HEPA Filters (High Efficiency Particulate Air)

It is a type of filter which has high efficiency to filter out about 99.997% that is why they are termed as High efficiency particulate air filter,

HEPA filters are made up of a mesh of fiber glass fibers of thickness ranging from 0.5 to 2 micrometer and are closely packed with each other with as low clearance as 0.3?m which may be bit greater.

Working of HEPA Filters Particles in air are trapped in to HEPA filter fibers when air caring these particles is blown or passed through these fibers, by mechanism of interception (particles adhere to fibers), impaction (particles embed in to the gap) and diffusion and then blocking, particles with lower particle size than the gap between these fibers are also trapped as the result above mechanisms fiber diameter, filter thickness, and face velocity are the factors which affect the efficacy of the HEPA filter.

Importance of HEPA filter in pharmaceutical industry very great, HEPA filters are used in industry where ever it is require to make the environment free of particulate matter as well as free from microbial contaminants (bacterial ,viruses etc) in clean roomsA HEPA Filter of efficiency of 99.97% is usually used in aseptic manufacturing filing and packing, parentral dosage manufacturing.These filters are mounted in Laminar Air Flow Bench which are then used as clean area for actual aseptic manipulations or aseptic filling where usually a clean aria of class 100 are required, such laminar air flow bench are typically found within a clean aria of class 1000, which again are maintained by HEPA filters installed in a HVAC system.

For High Efficiency Particulate Air filter , A velocity of 0.45 meters/second (90 feet per minute) has generally been established, with a range of plus or minus 20 percent around the set point. Higher velocities may be appropriate in operations generating high levels of particulates.

High-Efficiency Particulate Air (HEPA) efficacy test and test for integrity.There is a major difference between filter leak testing and efficiency testing. An efficiency test is a general test used to determine the rating of the filter. An intact HEPA filter should be capable of retaining at least 99.997 percent of particulates greater than 0.3 nm in diameter. The filters maximum resistance to airflow, or pressure drop, at its nominal flow rate is usually specified around 300 Pa.

Specifications of HEPA Filters

HEPA filters, as defined by the DOE standard adopted by most American industries, remove at least 99.97% of airborne particles 0.3 micrometers (µm) in diameter.  The filters maximum resistance to airflow, or pressure drop, is usually specified around 300 Pa at its nominal flow rate.The specification usually used in the European Union is the European Norm EN 1822:2009.

The original HEPA filter was designed in the 1940s and was used in the Manhattan Project to prevent the spread of airborne radioactive contaminants. It was commercialized in the 1950s, and the original term became a registered trademark and a generic term for highly efficient filters. Over the decades filters have evolved to satisfy the higher and higher demands for air quality in various high technology industries, such as aerospace, pharmaceutical processing, hospitals, health care, nuclear fuels, nuclear power, and electronic microcircuitry (computer chips).

HEPA filters are critical in the prevention of the spread of airborne bacterial and viral organisms and, therefore, infection. Typically, medical-use HEPA filtration systems also incorporate high-energy ultra-violet light units to kill off the live bacteria and viruses trapped by the filter media. Some of the best-rated HEPA units have an efficiency rating of 99.995%, which assures a very high level of protection against airborne disease transmission. Ultra low particulate air filter.(ULPA filter)The ulpa filter is similar to that of HEPA Filter with respect to its principal of operation and material of construction, except that the fiber diameter is lesser so as to produce high level of air filtration efficiency. An ULPA filter (theoretically) is capable of removing about 99.999% particles from upstream air it is very effective filter , and airborne particles of size 120 nanometres above are removed efficiently to an level of 99.999% hence standard ULPA Filter are said to have an efficiency of 99.9995% at .12 micrometers.

Leak test of HEPA filter

High-Efficiency Particulate Air (HEPA) filter integrity should be maintained to ensure aseptic conditions. Leak testing should be performed at installation to detect integrity breaches around the sealing gaskets, through the frames, or through various points on the filter media. Thereafter, leak tests should be performed at suitable time intervals for HEPA filters in the aseptic processing facility. For example, such testing should be performed twice a year for the aseptic processing room. Additional testing may be appropriate when air quality is found to be unacceptable, facility renovations might be the cause of disturbances to ceiling or wall structures, or as part of an investigation into a media fill or drug product sterility failure. Among the filters that should be leak tested are those installed in dry heat depyrogenation tunnels and ovens commonly used to depyrogenate glass vials. Where justified, alternate methods can be used to test HEPA filters in the hot zones of these tunnels and ovens.

Any aerosol used for challenging a HEPA filter should meet specifications for critical physicochemical attributes such as viscosity. Dioctylphthalate (DOP) and poly-alpha-olefin (PAO) are examples of appropriate leak testing aerosols. Some aerosols are problematic because they pose the risk of microbial contamination of the environment being tested. Accordingly, the evaluation of any alternative aerosol involves ensuring it does not promote microbial growth.
The purpose of performing regularly scheduled leak tests, on the other hand, is to detect leaks from the filter media, filter frame, or seal. The challenge involves use of a polydispersed aerosol usually composed of particles with a light-scattering mean droplet diameter in the submicron size range, including a sufficient number of particles at approximately 0.3 nm. Performing a leak test without introducing a sufficient upstream challenge of particles of known size upstream of the filter is ineffective for detecting leaks. It is important to introduce an aerosol upstream of the filter in a concentration that is appropriate for the accuracy of the aerosol photometer. The leak test should be done in place, and the filter face scanned on the downstream side with an appropriate photometer probe, at a sampling rate of at least one cubic foot per minute. The downstream leakage measured by the probe should then be calculated as a percent of the upstream challenge. An appropriate scan should be conducted on the entire filter face and frame, at a position about one to two inches from the face of the filter. This comprehensive scanning of HEPA filters should be fully documented.

A single probe reading equivalent to 0.01 percent of the upstream challenge would be considered as indicative of a significant leak and calls for replacement of the HEPA filter or, when appropriate, repair in a limited area. A subsequent confirmatory retest should be performed in the area of any repair.HEPA filter leak testing alone is insufficient to monitor filter performance. It is important to conduct periodic monitoring of filter attributes such as uniformity of velocity across the filter (and relative to adjacent filters). Variations in velocity can cause turbulence that increases the possibility of contamination. Velocities of unidirectional air should be measured 6 inches from the filter face and at a defined distance proximal to the work surface for HEPA filters in the critical area. Velocity monitoring at suitable intervals can provide useful data on the critical area in which aseptic processing is performed. The measurements should correlate to the velocity range established at the time of in situ air pattern analysis studies. HEPA filters should be replaced when non uniformity of air velocity across an area of the filter is detected or airflow patterns may be adversely affected.Although contractors often provide these services, drug manufacturers are responsible for ensuring that equipment specifications, test methods, and acceptance criteria are defined, and that these essential certification activities are conducted satisfactorily.

Cleaning technique of  HEPA filter:

HEPA filters can be cleaned with a jet of air from down stream to the upstream direction so as to dislodge the accumulated particles, and then by a suction from reverse side if required (there should be a sanitisation procedure in place for suction clenear) followed by a jet of water gently, the quality of water is important in final rinsing. And the drying in a suitable place.
Decontamination of HEPA filters:

It is important to decontaminate HEPA filter when it is used in a clean room which handles vaccines , or a viruses ,bacteria.HEPA must be decontaminated once it off line , it is decontaminated along with housing filters.Decontamination procedure and chemicals are required to be chosen after consideration of microbial load and their resistance factors; validation of  the entire process must be done. Integrity of a HEPA filter should be verified when it is being replaced again. Person carrying out the activity of decontamination of HEPA filter should be trained and provided a protective or a breathing apparatus so as to protect him from harmful affect of decontaminating chemicals like formaldehyde or H2O2 fumes. When HEPA filters are required to be disposed, they must be incinerated before disposal so as to avoid contamination of surrounding.

May 5, 2011

1 responses on "HEPA Filters (High Efficiency Particulate Air)"

  1. Wow! Thank you! I always wanted to write in my site something like that. Can I take part of your post to my blog?

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