ANDREW URQUHART of Clean Air Australasia explores the diseases HVAC can carry and how the transmission of airborne diseases can be prevented rather than cured.
Building-related illnesses (BRIs) and sick building syndrome (SBS) are alive and well, gradually exposing the lack of prevention management systems being put in place in facilities. When we start feeling sick, we go to the doctor to get a cure. At the end of the day, however, prevention costs less. Workers have to wear protective gear and playgrounds now have soft fall surroundings for this very reason – prevention being cheaper than cure (and litigation). We do, however, need to start preventing health and safety issues that are less obvious.
Most facilities are confined and most, if not all, have HVAC systems. Do we ever question whether these systems are hazardous? The highest rate of flu-related illness is generated through HVAC systems in contained areas. In addition, Legionnaires’ disease’s most common source is cooling towers, and fans and ducting distribute air carrying myriad pathogens, spreading around mould spores, which exacerbate slight respiration problems to critical levels. Not only do these systems spread bacteria, but they also become cosy breeding grounds.
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has conducted research into the health consequences of exposure to airborne infectious disease and on the implications of this knowledge for the design, installation and operation of HVAC systems. The society notes that the potential for airborne transmission of disease is widely recognised, although it generates much controversy and discussion – for example, which diseases are spread via the airborne route or via other mechanisms of dissemination.
ASHRAE states that there are three methods of transmission of airborne infectious diseases, namely through direct contact, large droplet contact and inhalation of droplet nuclei. HVAC transmits diseases through droplet nuclei, and ASHRAE’s conclusions regarding needed research and advice for the practitioner are listed in Table 1.
According to ASHRAE, airborne infectious disease transmission can be reduced using dilution ventilation, specific in-room flow regimes, room pressure differentials, personalised and source capture ventilation, filtration and UVGI (ultraviolet germicidal irradiation). Some of these solutions, however, can be cost or site prohibitive.
PREVENTING AIRBORNE DISEASES
You generally get out what you put in and, if the initial quality is low, then it’s a costly exercise to get the quality up. First up is the quality of air at the source of air intake. This should be filtered on the way through to remove airborne particles and pathogens.
As the air passes through the heating and cooling processes, moisture (condensation) and humidity play a big part in getting the desired effect, but can also cause the most problems. The source of water can be questionable if site-captured and -stored water is used. Water quality must be maintained with the introduction of chlorines, for instance, but this is only effective to a point.
Next up is the maintenance of refrigeration coils. Refrigeration coils need to be maintained so that the growth of mould and bacteria is not promoted. To maintain them, technology that can be easily applied and maintained should be used. This function is easily maintained during the off season.
Water droplets escaping via airstreams (natural breezes) from the evaporative system within the cooling tower into the surrounding areas need to be reduced to zero, as this component of the cycle is the leading cause of occupants being affected with Legionnaires’ disease. A curtain type barrier can be used to achieve this without affecting the system’s functionality. If an outbreak of Legionnaires’ disease is suspected, all cooling towers in the area are generally shut down, tested and treated, if deemed necessary.
Ducting is a breeding ground for bacteria and mould colonies, which detach and are blown out into the air inside a facility, causing no end of discomfort and all the while contributing further to ‘unclean surfaces’ throughout the facility.
Filter media on outlets can trap airborne particles and, if treated with an antibacterial, will trap and kill airborne particles as they make their way through. A major truck manufacturer in the US has incorporated this type of technology into its heating and cooling ducting filters, eliminating the build-up of mould spores and, consequently, not ‘drowning’ the driver and passengers in mould spores and bacteria build-up.
Some plastics stop bacterial growth from occurring, but these aren’t widely used in this area, if at all. Silver-based antimicrobial technology, which is used in consumer items such as cutting boards, toothbrushes, pillows and some high volume products, is not used in commercial applications due to volume restrictions. This technology can only be introduced into the polymer manufacturing process, therefore restricting end-use application. Surface bonded antimicrobials can be applied aftermarket, but efficacy is dependent upon the material and surface structure. No such technologies are implemented into HVAC systems at this stage, but there is no reason why they can’t be used for this purpose. Market pressures need to drive this.
Although it is ideal to start with a new facility where all measures of prevention can be introduced, older systems can be treated with all the same technologies through routine maintenance. All the available products and technologies add to a preventative management system that enables building-related illnesses to be prevented rather than cured.
Andrew Urquhart is the Victorian manager of sales and marketing for Clean Air Australasia.