FIELD OF INVENTION
This invention relates to a method for aero-microbial liltrauon control
of airborne pathogens in hospital environment. BACKGROUND OF THE INVENTION
1. Because indoor air quality (IAQ) problems are difficult to quantify and are not always readily apparent, poor indoor air quality is often not recognised as a problem until a crisis occurs. Because indoor air quality (IAQ) problems are difficult to quantify and are not always readily apparent, poor indoor air quality is often not recognised as a problem until a crisis occurs. Air quality in many hospitals has deteriorated to a point that airborne transmission of infectious, disease has become a significant problem. Given the fact that many infections are transmitted via the airborne route (examples in tuberculosis and Legionnaire's Disease), adequate ventilation becomes more critical than ever. Newly discovered strains of antibiotic-resistant bacteria make
nfeetion control one of the top priorities for health care providers. The ever—increasing numbers
of orthopaedic replacement procedures and organ transplants make sterile operating room, isolation
room and general patient room air quality critical issues in patient care.
2. Occupational exposure to toxic* and hazardous gases and participates are important concerns for health
care providers'. Nursing staff who routinely administer antibiotics, can themselves, develop resistant strains of microbes that can hinder their own treatment if they acquire infections.
Administration of chemo—therapeutic drugs can result in accidental toxic exposures to health care
workers involved in .treatment. Number of lifetreatening infections acquired in hospitals and
nursing facilities include in the order of prevalence, Urinary tract, TB, Surgical wounds,
Pneumonia, and Bloodstream. The fatality pneumonia infection is most, followed by blood stream,
surgical wounds, TB and Urinary tract.

3. The reduction in viable microorganisms in air is an obvious objective
that would reduce nosocomial infections. To minimize the risk of
airborne infections during orthopaedic surgery, practitioners have
demanded laminar flow operating rooms (both horizontal and vertical
air flows). Also many surgeons operate in fully-encapsulated suits
with High Efficiency Particulate Air filtered breathing air arid filtered
inhaled air. In essence, these operating rooms are "clean rooms" with
efficiencies as low as that of class 100 range. Interestingly, surgeons
are increasing their use of encapsulated suits out of concern for their
own well being, as well as for their patients benefit. The high-speed
cutting tools used in othopaedic surgery create significant aerosols
from blood and fluids at the wound site. Therefore, any blood-borne
pathogens present in these fluids could be inhaled, infecting the
operating-room staff. •
4. Growth in ah air conditioning system is caused by airborne organisms
•
and spores coming into contact with the wet environment of the system.
Xnefficient air filters allow these contaminants to penetrate and enter the air system. Once in contact with moisture, they grow and multiply, until they plug up the condensate lines and cause water leaks as well as re—circulate in . the air. Indoor air is found to be up to 78 times more polluted than outdoor air in the air-conditioned hospital spaces.
Filtration of the following airborne pathogens which, causes nosocomial infections (those acquired during the stay in the hospital)s
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Filtration of the following airborne pathogens which, produce fatal opportunistic infections in patients with suppressed immune system by inhalation.

Brief Statement of the Prior Art 1. Knowledge about Airborne Pathogens in Hospitals:
Contagious viruses and bacteria come almost exclusiely from humans and they appear only in the return air. Spores and environmental bacteria may enter from the outdoors, but once growth (amplification) occurs indoors they may appear in the return air at higher levels- than in the outdoor air. Environmental bacteria are rarely pathogenic for healthy people, but they may provide a nutrient source for pathogenic fungi.
Spores can initially enter a building by various routes, including inlet air or infiltration, or they may be brought in with building materials, carpets clothes, food, pets' or potting soil. In a normal dry building the return air will have lower levels- of spores than the outdoor air except when .snow covers the ground and outdoor spore levels approach zero. When indoor amplifiers are present, the return air could be expected to contain higher levels of spores than the outdoor air, except during dry, windy summer conditions when outdoor-levels of spores can become very high.
Once spores germinate and growth occurs in an Air Handling Unit (AHU) or anywhere inside the building, new spores may be generated and appear in the return air. Filters may intercept spores, but moisture may cause them to "grow through" the filteer media. Cooling coils
• .
can have a pronounced filtering effect on spores but the presence of condensation may also cause microbial growth and amplification downstream of the coils,' negating the effect.
Engineered, alternative for Air filtration in Hospitals:
Natural decay mechanisms operate too slowly inside most buildings to prevent secondary infections. Available engineering alternatives include purging with outside air, filtration, ultraviolet germicidal irradiation (uVGI), and isolation through pressurisation control. Each of these technologies has advantages and limitations but optimisation for any application is always possible if the microbial IAQ goals are clearly specified.
Pressiirization control is commonly used in biohazard facilities and isolation rooms to prevent migration of microbes from one area to another, but inherent costs and operational instability at normal airflow rates limit feasibility for other applications.
Pull outside air systems are often used in health care facilities and TB isolation rooms.
High Efficiency Particulate Air filters are the only choice for controlling
microbial Indoor Air Control, Combining purge air with High Efficiency
Particulate Air filtration results in performance that is essentially
additive and cost optimisation becomes straightforward. Energy
consumption, replacement costs, and microbial indoor air quality goals
will dictate the economic choice for any particular installation. The
performance of medium efficiency filters in combination with purge
airflow is not directly additive, but depends on the filter efficiency vs.
particle size curves, the sizes of pathogens of concern, and the system
operating parameters. .
Ultraviolet Germicidal Irradiation can be an efficient method to use in right applications, such as controlling microbial growth in cooling coils. The continuous exposure appears to
inhibit fungal growth, and may kill the spores as well. In applications involving the disinfection of air streams, the effectiveness of Ultraviolet Germicidal Irradiation depends on.factors that include air velocity, local airflow patterns, degree of maintenance, the characteristic resistance of the microbes, and the humidity. A single pass through a Ultraviolet Germicidal Irradiation system may have a limited effect, but re-circulation, either through stand-alone units or ventilation systems, will result in multiple exposures, or chronic dosing. Chronic dosing with Ultraviolet Germicidal Irradiation can have a major impact on airborne viruses and bacteria.
The unique performance characteristics of each technology is driven by the cost involved. Inclusion of these characteristics in any evaluation, along with the indoor air quality design goals, ambient conditions and internal generation rates will dictate the choices for any given application, subject only to economic limitations. . . -
3. Other uncommon alternatives;
Various current experimental technologies have the potential for reducing airborne disease transmission or indoor amplification. Biocidal filters can limit or

prevent fungal growth on the pre-filtration media. Electrostatic filters (i.e. electrets or electrically stimulated filters) are available but have not seen widespread use. Carbon adsorbers have pore sizes an order of magnitude too small to remove viruses, but they are effective at removing VOCs produced by some fungi and bacteria.
Other technologies currently under research include low-level ozonation, negative air ionisation, and photo-catalytic oxidation, a technology that may one day result in a type of light-powered, self-cleaning, microbial filter.
Perfect solutions to the problem of airborne disease transmission do not yet exist, but the available technologies outside purge air, filtration, and Ultraviolet Germicidal Irradiation can be successfully implemented when their characteristic effects are understood and the goals + clearly defined. Whether the application involves improvements of microbial Indoor air Quality in an office building or minimising the risk of infection in an operating room, these technologies can be optimised individually, or in combination, from a cost or a performance standpoint.
Typically, the minimum level filtration in a hospital combines 30 percent efficient prefilters with 90 percent efficient final filters. With few exceptions this is the highest level of efficiency, commercially available, short of High Efficiency Particulate Air filtration. The implementation of isolation rooms and certain other testing and critical care areas call for the use of High Efficiency Particulate Air filtration. The direction and rate of airflow plays a significant role in controlling the spread of bacteria. In almost, all hospitals air is allowed to flow into the nearby corridors. The negative pressure isolation for patients suffering from tuberculosis and pneumonia, equipped with the systems that vent air directly outside the hospital .building are cost prohibitive and hence seldom installed.
The long duration of orthopaedic surgeries increases the likelihood that the site would become colonized by pathogenic micro-organisms during the course of surgery. Because orthopaedic prostheses and implants are frequently cemented onto adjacent bone, infections cause serious postoperative complications.
OBJECTS OF THE INVENTION
It is .an object to this invention to provide a low-energy, adaptable, low-maintenance air filtration system and process for controlling air borne pathogen in the hospital environment.
It is a further object to the invention to provide an effective method of containing air borne pathogens to a minimum level for the safety of hospital patients from hosocomial infections.
It is a still further object to the invention to provide an affordable method .and system for the containment of airborne infections around their existing handling systems and with minimal additional investment.
Yet a further object to this invention is to propose a .cost-effective canister for the safety of personnel in a hostile biological environment shielding, them against pathogens such as bacteria, virus, yeast and moulds.
DESCRIPTION OF THE INVENTION .
According to this invention there is provided a method for aero-microbial filtration control of airborne . pathogens in hospital environment characterised by the steps of:-
a) first pre-filtering of air stream by passing through filters having fine irregularly distributed polyester fibres of diameter 0.65-6.5 microns and a thickness of 10 mm to withstand hot atmospheric air >60°C, causing not more than 250 Pa pressure drop which entrap large particles entrained in the air system,!
b) passing the air stream of step (a) to high energy filtration
designed for pleated micro-fine cellulose paper of thickness
304 mm, wherein the cellulose paper is characterized by
impregnated with potassium permanganate and
manganese dioxide for chemisorption and oxidation of toxic
gases, wherein average arrestance of 98% and average
efficiency of 95% is achieved; .
c) subjecting the air stream of step (b) to in-depth adsorption
occuring at the activated carbon surface comprising of
carbon bars of grain size 1.5 mm, diameter 5 mm secured
as plate with rim of polymethane foam, a four layer plates
offering 20mm thickness wherein indepth adsorption with
activated, carbon results from its micro porous capillary
structure and its correspondingly very high internal
surface area.
The invention features a three-stage filtration system that is completely self-contained and designed to work separately from the AC system. The synergistic effect of a regenerable prefilter of average arrestance of 85%, a high energy filter made of pleated microfine cellulose mallows impregnated with potassium permanganate, and a microbial adsorbing activated carbon plate capturing of up to 99.97% of all airborne . pathogens.
MEDICALLY PURE AIR
There are seven purification stages conceived to offer medically pure air
in a hospital environment. .
Stage 1: Mechanical separation of oil, liquid particulate matter.
Stage 2: Coalescing filtration of the above.
Stage 3: Adsorption of water vapour arid other contaminants.
Stage 4: Adsorption of trace contaminants. .
Stage 5: Catalytic conversion of carbon mono oxide
Stage 6: Dust filter
Stage 7: Bacterial filter
1. The Filtration Model
Two primary mechanisms operate in filtration, namely interception, and diffusion. The third generally considered mechanism, namely, impaction is considered not significant for velocities involved in hospital filters and microbial sizes.
Interception is seen as a normal airflow streamline carrying a .particle within contact range of a fibre, at which point it will become attached by natural forces. An air stream passes through so many fibres that the probabilities are high that any particle 1 micron or larger will be intercepted in a typical high-efficiency filter.
Diffusion is taken as a removal process that dominates for particles smaller than about 0.1 micron. These particles are taken as randomly . traversing areas much wider than their diameters and thereby causing attachment whether airflow streamlines bring a particle within a single diameter of a fibre or not. Lower air velocities increase the removal of small particles by diffusion since they spend more time in the vicinity of a fibre. The single fibre efficiencies for diffusion and interception are summed to obtain the total single fibre efficiency. The model is then extended .to form a multi-fibre model.
Both high efficiency and .High Efficiency Particulate Air filters consist of fibre diameters ranging from 0.65-6.5 microns usually in
three nominal diameter groups. Each collection of discrete fibre diameters is visualised as separate filters arranged in series. The sum of the volume fractions for the fibre diameters must equal the total volume fraction. The .proportion of the fibres at each diameter can be varied in order to obtain the desired grade or performance. This method of proportioning fibre diameters was duplicated mathematically to fit the filter models to empirical data.
2-_ Airborne Pathogen Model
Airborne micro-organisms differ from particulate matter in several regards, including their individually definable sizes, shapes, size distributions, surface characteristics, and density. Modelling of these pathogen characteristics on an individual basis is neccesary to assure predictive accuracy.
The pathogen characteristic that are taken primary determinants of filterability are size, shape and size distribution. Characteristics that have a minor or potential impact on filterability are the density, adherence or surface characteristics, and motility.
ince not all microbes are spherical, shape becomes a secondary determinant of size. The types of shapes that patKbgens may have are identified as follows:
Larger groups of microbes, strepto-cocci, staphylo-cocci, and droplet nuclei, are held together by very weak natural forces and are likely to break up on aerosolization or on impact with filter fibres. The end result is that microbes will be reduced to singular forms during the process of filtration. If not, for whatever reason, then they remain as larger particles and predicted filtration efficiency will be conservative.
Most microbes are spherical, ovoid, or short rods and were, therfore taken as spheres for the purpose of filtration. Longer rods can be conveniently defined in terms of an aspect ratio (AR), or the ratio of length to width. The aspect ratio provides the basis for determining the equivalent diameter of non-spherical microbes. For microbes with an aspect ratio of less than about 3.5, the minimum diameter or width is a conservative value to us for the effective diameter. For microbes with a large aspect ratio that arrive at the filter surface un-oriented, the empirical formulae were used to calculate the effective diameter.
SCRIPTION OF THE PRE-FILTER
The pre-filter is a homogeneous dry filter medium
consisting of fine irregularly distributed polyester
o fibres that can withstand hot atmospheric air (>60 C)
and causes not more than 250 Pa pressure drop. A thickness of 10 mm considered adequate to filter particles larger than 1 micron in size with 80% efficiency.
DESCRIPTION OF THE HIGH ENERGY MICRQBIAL FILTER
The high energy microbial filter is designed for pleated micro—fine cellulose paper. The interchangeable pleats pack is fastened to the metallic frame using magnetic strips. The design offers average arrestance of 98% and NX average efficiency of 95%. A thickness of 304 romv considered adequate to provide not more than 0.2 micr
is impregnated with manganese dioxide and potassium
permanganate to offer (1) a catalytic bed for
chemisorption and oxidation of toxic gases such as carbon mono-oxide to carbon and water and (2) to disallow pathogen growth in the water thus generated.
In contrast to the absorption action in the earlier stage, wherein the air associates with Manganese dioxide and Potassium permanganate, adsorption is provided to occur at the activated carbon surface. The residual microbial adsorbent is designed as activated carbon bars of grain size 1.5 mm, diameter 5 mm secured as plate with rim off polyurethane foam. A four layer plate,
offering 20 mm thickness medium considered adequate to adsorb any residual microbe. The carbon media will stand
sterilisation and will not add to the potential to
support organisms. The in-depth adsorption which occurs
with activated carbon results from its microporous capillary structure and its correspondingly very high internal surface area.
EXAMPLE 1
In this and the subsequent examples, aero—microbial filter system is tested for its intended performance, namely delivery of air free from airborne pathogens, vis-a-vis a conventional high energy air filter and a HEPA filter.
Pathogen: Pseudomonas aeruginosa Culture Mediumi Cerimide agar medium Flow rate: 540 CFM Duration of Exposures 3 Hrs.

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SGreenish colonies that show greenish fluorescence in UV light.
BCAMPLE 2
Pathogen: Staphylococcus Culture Medium: Mannitol agar Flow rate: 500 CFM Duration of Exposure: 3 Mrs

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* Yellow colonies with a surrounding yellow zone
EXAMPLE 3
Pathogen: Enteroqoccl
Culture Medium: a) • Eosln Methylene Blue agar for gram-negative enteric bacilli
b). MacConkey Agar for non-fermenting conforms Flow rate: 500 CFM Duration of Exposure: 6 Hrs
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Amber colour transperant colonies for gram-negartive Salmonella Opaque, clourless, swarming colonies for gram-negative Proteus Drlck Red colonies for Escherla coli
EXAMPLE 4:
Pathogen: Mycobacterlum tuberculosis
Culture Medium: Middlebrook's 7H10 & 7H11 ad,ar media and Middlebrook's 7H9 broth
medium prepared from dehydrated powders (DIFCO)
Flow rate: 500 CFM
Duration of Exposure: 6 Hrs

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EXAMPLE 5
Pathogen : Streptococcus pneumoniae '.
Culture Medium: Blood Agar Medium (Sterile 5% blood in sterile nutrient agar. melted
and cooled at 50*c)
Flow__rate: 500 CFM
Duration of Exposure: 6 Mrs

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* Pale-yellow colonies showing surrounding zone of haemolysis.
Based on the experimental data, the aero-microbial filter is capable of delivering medically pure air in a hospital environment filtering the most prevalent airborne pathogens that are known.
The invention has been described with reference to the described and presently preferred embodiment. It is not intended that the invention be unduly limited by this disclosure of the presently preferred embodiment. Instead, it is intended that the invention be defined, by the means and there obvious equivalents, set forth in the following claim:

WE CLAIM:
1. A method for aero-microbial filtration control of airborne pathogens in hospital environment characterised by the steps of:-
a) first pre-filtering of air stream by passing through filters having
fine irregularly distributed polyester fibres of diameter 0.65-6.5
microns and a thickness of 10 mm to withstand hot atmospheric air >60°C, causing not more than 250 Pa pressure drop which entrap large particles entrained in the air system,
b) passing the air stream of step (a) to high energy filtration
designed for pleated micro-fine cellulose paper of thickness 304
mm, wherein the cellulose paper is characterized by
impregnated with potassium permanganate and manganese
dioxide for chemisorption and oxidation of toxic gases, wherein
average arrestance of 98% and average efficiency of 95% is
achieved;
c) subjecting the air stream of step (b) to in-depth adsorption
occuring at the activated carbon surface comprising of carbon
bars of grain size 1.5 mm, diameter 5 mm secured as plate with
rim of polymethane foam, a four layer plates offering 20mm
thickness wherein indepth adsorption with activated carbon
results from its micro porous capillary structure and its
correspondingly very high internal surface area.

2. A method for aero-microbial filtration control of airborne pathogens in hospital environment substantially as herein described.