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No Cell Phones Please

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Cleanroom Filters:Design , Testing, Standards

Sheesh Gulati, MeasureTest

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HEPA FILTERS• The HEPA acronym is from ‘High Efficiency

Particulate Air Filter’, used in earlier US military

specifications

• The Institute of Environmental Sciences (IES) defines a HEPA filter as "a throw-away extended-media dry-type filter in a rigid frame, having minimum particle-collection efficiency of 99.97% for 0.3 micrometer (micron) thermally-generated dioctyl phthalate (DOP) particles or specified alternative aerosol, and a maximum clean-filter pressure drop of ... 1.0 in w.g. when tested at rated air flow capacity."

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HEPA FILTERS

What HEPA Filters can’t Do:

HEPA filters cannot remove contamination introduced downstream of the filter.

Repeat: No HEPA filter can reduce the amount of contamination introduced downstream of the filter.

– While this may seem inherently obvious, it is amazing how many times the excuse that “the HEPA filters will take care of it” is used!

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Filtration Mechanism and Theory

•PRESSURE DROP•SINGLE FIBRE EFFICIENCY•COLLECTION MECHANISMS

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In the Darcy Law regime,?P = KUµL?P = pressure dropK = Darcy Law constantU = approach velocity of fluid = face velocity, cm/sµ = viscosity, poise (g/cm –s)L = thickness of filter, cm

Pressure drop and fiber drag

?P = Fdlf =

Fd = specific fiber drag= drag force per unit fiber length

Darcy’s Law Governs Pressure Drop

FdSDf

1 cm

1 cm

?P

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DARCY’S LAW SIMPLIFIED

Delta P = KUi.e. Pressure Drop is proportional to Flow

It is a linear equationPressure Drop = Resistance to air flow

The resistance to air flow created by an air filter is an important consideration. The higher the resistance, the greater the energyrequired to overcome it. Consequently, all other considerations being equal, the filter with the lowest resistance is preferred.

Single Fibre Efficiency = how many particles can a single fibre remove from air stream

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Pressure DropP

ress

ure

Dro

p

Linear Pressure Drop Inertial Velocity(Darcy Law) Regime Regime

CLEANROOM

HVAC

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EFFECT OF VELOCITY

• Resistance to air flow through a filter is similar to air flow through a porous structure and follows D’Arcy’s law. That is, the resistance to air flow varies linearly with velocity. Although as shown in figure, the linear relationship breaks down at higher flow rates, air flow velocities in a cleanroom filter is usually well within the linear regime.

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EFFECT OF VELOCITY

• The velocity of air flow through the media is the most critical design parameter that affects the performance of filters. Cleanroom filters typically operate at face velocities between 75 and 100 fpm. Thus, a typical 48 x 24 in cleanroom filter is designed to handle about 800 cfm, which is about half the operating velocities for HVAC filters. Reducing the velocity of air flow reduces the resistance linearly. However, the penetration through the media changes almost exponentially with velocity . A typical ULPA media that is 99.999% efficient at 8 ft/min for 0.15 µm particles is nearly 99.99999% efficient at 2.5 ft/min.

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PARTICLE REMOVAL MECHANISMS

• SIEVING

• INTERCEPTION

• INERTIAL IMPACTION

• DIFFUSION

ALL OF THEM COEXIST IN REAL WORLD FILTRATION

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PARTICLE CAPTURE MECHANISMS --Continued

• Sieving - usually taken care of by pre-filters not HEPA filters

• Inertial impaction - here the inertia effect (kinetic energy) imparted to the particle causes it to remain on a straight line or path instead of following the streamline flow round the media filaments. i.e.particle cannot go round fibre fast enough

• Diffusion = Brownian motion (random motion), when a particle does not follow any particular flow line, but diffuses across the flow line, thereby increasing the possibility of contacting a fibre

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PARTICLE REMOVAL MECHANISMS

• Interception is like an “accident” -- usually bigger particles between 1 and 5 microns. The particles tend to follow the streamline flow round the fibres, and as they pass very close to a fibre they are intercepted and remain on the fibre surface

• Electrostatic Deposition = if particle is charged, it gets attracted. Only relevant for some media, to achieve any permanent benefits from electrostatic effects, the media must remain dry. If moisture is present the charge leaks away.

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Particle Collection:Sieving

Fibers

Particle Flow

Favours larger particles

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Particle Collection Mechanisms: Interception

Less dependent on particle size, but favours larger particles

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Particle Collection Mechanisms: Interception

Less dependent on particle size, but favours larger particles

Design

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Particle Collection Mechanisms: Inertial Impaction

Favours larger particles

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Particle Collection Mechanisms:Inertial Impaction

Favours larger particles

Design

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Particle Collection: Diffusion

Favours smaller particles

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Particle Collection: Diffusion

Favors smaller particles

Design

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Particle Removal Mechanisms

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MPPS

• MPPS = Most Penetrating Particle Size

• Competing Filtration Mechanisms lead to MPPS (see next slide)

• MPPS is around 0.08 to 0.18 micron

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Figure illustrates the contribution to total filter efficiency from the components of diffusion and interception. These are computed as if each component were a separate filter. Since interception efficiency increases with increasing particle size while diffusion efficiency decreases, a minimum occurs near where the separate efficiency curves of diffusion and interception cross. This minimum efficiency defines the most penetrating particle size.

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FILTER DESIGN PARAMETERS

• Pressure Drop

• Velocity or Flow Rate

• MPPS (most penetrating particle size)

• Grade of Media

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HOW CAN YOU IMPROVE FILTER PERFORMANCE?

• The goal is to reduce velocity to gain Efficiency and reduce Pressure Drop

• You can do One of Two Things:– Choose alternate Media with better

performance

OR

– Add More Media (larger filter size/ deeper filter/more pleat density)

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Filter Test Methods• Efficiency Tests

– Go / No Go– Actual Efficiency– Particle Counter– CNC– Photometer

• Leak Test– Two flow Tests– Scan Test

• Particle Counter• CNC• Photometer

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Particle Counter vs. CNC vs. Photometer• Particle Counter

– Detects and sizes particles– Counts by size– Measures down to 0.1 µm– Can use any aerosol

• CNC– Particle detector only– Counts all particles– Can measure less than 0.05 µm– Requires monodispersed aerosol

• Photometer– Measures overall aerosol, not individual particles– Best for particles 0.3 µm and larger– Requires known aerosol and relatively high concentration

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What is a Leak?A gap or void in the medium, gaskets or framework of a filter, that allows unfiltered air to bypass the filter and enter the clean room or clean zoneLeak is a local measurement whereas efficiency is a global measurementEfficiency: ratio between concentration downstream of the filter compared to the upstream concentration

Filter leak is generally defined as

media/filter with 5-10 times more

penetration than through “good”

media/filter

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ON- SITE HEPA FILTER TESTING

Performed to verify that:

• 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

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Differences Between Leak and Efficiency Test

Leak Testing Efficiency Testing

Pinpoint Leaks Yes No

Determine % Penetration Yes Yes

Monodispersed No Yes

Polydispersed Yes No

Field Test Yes No

Hot DOP No Yes

Aerosol Photometer Yes Yes

Failure Limit 0.01% 0 .03%

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LEAK TESTING OF HEPA FILTERS

• Probing or scanning -- a method for disclosing leaks in HEPA or ULPA filters, whereby the inlet of the sampling probe of an aerosol photometer or discrete particle counter is moved in a series of parallel slightly overlapping strokes across the test area at a distance of approx. 2.5 cm (1 inch) from the filter face at a rate based on the leak penetration to be detected and the upstream concentration of the challenge aerosol

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LEAK PENETRATION

• Leak Penetration -- when using a photometer, it is the response when the probe is stationary over a leak, divided by the response upstream of the leak.

• When using a particle counter, it is the concentration of particles counted when the probe is stationary over a leak, divided by the concentration of particles that would be counted upstream in the same time, if the counter could sample upstream

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LEAK PENETRATION

• Measured leak penetration depends on the flow rate of the photometer or particle counter

• Standard leak penetration is the leak penetration that would be measured by a photometer or particle counter, with 28.3 l/min (1 cfm/min) sample flow rate

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PHOTOMETER FILTER SCAN TEST METHOD

Agreement between customer and supplier regarding specific test conditions should specify:

• The aerosol photometer to be used• The filter exit airflow velocity at which the leak test is

to be conducted. Unless otherwise specified it is 90 +-10 ft/min

• The challenge aerosol material and generation method. Unless otherwise specified it is aerosol generator with one or more Laskin nozzles operated at 20 lb/in2

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PHOTOMETER FILTER SCAN TEST METHOD

• For cleanrooms, the frequency and locations at which

the challenge concentration is verified

• The standard leak penetration of the designated leak.

Unless otherwise specified, it is 0.01%

• The maximum scan rate. Unless otherwise specified

the maximum scan rate when using a rectangular

probe should not be more than 10 ft/min (3

metres/min)

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STANDARDS -- ISO 14644-3

• Permits both particle counter and photometer for installed filter leakage tests

• Under C.1 the specifications of the particle counter are given as 0.1 to 5 microns. No mention of the flow rate

• Such a counter would cost approx. $ 18,000 I.e. twice the price of a photometer

• A suitable dilution system would also be required to avoid exceeding the concentration tolerance of the particle counter

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U.S. FDA RECOMMENDATIONS

• HEPA filter integrity testing should be performed twice a year for the aseptic processing room. Additional testing may be needed when air quality is not found acceptable, or as part of an investigation into media fill or drug product sterility failure

• DOP or PAO aerosol challenge may be used

• Concentration of aerosol should be 25 to 100 ug/litre of air

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U.S. FDA RECOMMENDATIONS

• Scanning should be conducted one or two

inches from face of filter

• Reading equal to 0.01% of the upstream

challenge should be considered a significant

leak

• Downstream side should be scanned with

photometer with sampling rate of 1 cfm

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IEST STANDARDS

Relevant Institute of Environmental Sciences & Technology USA Standards are:

• IEST-RP-CC006.2 Testing CleanroomsClause 6.2 HEPA & ULPA filter installation leak testsConcentration of 10 ug/L is stated to be adequate

• IEST-RP-CC001.3 HEPA and ULPA FiltersClause ( Testing). Table 1 -Recommended test and minimum rating for Filter types A through F is particularly important

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IEST STANDARDS

• IEST-RP-CC021.1 Testing HEPA and ULPA Filter MediaClause 4.2 HEPA Filter media penetration test is relevant

• IEST-RP-CC034.1 HEPA & ULPA Filter Leak TestsClause 5 Choice of Tests Table 1 - Guide for selecting appropriate leak testing strategies Table 2 (next slide) is important

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DESIGNATED LEAK SIZES FOR VARIOUS EFFICIENCIES OF FILTERS

Filter Type Efficiency at Particle Size

Standard Leak Penetration for Factory Tests

Standard Leak Penetration for Tests after installation

HEPA type A 99.97% 0.3 um Not normally scanned HEPA type C 99.99% 0.3 um 0.01 % 0.01 % HEPA type D 99.999% 0.3 um 0.01% 0.01% ULPA type F 99.999% 0.1 to 0.2

um 0.005% 0.005%

ULPA type F 99.9995% 0.1 to 0.2 um

0.0025% 0.0025%

ULPA type F 99.9999% 0.1 to 0.2 um

0.001% 0.002%

Super ULPA type G

99.9999% MPPS 0.001% 0.002%

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Common Standards:EN 1822

- Filter Tested At MPPS- Efficiency As Low As 85% rated as HEPA- Efficiency Measured Or Estimated From

Scanning- Leak Testing also at MPPS- Particle Counter And CNC Only, No

Photometers- European Standard

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CLASSIFICATION OF FILTERS TO EN 1822Filter Class Overall Value Local Value

Efficiency %

Penetration % Efficiency %

Penetration %

H 10 85 15 --- ---

H 11 95 5 ---- ----

H 12 99.5 0.5 ---- ----

H 13 99.95 0.05 99.75 0.25

H 14 99.995 0.005 99.975 0.025

U 15 99.9995 0.0005 99.9975 0.0025

U 16 99.99995 0.00005 99.99975 0.00025

U 17 99.999995 0.000005 99.9999 0.0001

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ASHRAE

• One Of The Oldest Test Standards• Aimed At HVAC Filters• Older Standard Based On Reduction In

Soiling And Ability To Remove Dust Loading

• New Revision Rates Filters On The Basis Of Particle Size Specific Efficiency

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ASHRAE 52.2

• Filter Efficiency Measured For Particles From 1.0 To 10 µM

• Measurements Made As Filter Is Loaded To Final Resistance

• Minimum Efficiency Rating Value (MERV) Determined As Minimum Of Measured Efficiency

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TOO MANY STANDARDS - THE RESULT

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Leak Testing with Particle Counters:Problems Testing Filter Systems with a Particle Counter

• Particle counters count the number of particles in a cubic foot of air. To do so accurately, a sample must be taken at a specific location for 1 minute. If a sample is taken for only 6 seconds (one-tenth of a minute), a '0' must be added to the total count, introducing a possible 10 % > error

• Particle counters will only give accurate counts up to approximately 300,000 particles per cubic foot per minute (or 30,000 particles per cubic foot in 6 seconds). Concentrations higher than this introduce large COINCIDENCE LOSS which leads to errors of 5-20%, depending on the aerosol concentration and the particle counter.

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Leak Testing with Particle Counters• From a practical standpoint (forgetting diluter error,

count error, etc.) and just calculating scanning time, a filtration test system using particle counters becomes unwieldy. Using an isokinetic probe, per IEST Standards, sampling at 1 cfm and with an opening of 3" x 0.5", it would take 384 readings (counts) at 6 seconds each= 38.4 hours to scan a 24" x 24" HEPA filter.

• Remember, in addition, a 10 - 20% error rate due to extrapolating what the particle count would be for a full minute by multiplying the count obtained in just 6 seconds by 10.

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LEAK TESTING WITH PARTICLE COUNTERS

• A particle counter counts the number of particles passing through its viewing area. Most particle counters don't pass the entire 1 cfm sample through the viewing area but only a portion which introduces more room for error.

• Knowing the sample flow rate (1 cfm) and the duration of sample time (1 minute), it can be determined how many particles were in that one cubic foot sampled for one minute. This is what they were designed to do, and as such, make an excellent monitor for clean or sterile areas.

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Leak Testing with Particle Counters

• An aerosol photometer is a true ratio detector since it measures particles "en masse" and all of the particles travel through its viewing or detection area. ATI photometers are capable of measuring concentrations of particles as high as 600 micrograms per litre and are sensitive enough to measure accurately and instantaneously concentrations down to 0.00001 micrograms per litre.

• Using an ATI photometer, the same 24" x 24" HEPA filter can be scanned in accordance with IEST and other Standards in 1.6 minutes. If there is any area that has leakage > .01%, it can be pinpointed in seconds.

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RECOMMENDED LEAK TESTS FOR DIFFERENT APPLICATIONS

• HEPA FILTERS TYPES C&D Photometer Scanning.

• ULPA FILTERS TYPE F Both photometer and counter

• ULPA FILTER OVER 5 9s

AND SUPER ULPA FILTERS Particle Counter

• DIRTIER THAN CLASS 100 Photometer Scanning. Particle

Counter not recommended. • CLEANER THAN CLASS 100 Photometer or Particle Counter

scanning. • MICRO-ELECTRONICS Particle Counter scanning as no oil

aerosol can be used. PSL (PolystyreneLatex Spheres) aerosol preferred

• PHARMACEUTICAL Photometer preferred practice. Particle Counter scan only ifacceptable to user and FDA

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Filter Testing Instruments

PHOTOMETERSAND

AEROSOLGENERATORS

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Mono vs. Polydispersed Aerosol

Monodispersed Polydispersed

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Aerosol Generator

• Oil-based aerosols (DOP/PAO)

• Types–Laskin nozzles

–Thermal Poly Generator

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Laskin Nozzle Generator

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AEROSOL OUTPUT VS. LIQUID LEVELS

Generator Liquid Level

Gravimetric concentration ug/L

Photometric Concentration %

0.5 inch 99.3 99

0.75 inch 98.6 98

1.00 inch 102 100

1.25 inch 96.3 98

1.75 inch 93.2 99

Conclusion: Liquid level does not significantly affect the concentration output of the generator

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Aerosol Output - DOP & Substitute Liquids

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DOP AND SUBSTITUTE LIQUIDS

• Different substitute liquids give concentrations that vary over a wide range

• Photometric reaction to various substitute liquids does not seem to correspond to their gravimetric concentrations

• Corn oil most difficult substitute liquid to work with as it tends to gel

• Correction factors should be applied when using substitute liquids

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Laskin Nozzle Generator

DOP output of Laskin Nozzle• The aerosol concentration depends upon the

compressed air pressure and flow available for consumption by the nozzle. With 20 psi applied, each jet emits 18.75 lpm of air containing 1275 ug/l of aerosol. When this aerosol is diluted with 135 cfm of air, the concentration becomes approx.100 ug/litre.

• The equation below is for calculating the aerosol output in ug/l when 20 psi is applied toi the nozzles:

13,500 times the number of nozzles being used/ total airflow in cfm

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Thermal Aerosol Generator

• Thermally generated aerosol is an aerosol generated by

quenching (condensing) vapour that has been evaporated from

liquid DOP by heat. The aerosol has a light scattering mean

dia.of approx.0.3 micron with a geometric standard deviation of

1.4

• Produces a higher concentration level of aerosol than Laskin

nozzle

• Applications include higher flow systems

• Different distribution than Laskin Nozzle

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Thermal Aerosol Generator

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Aerosol Output Range: 500-65,000 cfm

Aerosol Concentration 100 ugm/l @ 6,500 cfm

10 ugm/l @ 65,000 cfm

Generator Type: Heated Chamber

Compressed Gas (inert)* 20 cfh @ 50 psi

Aerosol: 0.2UM CMD

Compact foot print: 14" L × 10" W × 10" H

Weight-20 lbs.

Power Supply: 110 VAC / 60 Hz or 220 VAC / 50hz

THERMAL AEROSOL GENERATOR

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Concentration Calculations• You must know the Air Volume (CFM)

• Q = AV i.e.Quantity in cfm = Area in sq.ft. x Velocity in fpm

FORMULA;

No. of Nozzles x 135 divided by CFM x 100 = Concentration in ugm/L

Example: Total air flow is 1200 cfm and we have enough air to operate

3 Laskin nozzles @ 20 psig

3 x 135/1200 =.3375 x 100 = 33.75

Answer is 34 micrograms/litre

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AEROSOL PHOTOMETERSAerosol photometer is an instrument that measures mass concentrations of aerosols by using the forward light scattering principle.At a minimum, the instrument is capable of measuring concentrations of up to 100 mg/m3 and has a threshold sensitivity capable of measuring 1ug/m3

The way it operates is to generate a cone of light from the illuminating side.That is why the scattering chamber is in theshape of two cones connected by their points.

The cone on the illuminating side converges at the point, where the sample is detected.

The cone of light on the collection side expands, with a dark spot in the centre. That is what is shown as the Focal Spot.

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How Aerosol Photometer works

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PHOTOMETER

• Total scattered light is detected by

photomultiplier tube

• Gives Total Concentration only

• Does not measure individual

particles

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Model TDA-2H AEROSOL PHOTOMETER

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Photometer Features• Down stream, Up stream, Clear Valve

• Auto-ranging , 4 digits of accuracy

• Easy to set zero and 100%

–compensates for sensor contamination

• % penetration (Leak Rate)

• Internal reference

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New features of the 2HVisible Improvements:• Airflow monitoring with LED indicator• Optics monitoring with LED indicator• New improved case• Pump exhaust filter

“Behind the Scenes” Improvements:• Improved maintenance & calibration

procedure• “Refactored” firmware for upgradeability• High concentration override

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Optics LED

• A baseline reading of phototube response is measured and stored at the time of manufacture

• Optics light is set as follows:– Within 10% ………………. Green Light– Within 20% ………………. Yellow Light– More than 20% ………….. Red Light

What does this mean?• When the “Optics” light is red, the internal

reference is not reliable.• Unit may still be operated and data can still be

collected.

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Flow LED

• Most standards require the photometer sample flow to be 28.3 lpm ± 10%.

• Flow light is set as follows:– Within 5% ………………. Green Light– Within 10% ………………. Yellow Light– More than 10% ………….. Red Light

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High Concentration Override

• Feature allows operator to test filtration systems using aerosol challenges greater than 130ug/l (not recommended) if required without getting E1 Error display.

New Feature:

• Unit will now keep its INT-REF setting when power is turned off. This allows operator to move unit to another area of a cleanroom without performing the INT-REF operation again.

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DAS SoftwareData Acquisition System

• Real-time Data Acquisition.• Real-time Statistical Information.• Easy To Use File Organization Scheme.• Ability To Create Graphs, Written Notes,

Drawings, And Voice Recordings*.• Data Is Write Protected, Thereby

discouraging The Unethical Manipulation Of data.

* Voice recordings only available on some models of Pocket PC.

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DAS Flavours

Das 1:• Pocket PC Version.• Highly Portable.

Das 2:• Desktop / Laptop PC Version.• Convenient For Permanent And Semi-permanent

Setups.

Upstream Aerosol Concentration Measurement Procedure

Challenge is introduced upstream of the HEPA filter.

Aerosol

Airflow

To Photometer

A good mixture is assured calibration of photometer is made to read 100%.

Filter Scanning

• Photometer is set to a scale which will read <0.01% of the upstream concentration.

• The entire filter face and gasket seal are scanned at 2 inches per second to detect any bypass or pinhole leaks.

• Scan 1 inch from filter face.

To Photometer

Filter Locations

A layout drawing showing the location of HEPA filters along with some kind of identification is necessary.

F

E

11

8

7 6 54

3

21

4 3

21

12

VIAL

FILLING

1/47

N

It is important to show where leaks (if any) were found.

Upstream AerosolConcentration 26µg/lFinal Penetration <0.01%Sq. In. Medium 968Sq. In. Repairs 16Percent Repairs 1.7%Acceptance Met? Yes

Reporting

HEPA # 68

xxxxxx = Media Leak Detected

wwww = Gasket Leak Detected

xxxxxx = Leak Repaired

xxxxxx = Leak Unrepairable

.08% = Leak Rate Before Repair

N

HEPA # 67

xxxxx

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No need to jump --this talk is over !!