A journey from gas mask to clean rooms where air quality matters.
The gas mask used in word war ll
The Origin
US Army was working on a secret mission, The Manhattan
Project where they were developing the first atomic bomb, the first-ever
nuclear weapon, but the problem was that during its manufacturing, the small
particles become contaminated with radioactive sources hence there was a critical need to control environmental pollution.
These were the early days of World War ll when the
British Army sent a piece of paper to the US army which they got from a
captured German canister of a gas mask. The US army investigates and found it
was highly remarkable efficient against the chemical smoke, so they start
duplicating it, and hence the first very highly efficient Hepa filter came into
being. This filter was first used in the gas mask then US Army which was
finding a way to purify the air in the area where the manufacturing nuclear bomb
was carried out, they develop the very first air purifier with this filter
paper for the headquarters, thus making the hazardous and toxic-free
environment, safe for all humans. The US Army combined the air purifier with a
blower and making pleats of the paper to serve as an air passage. The
researchers were asked to test the filter efficiency and set it to 99.9% up to
0.1 mm size particles. Later Lamer developed DOP aerosols testing system for
filters. Irving Langmuir was asked by US Army to set a recommendation for Hepa
filter testing, keeping in view the size of particles of radioactive material
he recommended 0.3 microns.
In 1950 these filters were called “absolute filters”
after 1950 these filters were named “HEPA filters”. They were commercialized in
1950 and within fifty years it becomes a technology breakthrough in air
cleanliness, where the highest level of air cleanliness is required in all
fields such as the pharmaceutical industry, hospitals, aerospace, data
manufacturing, photographic film manufacturing, etc. Its uses expanded to
residential areas also where prevention from dust mites, bugs, lead, mold spores,
pet dander, smoke, pollens, hair, etc. is required the most. Moving towards
high standards, the cleanroom areas are getting more precise day by day from hospitals to industrial production where
air quality matters a lot, the Hepa Filters are essential. From making to
maintaining a cleanroom set methods for checking the efficiency of these
filters is needed regularly.
TESTING THE EFFICIENCY OF HEPA FILTERS
Their profound benefits and expanded and extensive uses
make them available all over the world and countries developed their national
standards according to their requirement. The world is a global village so the requirement of International standards that can be used as, set values globally,
as well as merge their national or regional values is needed most. To plan such
a classification scheme for an industry that already has both regional and
national standards all over the world is a tough job, as the class of filters
changes as with the difference of a decimal place of a point. When talking to
high-efficiency air Filtration especially for Hepa filters that include hygiene
of human beings to prevent them from air-borne contaminations the standards
must be internationally recognized.
From its origin till now, different regional and national
standards were developed.
1.In 1956 the first standard introduce was MIL-STD -282 that includes the IEST-RP test procedure specifies certain particle size 0.3, 0.2 -0.3, or 0.1-0.2 micron.
2.In 1988 Standard EN-1822 was introduced in Europe based on MPPS(Most Penetrating Particle Size)
3.ISO has issued a new standard in 2011 i.e. ISO 29463 that includes the old classification with additional criteria thus making it internationally acceptable. It has now extended filter classes to compromise between all current classifications.
In the below table, I have shown the comparison of all three standards.
It is clear from above the table that all standards are now compromised by moving towards more precision
classification of filters according to MPPS in ISO 29463.
This standard has obsoleted
the use of traditional methods using photometric and polydisperse aerosol and
focusing on discrete particle counting with MPPS(Most Penetrating Particle
Size).
Since it diverges from traditional non-discrete particle
measurement to individually distinct particle counting, a comparison of values
of both methods still has to find out.
This method includes a
five-step procedure for checking Hepa filter efficiency.
ISO 29463 2011,
Part 2: Aerosol production, measuring
equipment, and particle-counting statistics.
Part 3: Testing flat sheet filter media.
Part 4: Test method for determining leakage
of filter elements-Scan method
Part 5: Test method for
filter elements
Since the test method using non-discrete particle
measurement is not included as we have not yet find the comparison measurement
of both methods.
It establishes a procedure for the determination of the
efficiency based on a particle counting method using a liquid (or a solid) test
aerosol and allows a standardized classification of these filters in terms of
their efficiency, both local and integral efficiency.
References
https://journals.sagepub.com/doi/pdf/10.1177/109135059800300111
https://www.iso.org/obp/ui/#iso:std:iso:29463:-1:ed-2:v1:en
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