There has been much debate about the effects humans are having on the natural environment. Global warming, deforestation, habitat loss and sustainability issues all raise passions and argument.
Less intense are the debates about the built environment and its impact on health.
Environmental health is concerned with the effect the environment in which we live is having on human populations. We now take for granted the solutions implemented over the centuries for early challenges such as effective sewage, waste and clean water systems.
In the 1800s, governments in the UK had a policy of not interfering in matters of public health. The outbreak of cholera in London around 1850 changed that thinking and parliaments, galvanised by the engineering measures adopted by John Snow in 1854 to prevent the outbreaks of cholera, began to implement regulations concerned with sanitary conditions. The last epidemic of cholera in the UK occurred in 1866. Australia was not far behind these advances in public health. In most of the western world these days, water-borne diseases are rare although prevalent still in developing countries.
Engineering measures behind these advances historically seemed to take a back seat to an increasingly medical and clinical road with prominence given to approaches such as vaccination and antibiotic treatments plus, more recently, behaviour and lifestyle improvements.
But there are newer challenges. The effects of global warming, ozone depletion, chemical pollution, natural environment degradation and communicable diseases created by the human-environment interface: namely the built environment.
Legionella
Water is the reservoir for the Legionella family of bacteria in the natural environment. Many lakes and streams, especially those that are thermally polluted, have been found to harbour Legionella. The most virulent species, Legionella pneumophila, has been found in the slimes and biofilms associated with lakes, rivers and artesian water supplies.
It appears that Legionella survives the routine water treatments applied at our city water systems used to provide potable water and is able to be carried into building services such as hot and cold water, cooling towers, decorative fountains and other plumbing systems.
Low levels of the microorganism as present in natural water systems have not yet been shown to be associated with disease. But elevated levels, associated with Legionella encountering ideal conditions for its growth, have been associated with many unfortunate outbreaks of Legionnaires’ disease.
Environmental conditions that promote the growth of Legionella include heat, the presence of sediments and an abundance of other microorganisms. Common aquatic microorganisms are algae, which alone can supply all the nutrients required for Legionella growth; harbouring amoebas, which permit parasitic intracellular Legionella growth; and other bacteria, which provide protection and supply further nutrients.
Much is now known about the growth characteristics of Legionella. Although the scientific knowledge remains incomplete, there is sufficient research data and experience to encourage preparation of guidelines that form the reference documentation for state-based laws and regulations as well as building and plumbing codes and the like.
In Australia
Australia has been a leading nation in adopting the regulatory option to control afflictions such as those caused by Legionella rather than other options such as that of “prudent avoidance” (which assumes each individual is knowledgeable about public health threats such as Legionnaires’ disease and its causative microorganism).
The relevant standard for prevention of Legionnaires’ disease and other infections and allergies associated with building services is AS/NZS3666: Air handling and water systems of buildings – microbial control. This standard targets not only Legionella but all microbes associated with building services, many of which are not likely to be life-threatening but may nonetheless cause allergies, non-clinical infections or other debilitating conditions.
The standard
The standard was produced by Standards Australia as a single prescriptive document in 1989. In 1995 it was re-written in two parts, both of a prescriptive nature and, in 2000, a performance-based option was prepared for cooling tower applications.
In November 2011 all parts were revised and a fourth part was added to provide a performance-option for key aspects of air handling systems. The four parts are:
Part 1: design, installation and commissioning (for air handling and water systems)
Part 2: operation and maintenance (for air handling and water systems)
Part 3: performance-based maintenance of cooling water systems
Part 4: performance-based maintenance of air handling systems (ducts and components).
It is anticipated that introduction of the revised Parts 1 and 2 into the Building Code of Australia is imminent. These parts are deemed-to-satisfy requirements. State health authorities may await the next round of regulatory changes before incorporating the revisions. However, in the ACT, the application of all revised parts to the AS/NZS3666 suite of standards, per an ACT Health Code of Practice, is automatic upon publication by Standards Australia.
The changes
Some changes are correctional in nature or reflect better descriptive wording and are therefore minor; significant changes follow.
In Part 1, for cooling water systems the water treatment is now required to be suited to controlling those microbes that are attached to surfaces (called sessile) as well as those circulating in the water (called planktonic) including the stage when water is first introduced to the system during construction. Building plans must show locations for cooling towers as well as ventilation air intakes.
Operating and maintenance (O and M)manuals are to be provided at the commissioning stage for building services and are to be more comprehensive than may have applied in the past. For example, commissioning data is to be included for future reference and for sustaining original conditions throughout the life cycle of the plant; and cooling water system details such as water volume and evaporation rate are to be included in the O and M manual too.
A companion standard is AS4180 on measurement of drift loss from cooling towers. This standard is now in two parts: Part 1 (original) provides a laboratory test method while the newer Part 2 provides a methodology for field application.
Either technique is acceptable, per the revised AS/NZS3666.1.
In Part 2, detailed requirements in operating and maintenance manuals are more extensive than previously. For example, for cooling towers, the water treatment equipment details and maintenance recommendations are to be included in the manual. Recommendations on the cleaning of control sensors and probes are now needed.
Routine service reports for all plant must be prepared and available to an independent authority.
In Part 3, again the need for improved operating and maintenance manuals is emphasised.
Risk factors (an inherent feature of the risk management approach) are regrouped into major risk categories.
These categories are the same as set out in both a companion standard, AS5059: 2006, which is primarily concerned with Legionnaires’ disease risk management at power station cooling water systems, and the Victorian Health Department’s template as published in its Guide to Developing Risk Management Plans.
The optimal growth temperatures for Legionella are noted in this Part 3 standard. The values, 25° to 43°C, are based on evidence from numerous research findings. While Legionella may well grow at temperatures below and above these values, the rate of growth is much slower and interventions such as use of water treatment biocides would be expected to more readily counter tendencies towards bacterial multiplication than if a system were operating at the growth range temperatures. The standard recommends that cooling water systems be operated outside the optimal temperatures if possible. With typical process water temperatures and ambient wet bulbs applying in Australian sites this objective should be routinely achievable.
Note that use of the Part 3 performance-based option does not absolve an owner of a cooling water system from compliance with Part 1 (design and commissioning stages) nor from the general requirements of Part 2 (operation and maintenance) other than those requirements pertaining specifically to maintenance (particularly frequency of cleaning).
Monitoring of corrosion rate is emphasised and use of standardised laboratory methods encouraged.
A new clause about record keeping has been added. This requires on-line disinfection events to be recorded; similarly for decontamination events.
Part 4 is a new part to AS/NZS3666 and a future assessment will need to be made by the Standards Australia working committee in the light of experience with its use.
It applies a risk management framework to the maintenance of air handling plant based on observed performance and judgements about the frequency of servicing and repairs.
Attention to plant maintenance may need to differ depending on climatic zones across Australia and New Zealand; this performance-based option may be more suitable for many plants than use of the Part 2 prescriptive option with its one-size-fits-all approach.
Tabulated details about the site and system characteristics are provided. They may appear to be onerous but they are not intended to be so. With experience, the management procedures should shake down into the use of comparable check sheets tabulating risk factors appropriate to the organisation owning the facility. Facility managers responsible for multiple sites should find this standard useful as it provides a standardised risk assessment methodology covering field variations while providing a plan for each site.
Finally
These standards recognise that air handling and water systems are essential to human sustenance in the 21st century. Its application, either voluntarily or by regulators, is consistent with other priorities such as plant longevity, minimal energy use and environmental impact. It is an irony that the systems that have such an important role to play in population wellness are also potentially able to encourage microbial growths and cause much pain and suffering.
This latest revision to AS/NZS3666 should further improve our control over the microbes presented by the built environment we have created. While microbes such as Legionella, derived from the natural environment, will always exist, the control measures that are able to prevent disease are now sufficiently understood as to be readily documented.
The standard has been in use for over 20 years and has no doubt been successful in greatly improving the hygienic condition of our building services and thereby protecting public health. The latest revision builds on this history. But we cannot forget that microbes will continue to have profound effects on our lives and surroundings if not controlled.