faq hepas and ulpas

8/9/2019 FAQ HEPAs and ULPAs

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What is the recommended finalpressure drop for a terminal andair handling unit (AHU) or Exhaustmounted HEPA to be changed?

The ‘rule of thumb’ in our industryhas been double the initial assuming

‘normal’ design airflows. For example,a Camfil Farr Megalam® panel appliedin a terminal filter housing or plenumwill have a clean pressure drop ofapproximately 100 Pa or 0.4” w.g.at 0.45 M/s or 90 fpm. Doubling thepressure drop as a change target to200 Pa or 0.8” w.g. is reasonable andprudent for filter performance andenergy use considerations. For an AHUmounted, exhaust, or Bag-in/Bag-out(BIBO) HEPA filter the clean pressuredrop is normally targeted at around 250

Pa or 1” w.g. using double the cleanpressure drop at 2.5 M/s or 500 fpmthen the change out point would be 500Pa or 2” w.g. respectively. Filter packdepth, filter efficiency and velocity canvary depending upon filter design so besure to consult with your nearest CamfilFarr office for technical assistance.

TECHNICAL

BULLETINFAQ: HEPA & ULPAAir Filters

This information pertains to HEPAfilters manufactured by Camfil Farronly. It should not be assumed that thisinformation is accurate for productsmanufactured by other companies.

What is the recommended shelf lifeof a HEPA Filter?

Camfil Farr agrees with therecommendations of Werner Berman in

Appendix C of the Nuclear Air CleaningHandbook, a 10 year shelf life. Thisassumes that filters are stored in theoriginal packaging, in a dry climatecontrolled area and not subjected toextremes in temperature or humidity.

How long will a HEPA Filter last?

Filter life depends upon the operatingconditions. A general recommendationis that, at minimum, the filter bereplaced when the pressure dropreaches two times the initial pressure

drop (assuming ‘normal’ designairflows).

HEPA filters that are not subject tohigh contaminant concentrations mayhave an indefinite life, dependingon the operating conditions.Generally speaking, 10 years is therecommended life. Camfil Farr hasexperience with HEPA filters that havebeen in operation in excess of 15 plusyears without problems. In Bio-Pharmaapplications, especially in ‘critical’

zones (Grade A space for example),we have seen certain major Pharmacompanies establishing a time periodand not pressure drop as the guidelinefor change. One guideline suggests fiveyears for the Grade A space and sevenyears for less critical spaces. Factorsthat may influence filter service live

include: volume of outdoor air filtered,volume of re-circulated air filtered,aerosol challenge exposure frequencyand duration, the total amount ofchallenge aerosol impingement onthe filter, the method of aerosolintroduction to the system and the filter

efficiency of pre filtration. The use ofcoarse fiber (i.e. charged syntheticmedia filters) as prefilters may shortenHEPA filter life due to prefilter drop inefficiency over time due to inherentcharge dissipation of the media. Wetfilters should be replaced as soonas possible and the conditions thatcaused the filter to become wet shouldbe corrected. Filters that are allowedto remain wet for 48-hours or morecould be subject to mold growthwithin the media. The constructioncomponents of the filter are inertto contaminant amplification. Filtersthat are allowed to dry after beingwet may have a higher pressure dropwhen compared to their pressure dropbefore they were wet.

Sofilair® and Megalam® Green panels are Camfil Farr’s latest HEPA filters that nowinclude plastic frames to adress sustainability.



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TECHNICAL BULLETIN

HEPA & ULPA Air Filters

What is the gel seal filter lifeexpectancy?

Both urethane and silicone gels are

acceptable for the Life SciencesIndustry applications. When using Gelwe recommend a specific grade ofSilicone gel, it is recommended forLife Science industry applications.Undisturbed gel will last the life ofthe filter. Camfil Farr has carried outmultiple studies how the commondecon and cleaning agents such asVHP, Formaldehyde, Chlorine Dioxide,Spor-Klenz & Vaprox etc has affectedurethane & silicone gel. Historically,some HEPA filter manufacturers used

certain formulations of silicone gelthat, over time, can break down in thefield. Detailed reports are available onrequest. Specifying the correct type ofgel is as critical as the filter efficiencyand pressure drop requirements.

What aerosol should I use whentesting HEPA Filters?

Polystyrene latex spheres (PSL) aremost commonly used in microelectronicapplications, PAO in Life Sciences.

Related definitions; Aerosol: a gaseoussuspension of fine solid or liquidparticles. Challenge Aerosol: an aerosolderived from the selected sourcematerial and used as the leak testchallenge for filter medium testing.

Aerosol Generation Methods

Laskin Nozzle Generator - (‘cold PAO’)(average 0.5-0.7 micron)

Thermal Generator - (‘hot PAO’)(average particle between the MPPSrange)

Ultrasonic Generator - ( PSL)

Measuring Equipment

Photometer or discrete particle counter(DPC) dilution system is required whentesting with an oil based aerosol.

Aerosol Concentrations

10-20 mg/m3 - (IEST-RP-CC034)

10-100 mg/m3 - (ISO-14644-3)What is the correct definition of aHEPA or an ULPA Filter?

HEPA - 99.97 efficiency at 0.3 micron

ULPA - 99.999 efficiency at 0.12micron

What is MPPS?

MPPS; Most Penetrating Particle Size.

MPPS is ‘typically’ between 0.1 and 0.2micron. It will vary with velocity but at‘normal’ design for a terminal filter thisrange is accurate 80% of the time witha H14 filter at 90 fpm/0.45m/s it is0.17/0.18 micron. The MPPS is alwaysidentified in Camfil Farr’s factory scantest and noted on the HEPA filter label.

What is the correct Filter Efficiencyto select?

H14 in accordance with EN1822(leakage factor should be 0.008%) toavoid ‘bleed-through’

Type K in accordance with IEST RP-CC-034

ISO 45 E in accordance with ISO 29463

What is bleed-through?

Filter ‘failure’ or bleed-through’ (aterm adopted in the USA), has beenattributed to a number of factors.

The ’failure’ of HEPA filters cansometimes be attributed to theselection of the wrong filter efficiency,type & concentration of the selectedaerosol, how it is generated (hot orcold), excessive filter velocities anda misunderstanding of calculatedupstream concentrations. An article onbleed-through is available upon requestas well as a HEPA specification writtento the latest international industryrequirements.

Challenge Aerosols Frequently Used for HEPA Testing

DEHS (DOS), a liquid Di-ethyl hexyl sebacarte

DOP, liquid Di-octyl phthalate

Emery 3004, liquid Product name for a type of PAO

PAO, liquid Poly-alpha olefn

PSL Poly-styrene latex spheres

Shell Ondina EL, liquid Refned mineral oil

Total Finaveston A80B, liquid Refned mineral oil

The Photometer is normally used forin-situ scan testing of HEPA filters.

Typical aerosol generation equipmentused in the field.



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TECHNICAL BULLETIN

HEPA & ULPA Air Filters

What is a leak?

A leak is local, but efficiency is global! Aleak is generally 5-10 times the average

penetration at a specific local point.Local Leak is = 0.01% of penetration.

Global (also known as Overall orVolumetric test) is 0.01% (0.005% isutilized by some end users when testingwith photometers).

Five times MPPS is the volumetricacceptance criteria when testing with adiscrete particle counter.

What is the difference betweenlocal and global (overall or

volumetric) efficiency? Efficiency is the measure of the entirefilter product and is the average ofvariations in the performance of themedia.

The local leak is the measurementunder a probe (scan head) that scansfor the possible defects, not localvariations.

What standard(s) should I followwhen testing HEPA filters?

IEST RP-CC-001 HEPA and ULPA Filters

IEST RP-CC-034 HEPA and ULPA FilterLeak Tests

ISO 14644 Part 3 Test Methods

EN1822 PART 5

Cross references charts and cleanroomstandards publications by Camfil Farrare available upon request. (LifeSciences Industry Insights andCREO publications)

Should I use a gasket seal or a gel

seal on a HEPA filter? In general, the United States hasused gel, Europe/Asia have usedgaskets for Life Sciences applications.Microelectronics is about a 50/50 splitglobally depending upon the design(fan filter units (FFU), recirculating units,etc.). It has been common in the past

for gel to be poured into the ceiling gridand to use a top-load knife-edge filter.Today, it is more common to have abottom-load gel seal filter. Gasket sealis most common for FFU applications.

Like gel, there are different gaskettechnologies. Camfil introduced the ‘onepiece’ seamless poured-in-place gasketthat minimizes potential corner leaks

that are typical with traditional neoprene‘dove-tail corner’ type gaskets. Gasketsneed more study, like we have donewith gel, on common cleaning anddecon agents but the technology isproven when applied correctly.

Housing ‘planarity’ tests should bestandard when employing a gasket.Consideration to the filter clampingsystem is equally important for a solidfilter to housing seal.

A note to remember when selecting

filters and housings.........’The filter sealis only as good as the housing/grid into which it is installed’. We can havethe most studied gel/gasket seal andtested HEPA filter, but if the housing orclamping system has a flawed design,the ‘filters will leak' and the system willbe compromised.

What is the temperature limit of thegel material?

USA Silicone Gel: Useful temperaturerange -58º to 400º F (-50º to 204º C).

Europe / Asia Silicone Gel: Usefultemperature range -40º to 392º F (-40ºto 200º C).

Global – Polyurethane Gel: Usefultemperature range -9º to 150º F (-23ºto 65º C).

Does PAO affect gel performance?

The simple answer is ”no”. Manystudies by Camfil and significant endusers have been presented at globalorganizational meeting including ISPE,NEBB, IEST and other industry forums.Additional support information isavailable upon request.

Is there a recommended practicefor mixing and pouring gel in the

field and in the factory? Camfil has specific computer-optimizedcontrols implemented with productionmixing and pouring equipmentutilized to dispense gel in our plant.Temperature and humidity is controlledprecisely. Guidelines for field installationare available upon request.

Useful technical guides recently published by Camfil Farr available from www.camfilfarr.com

faq hepas and ulpas

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