A reliable ventilation system has always been a central component in maintaining the overall well-being of building occupants but as employers begin the difficult process of adapting workspaces in order to facilitate the safe return of staff to their usual places of work, fresh air requirements will undoubtedly come under renewed scrutiny.

Current advice

The Federation of European Heating, Ventilation and Air Conditioning associations (REHVA) is an umbrella organisation which represents over 120,000 HVAC designers, building services engineers, technicians and experts across 27 European countries. REHVA has recently advised that humidification, air conditioning and the cleaning of ductwork has no practical effect on the transmission of COVID-19 – advice that directly contradicts previous assertations by other organisations suggesting that ductwork cleaning is effective against room-to-room infection. REHVA therefore suggests that no changes are currently needed to normal duct cleaning and maintenance procedures.

While there is always the possibility that advice of this nature will be subject to change if new evidence comes to light, the science currently indicates that viruses attached to small particles will not deposit easily in ventilation ducts and will normally be carried out by the airflow. The Chartered Institution of Building Services Engineers (CIBSE), a member of REHVA, will continue to review and evaluate evidence to provide guidance for the cooler autumn and winter seasons.

The National Association of Air Duct Specialists UK (NAADUK) has issued its own separate COVID-19 Guidance for Ventilation Hygiene to its members and some of the points relating to the cleaning of air extract systems do differ from the REHVA advice.

Anyone involved in the industry would therefore be well-advised to seek out assessments from a number of different sources and stay up to date with developments as information is reviewed and revised. 

Best practice

While the general advice may not have changed dramatically, it’s always worth reiterating that poorly maintained ductwork can facilitate the spread of other contaminants, quietly carrying dust, dirt and other particulates around a building. This is why routine inspections and cleaning by specialists with suitable tools and expertise should be carried out at routine intervals. A clearly laid out cleaning and maintenance plan should ideally be in place immediately before commissioning so that everyone involved can be certain that any newly installed system is dust and contaminant-free.

Experience has shown that even if an installer has followed the guidelines laid out in Table F.2 in the TR/19 Guide to Good Practice – Internal Cleanliness of Ventilation Systems, there is still a chance that it will fail on acceptable dust accumulation levels as defined in Table F.1 of the same document. The often dirty and dusty environment of the worksite means it is almost impossible to completely eliminate every impurity and highlights the importance of scheduling post installation cleaning.

It is always recommended that system designers should specify their expectations for the routine cleaning of the ductwork system and highlight the need for suitable access points for maintenance personnel. Once a suitable number of cleaning access panels has be determined and fitted the contractor can verify the practical access requirements for future cleaning and maintenance operations, identifying potential issues that could disrupt the scheduled upkeep further down the line.

All ductwork should be kept free of contaminants but kitchen ductwork can require special attention because of the fire risk caused by a build-up of grease and oil.

Careful placement of access panels is vital and the DW/144 document contains detailed tables specifying recommended access panel locations and sizings. This information is also consolidated in the ADCAS Guide to Ductwork Cleaning Requirements and Access Doors. Furthermore, it is a legal obligation under the requirements of EC852/2004 Annex II Chapter 1 paragraph 5 enforced by the Food Standards Agency that the construction and installation of all kitchen related ductwork is ‘readily accessible’.

A number of different tests can be used as part of the kitchen ductwork maintenance, including wet film thickness tests (WFTT) for grease and deposit thickness tests (DTT) for harder, carbonised deposits. All tests, measurement locations and cleaning methods are listed in the TR19 document and certain insurance companies will only offer insurance to companies that have a certificate of cleanliness that proves their kitchen ductwork has been cleaned in line with the recommendations contained within.

Following a full kitchen ductwork clean, a verification report is often required to document the pre and post clean measurements, details of any additional works carried out, COSHH data on chemicals used, observations on the condition of the ductwork, photographic records and recommendations on future cleaning requirements.

Maintaining standards

In the midst of a global pandemic it’s inevitable that there will be plenty of discussion over ventilation and what we can do to lower the rate of transmission.

There is currently no evidence to suggest that additional ductwork cleaning should be carried out but maintaining indoor air quality levels and safeguarding building occupants should always be a priority in our industry. It is also worth bearing in mind that cleaning can ensure HVAC systems perform as they were designed to, with airflow rates that can adequately ventilate a building.

All planned cleaning and maintenance should continue to be carried out in line with industry best practice guidance and, although viral material that settles in ductwork will become unviable over time, appropriate PPE should be worn and all old materials bagged and safely disposed of.

As we continue our gradual return to offices and other places of work, occupancy levels will no doubt fluctuate, with businesses looking to introduce alternative working patterns as part of the ‘new normal’. Regardless of the number of individuals present, a properly maintained ductwork ventilation system can help improve the well-being of employees, allowing owners and operators to uphold the highest standards when it comes to indoor air quality.