Ian Wall, sales director of Ductbusters, talks through the issues around ductwork cleaning and offers pointers as to how it should be done and why.
FROM time to time clients who operate ventilation systems within clean rooms and sterile areas will seek verification of cleanliness on a particle and/or micro-biological basis.

When the anticipated results do not match expected requirements it is not uncommon immediately to point the finger at the ductwork cleaner as often the sole reason for employing his services was to eliminate this type of contamination. With regard to particle levels in ductwork all HVCA accredited ductwork cleaning companies will be familiar and work within the guidelines of TR19.

This does allow for low levels of residual dust - an average dust thickness of 60 micron on supply and 180 micron on extract.
Therefore it is conceivable that any particle tests used as part of the verification process will show dust level readings. This could indeed still be the case when surfaces are shown by Dust Thickness Tests or Vacuum Test measurements to be below the TR19 thresholds. This may or may not constitute a problem depending on the criteria being applied to the area in question.

Furthermore, evidence of dust does not necessarily mean that the ductwork system has become microbiologically compromised. An experienced ductwork cleaner using a rotary brush and vacuum method of work can reduce dust levels in ductwork to between 20 and 30 micron. This is well below the TR19 threshold and allows sterilising techniques such as hand spraying, spinning disc and fogging units to penetrate these residual dust levels and render them sterile. Failure to clean the ducts before sterilisation will not achieve absolute results and is unlikely to be offered by HVCA accredited contractors.

Problems with verification can also arise if the tests are not taken immediately after the cleaning process is completed. In new build or refurbishment projects it is possible that further construction or cleaning works continue on after the duct cleaners have left site. If fresh air inlets or grille are left exposed it is possible that the ductwork system can become re-contaminated and subsequently breech the aforementioned threshold levels. Timing and protection would appear to be the watch words here.

The security of the areas being served by the cleaned ductwork systems must also be guaranteed until the tests are taken. Any staff or contractor traffic in these zones can introduce dust levels that will lead to test failure. There is little point in conducting a theatre deep clean until all snagging is complete thus avoiding any reintroduction of dust from materials and people.

And with theatre deep cleans, it is also important to conduct the final wipe down with an alcohol impregnated cloth. Not only will this provide a final act of sterilisation but also reduce the likelihood of dry cleaning chemical dust residue being left on structure surfaces. This can become airborne as the ventilation systems are switched on for verification testing.

The grade of filters in the air handling unit needs to be checked against modern best practice procedures. If the unit has a few miles on the clock, it is likely the filters originally specified do not meet current day requirements - an operating theatre ahu should have pre-filtration of at least EU6 and after filters to a minimum of EU8.
Anything less could permit fines to travel through the system contributing to a high test count. Filters must also be fitted during the cleaning process so that they can also be part of the sterilisation exercise. Retro fitting of filters immediately compromises the system as the previously clean surfaces are exposed to airborne and touch contamination.

The duct cleaner is not likely to be present when the verification tests are taken. While not necessarily an expert in these matters ultimate faith in the method and interpretation of testing procedures can sometimes be mis-placed. Should micro-biological tests be taken without latex gloves and facemask then there is a high likelihood of failure. Micro test can be taken remotely to avoid any human contamination. Similar precautions should be taken when measuring particle levels with test personnel being attired in lint free protective clothing if remote testing is not possible.

In summary the following points must be taken into consideration before the ductwork cleaner is 'hauled over the coals'.

1. Time lag between cleaning completion and testing;

2. Area security;

3. Correct cleaning materials, chemicals and procedure;

4. Filter specification;

5. Testing protocol.

It could be the duct cleaner is at fault and the tests have identified areas of concern. These will be handled quickly and efficiently by competent organisations which have client relationships and quality of work at the heart of their mission statement.

However should the fault not lie with the duct cleaner there should be little complaint if they seek financial redress for any work they are forced to repeat if the client has not given consideration to the above five factors.