What air filters do I need for a high risk area?
I recently was working with a high risk site and we got onto the subject of air filtration. My expectation was that high risk areas should have filtered air, using a HEPA filter, but the site didn’t have this in place. Rightly so, the site challenged me to justify why they needed HEPA filters, as they’d never been asked to do this before. So, I set off looking for information to back up my request. Problem was, I couldn’t find any such information.
Standards such as BRC say that you need air filtration for high risk, but they put the responsibility of defining what filters are used on the site – by stating that you should complete a risk assessment…
“4.4.13. High-risk areas shall be supplied with sufficient changes of filtered air. The filter specification used and frequency of air changes shall be documented. This shall be based on a risk assessment, taking into account the source of the air and the requirement to maintain a positive air pressure relative to the surrounding areas.”
Reference: BRC Food Safety V7
So, I then checked the retailer standards and found a little more guidance in an old version of one particular standard, which stated…
“High care – filtration to a minimum F7* filter grade must be in place. High risk – filtration to a minimum F9-H11* filter grade must be in place and positive air pressure. *Under Classification of General Ventilation Filters EN779:2002. Note: Grades are based on the efficiency of the filter to trap defined particle sizes. F7 grade is 80% efficient and F9-H11 is 98% efficient.”
As you can see, the filters specified here range from F9 to H11, so even this doesn’t specify the requirement completely and leaves it down to the site to risk assess which they actually need. Plus, they reference filter standards that are out of date, i.e. no longer in use. So, we can’t compare the % filter efficiencies quoted here as they are from two different standards, so it would be like comparing apples with oranges!
As you may know by now, I find this type of situation really frustrating. If air filtration is important in protecting high risk environments, why is there no clear guidance as to what filtration should be used?
Asking a site to do a risk assessment to determine the filter they need, in my opinion, is a big ask – I would find this difficult to do. Surely, all high risk environments require the same level of filtration, because after all they’re high risk – there aren’t different ‘levels’ of high risk, so why not just have one risk assessment, with one conclusion, that everyone can use?
So, this is what I set off to do – provide an answer to – “What air filters do I need for a high risk area?”
To do this properly though, I needed help from the experts, so I asked for help from Camfil who are air filtration specialists.
Here’s what I learnt! The topic of air filtration is a complicated one, so I’m going to spare you all the details and focus on what you really need to know…
First of all, we need to tackle the question of what we’re trying to achieve through filtering the air for our high risk area. We want to remove particles such as dust etc, but above and beyond that, we’re trying to decontaminate the air entering the area. By decontamination, we mean remove pathogenic bacteria from the air supply.
We have defined what we’re trying to remove – pathogenic bacteria. So, we now need to know how big these pathogenic bacteria are, to know what size filter we would need to remove them…
Salmonella is about 0.5 μm 1.5 μm
Listeria is about 0.2 μm to 6.0 μm
E.coli is about 0.2 μm to 1.0 μm
Note, μm is micrometer (commonly known as a micron). 1000 micrometer is 1 millimetre (mm).
Interesting fact – the human eye can’t see much under 40 μm and the average human hair is 70 μm in diameter.
Looking at the above measurements, if we could have a filter in place which removes pathogens down to 0.2 μm, we could guarantee that the air entering the high risk area was 100% decontaminated.
This is where it gets complicated and I need to give you a little bit of background so this will make sense. There are no standards which define what filters should be used. However, there are standards that define how filters are tested and what ‘grade’ (i.e. efficiency and protection) of filter is applied. Today, as I write this, the standards which apply to how filters are graded are:
- EN779:2012 (general air filters)
- EN1822:2009 (high efficiency air filters)
The grades of filters under the EN779:2012 standard are:
G1 to G4 (these are coarse filters)
M5 to M6 (these are medium filters)
F7 to F9 (these are fine filters)
The purpose of these filters is to remove what we would define as physical contamination of varying sizes, dust etc.
The grades of filters under the EN1822:2009 standard are:
E10 to E12 (these are EPA, which stands for efficient particle air filters)
H13 to H14 (these are HEPA, which stands for high efficiency air filters)
U15 to U17 (these are ULPA, which stands for ultra low penetration air filters)
The purpose of these filters is to remove microbial contamination.
The grade of filter is given a %, which defines how effective the filter is to capture the contamination moving through it. So, if we go back to the retailer standard that specified F9 to H11 for high risk, we can now see that they were specifying a range of filter from fine (F9), all the way to H11, which was an old standard before EN1822:2009 that referred to HEPA filters.
This doesn’t make much sense, as you can see already, a fine filter won’t remove pathogenic bacteria. So it’s not appropriate on its own for a high risk area. So, let’s continue; here’s where it gets a bit complicated.
In July 2018 the EN779:2012 standard replaced the ISO16890 standard.
In the EN779:2012 standard we had 9 grades (G1-G4,M5-M6,F7-F9). These grades will be replaced with 49 grades instead. Plus, the way these grades are defined means you can’t compare the old and the new grades. So that means, we need to understand how the 49 grades are defined.
Before you freak out and stop reading – don’t worry, we can make this simple…
The 49 grades are graded based on 2 elements:
- The particle range (for which the filter is effective)
- The efficiency of the filter (I.e. how effective is it at stopping particles of the defined size from passing through the filter), which is reported as a %
Here we can answer one of the important questions we had: What size of filter do we need to remove pathogenic bacteria?
The particle ranges for which the filters are effective, are split into 3 groups:
ePM1 (removes particles in the range of 0.3 μm to 1.0 μm)
ePM2.5 (removes particles in the range of 0.3 μm to 2.5 μm)
ePM10 (removes particles in the range of 0.3 μm to 10.0 μm)
Anything lower ePM10 is called a coarse filter
You can see that none of these filters do not go down to the 0.2 μm we need. But that’s ok, as these are just these filters we use to remove the physical contamination (dust etc) and also to protect the finer filters that we will use to remove the micro contamination.
To achieve the micro clean air, we need to combine one of these filters with a finer filter which removes the micro contamination. The filter that we’d use for this is a HEPA filter – a H13, as H13 removes down to well below 0.15 μm.
So, we use one of the ISO16890 filters combined with a H13 filter, to remove the micro contamination.
You may be wondering, if the H13 filter is the important one, why should we bother with the other ISO16890 filter that removes the physical contamination? Well, this is where cost and capability of your air system comes in.
If you put just a H13 filter in your system, yes it will remove all the physical contamination as well as the micro contamination. But it isn’t designed to hold a huge amount of physical contamination and so will suffer a very short life, before it clogs up completely. And what happens when it clogs up? The air flow stops and we lose our positive air pressure in the high risk area.
Plus, bear in mind a H13 filter costs about £300 and so replacing it on a regular basis is a costly solution. So, we use at least one ISO16890 filter first to remove the physical contamination and protect the H13 filter. This is a much more cost-effective solution as an ISO16890 filter costs about £60.
Efficiency of the filter
Now, I said the ISO16890 filters were graded by 2 elements; particle range (ePM1, ePM2.5, ePM10 and coarse) and also by efficiency percentage. Here’s where the efficiency comes in. Efficiency is graded by a percentage of how much contamination the filter stops passing through it. The grades are from 50% to 95%, in 5% increments.
So, for ePM1 (remember these are our particle ranges that we talked about earlier) the filter would be graded 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% and 95%. If the filter doesn’t meet the 50% efficiency for ePM1, it’s then downgraded to the ePM2.5 grade and this efficiency percentage is reported instead.
So how do you choose which filter to use to protect your HEPA H13 filter? Well, that depends on the capability of your air system. Many systems, which were fitted years ago, do not even have the capability of holding all the required filters, so you have to be flexible with the ISO16890 filter(s)you use to achieve the best result. And, you need to balance this with the fact that you need to maintain positive air pressure. That being said, I need to stress, having an old air system which cannot provide both positive air pressure AND the correct filters to provide micro free air, is not an excuse. If these two things cannot be achieved, we should consider if the equipment we have needs upgrading.
Here is an example of what the air system should look like:
You can see there is a filter before the fan. This filter removes the gross debris – flies, leaves etc. You would probably pick a filter here that allows plenty of air flow, like an ePM10 or coarse filter with 70% efficiency.
Then, there’s a filter after the fan. This filter removes the particles, therefore ensuring the H13 filter is only presented with just the micro contamination. This extends the life of the H13 filter and ensures optimum air quality throughout.
The choice of which ISO16890 filters to use depends on the capability of the fan and the overall capability of the air system, and would need to be assessed and trialed by your site.
The high risk air filter you need for a high risk area is a H13, as this removes the pathogenic contamination from the air system. To protect this H13 filter, you need ISO16890 filters, which are optimised to maintain positive air pressure.
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