pharmaceutical industries use particle counting to assess air quality, but currently this is rarely used in healthcare premises within the UK. ISO 14644 part one gives acknowledged levels for air cleanliness using particle counting which equate to the American standard FS 209E. The highest levels of these are aimed at very critical environments but levels 7 through to 9 could be applied to healthcare (see Table 3). The world of filtration can be a very confusing environment and currently there are a plethora of companies making all sorts of claims regarding their system’s performance. The first thing to understand is that any claim to test filters for 24 hours needs to be inspected very carefully. It is true that the standards EN1822 and now ISO29463 require a 24-hour test. This is because there are such low amounts of particles passing through these filters, it takes time to be able to evaluate this. The question should be: what is actually being tested? In all cases this relates to the media being used, which is an approach geared to favour manufacturers.

The media is tested in large sheets for 24 hours and, once graded, it is then cut to make the filter. This favours manufacturers because if a test fails H14, then it can be down rated to H13 or E12 etc, thus reducing wastage. This isn’t too bad for flat filters, with one layer, because the cut media is simply being clamped between two frames. It isn’t the best approach for cartridge filters which tend to offer more capability, because the oval or round shape of these require a join and it is for these reasons WHO and the standards organisations recommend independent testing.

The next thing being seen are the virus killers which tend to throw in a little bit of UV-C for good measure. I always ask the question, ‘if your filter is stopping everything what is it you are claiming to kill?’ Of course, there is a good reason for UV-C being added post filtration and that is the device in question has used a lower quality media and then tried to offset this using UV-C light. The problem is that UV-C needs an exposure time to be truly effective. It is very useful within a ductwork where long arrays can be laid out, but its efficiency reduces as air flow increases.14

Thus, efficacy claims

do not always stand up to scrutiny, since it requires an array 2m long to ensure the exposure dwell time for high air flow rates. There are many other approaches, which include plasma, ozone, free radical releases but, in my view, none of these offer the assured stop that a good quality filter can. It is one thing to claim 99.9% capability in optimal conditions, but this may not offer a robust solution in a healthcare environment, when tackling viruses. Finally, we need to look back at the


EN1822 Class

E10 E11 E12 H13 H14 U15 U16 U17


Efficiency 0.3µm >85%


>99.5% >99.95% >99.995% >99.9995% >99.99995% >99.999995%

ISO29463 /


Table 2: European High Efficiency Filter Grades Level


0.3 micron /

/ /

0.5 micron 352000

3520000 35200000


Efficiency 0.3µm /


>=99.5% >=99.95% >=99.995% >=99.9995% >=99.99995% >=99.999995%

1 micron 83200

832000 8320000

Table 3: Lower ISO Particle Level requirements which run ISO1 to ISO9

essence of HTM 03-01. While it does tackle ultra clean ventilation systems, it only does so with a view to orthopaedic type theatre areas.15

The main part of this is that all ventilation systems should allow a degree of external air to enter the room. Supplementary systems can be used to enhance the existing system, so that so called ‘fresh air’ is entering for respiration through the background system, while the supplementary system deals with air quality. This is acceptable for a short term ‘fix’, but it doesn’t interface well with the aim of the regulations themselves. All supplementary systems should ideally have the ability to admit ‘fresh air’ and, if possible, also allow for pressure differential management. This appears to be a little bit of a ‘dark art’, but it is actually very straight forward. Positive pressure, as used in most operating rooms, protects the patient and negative pressure protects others from the patient. Using a system that is able to be regulatory compliant means that it can be used in a supplementary role today, but then can be upgraded to offer a long-term solution without additional expenditure. To try to assist with this, I have developed a simple check list which may assist in evaluating supplementary air quality systems. 1 Filtration: Is the system offering H14 for all flow rates? (Check carefully; some systems on the market make various claims but actually offer H13 dropping to H12).

2 Does the system use another technology on top of filtration?

(This normally indicates lower filter performance; no assured stop can be made less than H14 and it adds unnecessary complexity).

3 Is the system only EN1822 or ISO29463? (If ‘yes’ then it will require independent verification to assure performance each

time the filter is changed). 4. What is the filter life? (Good filters normally exceed 18 months).

5. What is the maximum flow rate of the system?

(A single bed ITU room, as an example, is approximately 26m2

. With a ceiling height of 2.7m the volume is 70.2m3

To achieve 6 air changes in this area requires a flow rate of 421m3

/hr and

to achieve the recommended 10 air changes for ITU needs to be at least 702m3

/hr. We would recommend a

supplementary system has at least 700m3


6. Is the system compliant with HTM 03-01? (This is easy to check, is it simply an air cleaner or can it accept incoming air via a duct or offer pressure differential).

7. Is the system a whole room system or a basic local air cleaner?

(The best systems generate whole room air currents rather than merely relying on diffusion alone).

8. Does the system check its own filter and how often?

(It is essential that filter monitoring is occurring, or an external regime needs to be implemented to undertake this manually. As an example, Air Sentry’s system undertakes this every five minutes, 24/7).

9. Is the filter a single change or several different units? (Cartridge filters minimise risk during change, whereas several filters increase risk of contamination to the environment or the operator).

10. Does the filter include aspects for environmental pollution control? (Today, ‘fresh air’ often provides its own risk. NHS data shows a mortality rate in excess of 50,000 per annum due to pollution in healthcare premises. Systems that remove pollutants offer


5 micron 2930

29300 293000

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