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Particulate Filtration

The Air We Breathe

Air is a mixture of gases composed of approximately 21% oxygen, 78% nitrogen, 1% argon, and traces of other gases. The air we breathe also includes particulate material and gases generated by nature, by man, and by industrial processes as seen in the Figure. We are concerned with the particulate matter and gases which influence our health or comfort, which damage the spaces we occupy, or which effect the products or components we are manufacturing 


a) Vartable gases, water vapor, carbon dioxide, methane, carbon monoxide, ozone, ammonia, nitrogen oxides and hydrogen sulfide
b) Trace amounts of argon, neon, helium, krypton, hydrogen and xenon
c) Atmospheric Impurities: volcanic ash, sea sait, dusts, sand pollen, mold and bacterial spores


                                                      Soluduğumuz Hava

Regardless of its source, an airborne contaminant can be either an aerosol or a gas.


An aerosol is a suspension of solid or liquid particles in the air.

Figure helps us visualize the size of aerosols by relating their dimension to the size of a human hair and other objects.



Measuring Particulate Contamination

The concentration of different size particles in the atmosphere is usually measured by weight or count. A third method, based on the area projection (shadow) of a particle, can be used for relative measurements of the staining portion of atmospheric dust. Methods for testing filters are based on these three techniques.




Effect Of Measuring Method

Work done under the sponsorship of ASHRAE and private organizations such as filter manufacturers showed that the percentage distribution of particle sizes in the atmosphere depended significantly on the method of measurement. Figure attached shows the relationship between particle size distribution and measurement. For instance, particles smaller than 1.0 micron comprise only 3% by weight of all atmospheric dust particles, but make up 98.5% by count. On the other hand, atmospheric dust particles in the 5.0 to 10 micron size range comprise 52% by weight, but only 0.175% on a count basis. Note that almost all the particles in the atmosphere are less than 1 micron in diameter.

Airborne Gases 

In addition to the normal gases in the atmosphere, the air we breathe contains a variety of gases in different mixtures and concentrations depending on our location. Most of these gases have odors which give us pleasure (from fragrances such as roses) or which are disagreeable (hydrogen sulfide from rotten eggs). Many gases are corrosive or toxic. Fortunately there are filters which works on adsorption principles which can catch most of these dangerous gases.

Air Filter Mechanisms

Filters have different mechanisms to capture particles, these mechanisms are;

  • Straining
  • Impingement (Impaction);
  • Interception
  • Diffusional

Straining occurs when the smallest dimension of a dust particle is greater than the distance between adjoining filter media fibers. Straining is not an important influence in filtration except in the removal of long-fibered materials such as lint.

Interception occurs when a dust particle follows the air streamlines, but still comes in contact with the fiber as it passes around it. If the forces of attraction between the fiber and the dust particle are stronger than the tendency of the airflow to dislodge it, the particle will be removed from the air stream.

Impingement is the mechanism by which large, high-density particles are captured. As the dust-laden air passes through the filter media, the air tends to pass around the filter fibers. However, due to inertia, the dust particles do not follow the air streamlines around a fiber. Instead, they move straight ahead to collide with the filter fibers to which they become attached.

Diffusional effect explains the capture of very small particles. As the dust-laden air passes through the filter media, minute particles do not precisely follow the streamlines. Instead, they are bombared by air (gas) molecules which cause them to take an erratic path described as Brownian movement. This erratic path increases the probability that particles will come in contact with fibers and will stay attached to them

As the total collecting efficiency of the filter is the sum of different filtration effects, it is natural to assume that the collecting efficiency has a definite minimum value under certain condition. Both the interception effect and the inertial effect increase with increasing particle size, whereas the diffusion effect decreases. This should therefore imply that there is a definite particle size, which is the hardest to collect in an filter (MPPS). Fig shows the collecting efficiency of both the total and the individual filtration effects in a fine filter with a glass fibre mat.

As can be seen from the collecting efficiency curve it has a minimum for particles of 0.15 to 0.3µm diameters.

Test Methods

There are basically two sources for filter testing; USA based standards (ASHRAE, IEST; MIL) or European based standards (CEN; EN779 and EN1822). For coarse dust filters ASHRAE specifies weight based filter efficiency called “Average Weight Arrestance” and “Average Atmospheric Dust Spot Efficiency” based on staining for fine dust filters. On the other hand the new EN779 : 2002 is used both for coarse and fine filters which utilizes a challenge aerosol DEHS (or equivalent) where upstream and downstream samples we analyzed by an optical particle counter to provide filter particle size efficiency data.

For HEPA and ULPA filters similarly CEN standards are used in Europe, IEST and MIL recommended practices are used in the United States. The filter efficiency is defined at 0.3 µm particle size for HEPA filters in IEST standards. In contrast, EN1822 defines the filter efficiency at MPPS’s (Most Penetrating Particle Size). The filter test methods also differs in these two standards. IEST recommends particle counters and photometers for filter tests, while EN1822 requires particle counters.

Smoke Test 1822-4

The leak test serves to verify that filter elements have no leaks which mean local penetration values above the permissible limits (see EN 1822-1, table 1). The Oil Thread Leak Test may be carried out as an alternative leak test method for filters of group H (classes H13 and H14). The reference for this leak test is however the particle count scan method as described in the body of this standard. The Oil Thread Leak Test is also acceptable as a test procedure for filter shapes for which the scan method cannot be applied (e.g. filter elements with Vbank media panels or for cylindrical filters).

The Oil Thread Leak Test is a qualitative test method where the absence of leaks is demonstrated visually. Therefore, it is essential to carry out regular training of the test personnel and to verify the sensitivity of the procedure and the method at regular intervals by using reference filter elements with well defined leaks, characterized by the reference scan test method. The local penetration of the leaks in the reference filter elements shall be between the limit values for the filter class defined in EN 1822-1, table 1 and maximum double the corresponding limit value. In the test set-up the filter shall be subjected to a flow of a polydisperse oil-drop aerosol with a speed of approximately 1.3 cm/s (42 m3/m2/h), which may be varied to optimize the procedure. The filter shall be placed horizontally on a diffuser or box. The test filter mounting assembly shall ensure that the test filter can be sealed and subjected to the flow in accordance with the requirements. It shall not obstruct any part of the filter cross sectional area.

The polydisperse test aerosol shall be generated by nebulising from a liquid aerosol substance in accordance with para. 4.1 of EN 1822-2. The median value of the particle diameter shall lie between 0.3 and 1.0 μm. The mass concentration shall be 1.5 g/m3 (determined by gravimetric methods).

The downstream side of the filter shall be illuminated from vertically above with a white (³ 4000 K) fluorescent lamp or halogen lamps. The brightness of the lamp shall be > 1000 Lux at the working plane. The surroundings of the filter shall be darkened, and the observational background shall be black. Uncontrolled air currents from the surroundings shall be screened out.

Under these conditions, leaks can be recognized in from of a clearly visible oil thread which appears due to the leakage. If no oil threads can be seen the filter up to class H14 is free from leaks as per the leak limit values defined in EN 1822-1, table 1.

The position and the brightness of the lamp may be adapted to the examiner’s subjection perception by using reference filter elements with well-defined leaks characterized by the scan test method. It is also recommended that reference filters are used with well defined leaks in the medium, in the frame corners and in the medium, close to the sealant.

Emery DOP Test

HEPA filters are normally used only where an extremely high level of cleanliness or purity is required. The requirement may be due to problems caused by the presence of particulates or physiological problems caused by viable airborne organisms. In any event, the efficiency of every filter is of paramount importance and must be measured in an appropriate way.

Mil-Std-282 is recognized as the standard for "hot" DOP efficiency testing and is used for compliance with many HEPA filter specifications. It is also recognized as being "monodisperse 0.3 micron particles" as referenced in EPA and OSHA definitions for HEPA filters.

DOP (dioctylpthalate) is an oil commonly used with vinyl resins to make soft vinyl plastics. It is also used by air filter manufacturers and various testing agencies to make an aerosol to test the effectiveness of air filters. Other oil-like materials, like DOS, can be substituted with similar results.

The DOP aerosol used to challenge HEPA filters to test for efficiency by this standard is known as "hot" or "thermally generated" DOP because it is derived from heated dioctylpthalate oil. Sophisticated equipment is used for carefully controlling oil and air temperatures, air flow rates and mixing conditions. This "hot" DOP aerosol has a very narrow particle size distribution (monodisperse). Because the only way to determine the efficiency of a filter on a specific particle size (fractional efficiency) is to test with particles of that size, DOP is used to produce a high concentration of 0.3 micron particles - that which theory indicates and has historically been considered to be the most penetrating of filter media.

For each test, the average aerosol concentration is measured both upstream and downstream of the filter with a photometer. The inefficiency or penetration in percent can therefore be determined and recorded on the filter label. For example, a filter with a penetration of .008% would mean it was 99.992% efficient, well above the minimum of 99.97% for HEPA efficiency.

DOP aerosol can be generated in the field but the equipment used, while relatively simple and portable, cannot produce truly "hot" DOP that is monodisperse. The DOP generated by such equipment is "cold" DOP which having a broad particle size distribution is polydisperse. Such an aerosol is useful for field testing for leaks and ensuring the integrity of an installation, however, without the ability to particle count the 0.3 micron size particles, "cold" DOP does not provide the ultimate test of filter efficiency.

The penetration or efficiency of a filter is strongly affected by the particle size of the challenge aerosol. A small change in particle size can have a significant effect on penetration. The smaller the particle, the lower the efficiency until the maximum penetrating particle size is reached.

As indicated earlier, "cold" DOP has a broad particle size with larger average size than "hot" DOP. Efficiencies are, therefore, higher with "cold" DOP than with "hot" DOP. The control of temperatures and flow rates with the equipment is critical to maintaining a consistently tight particle distribution which allows for consistent and reproducible efficiency measurements.

Where "cold" DOP can be useful in determining HEPA filter efficiency is when testing in accordance with IEST-RP-CC007.1. For each test, particle counters are calibrated to simulaneously count the number of 0.3 micron particles both upstream and downstream of the filter. Providing the "cold" DOP challange aerosol contains a statistically significant number of 0.3 particles, the inefficiency or penetration in percent can determined. In this test, the polydisperse nature of "cold" DOP is irrelavent because the other particle sizes are not measured.

Scanning Test

The leakage test serves to test the filter element for local penetration values which exceed permissible levels (see EN 1822-1). For leakage testing the test filter is installed in the mounting assembly and subjected to a test air flow corresponding to the nominal air flow rate. After measuring the pressure drop at the nominal volume flow rate, the filter is purged and the test aerosol produced by the aerosol generator is mixed with the prepared test air along a mixing duct so that it is spread homogeneously over the cross-section of the duct.

The particle flow rate on the downstream side of the test filter is smaller than the particle flow rate reaching the filter on the upstream side by the factor mean penetration.

The manufacturing irregularities of the filter material or leaks lead to a variation of the particle flow rate over the filter face area. In addition, leaks at the boundary areas and within the components of the test filter (sealant, filter frame, seal of the filter mounting assembly) can lead locally to an increase in the particle flow rate on the downstream side of the test filter.

For the leakage test, the particle flow distribution shall be determined on the downstream side of the filter in order to check where the limit values are exceeded. The coordinates of these positions shall be recorded. 

The scanning tracks shall also cover the area of the filter frame, the corners, the sealant between filter frame and the gasket so that possible leaks in these areas can also be detected. It is advisable to scan filters for leaks with their original gasket mounted and in the same mounting position and air flow direction as they are installed on site.

In order to measure the downstream particle flow distribution, a probe with defined geometry shall be used on the downstream side to take a specified partial flow as sample. From this partial flow, a sample volume flow rate shall be led to a particle counter which counts the particles and displays the results as a function of time. During the testing, the probe moves at a defined speed in touching or overlapping tracks without gaps close to the downstream side of the filter element. The measuring period for the downstream particle flow distribution can be shortened by using several measuring systems (partial flow extractors/particle counters) operating in parallel. The measurement of the coordinates of the probe, a defined probe speed, and measurement of the particle flow rate at sufficiently short intervals allow the localisation of leaks. In a further test step, the local penetration shall be measured at this position using a stationary probe.

The leakage tests shall always be conducted using MPPS particles (see EN 1822-3), except for filters with Membrane medium as per Annex E of this standard. The size distribution of the aerosol particles can be checked using a particle size analysis system (for example a differential mobility particle sizer, DMPS).

The leakage testing can be carried out using either a monodisperse or polydisperse test aerosol. It shall be ensured that the median particle diameter corresponds to the MPPS particle diameter, at which the filter medium has its minimum efficiency. When testing with a monodisperse aerosol, the total particle counting method can be used with a condensation nucleus counter (CNC) or an optical particle counter (OPC; e.g. a laser particle counter).

When using a polydisperse aerosol, an optical particle counter shall be used which counts the particles and measures their size distribution.

If scan testing is carried out as an automatic procedure it also allows determination of the mean efficiency of the test filter from the measurement of the particle concentration. The mean particle concentration on the downstream side is calculated from the total particle number counted while the probe traverses the passage area. The reference volume is the volume of air analyzed by the particle counter over this period of time. The particle concentration on the upstream side of the test filter shall be measured at a representative position on the duct cross-section. This method for determining the integral efficiency is equivalent to the method with fixed probes specified in EN 1822-5.

   1- NAFA Guide to Air Filtration

HEPA Filters


Prof.Dr.F.Taner ÖZKAYNAK

Liseyi Robert Academy’ de okuduktan sonra 1971’ de İ.T.Ü.’ de Y.Makina Mühendisi, 1974’ de A.B.D. Lehigh Üniversitesinde Doktor, 1981’ de Doçent, 1995’ de İ.T.Ü. Makina Fakültesinde Profesör olmuştur. Öğretim üyeliği yanı sıra A.B.D.’ de General Elektrik (GE), Amerikan Atom Enerjisi (AEC) ve Enerji Araştırma Merkezi (ERC) gibi kuruluşların çeşitli projelerinde görev almıştır. Endüstriyel ve temiz oda klima sistemleri, kurutma, ısı geri kazanım, baca gazı temizleme, pnömatik transport, arıtma gibi çeşitli konularda proje ve taahhütleri yönetmiştir. Halen İ.T.Ü. Makina Fakültesinde kısmi statüde öğretim üyeliğini sürdürürken Tetisan Ltd.şirketinde yöneticilik yapmaktadır. Evli ve iki çocuğu olan Prof.Dr.F.Taner ÖZKAYNAK’ ın çeşitli konularda yayınlanmış 35’ i aşkın makale ve kitabı bulunmaktadır.


Temiz odalarda klima sistemlerinde kullanılan HEPA filtrelerin ilaç, gıda ve hastanelerdeki kullanımları her geçen gün artmaktadır. HEPA filtreler ile ilgili Avrupa Birliği ülkelerinin bağlı olduğu CEN (European Committee for Standardization) tarafından yayınlanan EN 1822 standartları ile A.B.D. menşeli IEST (Institute of Environmental Sciences and Technology) tarafından yayınlanan standartlar bulunmaktadır. Her iki standartta verim tanımları ile verim ölçme yöntemleri birbirinden farklılıklar göstermektedir. IEST standardına göre verim 0.3 µm tanecik çapında tanımlanırken EN 1822’ de MPPS (Most Penetrating Particle Size) yani yakalanması en zor tanecik çapı esas alınmaktadır. Filtre testleri için IEST fotometre ve tanecik sayıcıları tavsiye ederken EN 1822’ de sadece tanecik sayıcılar önerilmektedir.

Standards for HEPA Filter Used in Clean Rooms

Usage of HEPA filters in cleanrooms is increasing rapidly, especially in the applications concerning food processing, pharmaceutical plants and hospitals. Basically there are two independent standards concerning the HEPA filters; CEN standards used in Europe and IEST Recommended Practices used in the United States. The filter efficiency is defined at 0.3 µm particle size for HEPA filters in IEST standards. In contrast, EN-1822 defines the filter efficiency at MPPS’s (Most Penetrating Particle Size). The filter test methods also differs in these two standards. IEST recommends particle counters and photometers for filter tests, while EN 1822 requires particle counters.

Avrupa Birliği ülkelerinde kullanılan CEN’ (European Committee for Standardization) in yayınladığı EN779 ve EN1822 standartlarına göre hava filtreleri Kaba (G1, G2, G3, G4) Hassas (F5, F6, F7, F8, F9), Yüksek verimli-HEPA (H10, H11, H12, H13, H14) ve Ultra yüksek verimli-ULPA (U15, U16, U17) şeklinde gruplandırılmıştır. Bilindiği gibi G ve F tipi filtreler normal konfor uygulamalarında ve yüksek verimli filtreleri koruma amaçlı olarak kullanılmaktadır. Bu çalışmada temiz odalarda kullanılan yüksek verimli filtreler, yani HEPA filtrelerle ilgili standartlar incelenecektir.

Bütün dünyada olduğu gibi yurdumuzda da temiz oda veya temiz ortam uygulamaları sürekli olarak artmaktadır. İlaç sektöründeki globalleşme sonucu üretilen ürünlerin pazarlanabilmesi için üretimlerin mevcut standartlara uygun ortamlarda imal edilmesi temiz oda uygulamalarını yaygınlaştırmaktadır. Daha önceleri GMP kurallarına göre sadece A, B, C Klas ortamlarda kullanılan HEPA (High Efficiency Particulate Air) filtreler son yıllarda bazı ilaç firmaları tarafından D Klas odalarda da standart olarak kullanılmaya başlanmıştır.

Gıda sektöründe gıdaların konduğu kapların imalatından başlayarak, dolum mahallerinde ve paketleme esnasında temiz oda veya temiz ortamlar yaratılarak sağlıklı gıdalar üretilmekte ve ürünlerin raf ömrü arttırılmaktadır. Bu amaca uygun olarak da HEPA filtreler yaygın olarak kullanılmaktadır.

Hastanelerde ameliyathaneler, yoğun bakım ve yanık tedavi odalarında hava kalitesinin ne kadar önemli olduğu artık herkes tarafından kabul edilen bir gerçektir ve bu mahaller de bir temiz oda gibi tasarımlanarak HEPA filtrelerin kullanıldığı klima sistemlerinden faydalanılmaktadır. Yurdumuzda da bu tip uygulamalar yavaş yavaş standart hale gelmekteyken Avrupa’ da da DIN 1946/4’ ün yerine hazırlanan standartlarda hastanelerdeki temiz ortam alanları arttırılmakta ve HEPA filtre kullanım sahaları genişlemektedir.

HEPA ve ULPA (Ultra Low Penetration Air) filtreler için bütün dünyada kabul görmüş ve en yaygın kullanılan iki adet test standardı bulunmaktadır. Bunlar A.B.D.’ de kullanılan IEST (Institute of Environmental Sciences and Technology)’ nin yayınladığı tavsiye şeklindeki standartlar ile Avrupa’ da kullanılan CEN’ in yayınladığı EN standartlarıdır.

IEST’ nin tavsiye ettiği uygulamalar içinde HEPA filtreler ile ilgili standartlar şunlardır.

- IEST-RP-CC001.3 HEPA ve ULPA Filtreler
Burada terimler, tanımlar, HEPA ve ULPA filtrelerin klasifikasyonu, imalatta kullanılan malzemelerin tanımlanması, test aletleri ve markalama yöntemleri anlatılmaktadır.

- IEST-RP-CC034.1 HEPA ve ULPA Filtre Kaçak Testleri
Burada HEPA ve ULPA filtreler için kaçak testi yöntemleri, test şartları, aerosol üretimi, aerosolun algılanması (fotometre veya partikül sayıcılar) ve test metotları anlatılmaktadır.

- IEST-RP-CC021.1 HEPA ve ULPA Filtre Elyafının Testi
Burada HEPA ve ULPA filtre imalinde kullanılan kağıt veya sentetik malzemelerin basınç düşümü, verim, kalınlık, mukavemet, uzama, sertlik, yüksek sıcaklıklarda ağırlık kaybı gibi testlerinin yapılma yöntemleri ile raporlama teknikleri anlatılmaktadır.

- IEST-RP-CC007.1 ULPA Filtrelerin Testi
Burada ULPA filtrelerin tanecik sayıcılar kullanılarak verim testi yapılma yöntemleri anlatılmaktadır.

Sonuç olarak IEST tarafından tanımlanan HEPA ve ULPA filtreler ile önerilen test yöntemleri Tablo-1’ de görülmektedir.

Yukarıdaki tablodan da görülebileceği gibi HEPA filtreler belirli bir tanecik çapındaki (0,3 µm) verimleri ile tanımlanırken ULPA filtrelerde bu çap daha küçük ve bir aralık olarak (0.1 – 0.2 µm) verilmektedir. Ayrıca HEPA filtrelerin sızdırmazlık testleri fotometre yardımıyla yapılabilirken, daha hassas filtreler (ULPA) tanecik sayıcılar ile test edilebilmektedir.

CEN’ in yayınlandığı EN-1882 standardı 5 kısımdan oluşmaktadır. Bunlar sırasıyla şunlardır :

- EN 1822-1 Klasifikasyon, Performans Testi Ve Markalama
- EN 1822-2 Aerosol Üretimi, Ölçme Aletleri, Tanecik Sayımı
- EN 1822-3 Filtre Elyafının Test Edilmesi
- EN 1822-4 Filtre Elemanında Sızdırmazlığın Tespiti
- EN 1822-5 Filtre Elemanının Verim Tespiti

EN 1822’ ye göre HEPA ve ULPA filtreler ile bunların verimleri Tablo-2’ de görülmektedir.
EN 1822' ye göre HEPA ve ULPA Filtreler
Filtre Tip Verim
Tanımlandığı Çap
Ortalama Penetrason
H10 85 MPPS 15
H11 95 MPPS 5
H12 99,5 MPPS 0,5
H13 99,95 MPPS 0,05
H14 99,995 MPPS 0,005
ULPA Filtreler U15 99,9995 MPPS 0,0005
U16 99,99995 MPPS 0,00005
U17 99,999995 MPPS 0,000005

Burada IEST’ den farklı olarak sabit bir tanecik çapı yerine verim için tanımlanan MMPS, (Most Penetrating Particle Size) en zor yakalanabilen tanecik çapını ifade etmektedir. Bilindiği gibi HEPA ve ULPA filtrelerde 4 ayrı filtrasyon mekanizması yani elek, yakalama, atalet ve difüzyon mekanizmaları farklı fiziksel kurallara göre tanecikleri yakalamaktadır. Tanecik çapının artması atalet ve yakalama etkisini arttırırken difüzyon etkisini azaltır. Bu nedenle Şekil-1’ den de görülebileceği gibi bir filtre elyafında ve seçilen bir hız için tutulması en zor olan yani verimin minimum olduğu bir tanecik çapı bulunur (MPPS).

Şekil – 1
Çeşitli filtrasyon mekanizmalarının tanecik çapına göre verime etkisi ve MPPS.

Tablo-2’ de tanımlanan penetrasyon terimi filtreden sonraki tanecik konsantrasyonunun filtreden öncekine oranını (1-verim) ifade etmektedir.

EN 1822’ ye göre HEPA ve ULPA filtreler için birbirinden bağımsız 3 farklı test bulunmaktadır.

1) Filtre Elyafının Verim Testi
Genellikle filtre malzemesi üreten firmalar tarafından elyafın kullanılacağı alın hızında ve MPPS’ de yapılan bir verim testidir.

2) Filtre Kaçak Testi
Tanecik sayıcılar kullanılarak MPPS’ de yapılan bir testtir. Ancak H13 ve H14 filtrelerde bu teste alternatif olarak yağ dumanı kaçak testi de uygulanabilir.

3) MPPS’ de filtre verim testi
Filtrenin toplam verimi sabit bir sonda ve buna bağlı bir tanecik sayıcı ile veya bütün filtre yüzeyi taranarak bulunmasıdır.

Yapılan bu testler sonucu Tablo-2’ ye göre filtreler klasifiye edilir.

IEST ile CEN standardının diğer bir farkı da sızdırmazlık testlerinde kullanılan yöntemdir. Tablo-1’ den görülebileceği gibi IEST filtre tipine göre fotometre ve tanecik sayıcıların kullanılmasını önerirken, EN1822 sadece tanecik sayıcıları veya diferansiyel hareketlilik tanecik sayıcılarını (DMPS) önermekte fotometreyi önermemektedir.

Ayrıca EN1822 yüzey taranarak sızdırmazlık testi yapılırken, aynı değerler kullanılarak filtre veriminin bulunmasına da imkan tanımaktadır. Sızdırmazlık ile verimin beraber saptandığı bir yöntem IEST’ de bulunmamaktadır.

IEST’ de tanımlanan A, B, C, D, E, F tipi filtrelerin EN-1822’ deki karşılıklarını tam olarak bulmak oldukça zordur. MPPS ve verim hıza göre değiştiğinden, hız önemli bir etken olmaktadır. Örneğin belirli bir hız değerinde EN1822’ ye göre H14 olan bir filtrenin IEST’ deki karşıtı C iken, hız arttığında filtre EN 1822’ ye göre H13 özelliklerini sağlarken, IEST’ ye göre hala C Klas filtre özelliklerini sağlayabilmektedir.

Söz konusu standartların dışında ayrıca denetleyici kuruluşların da özel istekleri olabilmektedir. Örneğin A.B.D.’ de bu konudaki en tanınmış kuruluş olan FDA (Federal Drug Administration) yani Ulusal İlaç İdaresi HEPA filtrelerin kullanım mahallerinde yapılacak sızdırmazlık testlerinde sadece fotometrelerin kullanımına izin vermektedir. Ayrıca steril sahalarda yapılacak testlerde katı taneciklerin kullanılmasını da müsaade etmemektedir.

Genel olarak verim ve sızdırmazlık dışında HEPA filtrelerden istenen özellikler arasında basınç kaybının az olması, yüzey boyunca hızın düzgün dağılması, yapım sırasında kullanılan malzemelerden kaynaklanabilecek gaz çıkarmaması, kolay takılıp çıkarılabilmesi, uzun ömür, neme dayanıklılık gibi özellikler sayılabilir.

[1] ÖZKAYNAK F.T., “Temiz Oda Tasarımı ve Klima Sistemleri”, Tetisan Teknik Yayınları, 2001.

[2] IEST, “IEST-RP-CC001.3 HEPA and ULPA Filters”, 2003.

[3] IEST, “IEST-RP-CC034.1 HEPA and ULPA Filter Leak Tests”, 2003.

[4] IEST, “IEST-RP-CC021.1 Testing HEPA and ULPA Filter Media”, 2002.

[5] IEST, “IEST-RP-CC007.1 Testing ULPA Filters”, 2002.

[6] CEN, “EN 1822-1 Classification, Performance Testing Marking”, 1998.

[7] CEN, “EN 1822-2 Aerosol Production, Measuring Equipment, Particle Counting Statistics”, 1998.

[8] CEN, “EN 1822-3 Testing Flat Sheet Filter Media”, 1998.

[9] CEN, “EN 1822-4 Determining Leakage of Filter Elements (Scan Method), 2001.

[10] CEN, “EN 1822-5 Determining the Efficiency of Filter Elements”, 2000.