Whenever a Commercial Building, Healthcare Facility or Critical Indoor Area undergoes refurbishment a specific plan needs to be in place for the preparation, inspection and cleaning of the HVAC system before commissioning.
An HVAC system can become a source of serious health risk if not managed inline with current Indoor Air Quality guidelines and is the responsibility of architects, engineers, construction managers, facility managers and building owners  to ensure that the correct measures are in place.
Contamination can occur in multiple ways, for example, ducting may need to be modified as part of the remodelling process leaving open ductwork during phases of the build, or air-handling units and ducting can become contaminated during the delivery stage or while being stored on site, and even in some cases due to HVAC systems being switched on during the refurbishment process.
This accumulation of bioaerosols, soils, dirt and debris, if left to remain within the duct work, creates a health risk to occupants when the system is commissioned and promotes conditions for mould growth.
“Dust is a source of contamination which causes mould growth within HVAC systems. Always comply with NADCA ACR 2021 to prevent these types of Indoor Air Quality problems arising.”
MUNI KUMAR, Indoor Air Quality Expert at Clean-Air
- If construction debris is not removed from air ducts, occupants may breathe in leftover construction materials that are being moved through the building via air circulation.
- When air ducts contain debris it can reduce the efficiency and longevity of the HVAC system and depending on the amount of debris in the ducting, it is possible for airflow to be blocked.
- Leaving a build-up of construction material in ducting can cause moisture to condense or pool, causing a greater likelihood of the growth of mould and other harmful bacteria.
Mould will grow in places with a lot of moisture. Mould can also grow in dust. Common indoor moulds are Cladosporium, Penicillium, and Aspergillus.” 
The photos below form part of an inspection report conducted after renovation work had been completed at a Queensland Hospital, detailing the condition of the HVAC system post-construction.
Image source: Clean-Air Aust. Photo Archive
(left) Shows a layer of dust contamination present within the ducting. (center/right) Construction debris and dust found inside the ducting
Clean-Air plays a critical role in the success of construction projects – safeguarding the health of occupants by providing safe air within the newly refurbished building. Post-construction inspections and cleaning of HVAC systems are a fundamental Health and Safety requirement – negligence in this area can lead to serious cardiovascular and respiratory diseases for occupants of the space. If left untreated, mould growth and carcinogen-containing construction dust can become airborne, causing health issues ranging from the exacerbation of asthma, coughs, wheezing and shortness of breath, to cardiovascular and respiratory diseases, lung cancer and strokes.
Image source: shutterstock/serkanyalcinkaya
Curtin University study predicts workplace silica exposure could cause 10,000 Australians to develop lung cancer 
– ABC Radio Perth, Jul 2022
Whenever construction or renovations are being carried out within an indoor space, and especially when there is a large amount of dust being created, precautions are taken to seal off supply and return registers, and as soon as the construction work is completed a full inspection and cleaning of the HVAC system is required inline with AS 3666. Construction work can produce harmful Air Pollutants and VOCs which, if left untreated, can circulate in the HVAC system, driving not only dust particles but other harmful compounds like silica and concrete, collectively classified as PM10, into an occupied space.
Image source: epa.gov
PM10 is particulate matter less than or equal to 10 micrometres in diameter that is invisible to the naked eye. Other air pollutants include paints, glues, oils, thinners and plastics, which all produce noxious vapours.
Those working in the construction industry are potentially exposed to between 15 and 20 carcinogens as a result of common work activities. Construction workers take precaution by using PPE to avoid breathing in harmful air, whereas returning building occupants would be fully exposed to those contaminants if circulated by the HVAC system. Of the occupational cancers in men, 56% are within the construction industry. This includes mesothelioma, a type of cancer that develops on the lining of the lungs and chest. Frequent exposure to dusts and fibres, such as silica and asbestos, as well as the fumes and gases emitted by solvents and machinery explains why lung cancer is particularly common in this industry, a factor which demonstrates the abundance of harmful air contaminants present during stages of a refurbishment and before the final cleaning of an HVAC system takes place – contaminants which could lead to severely detrimental health implications of returning occupants.
That's why it's crucial to consult a qualified HVAC Hygiene Expert at the beginning of the process, before on-site work commences. Clean-Air mitigates these risks by providing pre/post verification measures, inspections, remediation and testing, all carried out to strict procedures and predefined industry processes inline with an approved Construction Indoor Air Quality Management Plan.
HVAC Cleaning Methods
Under floor plenums require specialised cleaning methods. Using a HEPA filtered vacuum machine that is certified 99.97% efficiency at 0.3 microns and negative air extraction systems with mechanical cleaning to achieve Post construction cleaning to ISO 14644-1 Class 8 Standard for Cleanliness.
Location: Brisbane CBD, Queensland
(Above) Clean-Air Australia undertook the cleaning of under floor plenums from the Basement through to Level 14 of the building to remove construction debris.
A Construction Indoor Air Quality Management Plan details a set of standards to be followed, for example SMACNA (Sheet Metal and Air Conditioning National Contractors Association) IAQ Guidelines for Occupied Buildings Under Construction , NADCA ACR  or ASHRAE Standards, and would outline the Roles, Responsibilities and Monitoring of an effective IAQ Plan, detailing practices and procedures. This might consist of safety measures for:
HVAC Protection: Identifying IAQ contamination sources, dust, moisture and VOCs. Measures for preventing dust migration, the accumulation of dust and debris in the duct system. Appropriate Filter media requirements, i.e. meeting ASHRAE standards for MERV Level 8. Inspection responsibilities, procedures and frequency.
Source Control: This may include, regulating the use of low or no VOC products to reduce potential problems. Responsibilities of Verifications and checks. Requirements of cross ventilation during building tasks. The use of equipment or the machinery and the areas permitted. The storage of construction materials and products.
Ventilation Procedures: Infection control procedures in order to avoid contaminating other occupied spaces. Zoning, Ventilation, Exhaust, Pressure differential requirements to separate the construction area from the occupied area.
Cleaning and Testing: Removing contaminants from the building prior to occupancy. Cleaning of coils, air filters, and ductwork during installation and cleaning prior to testing of the systems. Provision of photographs to document compliance. Replacing of any materials contaminated through direct exposure to moisture from precipitation, plumbing leaks or condensation.
Following a plan like this protects a building owner from liability, protects returning occupants to the indoor space from health risks and ensures the HVAC system is running safely and efficiently.
References / Further reading:  SMACNA IAQ Guidelines for Occupied Buildings Under Construction,  ABC Radio Perth,  NADCA Standard ACR2021,  CDC Basic Facts about Mould and Dampness