Mould risk minimisation: Remediation and removal

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Following on from the first half of this article, Inspection and assessment, DR PETER KEMP, DR HEIKE NEUMEISTER-KEMP, CEDRIC CHEONG and KEVIN WHITE from Mycologia discuss mould remediation and the removal of contaminated materials.

The primary factors contributing to fungal proliferation in a building context are moisture, temperature and nutrient availability. These factors also impact the types of species found and the fungal community structure and ecology present in buildings. Water availability is the most important factor when it comes to preventing fungal growth and the easiest for control (Prezant et al, 2008). As such, the success of any remediation project is highly dependent on whether the initial cause of the moisture ingress or development has been rectified.
The remediation process is simplified when moisture has been eliminated and mould growth has not yet occurred. Wetted materials may not require removal and or replacement if they have been dried, are structurally sound and lack visible mould growth (Prezant et al, 2008). The remediation of mould then follows two tasks:

  1. Management of materials upon which mould growth has become visible. This may require isolation, cleaning and or replacement of these materials for structural and health considerations.
  2. Management of mould particulates that have been generated prior to and during the remediation of mouldy materials and have migrated away from the growth site.

The goal is to return the structure as closely as possible to its pre-damaged condition. There is no intention or requirement to create a sterile environment.
In Australian Mould Guideline (AMG) the 11 fundamental steps for effective mould remediation are noted as:

  1. Assess the level of mould damage.
  2. Inspect to find the cause of the mould damage.
  3. Define and agree on the scope of works (SOW).
  4. Notify all tenants and occupants of the SOW.
  5. Fix the original problem with a permanent solution.
  6. Remove contents for remediation or disposal (where appropriate) and remove contaminated materials.
  7. Dry the structure to equilibrium (if required).
  8. Clean all affected surfaces.
  9. Clear the area for reuse with air and surface testing.
  10. Return the remediated contents.
  11. Hand over the property.

There are a number of different mould remediation methods, some recommended, some not recommended. The method chosen should be one that produces the least amount of aerosolisation and limits worker exposure. More than one method may be necessary.
Sometimes mould contamination on materials is so extensive that the material cannot be successfully remediated. In other words, hyphae embedded in the material can’t be removed or killed such that it can be reasonably confident regrowth will not occur under normal conditions. The determination of what can’t be remediated is generally undertaken via visual assessment by competent persons followed by destructive testing; for example, removal of a section of wall and/or sampling, if necessary. The assessment should be made in the context of what is considered reasonably practicable. In some circumstances, where cost of service is secondary to the value of the product, other remediation technologies may be required.
Physical removal of mould and fungi is the primary process when undertaking remediation. In some circumstances, physical removal may not be possible – in such places as within cavities and voids and narrow gaps between surfaces. In such circumstances, sanitisation or other adjunct techniques can be an effective method of killing mould and fungi material. Sanitisation by hydrogen peroxide vapour (HPV) is not considered corrosive. HPV, like ozone and hydroxyl radicals, is classed as a reactive oxygen species or oxidant. HPV in association with water vapour forms a micro-thin (~5 micron) film on surfaces that reacts with the enzyme Catalyse present on cell walls of mould and fungi to destroy both live and dead organisms. Use of HPV is seen as superior to ozone, because it is less toxic and corrosive.

In general, porous materials that are visually mouldy need to be removed as they cannot be effectively cleaned. On-site microscopy of the extent of fungal penetration into the material by a competent mycologist can determine the extent of penetration and determine if complete removal is required.
Non-porous materials, such as metal, plastic and glass, can usually be surface cleaned to remove mould growth. Unless the mould has penetrated into the material, the surface of semi-porous materials, such as wood framing, can often be cleaned and the material left in place. Previously mouldy semi-porous materials are more susceptible to mould growth if they are exposed to moisture.
Materials that have been in proximity with mould growth may act as reservoirs for mould spores. Although not damaged by mould growth, potential spore re-entrainment can occur from materials such as soft fabrics, carpeting and drapery. Such items should be HEPA (high-efficiency particulate air) vacuumed or subjected to other cleaning techniques used to reduce the accumulation of particulate levels.
Caution is required to prevent cross-contamination when handling contaminated materials. Contaminated materials must be wrapped in plastic and sealed with tape. Materials and items that are to be disposed of should be placed in a covered disposal container. Contaminated materials should never be thrown from a distance and should not be located close to openings such as windows or doors where cross-contamination issues may occur.

A clean, hygienic and functional HVAC system would deliver the following:

  • healthy and sufficient indoor air quality (IAQ)
  • a reduction in occupant dissatisfaction and complaints
  • increased operational efficiency and useful operating life
  • increased investment return on building asset, and
  • a reduction in overall system maintenance requirements and system failure events.

A thorough inspection of the HVAC system should be conducted by a suitably trained and competent HVAC inspector/technician. A typical ducted HVAC inspection should cover the following components:

  • the air-handling unit, including the condition of thermal insulation, cooling coils, fan barrel and blades, filters, condensate pans, drain lines and door gaskets
  • dampers, mixing and VAV (variable air volume) boxes, turning vanes, supply and return air ducts, and plenums, and
  • diffusers, grilles and noise attenuators.

Components should be graded according to hygiene levels – clean, light, moderate or heavy – as set by the AIRAH Best Practice Guideline for HVAC Hygiene.
The remediation of a ducted HVAC system involves two separate major tasks:

  1. the remediation of the air-handling unit, including the filters, cooling coil and supply air fan, and
  2. The remediation of the ducts, including registers, diffusers and turning vanes.

The treatments applicable to a ducted HVAC system include:

  • Filter treatment: a multi enzyme-based cleaner can remove all biological contaminants.
  • Coil cleaning: a multi enzyme-based cleaner can eliminate all biological contaminants.
  • Coil treatment: this prevents fungal growth, extends filter life, improves IAQ, reduces energy consumption and actively protects all coil surfaces from biological contamination.
  • Surface and duct cleaning: source removal using contact vacuum, compressed air, whips and brushes ensures that all surface contaminants are removed from various components.
  • Surface and duct treatment: this ensures treated surfaces remain effective and free of bio-contamination for an extended period of time. Protection effectively lasts up to 12 months and energy savings go beyond 12 months.
  • Condensate pan treatment: this prevents bio-film blockage of drains through the use of multi enzyme technology.

The essential performance criterion in judging the effectiveness of remediation is documentation that all areas identified, and other wet and or mouldy areas uncovered during the remediation process, have been appropriately remediated. For this task, it is typical that all of the areas affected by mould growth are physically re-inspected, the justification being the ease and speed of visual inspection (Morey et al, 2008).
As stated in AMG, visual inspection is the most important part of the verification process and should include checking to make sure that:

  • all visible mould damage has been removed
  • all contaminated material has been removed
  • the original problem has been fixed
  • no mouldy odour remains, and
  • the moisture has been completely removed.

The effectiveness of cleaning can also be tested by either quantitatively measuring the degree of residual dust or the quantities of viable or non-viable spores remaining after remediation using similar techniques used to evaluate air concentrations – culture plates, RODAC contact agar plates, sticky tape Bio-Tapes, slit-type impactors, according to an American Industrial Hygiene Association (AIHA) document on indoor mould titled Recognition, Evaluation and Control of Indoor Mould.
In AMG, complementary to visual assessment, the conducting of clearance testing prior to occupants or tenants being allowed to reuse the area being remediated is suggested. This includes moisture testing, and air and surface testing. Air and surface mould testing should be undertaken by an independent mould testing and analysis laboratory qualified to analyse indoor fungal species.
Location of post verification testing depends on the areas that were both tested in the initial investigation and were cleaned and/or remediated. Air and surface testing should be targeted at building contents, HVAC system components and the building surfaces that were cleaned. Contents should only be returned to a cleared area after they have been cleaned and have passed their own separate clearance testing.
Airborne and surface clearance testing can be undertaken using non-viable methods for speed of analysis (Air-O-Cell sample cassette with a Bio-Pump for air samples and Bio-Tapes for surface samples). Moisture testing can be conducted with a Protimeter and targeted at surfaces that have been structurally dried, areas where previous water damage had occurred and a moisture profile of the entire area compared against a moisture equilibrium level.

When a building is flooded or sustains water damage, one of the first things people tend to do is rip out and replace the cladding, but this is not generally required if mitigation and structural drying is undertaken early. When water ingress is ignored or design issues are not rectified, mould can damage wall and ceiling cladding and even structural elements of the structure – all of which can be avoided with trained observation, monitoring, holistic cleaning and appropriate remediation.
At the heart of any HVAC system are cooling coils (both within and external to the air-conditioner). During operation, the cooling coil gets damp and can build up with organic residues, which decrease the efficiency of the heat transfer process and uses more energy. Routine hygiene maintenance of the coil not only improves the quality of the air circulating across the coil, but also reduces energy use by up to 25 percent, particularly when bio-active enzymes are used to help retard future growth of bio-films.
Asset protection via mechanical maintenance is commonplace, but what is also needed is a hygiene maintenance program. Examples of increasing the service life of assets via appropriate cleaning include prolonged life of carpet: regular deep fibre cleans, as opposed to the all too common aesthetic vacuuming, can add many years to carpet; minimisation of corrosion on fan blades and other ducted air handler components from bio-film build-up and rust can generally add five years to plant life.
In the push to use less energy, we are seeing more building with less potential for natural venting, insightful design can reduce the need for mechanical heating and cooling. Generally increased ventilation increases air quality and comes with reduced potential for costly mould remediation. Above all, design must be in harmony with the local environment; what works in one climatic area may not work in another due to differences in temperature and relative humidity.
Ultimately scheduled hygiene maintenance not only increases the service life of assets, which goes a long way towards sustainability, but it also assists in providing occupants with improved air quality and with that comes enhanced occupant satisfaction, which leads to lower tenancy turnover and less frequent fitout, which also contributes to sustainable building behaviour.

By gaining a better understanding of why and how mould grows, its impact on buildings and upon occupants, and its relationship with IAQ and the building envelope, you can better understand potential health risks, as well as risk minimisation and management methods. Armed with such knowledge, you can more competently manage such risks and make more informed decisions on behalf of property owners.

Dr Heike Neumeister-Kemp is the CEO and mycologist at Mycologia. Dr Peter Kemp is a director and IAQ and SBS Consultant at Mycologia. Cedric Cheong is a director and the operations manager at Mycologia and Mould Worx, and Kevin White is a consultancy and training manager at Mycologia.

Dr Neumeister-Kemp and Dr Kemp are co-authors of Australian Mould Guideline (AMG), which was developed specifically for the Australian market and links key international standards and guidelines, particularly the IICRC S520 Standard. The duo also co-authored The Mould Worker’s Handbook: A practical guide to remediation.

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