Filtering Airborne Aspergillosis
Aspergillus What’s required to filter it? Including best filtration practice
Prepared By Don Donovan - Camfil Farr Ireland
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1
Filtering Airborne Aspergillosis
Contents
1.0 2.0 3.0 4.0
Introduction Aspergillus Principles of filtration Filtration Standards 4.1 Manufacturing Standards 4.1.1 General Air Filter Standards 4.1.2 High Grade Filter Standards 4.2 In-situ Testing Standards 5.0 Energy and Indoor Air Quality (IAQ) 5.1 Eurovent 4/11 Energy Standard 5.2 EN 13779 Ventilation Standard 6.0 Are HEPA filters required to filter aspergillus 7.0 Filter optimum selection 8.0 Recommendation 9.0 Summary and conclusions 10.0 Appendices
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03 04 05 09 09 10 13 16 17 17 18 21 24 26 27 28
Filtering Airborne Aspergillosis
1.0
Introduction
There is much written about the prevention of Nosocomial Invasive Aspergillosis, how outbreaks can happen and the effect that it can have in immune suppressed patients.
While this paper looks briefly at Aspergillous its main focus considers filtration steps to prevent airborne Aspergillus entering the hospital ventilation systems but as requested it will also consider other fungi spores in its recommendation.
Many commentators have suggested that HEPA (High Efficiency Particle Air) filters should be installed as a final stage of filtration and this has now been written into many hospital guidelines and standards. This document will review this in more detail
In compiling this report it was felt that it was worthwhile taken into account the general indoor air quality and how it can be improved by the installing the optimum filter selection while at the same time taking into account the cost of energy, labour and waste disposal.
In most cases the particle size of different contaminent are known however to understand how these particles are actually filtered this document will include a section on the principles of filtration.
Over the years, many of the standards and regulations that govern air filters have been updated, and this document will review these and look at why they have changed for the better. The new standards have more emphasis now on the protecting of people’s health (IAQ) and the conservation of Energy.
At the end of this report recommendations will be put forward.
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Filtering Airborne Aspergillosis
2.0
Aspergillus
Over the years the main concern for hospitals and other healthcare facilities regarding aspergillus has been associated with on-site or nearby construction work. There are many species of Aspergillus but only a small number of these are shown to be a concern with human diseases. The spore sizes can vary however the smallest diameter is in the range of 2.5 to 3.5 microns (1 micron = 1/1000 mm - A human hair is approx 70 micron in thickness) .
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Filtering Airborne Aspergillosis
3.0 Principles of Filtration Knowing the the size of the particle of concern is important however to get a better understanding of how filters work we need first to look at how different particles move within the airsteam. With this knowledge we can then look at what is required to ensure that the product that is produced is fit for purpose. When it comes to air filtration there are two forms of filtration used, the first being mechanical and the second is electrostatic attraction. Mechanical air filters remove particles from the air stream because particles come into contact with the surface of fibres in the filter media and adhere to the fibres. The mechanisms by which the particles come into contact with the fibres in the filter media are Straining (sieving), Interception, Diffusion, Inertial seperation and Electrostatic attraction.. The first of these mechanisms applies mainly to mechanical filters and is influenced by particle size. Electrostatic filtration is obtained by charging the media as a part of the manufacturing process.
Straining This occurs when the opening between the media members (fibers, screen mesh, corrugated metal, etc.) is smaller than the particle diameter of the particle the filter is designed to capture. This principle spans across most filter designs, and is entirely related to the size of the particle, media spacing, and media density
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Filtering Airborne Aspergillosis Interception In order to be intercepted, a particle must come within a distance from a fibre of one radius of itself. The particle thus makes contact with the fibre and becomes attached. The interception mechanism can be contrasted with the impaction mechanism in that a particle which is intercepted is smaller and its inertia is not strong enough to cause the particle to continue in a straight line. It therefore follows the air stream until it comes into contact with a fibre
Diffusion This occurs when the random (Brownian) motion of a particle causes that particle to contact a fiber. As a particle vacates an area within the media, by attraction and capture, it creates an area of lower concentration within the media to which another particle diffuses, only to be captured itself. To enhance the possibility of this attraction, filters employing this principle operate at low media velocities and/or high concentrations of microfine fibers, glass or otherwise. The more time a particle has in the "capture zone", the greater the surface area of the collection media (fibers), the greater the chances of capture. Filter manufacturers have two distinct methods of addressing this principle — employ more square footage of fine glass-mat type media or employ less square footage of high lofted glass media
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Filtering Airborne Aspergillosis Inertial seperation This uses a rapid change in air direction and the principles of inertia to separate mass (particulate) from the air stream. Particles at a certain velocity tend to remain at that velocity and travel in a continuous direction. This principle is normally applied when there is a high concentration of course particulate, and in many cases as prefiltration mode to higher efficiency final filters.
Electrostatic attraction Filters utilizing large diameter fibre media rely on electrostatic charges to increase their efficiency of fine particle removal. Large diameter fibre media is normally chosen due to low cost and air flow resistance. However, these filters often start to lose their electrostatic charge after a short time because the particles captured on their surface occupy charged sites, thereby neutralizing their electrostatic charge
Mechanical and Electrostatic filters As mechanical filters load with particles over time, their collection efficiency and pressure drop typically increase. Eventually, the increased pressure drop significantly
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Filtering Airborne Aspergillosis inhibits airflow, and the filters must be replaced. For this reason, pressure drop across mechanical filters is often monitored because it indicates when to replace filters. Conversely, electrostatic filters, which are composed of polarized fibers, may lose their collection efficiency over time or when exposed to certain chemicals, aerosols, or high, relative humidity. Pressure drop in an electrostatic filter may increase at a slower rate than it does in a mechanical filter of similar efficiency.
This will be covered in more detail later in this paper.
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Filtering Airborne Aspergillosis
4.0
Air Filtration Standards
Nothing is ever black and white. The perfect air filter would operate at 100% efficiency on the target contaminants, require zero energy input, and last forever. However, no filter of this type has been invented. Filter efficiency, dust holding capacity and differential pressure can be measured in many ways, and an air filter's performance changes over time. The challenge imposed on air filters changes as the environment inside and outside a building change. Many air filter testing methods have been developed by various organisations for predicting the in-use performance of filters and comparing the performance of air filters of different designs. It is important to understand the complexity of differentiating air filters. Many variables impact on the results of a comparison study, some of which are obvious and some of which aren't. Most air filters will remain in a system for months or even years. However, testing of these filters often occurs in a few minutes or hours. During its life, an air filter will see hundreds of environmental changes such as temperature, humidity, air flow velocity and particle load. However, filters are often tested in a controlled environment.
The are two types of test critrea standards, the first is based around the manufacturing and performance of filters (the so called factory test) and then we have the in-situ test. While the factory tests will not alter greatly, the in-situ tests can vary based on industry, environment or demand. In this section we will first look at the factory test and then cover in-situ test briefly.
4.1
Manufactures Standards
Manufacturing standards can be broken up into two, one being for genaral air filtration (low and middle grade. Eg; Panel & Bag Filters) and the other for high grade filtration (HEPA & ULPA Filters).
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Filtering Airborne Aspergillosis
Filter Standards – CEN 779-2002 / ASHRAE 52.2 Up until the 90’s there were many national standards in Europe such as BS for UK and Din for Germany to mention only two, however these have all been replaced with one European standard which is governed by CEN (the Comite European de Normalization) ,which originally took all the best criteria from each of the national
standards. The CEN standard has greatly improved since this time to protect both people and industrial processes, the lastest being CEN 779-2012.
ASHRAE
(American Society of Heating, Refrigeration, and Air-Conditioning Engineers) in the USA have also moved with CEN by upgrading their standard based on the same lines of CEN. Below is an overview of where we are today in terms of what a manufacturer must adhere to under these standards.
CEN 779 –2002 and ASHRAE 52.2 operated on an average efficiency that was performed in lab conditions where a dust loading is applied and readings are taken at various final pressure drops. These average efficiencies then give the filter its rating. While the two standards are slightly different they operate under the same principle. See below details of the ratings.
CEN 779-2002
ASHRAE 52.2-1999
Final Average (Test) EN779 Class Efficiency (EM) 0.4 Pressure Drop Micron (%) (Pa) F5 40< Em < 60 % 450
N/A
Final Average Efficiency (Test) (E1) 0.3 - 1 Micron Pressure Drop (%) (Pa) No rating at this size n/a
ASHRAE 52.2-1999 class
F6
60< Em < 80 %
450
N/A
No rating at this size
n/a
F7
80< Em < 90 %
450
MERV 14
75< E1 < 85 %
350
F8
90< Em < 95 %
450
MERV 15
85< E1 < 95 %
350
F9
95< E m %
450
MERV 16
95< E1 %
350
However what became clear over the years was that the tests that were carried out in a lab scenario were different than that witnessed in “Real Life” which is finally acknowledged (and welcomed). The real life test showed that filters with an electrostatic charge (Synthetic coarse fibres) media would start to lose their efficiency after a very short time in service. During the CEN 2002 Lab test the filter is tested for Prepared by Don Donovan - Camfil (Irl) LTD + 353 1 8484977
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Filtering Airborne Aspergillosis it average efficiency based on the dust loading as highlighted above however there is also an initial efficiency test that takes place before any loading of the dust and this gives a fairer comparison between the difference in the lab test and the real life test. The real test has shown the filters with the electrostatic charge to drop as low as 20% from an initial value of 90% in some cases. Based on this fact the above two standards included a Annex A to CEN 779-2002 and Appendix J to ASHRAE 52.2- 2007, where by the manufacture states the efficiency without the charge applied on their test certs, (this is non-mandatory for Appendix J).
The EN779 : 2002 standard states: "Certain types of filter media rely on electrostatic effects to achieve high efficiencies at low resistance to air flow. Exposure to some types of challenge, such as combustion particles in normal atmospheric air or oil mist, may neutralise such charges with the result that filter performance suffers. It is important that the users are aware of the potiential for performance degradation when loss of charge occurs. It is also important that means be available for identifying cases where the potential exists. The normative test procedure, described in annex A, provides techniques for identifying this type of behaviour. This procedure is used to determine whether the filter efficiency is dependent on the electrostatic removal mechanism and to provide quantitative information about the importance of the electrostatic removal"
The ANSI/ASHRAE 52.2-1999 Standard includes an introductory paragraph that states: "Some fibrous media air filters have electrostatic charges that may be either natural or imposed upon the media during manufacturing. Such filters may demonstrate high efficiency when clean and a drop in efficiency during their actual use cycle. The initial conditioning step of the dust-loading procedure described in this standard may affect the efficiency of the filter but not as much as would be observed in actual service. Therefore, the minimum efficiency during test may be higher than that achieved during actual use."
These paragraphs clearly indicates that air filter experts recognize the effect that time has on the efficiency of filters which rely on passive electrostatic charges. Moreover, there are concerns about the potentially inaccurate test results which may occur when Prepared by Don Donovan - Camfil (Irl) LTD + 353 1 8484977
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Filtering Airborne Aspergillosis applying the standard to coarse fibre filters that rely on an electrostatic charge. Below are two filter medias with the same magnificaton.
Fine Fibres
Coarse fibres
The problem here is that manufactures can still market their product as the rated efficiency according to the Average Efficiency test carried out in the Lab. So if a manufacturer states that they are supplying filters to the above standards ask them for the test results under the above Annex A or Appendix J procedure to evaluate the filter in more detail and see what effect that the filter could have on your Indoor Air Quality (IAQ) or the protection of your patients.
So why the new CEN 779-2012 standard and what does it mean?
The new standard is a step forward and while the average efficiency will still be maintained it will make sure that the end user will at least know the minimum lifetime efficiency (MLE) of a product (From F7 to F9 according to CEN-779-2012) where by the manufacturer cannot market a product that would drop below this efficiency. Does this mean that all manufacturers have to work on new material for their products? The answer here is no, if you are currently buying filters with fine fibres such as Fibreglass bag filters these will surpass the minimum efficiencies as highlighted in the table below. (To give the reader an idea of these increased values, fibreglass filter supplied by Camfil Farr are included in the table).
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Filtering Airborne Aspergillosis
Group
Class
G1 Coarse
Medium
Fine
Classification of Air Filters (1) Final Average Camfil (3) Minimum Average (Test) Arrestance Glassfibre Bags Efficiency Pressure (Am) of Efficiency (EM) Minimum (2) 0.4 Drop synthetic dust 0.4 Micron (%) Efficiency (2) 0.4 Micron (%) (Pa) % Micron (%) 250 50< Am < 65 % n/a n/a
G2
250
65< Am < 80 %
n/a
n/a
G3
250
80< Am < 95 %
n/a
n/a
G4
250
95< Am %
n/a
n/a
M5
450
n/a
40< Em < 60 %
n/a
M6
450
n/a
60< Em < 80 %
n/a
F7
450
n/a
80< Em < 90 %
35%
55-56%
F8
450
n/a
90< Em < 95 %
55%
65-66%
F9
450
n/a
95< Em %
70%
85-86%
1) The characteristic of atmospheric dust cary w idely in comparison w ith those of the synthetic loading dust used in the test. Because of this, the test results do not provide basis for predicting either the operational performance of service life. 2) Minimum efficiency is the low est of any of the follow ing three values: Initial efficiency, discharge efficiency or efficiency throuhout the test's loading procedure. 3) These figures are typical for fibreglass filters at recommend airflow s. Please note that Camfil Farr w ill keep these values for the F7,F8 & F9 rated fibreglass filters even w ith the new standard.
Are there negatives to the new standard? Yes we believe that some manufacturers may start marketing current lower grade fibreglass as higher grades and while this is okay as it will not breech the standard, the end user will lose out in terms of the protection as highlighted above with regards to Indoor air quality, the EN 13779 Ventilation standard (more detail on this later in this document) recommend a minimum of F7 according to EN779-2002 at its rated efficiency for adequate IAQ. There may also be an issue with some synthetic medias having higher-pressure drops due to increase efficiencies, which will increase energy costs.
For example, if we take the (UKâ&#x20AC;&#x2122;s) HTM-03 where F7 filters are specified and if under CEN779-2002 a client was receiving F7 synthetic filters with coarse fibres with an electrostatic charge, after a short time these may be as low G4. However fine fibre filters would have maintained that efficiency and stayed in spec. If we now take CEN779-2012, HTM-03 will need to change F7 to F8 if it is still to maintain MLE value of 55%
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Filtering Airborne Aspergillosis
4.1.2 High Grade Filtration Standards (HEPA & ULPA) There are two main bodies than govern standards for this type of filter. In the USA it is Institute of Environmental Sciences and Technology (IEST) and here in Europe it is again CEN. Just like with the General Air Filters there were many national standards before the introduction of one single one here in Europe. For the purpose of this paper we will just focus on the European standard EN 1822. This standard has five parts and it covers everything from classifcation, testing marking, construction and performance of the filters but also takes into account the equipment used to produce and test the filters. EN 1822-1:1998, was based on particle counting at the Most Penetrating Particle Size (MPPS) where as some older standards use between 0.3 -0.65 microns as a manner to rate filters efficiency. This European Standard applies to High Efficiency Particulate Air (HEPA) and Ultra Low Penetration Air (ULPA) filters used in the field of ventilation and for technical processes
(e.g., for clean room technology or
applications in the nuclear, pharmaceutical industries & hospitals).
Key definitions from this Standard include: Penetration — The ratio of the particle count downstream of the filter to the particle count upstream. Efficiency — The ratio of the number of particles captured by the filter to the number of the particles challenging the filter. Overall Efficiency/Penetration — The efficiency/penetration averaged over the "superficial/useable" face area of a filter element under given operating conditions of the filter. Superficial/Useable Face Area — The cross-sectional area of the filter element, through which the air passes. Local Efficiency/Penetration — The efficiency/penetration at a specific point on the superficial/useable face area of the filter element under given operating conditions of the filter. In 2009 the 1998 standard was supereded by EN 1822:2009. This differs from its previous edition (EN1822:1998) slighty but the main difference is related to the classification for the filter classes H10 - H12, which has now been changed to E10 E12. Prepared by Don Donovan - Camfil (Irl) LTD + 353 1 8484977
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Filtering Airborne Aspergillosis The following table shows the various classifications of high-efficiency filters per EN 1822:(2009) Integral Value
Local Value
Collection
Penetration
Collection
Penetration
Efficiency %
%
Efficiency %
%
E10
85
15
-
-
E11
95
5
-
-
E12
99,5
0,5
-
-
H13
99,95
0,05
99,75
0,25
H14
99,995
0,005
99,975
0,025
U15
99,9995
0,0005
99,9975
0,0025
U16
99,99995
0,00005
99,99975
0,00025
U17
99,999995
0,000005
99,9999
0,0001
Filter Class
The filter class descriptions are: •
EPA 10 - EPA 12: Efficiency Particulate Air Filters
•
HEPA 13 - HEPA 14: High Efficiency Particulate Air Filters
•
ULPA 15 - ULPA 17: Ultra Low Penetration Air Filters
Testing Testing per EN 1822 is normally done with an aerosol probe which can be moved over the entire surface of the filter. This moving of the aerosol probe, or scanning, results in the measurement of many local collection efficiencies. These local efficiencies can be used to calculate the overall efficiency of the filter or the leak rate of a specific area of the filter. The overall efficiency calculation is often termed the integral value, while the leak rate is often termed the local value. Tests are performed on new filters at specified nominal volumetric air flow. Filters of U15 or above must be scanned with a particle counter probe designed for this purpose. An oil thread test can be utilized on filters of H13 and H14 classification.
Filter testing includes the following measurement: 1. Pressure drop at nominal air flow
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Filtering Airborne Aspergillosis 2. Overall collection efficiency at most penetrating particle size (MPPS) 3. Local collection efficiencies at MPPS 4. No leaks above H13 as specified in the table above Please note that the MPPS value is at a rated airflow for that filter. Should the airflow increase the MPPS might change. Now has this change got implications for the basis on why this paper is being written, the answer is yes. Some guidelines will express HEPA's must be used for various levels of patient care, however the HEPA family has now become smaller and only has two grades, H13 & H14. This will be covered in more detail later in the paper.
4.2
In-situ Standards
This could be broken up into two further sections. First of all we would have standards for the environmental control where a level of cleanliness is required. For example; the Pharmaceutical or medical device industry work on levels of clean air in their production process and these can be under a number of standards such as ISO or the European "Good Manufacturing Pratice" guide. The hospital industry around the world follow guidelines put forward by specialist bodies or local goverment. In Ireland we tend to follow the HTM-03 guide. There are many factors to considered in the above of which filters are only part of, items such as temerature, humidity and of course air change rates. When it comes to filtration we should note that the factory test EN1822 cannot be performed on site as the test equipment and method differs. When testing on site not only is the filter consider but so it the housing that accommodate it. The EN1822 standard rates the efficiency/leak rate at the MPPS (most penetration particle size) but this cannot be determind on site. So the efficiency of these filters are tested for the ratio of the particle count downstream of the filter to the particle count upstream. Various type aerosols (smoke) are used to perform this test and the known mean particle size has been established for these products. In most cases where filters are tested an efficiency of 0.01% is considered a pass. This is what the FDA requires, amongst others. .
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Filtering Airborne Aspergillosis
5.0 Energy and Indoor Air Quality This section will first look briefly at two standards based around Energy (Eurovent 4/11) and Indoor Air Quality (EN 13779). These standards along with CEN779 –2012 will form the basis for the recommendations given at the end of this document in relation to the general AHU filters.
5.1 EUROVENT 4/11 Standard A lot of the time the air filters are overlooked as an opportunity to save energy, where about 30% of energy consumed within the system relates to the filters.
Purchasers of air filters are finding it much easier to select the right air filter for energy efficiency and indoor air quality (IAQ), thanks to a new energy efficiency classification system introduced by Eurovent Certification*. Filters are now graded from A to G, with “A” standing for the lowest energy consumption and “G” for the highest.
The new classification, based on the CEN779-2012 gives customers a clearer understanding of a filter’s annual energy consumption, initial efficiency and minimum efficiency. This information clearly points out the differences between filters, making it easier to select the right filter for the right application for the best energy efficiency and filtration
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Filtering Airborne Aspergillosis This will become more and more important as EU directives require public and commercial buildings to improve their energy efficiency. A large precentage of all electrical power in buildings is consumed to operate heating, ventilation and air conditioning systems. In addition to reducing energy consumption and environmental impact for sustainability reasons, building owners also need to cut operating costs as power prices increase. Selecting the right quality air filters with the lowest energy consumption can boost their energy efficiency and also increase IAQ for a better and healthier working environment Buyers of filters should check that their supplier is Eurovent-certified. There should be Eurovent labels on all filter boxes and filters should have test protocols Based on CEN779-2012 With soaring power prices and new energy directives, it will always pays to save energy
in
ventilation
systems
by
using
the
right
air
filters.
*Eurovent Certification Company is the representative of the refrigeration, air conditioning,
air
handling,
heating
and
ventilation
industry
in
Europe.
www.eurovent-certification.com
5.2 EN 13779 Standard The European standard EN 13779:2007 focuses on achieving a comfortable and healthy indoor environment in all seasons with acceptable installation and running costs. It is now a national standard in all countries. It specifies the required filter performance in a system to achieve good Indoor Air Quality (IAQ) taking into consideration the outdoor air. The outdoor air is categorized in 3 levels, from ODA 1 where the air is pure except for temporary pollution such as pollen, up to ODA 3 with high concentrations of both gases and particles. The particulate matter refers to the total amount of solid or liquid particles in the air. Most outdoor air guidelines still refer to PM10 (particle diameter up to 10 Âľm). However, for the purpose of health protection, there is growing acceptance that emphasis should be placed on particles far smaller than 10 Âľm. The gaseous pollutants refer to concentrations of CO2, CO, NO2, SO2 and VOCs.
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Filtering Airborne Aspergillosis The new standard classifies the indoor air quality from IDA 4 (low IAQ) up to IDA 1 (high IAQ). One traditional but limited method for determining the IAQ is to study the CO2 levels. CO2 is the product of human respiration. It is a good indicator of effective ventilation, but not of absolute air quality. Another established method for spaces with human occupancy is to specify the rate of external air added for each person. Values of this type are often used to size the ventilation system. The table below lists typical ranges for CO2 levels and recommended rates for added external air to achieve different categories of indoor air quality. Note that neither method takes into account the particulate and gaseous pollutants brought into the building with the external air.
Filter recommendations according to EN 13779 After the Outdoor Air Quality has been categorised, EN 13779 clearly specifies the filter class that is required to achieve preferred Indoor Air Quality. The filter classes are specified inaccordance with EN 779:2002 (this will need to be updated to CEN779-2012). The EN 13779 standard is clear, when you require a decent IAQ (IDA 1 or IDA 2) and you are situated in a city environment, not only is F9 required as the final filter, but also a gas filter (GF) is required to protect against gaseous (molecular) pollutants!
Outdoor Air
IAQ (Indoor Air Quality) IDA 1 (High)
IDA 2 (Medium)
IDA 3 (Moderate)
IDA 4 (Low)
ODA1
F9
F8
F7
F5
ODA2
F7 / F9
F6 / F8
F5 / F7
F5 / F6
ODA3
F7 / GF / F9
F7 / GF / F9
F5 / F7
F5 / F6
Quality
GF) gas filter
â&#x20AC;˘
In a city environment, it is recommended to use a molecular filter (gas filter). It is also a good solution in an area of categories ODA 3. The gas filter should be combined with a downstream F8 or F9 particulate filter.
â&#x20AC;˘
For hygienic reasons, it is recommended to use two-stage particle filtration: -
Minimum
F5,
but
preferably
F7
in
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the
first
19
step.
Filtering Airborne Aspergillosis –
Minimum
F7,
but
preferably
F9
in
the
second
step.
– If there is only one filtration step, the minimum requirement is F7. •
For recirculation air, at least F5 quality must be used in order to protect the system. Preferably the same filter class as the main external air stream should be used.
•
For protecting the extract and exhaust systems, use at least class F5.
•
Regardless of filter class used, the efficiency must not deteriorate below defined values. Always look for the untreated (discharged) efficiency. The untreated (discharged) efficiency is reported when a filter is tested according to the current valid European standard EN 779:2002, which replaced the former EN 779.
•
The interval of filter replacement must not be selected only on the basis of economical optimisation. Hygiene issues must also be taken into account. Three limits must be considered, and the one that is reached first will determine the time for replacement: final pressure drop, time installed and time in operation. – For first step filters: 2000 hours operation or maximum 1 year installed or when the final pressure drop is reached. – For second or third step filters: 4000 hours operation or maximum 2 years installed or when the final pressure drop is reached. – For exhaust- and recirculated air filters: 4000 hours operation or maximum 2 years installed or when the final pressure drop is reached.
•
To avoid microbial growth, the plant should be designed so that the relative humidity (R.H) always stays below 90% and so that the average R.H for three days is less than 80% in all parts of the system, including the filters.
Gas filters do not change pressure loss during normal operation. In the absence of a definitive statement within EN 13779, Camfil Farr recommends to change IAQ gas (molecular) filters after 1 year installed or 5000 hours operation.
An important note to take into consideration is that the combination of various stage filters can deliver a high MLE value and while it may be a couple of % lower than the recommended final filter the energy benefits outweight the drop in the % value.
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Filtering Airborne Aspergillosis
6.0 Are HEPA filters required to filter aspergillus? As mentioned at the outset, some commentators have expressed opinions that HEPA (99.97 @ 0.3 microns) filters are required to prevent airborne aspergillus from entering the ventilation system of a hospital. Based on the fact that we know that the particle size of the spore is between 2.5 and 3.5 micron this would seem to be overkill in terms of filtration, however before we can dismiss this we need to dig deeper and look at alternative solutions.
Early in this document the different principles of filtration were covered and also the different kinds of media available on the market today such as fine fibres and coarse fibres, which rely on the electrostatic charge as a mean to attract the particles. For the purpose of this discussion we should dismiss these coarse filters (Synthetic fibres) that rely on the charge as an alternative due to the fact that it has been proven that they will lose their efficiency shortly after been put into service. Even allowing for the new CEN779 2012 standard where manufacturers need to reach to a minimum efficiency so that they can rate their products these are still too low. For example in the CEN 779 2002 Standard an F7 had to have an initial efficiency of circ 56% @ 0.4 but now the minimum is only 35% @0.4 while and F9 has dropped from 85% to 70%. In the appendices, I have included an independent test report on an F9 filter (with fine fibres) according to CEN 779-2002, (see page 5). As you will see, if our only concern is spores in the size range between 2.5 and 3.5 micron an F9 (With an MLE Value of 85-86% @ 0.4 microns) would suffice. For the purpose of highlighting how a filter can lose its charge I have also included a test report for a coarse fibre filter that depends on a charge. (Look for the section which states â&#x20AC;&#x153;Untreated and discharge efficiencyâ&#x20AC;? on page 4 of S-FLO W UF7, it drops from 77% to 16%)
While this document's main focus is on aspergillus and what is required to filter it, we also want to look at the how we can eliminate other fungi with spore sizes of 1 micron upwards. So with this in mind and as requested lets take the 1-micron as the offending particles size.
It we were to use the F9 (CEN779-2002) as highlighted above we could achieve a very high level in terms of efficiency of approximately 96-99% so we cannot
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Filtering Airborne Aspergillosis guarantee 100% collection and this is where we would need to turn to the HEPA family of products to reach our goal of 100% for 1 micron. The NDSC document states that particle filter respirators (PFR 95) which gives a > 95% filtration efficiency @0.3 microns should be used when transferring Group 2-4 at risk patients through a construction area. This relates to the H10 according to the old EN1822-1998 and now E10 to EN1822-2009. I have included within the appendices a test cert of a H10 (E10 don't require test certs) filter, which highlights the efficiency at different particle sizes, however particle ranges around the 1 micron mark are 0.5-1 micron & 1 - 2 microns and as you will see some of the particle quantities fall into the lower range. Whether these are less than 1 is unknown.
Many of the guidelines are based on different levels of patients at risk, for example in France their standard NF S 90-351 states that a minimum H13 HEPA filters should be used for Level 3& 4 and there is a similar situation in the USA where 99.97 @ 0.3 microns and H13 (99.95% @ MPPS) is stated. The HTM-03 goes as high as H14 but these are for specific areas.
In relation to Aspergillus in France according to ANAES they state a HEPA should be used, however no grade of HEPA is stated. Pre 2009 this could have been anything between H10 â&#x20AC;&#x201C; H12 but now HEPA starts at H13 according to EN1822-2009.
Now going back to the start of this section where we asked was there alternatives to using HEPA filtration for aspergillus?. In my opinion the answer would be yes for outside air entering the ventilation system based on the fact that we know that the spore size is 2.5-3.5 microns. We also have a case study where aspergillus spores were present prior to installing our F9 Opakfil filters (With an MLE Value of 85-86% @ 0.4 microns) and no reappearance has occurred (this can be discussed in more detail at a further stage).
In relation to the particles size of 1 micron, while E10 will give a very high efficiency we cannot state that it will deliver 100% based on the test certs as mentioned above. However I believe that it is good practice to use HEPA filters on any exhaust reentering the ventilation system not just for aspergillus but other sources generated
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Filtering Airborne Aspergillosis within the hospital. In relation to portable cleanair units I would also agree on some level of HEPA filtration in these due to the same fact above
Please note that H14 would typically be used in UCVs
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Filtering Airborne Aspergillosis
7.0 Optimum Filter Selection Within this section we look at various options in terms of cost and minimum lifetime Efficiency (MLE%) values. The MLE values are based on a particle size of 0.4 microns, so we can assume they will be higher for the particle size of 1 micron, however our Life Cycle Program (LCC) program does not allow for calculation of this size. Therefore I have also included in the appendices copies of test reports where the efficiency @ 1 micron can be addressed.
The LCC program is designed to look at the total cost of the filters. This takes into consideration, the purchase cost of the filter, the energy cost to run it, the labour cost to change it together with the cost to dispose of it. Calculations have shown the filters to be as low as 15% of the total LCC.
It is all very well trying to reduce the total cost of the LCC, however this must be done without compromise to the air being delivered to first the AHU equipment but most importantly to the environment it is serving, whether this is common areas within the hospital, wards or theatres.
I have taken seven examples just to highlight how both the LCC and MLE values can change when different filters and combinations are selected. The reason for this is that not all areas of the hospital may require the same filtration levels but there should be a minimum set to protect patients and staff. As mentioned earleir in this document the HTM-03 states that F7 is required for most of the areas (Non Risk Patients) and I believe that this is an accpetable level however this is based on the CEN779-2002 and 55% MLE value, but based on CEN779-2012 this will now be F8. (Please note that although option one below was G4/F8 (2002) the MLE Value is only 40%
Below are the parameters that were selected to run the reports and following that is a summary of the results.
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Filtering Airborne Aspergillosis The Parameters
AHU systems
Values
Number of Filters
1 3
System Airflow
3400 m /h
System Velocity
2.5 m/s
Life of installation
5 years
Return Air
0
Outdoor Environment
Large Town (ODA2)
Indoor air
Clean (IDA2)
Running Time
8760 hours
Labour Cost filter change
5 Euro
Energy cost
0.14 Euro/ kwh (Inc Vat)
Disposal of filters
5 Euro
Efficiency of fan
50%
LCC - The Results ( 5 years Results)
Filter class AHU System
proposal
1st Stage
Filter Reference
2nd Stage 1st Stage
2nd Stage
Surface area 1st Stage
2nd Stage
Total LCC (Euro) Total MLE %
Supply
Option 1
G4
F8
Aeropleat
Synthetic Bag
1.6 m2
6.0 m2
4280.00
40.50%
Supply
Option 2
G4
F9
30/30
Hi-flo M9 Bag
1.6 m2
9.2 m2
4518.00
81.00%
2
2
4498.00
91.00%
Supply
Option 3
F7
F9
Hi-flo M7 Bag
Hi-flo M9 Bag
9.2 m
9.2 m
Supply
Option 3A
F7
F9
Hi-flo M7 Bag
Opakfil F9 Rigid
9.2 m2
19 m2
4886.00
91.00%
Supply
Option 4
F7
E10
Hi-flo M7 Bag
Opakfil E10 Rigid
9.2 m2
19 m2
6591.00
97.30%
Supply
Option 5
F7
E10
Hi-flo M7 Bag
E10 HEPA Style
19 m2
35 m2
5999.00
97.80%
Supply
Option 6
F9
H13
Hi-flo M9 Bag
H13 HEPA
9.2 m2
40 m2
6734.00
100.00%
•
The full reports are included in the appendices for review.
•
The MLE % values is basded on the combination of the filter
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Filtering Airborne Aspergillosis
8.0
Recommendations
These recommendations are given under two categories.
Aspergillus & Other fungi •
Based on the particle size of Aspergillus spore of 2.5-3.5 microns an F9 (CEN 779-2002) filter should prevent entry of this fungi into the ventilation system. Under the new CEN779-2012 the F9 will have a lower minimum efficiency, so the MLE Value should be quoted at 85-86% @0.4 micron). However please take into consideration that the air will take the route of least resistance, so all framework should be secure and let no air by-pass.
•
For Fungi with a particle size of 1 micron and larger an E10 filter would deliver excellent efficiency however to guarantee 100% you may need to install H13 where required.
•
Where HEPA's need to be installed always use filters with a large surface area. This will reduce the running cost and prolong their lifetime.
General Recommendation •
Avoid using filters that will lose their efficiency after a short time in service (Coarse Fibres with electrostatic charge- Synthetic)
•
Use filters that maintain their efficiency over their lifetime (Fine Fibres)
•
A minimum MLE% of 55% @ 0.4 micron (F7/2002 - F8/2012) will protect the AHU equipment, ductwork, patients & staff by delivering a good level of indoor air quality.
•
Use filters with large surface area. This will reduce energy costs and prolong the life of the filters.
•
Use filters (Bags) that have conical shaped pockets. This will reduce energy costs and prolong the life of the filters.
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Filtering Airborne Aspergillosis
9.0
Summary & Conclusions
The purpose of this paper was to address what filtration level is required to filter the Aspergillus spore size of 2.5-3.5 micron. I feel we have done that in terms of putting forward the F9 (With an MLE Value of 85-86% @ 0.4 microns) and the results that were achieved
in the case study. However it must be remembered that an F9
according to the new standard (CEN779-2012) will have a lower minimum efficiency, so if the HSE decide to specify this filter, it should be stated that the MLE value should be 85-86%. If we were to move up to E10 (EN1822) for the purpose of filtering Aspergillus to prevent the risk of an F9 being supplied with the lower efficiency, there would be unnecessary cost implication both in purchase terms but more so energy costs.
In relation to the 1 micron particles sizes, there is no doubt that the E10 will deliver extremely high efficiency, however it will be up to the client to decide if this level is sufficient before deciding on moving up to the HEPA range.
Apart from the above, the paper looked at Life Cycle Cost (LCC) and indoor air quality (IAQ). Filters work out at about 15% of the total LCC and this should be taken into consideration when selecting filters. The goal for everyone today is to reduce their overall LCC cost, however this must be done in a way where their is no or minimum compromise to the level of cleanliness of air being delivered. The paper puts forward recommendation of minimum levels of filtration based on the EN13779 standard.
Don Donovan Managing Director Camfil Farr Ireland www.camfilfarr.ie
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Filtering Airborne Aspergillosis
10.00 Appendices (Please contact your Camfil Farr Representative for copies of these) 1) Independent Test Report for a F9 Filter (Fine Fibres) 2) Independent Test Report for a F7 Filters (With electrostatic charged media) 3) E10 Analysis Report 4) H10 Test Cert 5) H13 Analysis Report 6) Option 1 - LCC 7) Option 2 - LCC 8) Option 3 - LCC 9) Option 3a-LCC 10) Option 4 -LCC 11) Option 5 -LCC 12) Option 6- LCC 13) Information Leaflet - Clean Air - A Human Right ? 14) Information Leaflet - Eurovent Energy Classification 15) Information Leaflet - Clean Air With Economic benefits 16) Information Leaflet - CEN779-2012 - A New Standard.
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