is charged and the particle is charged opposite that of the fiber (i.e. opposites attract). This is only relevant for some media. To achieve any permanent benefits from electrostatic effects, the media must remain dry and charged. If moisture is present the charge leaks away. Realistically, the high efficiencies attained by electrostatic media are typically quite transient and dissipate quickly.

56 High Efficiency Filter MPPS (Most Penetrating Particle Size)
Filtration: Theory, Design & Practice I 21 Feb 2002 High Efficiency Filter MPPS (Most Penetrating Particle Size) Impaction Diffusion MPPS 0.08 to 0.18µm Penetration The addition of all collection mechanisms leads to a Penetration Curve with an unique peak or max penetration. As the particle size increases, the diffusion effects decrease and the interception and impaction effects increase leading to the peak penetration. By adding the red and blue curves shown above, we obtain the yellow curve whose peak identifies the particle size at the maximum penetration. This is called the Most Penetrating Particle Size (MPPS). Keep in mind that the efficiency η = 1 – penetration. These two terms are often used interchangeably to define filter performance. It is intuitively obvious that efficiency at particles larger than the MPPS will be higher (or lower penetration). It is less obvious that the efficiency is also greater at particles smaller than the MPPS!! In other words, the MPPS is the worst case for a filter. More on the factors affecting MPPS in the next lecture. Particle Size ATI Technical School

57 Filtration is Selective Particle Collection
00 00 Small and big particles are more effectively collected

58 Impact of Flow Rate on Efficiency
As you decrease the flow rate from the specified flow rate, the % penetration will decrease (i.e. efficiency will increase); however, the MPPS will shift upward. The converse is also true. Typically, as a filter loads and the resistance increases, the flow rate will gradually decrease, shifting the MPPS upward, but the filter efficiency improves!

59 Filtration: Theory, Design & Practice I
21 Feb 2002 Media Velocity is Lower Than Face Velocity Media Velocity Face Velocity A Filter’s Performance is Determined at Media Velocity Media Velocity = Face Velocity x Face Area / Media Area in Filter More media area the lower the pressure drop ATI Technical School

60 Consideration in Filter Design
Penetration or efficiency Critical Particle Size Pressure Drop or resistance (Cost)

61 Filter Tests Efficiency Leak/Integrity Media Manufacturer
Filter Manufacturer 3rd Party Certification Leak/Integrity Field/In-Situ

62 Filtration: Theory, Design & Practice I
21 Feb 2002 Efficiency Testing Challenge filter with aerosol at or near the MPPS This requires a mono-dispersed aerosol (tight distribution) Measure upstream and downstream concentration Sequential or parallel (simultaneous) measurements Efficiency = 1 – Downstream Upstream Note: This is a ‘global’ measurement (i.e. entire filter) Efficiency testing is a simple concept: challenge a filter and measure what gets through. It is a ratio-metric measurement (i.e. Percentage) based on known parameters: flow rate and upstream challenge. Although simple in concept, there are always complexities which we will discuss later. ATI Technical School

63 Typical Filter Efficiency Test System
Filtration: Theory, Design & Practice I 21 Feb 2002 Typical Filter Efficiency Test System Note the original MilStd 282 testing methodology (i.e. photometry) has been omitted from this diagram, although it is still a viable methodology for efficiency testing per IEST RP It is important to note, the use of photometry in this manner is the same methodology specified and employed by most media manufacturers and specifically by both the Nuclear and High Efficiency Respirator industries. Recommended filter performance test system from IEST RP-CC-0021 ATI Technical School

64 Filtration: Theory, Design & Practice I
21 Feb 2002 What is a Leak? Leak is a local measurement. Leak is generally 5 –10 times the average penetration at a local spot. Therefore we do not require a mono-dispersed challenge aerosol at the MPPS Easier and less costly to generate larger particles with a broader distribution. Keep in mind that there are variations in the performance of media due to the random nature of the manufacturing process of fibrous media. ATI Technical School

65 A Good Filter Will Allow Few Particles to Penetrate
Filtration: Theory, Design & Practice I 21 Feb 2002 A Good Filter Will Allow Few Particles to Penetrate o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o 00 o o o o o 0 o Filter allows a small fraction of particles to pass through ATI Technical School

66 Filtration: Theory, Design & Practice I
21 Feb 2002 Add a Leak and… o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o 00 o o o 00 o o o o o 0 0 O o o o o o o 0 0o o o Now, if there is a hole (leak) in the filter, many particles go through ATI Technical School

67 Test for a Leak/Integrity
Filtration: Theory, Design & Practice I 21 Feb 2002 Test for a Leak/Integrity Measure local penetration at each sample location to determine: Filters are not faulty / not been damaged Filters have been installed properly There are no leaks in the mounting frame / between mounting frame and housing System contains no by-pass of the filter Leak testing is a local measurement; however, by scanning the entire filter and where it is ‘sealed’ into the overall system, the entire filtration system integrity is tested and validated. ATI Technical School

68 Leak/Integrity Scanning
Filtration: Theory, Design & Practice I 21 Feb 2002 Leak/Integrity Scanning Scanning is the method where a probe sweeps the entire surface of a filter and its sealing mechanism looking for local penetration. Typically the probe samples at the same velocity as the air flow in the filter. There are various instruments that may be used as the detector and we will discuss these later. The speed of the scan rate also affects the ability to detect a leak and is addressed more fully in IEST CC RP Ensure that all parts of filter are within specification ATI Technical School

69 Efficiency vs. Leak/Integrity in General Terms
Efficiency Testing Leak Testing Global Local Determine % Penetration Yes Yes1 Pinpoint Leaks No Manufacturer Test Yes2 Field Test We will review this in greater detail later, but for now, it is important to note that efficiency testing is to qualify the filter itself and Leak testing is to ensure the integrity of the filter, its housing, and the filtration system as a whole. Also, it is important to note that some manufacturers can/will perform a ‘Leak’ test of the media (i.e. scan test), but typically charge extra for this. This guarantees any variability in the media will not exceed the leak threshold in the field which may not be picked up with an overall, ‘Global’ efficiency test. 1 – Local % penetration, not overall efficiency 2 – Due to variations in the media manufacturing process

70 Discussion

71 When Testing a Filter What are We Looking For?

72 Let’s Review… Particulate penetration as Size of interest? However…..
Efficiency Leak Size of interest? MPPS from 0.08 to 0.18 micron Even when looking for a leak? However…..

73 What is a particle? Particles come in all shapes and sizes. Also, visible organisms can change shape a grow complicating things even further. So what is it we refer to when specifying a particle size?

74 The Simplest Particle? The real world is very complicated, so we try to simplify it as best we can. The simplest 3-dimensional shape to deal with is a sphere. And a sphere’s defining measurement is its radius or diameter (2r).

75 Equivalent Particle Size
Diameter of a Sphere that has the same magnitude of a chosen Property as the particle In question Optical Diameter (Eye/microscope) Scattering Diameter (Light Scattering) Electric Mobility (Charge On Particle) Mobility (Diffusion) Stokes Diameter (Drag Forces) Aerodynamic Diameter (Settling Speed) When we say “Particle Size” it is useless unless we also state how we measure it, it is not a unique measurement. Particle size as commonly noted implies spherical particles and their optical diameter, but this can be and usually is a big misconception. Also, if the particle size refers to its physical size, then a denser particle will settle faster than a less dense particle of the same size. Think of dropping a pound of cotton vs. a pound of lead. In commercial terms, we typically load a truck by volume, but pay by weight. So we need to be specific when referencing particle size. In this business we generally speak of scattering diameters and mass.

76 In Filtration, Collections of Particles Interest Us
Aerosol Solid/Liquid and Gas (dust, fog) Hydrosol Solid/Liquid and Liquid (milk, paint, lotion) Foam Gas in Solid or Liquid (sponge, shampoo) Aerosol is a collection of many particles. If they are all the same size, then it is termed mono-disperse. If they are multiple sizes, then it is poly-disperse.

77 Key Concepts Drag Force – proportional dp > 10µm
Slip Correction for dp < 10µm Stopping Distance and Relaxation Time Settling velocity Mobility and Electric Mobility Diffusion and Brownian Motion Coagulation Dimensionless Numbers These are key properties we deal with when discussing and measuring particles and aerosols. Dimensionless numbers? They are very common in all engineering and sciences. They relate two complimentary or competing forces and eliminate the need for units. For example, when the viscous drag on a particle balances the flow of the fluid it is traveling in, this equates to the Reynolds number, Re. Re is a fundamental concept in all fluid dynamics. The term ‘Laminar Flow’ which we all have heard is a condition that occurs at low Reynolds numbers.

78 Units of Measurement in Filtration
µm Micrometer, 10-6 meter Nm Nanometer, 10-9 meter A Angstrom Unit, meter 1 µm = 1,000 nm = 10,000 A Some perspective: 1cm is 1000 µm 1in = 2.54 cm = 25,400 µm

79 Approximate Particle Diameter
Particle Sizes of Interest Item Approximate Particle Diameter Eye of a Needle 1,230 microns Beach Sand 100 – 2000 microns Table salt ~100 microns Human hair microns Talcum powder ~10 microns Tobacco Smoke 0.01 – 1.0 microns Bacteria microns Virus <0.005 – 0.05 microns Many of these particles can be a chain or a collection of smaller particles. Cigarette smoke can be a chain or a ring. For inhalation, small particles behave like a gas and go in and out of the lung freely and, although are inhaled, do not settle in the lung to be absorbed. The larger ones get caught in the nose or fall past the nose to the ground. It is those particles in between (approximately um) that are of interest from a respirable perspective. It just so happened that DOP aerosol as generated to test filters back in the 50’s and 60’s had a 0.3um (Mass Mean Diameter)…a lucky break of nature…

80 Typical Particle Sizes
0.3um So why are we concerned with viruses? They require a transport mechanism…mucus, saliva, phlegm…all aerosolizes when someone coughs or sneezes.

81 Another Particle Size Chart

82 Typical Settling Velocity
Diameter (um) Feet/min The particles we are interested in tend to stay airborne for quite some time. Larger particles will settle very quickly.

83 How is an Aerosol Characterized?
Consider this data set Frequency X (range) Raw Data Normalized 0 to 5 100 20 5 to 6 70 6 to 8 60 30 Here, the count is the number between the X range. There are 100 counts between 0 and 5. Since the X ranges are not equal, we normalize the data by dividing the counts by the X range. Therefore the normalized count in the 0 to 5 range is equal to 100/(5-0) or 20. The result is shown graphically in the next slide.

84 Normalized Frequency Distribution
Y/ΔX

85 Size Distribution Terms
Independent variable, X Mean Xm Standard Deviation, σ Mode (peak) Median (50th percentile) For our business, the X variable is almost always the Particle diameter…the equivalent diameter!

86 Arithmetic Standard Deviation
This is the fundamental distribution taught in high school, commonly called the ‘Normal’ distribution. It is also known as the Gaussian or Standard Distribution. Some refer to it as the ‘Bell’ curve. Although simple to use, it requires the underlying data to meet very strict conditions of independence and normality. Believe it or not, most natural occurrences and even those man-made, do not meet these criteria.

87 Geometric Standard Deviation
The world is geometric. The symbol ‘ln’ is the natural logarithm. If X = ey, then Logarithm e X = Y or the common logs. In simple terms, if one substitutes X = ln x (or log x), the resulting data follows the Standard distribution.

88 Particle Size Distribution
Most Natural Processes are Geometrically Distributed and often multi modal Number (count), Surface, or Volume (mass) Distribution are common weightings The data can be weighted in any manner. Number, surface area, or volume (mass) are common.

89 Why is this important? Due to data weighting… …the 0.3um DOP particle measured in the 50’s is a volume (mass) mean… …whose number (count) median is actually closer to 0.18um…the MPPS

90 Geometric vs. Arithmetic
Consider Geometric as Arithmetic or Linear on a log scale Geometric spreads out the lower end In Arithmetic, equal differences result in equal spacing In Geometric, equal ratios result in equal spacing

91 Geometric vs. Arithmetic
Geometric scales are very useful when the data spread is very large. It helps enlarge the scale at the lower end. If one wants to divide the range into different intervals, we use equal differences in arithmetic scale and equal ratios in a geometric scale. Equal intervals Arithmetic: = = … (equal differences) Geometric: 10/7.48 = 7.48/5.62 = … (equal ratios)

92 Why Use Log Normal Distributions?
No Negative Values For known distributions, the Means of different weightings can be calculated from the others For example, Mass (volume) Mean calculated from Count (number) mean

93 Number and Volume Weighting
dp Number Counts Volume (πd3/6) 1 1,000,000 523,000 10 100

94 Key Points to Remember Particles come in many shapes and sizes
ALL measurements determine some physical property and provide an Equivalent Size In filtration, larger particles settle out and are not important, particularly cleanrooms Geometric Distributions (aka Log Normal) are used to define particle size distributions Mass and Number weightings are common in particle measurements

95 Discussion

96 Now we know we are looking for particles… The Light-Particle Interaction

97 Primary Light-Particle Interactions
Elastic Scattering Rayleigh Scattering MIE Scattering Phase Shift Polarization Absorbtion

98 LIGHT PARTICLE INTERACTION
Raman Fluorescence Reflection Diffraction Scattering Absorption Incident Light Refraction All materials absorb light Absorption is the negative of reflection and, in technical terms, it is also referred to as the imaginary part of the refractive index. A black body is good absorber. No light comes out and hence it appears black Emission

99 Common Properties Refraction – the apparent change in direction of light due to change in refractive index within one medium or between dissimilar medium Reflection – redirection of light at the surface of a material Diffraction – bending or deflection of light around a particle Polarization – oscillations of the light occurring in a defined plane Refraction is dependent upon the refractive index of the particle/medium. Polarization implies that the light waves are oriented in one plane.

100 Complex Numbers (4)1/2 = 2 What is (-1) 1/2 ?
It is defined by the symbol i A complex number is written as (a - b i) where the imaginary part is represented by the symbol i

101 Refractive Index Refractive Index of a material is a complex number
Usually given as 2 - 4i The imaginary part is due to absorption

102 Refractive Index of Common Materials
Quartz i Glass 1.5 to i PSL i Ca Sulfate i Carbon 2.0 – 0.33i Iron – 1.63i The refractive index is a complex number. The imaginary part is denoted by i and denotes the absorptive component of the refractive index. Most clear materials such as glass, oil drops, etc., have no imaginary or absorptive component of the refractive index. Many metals and colored materials absorb light.

103 Refraction Refractive Index = sine r / sine i i r
Refractive index is a ration of the velocity of light in a vacuum to that in the medium or particle. The imaginary part is proportional to the absorption index and the wavelength of light of interest. The refractive index is a complex number denoted as R – iA, where the imagininary part is denoted as iA. Refractive Index = sine r / sine i

104 Size and Scattering Regimes
Size Range of Interest A Hydrometeor is any water or ice particles that have formed in the atmosphere or at the Earth’s surface as a result of condensation or sublimation. Water or ice particles blown from the ground into the atmosphere are also classed as hydrometeors. Some well-known hydrometeors are clouds, fog, rain, snow, hail, dew, etc.

105 Elastic Scattering Redirection of Incident Light without change in wavelength Refraction – internal to particle, wavelength and composition dependent Reflection – at surface of particle, dependent on wavelength and composition Diffraction – external to particle, independent of wavelength and composition

106 Particle Size Affects Elastic Scattering
Optical Particle Size (α) α = πd / λ where: d = particle diameter λ = wavelength Scattering Intensity (Is) Is = λ2 f(α) where: f(α) is a size dependent function Simply put Scattering Intensity is a function of both the particle size and the wavelength of light it is subjected to.

107 Light Scattering Particles much smaller (< 0.025um) than the wavelength of light results in Rayleigh Scattering Particles comparable to the wavelength of light (0.025> x < 2.5um) results in MIE Scattering Much larger particles result in geometric scattering. Simply put Scattering Intensity is a function of both the particle size and the wavelength of light it is subjected to.

108 Light Scattering Particles much smaller (< 0.025um) than the wavelength of light results in Rayleigh Scattering Particles comparable to the wavelength of light (0.025> x < 2.5um) results in MIE Scattering Much larger particles result in geometric scattering. Visible Light is between 300 to about 600 nm or (0.3 to 0.6 um). The scattering intensity varies as the inverse of the fourth power of the wavelength of light. Most of what every photometer and particle counter manufacturer does is in the MIE scattering realm.

109 Rayleigh Scattering Particle diameter is much, much less than the wavelength of light. Scattering equal in forward and backward direction. Intensity increases as fourth power of 1/wavelength of light This is why the sky is blue – blue light has a much smaller wavelength than red.

110 Rayleigh Scattering

111 Mie Scattering Wavelength, λ Incident light
Particle size approaches wavelength Forward scattering more intense The intensity of scattering varies less than the fourth power of 1/wavelength This is the regime we operate in particle instruments Incident light

112 MIE Scattering Particle size approaches wavelength
Forward scattering is more intense The intensity of scattering varies less than the fourth power of 1/wavelength This is the regime we operate in with regard to particle instruments.

113 MIE Scattering

114 Discussion

115 Multiple and Single Particle Sensing and Sensors

116 Multiple Particle Sensing
Sampling Volume ≥ 1/number concentration Independent of sample volume (measuring a ‘cloud’) Precision depends on averaging time (due to variations in the ‘cloud’) Remember, 1/number concentration has the same units as volume.

117 Multiple Particle Sensors
Extinction (umbrella) Smoke Meter (soot content in exhaust stack) Transmissometer (visual ranging) Scattering Intensity (nephelometry) Backscatter (LIDAR) Photometry LIDAR is light detecting and ranging. It is used for remote sensing of aerosol by back scattering.

118 Photometer Aerosol is illuminated by a light source
Total scattered light is detected by PMT Total concentration is measured

119 Filtration: Theory, Design & Practice I
21 Feb 2002 Photometer 0 0 0 0 0 0 0 Aerosol Focus Optics Collector Optics Photodetector Electronics Light Source The photometer is calibrated with a known aerosol size, distribution, and concentration, DOP or PAO. It uses internal reference settings to accommodate other aerosol substrates. Instrument response is instantaneous and constant. Output response is based on mass level of aerosol – this is gravimetrically validated as part of the calibration process. Output magnitude dependent upon mass concentration of aerosol in sampling chamber. ATI Technical School

120 Photometer Focal Point

121 Nephelometer Particle density is a function of the light reflected into the detector from the illuminated particles Scattered light is a measure of the total scattering in the view volume. Larger volumes than in aerosol photometers. Used for ambient measurements (pollution and climate) and visibility measurements.

122 Multiple Particle Sensors Summary
Light-Particle interaction results in scattering Optical instruments in particle measurement is dependent upon the particle size and scattering properties Multiple particle scattering is independent of volume; depends on averaging time.

123 Single Particle Sensing
Sample Volume << 1/number concentration Requires a precise, known volume of sampled air Same as counting events; precision depends on total counts Remember, 1/number concentration has the same units as volume

124 Single Particle Sensors
Light attenuation (extinction) Scattering (Particle Counters) Laser White Light Angular Scattering Doppler anemometer

125 Filtration: Theory, Design & Practice I
21 Feb 2002 Particle Counter Light Source Focus Optics Collector Optics Photodetector O O Electronics A Particle Counter assumes all particles have the same physical characteristics as the material used to calibrate the instrument (i.e. PSLs) Light scattered by each particle is counted and its magnitude measured. The output is based on the size (or effective cross sectional area) of a discrete particle. The quantity of pulses is the particle count and magnitude the particle size. The size measurement is calibrated with various mono-dispersed poly styrene latex spheres. ATI Technical School

126 Common Particle Counter Challenges
Multi Valued Response Coincidence Problems at small particle sizes

127 Multi Valued Signal The scattering intensity response is not unique for small particle sizes. That is, particles of two sizes can give the same response making particle detection by size difficult as smaller sizes.

128 Coincidence O Photodetector Electronics Light Source Focus Optics
Collector Optics Photodetector O O Electronics Consider two small particles entering the light beam. They both scatter light at the same time. This coincident scattering results in a scatter equal to a larger particle. Hence coincidence will count small particles as a larger particle but at t lower concentration. Coincidence is common at higher concentrations. The cure is to dilute the sample.

129 Small Particle Detection
Scattering intensity is very small Common Solutions Increase intensity of light Change light source wavelength New techniques?

130 Small Particle Detection
Increase Intensity Improves signal from particles Increases noise from air molecules Reduce the wavelength Shifts the curves to smaller sizes Increases noise from molecules Reduce the viewing volume There are many ways to reduce noise, both electronic and physical. Reducing the viewing volume is the easiest; however, the sample volume is critical in single particle sensing!

131 Condensation Nucleus Counter
Filtration: Theory, Design & Practice I 21 Feb 2002 Condensation Nucleus Counter Condensation Nucleii Saturator Vapor Particles are introduced into an environment with saturated vapor, typically alcohol, although there are models using H20 and other liquids. The vapor condenses on the aerosol much like cloud seeding in artificial rain These droplets grow in the condenser to larger sizes and are detected by traditional light scattering. Since artificial clouds or drops are created around particles, particles as small as 0.03 µm can be detected. However, the formation of drops around particles makes it impossible to determine the original size. Aerosol Alcohol ATI Technical School

132 Single Particle Sensors Summary
Most optical measurements are in the MIE regime Single particle counting requires known volume of sampled air Same as counting events; precision depends on total counts – long sample times at low counts Problems of coincidence at high concentrations Non unique response and low signal to noise ratio at small sizes Small sizes handled by using smaller wavelengths or proprietary methods

133 Photometer vs. Particle Counter vs. CNC
Measures Total Aerosol Response Linear With Total Aerosol Volume Requires Known Aerosol And Relatively High Concentration Problems: No Particle Size Information Requires High Concentrations

134 Photometer vs. Particle Counter vs. CNC
Particle Counter (Laser) Detects and sizes particles Counts by size Measures down to 0.1 μm Can use any aerosol Problems: Assumes everything measured is a PSL Multi Valued Response Coincidence Problems at small particle sizes Long sample times to obtain a statistically valid results

135 Photometer vs. Particle Counter vs. CNC
Particle detector only Can measure less than 0.05 μm Problems: Requires mono-dispersed aerosol Counts all particles, noise at bottom end Long sample times to obtain a statistically valid results

136 Discussion

137 Aerosols and Aerosol Generators

138 What is a Standard? A KNOWN and Universally Accepted value of a physical property or quantity Meter for measure of length ◦C for Temperature

139 Why are Standards Necessary?
They establish accuracy of measuring instruments Calibrate the accuracy of instruments in use Temperature Scales Flow Meters Photometers Particle Counters

140 How Does this Affect Aerosols?
A Standard Aerosol has KNOWN properties Particle Size and Distribution Concentration Shape (usually spherical) Chemistry (inert) And Refractive Index in our business Quite often it is an instruments response to Concentration which we are calibrating. Mass for photometers and counts for particle counters. Care must be taken when diluting particles as particles can behave differently than gases and losses can skew readings and data. For sub micron particles, we are fortunate that this is not much of a problem unless there are charging issues at play or non typical factors at play. There are always nuances that must be considered.

141 Aerosol Standards Mono-disperse Aerosol Near Mono-disperse Aerosol
‘Single’ size particles σg ≤ 1.4 Instrument Calibration for PCs Research & Development Near Mono-disperse Aerosol Narrow distribution 1.4 < σg ≤ 1.6 Some Production QC Level of accuracy Poly-disperse Aerosol Broad distribution 1.6 < σg Industrial measurements Instrument verification Some instrument calibrations ATI uses both near mono-disperse and poly disperse aerosols. Since Photometers respond to the total mass of the aerosol, poly-disperse is not a big problem and, in fact, provides a more stable result.

142 Mono vs Poly Disperse Mono disperse has a sharp peak and narrow spread

143 Mono vs Poly Disperse Poly-disperse aerosol has a large σg typically > 2. Flatter peak and much broader spread.

144 Implication on Size Dispersion
For a log normal distribution 95% of the particles are between Mean σg2 σg2 & Mean

145 Implication on Size Dispersion
An aerosol with mean of 0.3um σg = 1.2 95% of particles are between 0.21 & 0.43um σg = 2.0 95% of particles are between and 1.2um

146 Mono vs Poly Disperse

147 Three Types of Aerosol Mono-disperse: σg ≤ 1.4
Near Mono-disperse: 1.4 < σg ≤ 1.6 Poly-disperse: 1.6 < σg There is no hard fast definition that is accepted in industry; however, from an application perspective and reviewing various global filter testing standards, this schedule tends to hold true.

148 Typical Poly-Disperse Aerosol Standards
Laskin Nozzle Wright Nebulizer Pneumatic Nebulizer Condensation Generators Spinning Disk Exploding Wire Standard Dusts

149 Laskin Nozzle Air Aerosol Entrained Liquid
The air jet bubbling through the liquid also entrains liquid and adds to the mass of the aerosol output as well as affect the mean size of the aerosol.

150 Laskin Nozzle

151 Laskin Nozzle

152 Laskin Nozzle Concentration Calculations
Output of Laskin Nozzle is defined: By # 20 PSIG Concentration = # Nozzles x 13,500 Total Flow (cfm) By # Jets at 20 PSIG Concentration = # Nozzles x 3,375 *Note: there are 4 jets in a standard Laskin Nozzle A Laskin Nozzle was selected by the Naval Research Laboratory as its output is mostly sub-micrometer and the aerosol size/distribution and concentration was very repeatable and reproducable.

153 Laskin Nozzle Concentration Calculations
You can calculate the system concentration, if you know: System Air Volume (CFM) Number of Laskin Nozzles/Jets at 20 PSIG You can calculate the number of nozzles/Jets, if you know: Desired system concentration

154 Wright Nebulizer The common aerosol can is similar to this type of nebulizer, except the compressed air/gas is inside the can and is released when the spray button is depressed. This is also the type of aerosol generator used for inhalers.

155 Pneumatic Nebulizer Compressed Air Aerosol Liquid
The high speed jet bubbling through the liquid creates the bubbles in the liquid that generate the particles at the surface. Very similar to water splashing in a boiling liquid. The small particles or droplets are entrained in the air and carried out. The large droplets fall back into the liquid. Liquid

156 Thermal Condensation Aerosol Generators
O 0 O o 0 Quench Air Vapor Aerosol Liquid Compressed Gas Heater The quench air condenses the vapor into drops. The quench air rate and temperature can have an impact on particle size/distribution. Quench Air

157 Thermal Aerosol Generator
Polydispersed Produces a greater level of aerosol concentration than pneumatic type nozzle Applications include higher flow systems Median particle size is smaller than pneumatic generation Output concentration cannot be calculated as output is variable Size and distribution shift with concentration

158 Ultrasonic Nebulizer Similar to the Pneumatic (Wright) Nebulizer except the agitation to produce the drops is created by a vibrating crystal at an ultrasonic frequency.

159 Spinning Disk Particle Generator
Size and concentration of the aerosol can be controlled by the liquid feed rate and the rpm of the spinning disk.

160 Exploding Wire The exploding wire generator works much like a spark plug in a car, except that the electrode disintegrates by the discharge of the capacitor. The vapors condense to form the aerosol. Rather exciting, but not very practical and not commonly used.

161 Test Dusts Standard Dust (Arizona Road Dust) Mainly Silica with
Mass Mean Diameter of 7 µm σg of 3.6 Specific Gravity of 2.7 Originally collected from Arizona Desert

162 Test Dusts ASHRAE Custom blend of:
72% ISO , A2 Fine Test Dust, 23% powdered carbon 5% milled cotton linters Attempt to simulate natural dust for HVAC

163 Test Dusts SAE Dusts – automotive filter testing Fine Coarse
Mass Median Diameter ~ 25µm No particles > 100µm Coarse Mass Median Diameter ~ 60µm 10%+ may be larger than 100µm

164 Common Mono-disperse Aerosol Standards
Poly Styrene Latex (PSL) Vibrating Orifice Electrostatic Classification Condensation Techniques

165 PSL Aerosols NIST Traceable PSL Particles Examples Methodology
Atomize PSL in Liquid (water) Evaporate the liquid NIST Traceable PSL Aerosol PSL Aerosol is the ONLY NIST traceable standard particle size

166 PSL Aerosols PSL is always atomized from a suspension in water or other liquid. The water is removed in the heater/dryer leaving PSL particles.

167 Residue & PSL Aerosols Impurities in water become small particles
These particles can be counted as particles in standard aerosol, especially by a CNC It is always a good practice to use clean water that has been filtered and distilled as the carrier.

168 Residue & PSL Aerosols Assuming a typical 2um atomizer droplet and 10 ppm purity water, Residue particle size can be computed 10 x 10-6 = (residue dia/drop dia)3 Residue Diameter = 0.04um Residue particles are especially a problem when generating small PSL sizes. The residue is not much of a problem when using particle counters since they are not sensitive to such small particles. It becomes a big problem when using CNCs.

169 Residue Particles There can be more residue particles than those of interest; however, they are extremely small and their respective mass will be very small as well.

170 PSL Aerosols Common for Cleanroom Applications
NIST traceable PSLs are expensive PSLs are easy to aerosolize, but output concentration is variable Limited by residue at small sizes Not available in large sizes PSL gives excellent optical response Used as calibration aerosol for particle counters

171 Electric Mobility Classification
Electric Mobility Classification exploits the physics of how movement of charged particles is affected in an electric field. The particle moves right with the fluid flow and down due to the electric field. Only a small fraction of particles with the predetermined electric mobility will arrive at the opening and get collected. For a given flow rate and electric field, the mobility range is determined by the width of the slit and the width of the aerosol flow. As shown, the upper mobility (or smaller particle size) is defined by the particle at the out edge of the air flow which enters at the upstream edge of the opening/slit. Likewise, the upper end of the particle size is defined by the particle at the inner edge of the flow which just enters the opening at the downstream edge. The aerosol extracted from the opening has a narrow and predetermined mobility range and will be mono-disperse.

172 Points to Remember Standards are required to verify and calibrate instruments and devices A Standard aerosol can be either poly or mono disperse R&D standards are more precise and are for laboratory use Industrial standards are easier to produce and are widely used

173 Points to Remember cont’d.
Poly-disperse aerosols are commonly generated by atomization, nebulization or mechanical means Only a few techniques are available to generate very tight, mono-disperse aerosols NIST traceable PSLs are generated in small quantities and are very expensive PSL concentration output is variable Residue particles can be a problem in small sizes

174 Discussion

175 Photometer Testing Standards & Practices

176 What is a “Filter” Testing Standard?
A DOCUMENTED and Universally Accepted method of obtaining a Qualitative Performance Measurement

177 Why are Standards Necessary?
They establish consistent methodology Provide a guide for understanding and compensating for variables encountered during practical application

178 How Does this Affect Filter Testing?
A Test Standard defines methods and limits Aerosol characteristics System Operating Conditions Testing protocols Allowable Challenge Concentrations Sampling Rate Maximum “Allowable” Leakage Scanning Speed

179 Standards & Recommended Practices Organizations
AACC (American Association for Contamination Control) ISO (International Organization for Standardization) BNL (Brookhaven National Laboratory) ASTM (American Society for Testing and Materials) EN (European Norm) IEST (Institute of Environmental Science & Technology) ANSI (American National Standards Institute) ASME (American Society of Mechanical Engineers) DOE (Department of Energy)

180 Filter Testing Standards
CS-IT (1968) Standard for HEPA filters CS-2T (1968) Standard for Laminar Flow Clean Air Devices - Installation Leak Test (filter and gaskets) CS-2T (1968) Standard for Laminar Flow Clean Air Devices - Induction Leak Test (seams and joints) (2005) Cleanrooms & Associated Environments, Annex B- Test Methods (Informative) IH62300 (2001) In-Place HEPA Filter testing, Section 6.2 Equipment EN High Efficiency Air Filters (HEPA & ULPA)-Part 2: Aerosol Production, Measuring Equipment, Particle Counting Statistics IES-RP-CC001 HEPA & ULPA Filters IES-RP-CC006 Testing Cleanrooms IES-RP-CC007 Testing ULPA Filters IES-RP-CC034 HEPA & ULPA Filter Leak Tests Fed Std 209E (1992 by IEST) Most referenced in “Filter” industry was replaced by ISO & 2 in November 2001 NSF 49:2008 (Annex A:2008) Biosafety Cabinetry: Design, Construction, Performance & Field Certification-Performance Tests NSF 49:2008 (Annex F:2008) Biosafety Cabinetry: Design, Construction, Performance & Field Certification-Field Tests ASME N509 (2008) Nuclear Power Plant Air-Cleaning Units & Components) N510 (2007) Testing of Nuclear Air Treatment Systems N511 (2007) In-Service Testing of Nuclear Air Treatment Heating, Ventilating and Air-Conditioning Systems DOE-HDBK-1169, DOE Handbook Nuclear Air Cleaning Handbook, Section In-Place Testing

181 Industries Using Photometry
Pharmaceutical Non-pharmaceutical Civilian Nuclear Power Military Nuclear Weapons Chemical Weapons Biological Weapons

182 Photometer vs. Discrete Particle Counter
1968 CS-1T Standard for HEPA Filters Photometer Upstream challenge aerosol must be at least 27ug/l Maximum Leakage = 0.01% Scanning rate = 2 inches per 1 inch from filter face Particle Counter No defined method

183 Photometer vs. Discrete Particle Counter
1968 CS-2T Standard for Laminar Flow Clean Air Devices Installation Leak Test (for filter & gaskets) Photometer Upstream challenge aerosol must be at least 27ug/l Maximum Leakage = 0.01% Scanning rate = 2 inches per 1 inch from filter face Particle Counter No defined method

184 Photometer vs. Discrete Particle Counter
1968 CS-2T Standard for Laminar Flow Clean Air Devices Induction Leak Test (for seams & joints) Photometer Ambient aerosol must be at least 10 E3 above FF Maximum Leakage = >FF Scanning rate = 2 inches per 1 inch from joint or seam within clean zone Particle Counter Ambient aerosol must be >300K particles/ft3 Maximum leakage >100 counts Scanning rate = 2 inches per 1 inch from joint or seam within clean zone

185 Photometer vs. Discrete Particle Counter
2005 ISO Cleanrooms & associated controlled environments, Test methods Installed Filter System Leakage Photometer Upstream challenge aerosol of between 20 & 80ug/l Maximum Leakage = 0.01% Scanning rate = 2 inches per 1 inch from filter face Limitations Efficiency < MPPS Oil aerosols allowed Ability to achieve required concentrations Particle Counter Upstream challenge aerosol (Too much detail to list 6 pages) sufficiently high that Np >2 & <10 Maximum leakage = 0.01% Scanning rate ≤ 3.14 inches per second (varies depending on probe dimensions, Np, sample rate

186 Photometer vs. Discrete Particle Counter
2005 ISO Cleanrooms & associated controlled environments, Test methods Containment Test Photometer Upstream challenge aerosol of between 20 & 80 ug/l Maximum Leakage = 0.01% Scanning rate ≤ 2 inches per second at 2 inches from joint, seal or mating surfaces Limitations Efficiency < MPPS Oil aerosols allowed Ability to achieve required concentrations Particle Counter The greater of: ambient count X E103 > 3.5 E106 particles/m3 Maximum leakage = ≤ ambient count X E10-2 Scanning rate ≤ 2 inches per second at 2 inches from joint, seal or mating surfaces

187 Photometer vs. Discrete Particle Counter
2001 IH62300:2001 In-Place HEPA Filter testing Photometer Upstream challenge aerosol 104 greater than ambient Maximum Leakage = 0.03% Duct measurement-No scan Particle Counter No defined method

188 Photometer vs. Discrete Particle Counter
IEST-RP-CC006 Testing Cleanrooms Photometer Upstream challenge aerosol of between 10 to 20 ug/l Maximum Leakage = 0.01% Scanning rate = 2 inches per 1 inch from filter face Particle Counter 3 x E108 particle size of interest (10 counts per Appendix B, Exp. 1) Maximum Leakage = 0.01% Scanning rate = [(Cc)(Ls)(Fs)(Dp)]÷ [(60)(Np)] Result in or inches per second (Appendix B, Exp. 1)

189 Photometer vs. Discrete Particle Counter
IEST-RP-CC034 HEPA & ULPA Filter Leak Tests Photometer Upstream challenge aerosol of between 10 to 90 ug/l Maximum Leakage = 0.01% Scanning rate = 2 inches per 1 inch from filter face Particle Counter 2.8 x E108 particle size of interest (10 counts per Appendix G, Exp. 1) Maximum Leakage = 0.01% Scanning rate = [(2.8)(108)÷1000][(0.0001) (28.3)(1.25)÷(60)(10)] Result = in or 0.5 in/sec (Appendix G, Exp. 1)

190 Photometer vs. Discrete Particle Counter
2008 NSF 49 Biosafety Cabinetry Photometer Upstream challenge aerosol of at least 10 ug/l Maximum Leakage = 0.01% Scanning rate = 2 inches per 1 inch from filter face Particle Counter No defined method

191 Points to Remember! Photometer & particle counter results are not likely to correlate due to the different weighting of the technology used. Photometry response is mass weighted while particle response is number weighted. Filter testing process is the same regardless of photometer or particle counter use. Measure upstream challenge Measure downstream penetration by scanning or point sampling Calculate penetration

192 Points to Remember! Filter testing process complexity varies between photometers and particle counters. Challenge concentration Photometers: Variable range of ug/l with ug/l being typical (Std defined) Particle counters: Variable range of 3.0 E105 to 3.0 E108 (Std defined, calculated to achieve desired Np) Measure Downstream Photometers : 0.01% leakage maximum while scanning rate of 2 inches /second in most cases (Std defined) Particle counter: 0.01% leakage maximum in most cases while scanning at a calculated, statistically, determined rate (Std defined) Particle counter challenge requires diluter to prevent coincidence error/optics saturation

193 Points to Remember! Calculate Penetration
Photometer: Ratio of upstream challenge to downstream expressed as a percent Particle counter: Ratio of upstream challenge to downstream expressed as a percent

194 Points to Remember! Each technology has design strengths and weaknesses which decide where its use is “reasonable” in filter leakage testing. Photometer Aerosol generator for upstream challenge “oil” aerosol No diluter necessary for Upstream measurements Consistent & essentially “Calculation Free” test method Limited to systems with efficiencies ≤99.997% Typically consistent results among multiple units Robust “core” technology Particle counter Aerosol generator required in most cases, but at a lower output Use of solid or liquid aerosol possible Ability to test systems to % efficiency Diluter required for upstream sampling Unit to unit result consistency difficult to achieve More sensitive detection system results in less-robust instrument Diluter adds additional errors to measurement

195 Discussion

196 Hands On Demo: Photometer Filter Leak Scanning

197 Review and Discussion

198 David W. Crosby Tim McDiarmid Don Largent
Your logo here. Important: Logo only on FIRST and LAST slides. Thank you David W. Crosby Tim McDiarmid Don Largent


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