Tight Buildings and Mould Problems

      Facility managers and building owners are faced with new responsibility and liability as the building industry follows a trend in tighter building construction with paper and chalk products (plasterboard) held together with tape and silicon sealer. The designed low air leakage (part L) and new general tightness requirements in part 3 and 4  means that moisture generated by occupation or dew point and condensation has nowhere to go and will condense or be adsorbed into hydrophilic materials such as plasterboard.

Moisture will activate the ubiquitous mould spore and subject to environmental parameters being met, usually present in the built environment, mould growth will follow. Historic buildings often had mould too, but differences in today’s building materials, surface finishes and air movement from leakage generally meant that mould toxic by-products, (mycotoxins)did not affect the occupants. 

Today less than 20 toxic moulds have been identified from over 100,000 species but these are the species usually found in modern construction. Toxic is not a misnomer, several genus of mould found in ventilation systems and building envelope have also been used by the US military as WMDs (weapons of mass destruction) in Afghanistan, Laos with thousands of casualties confirmed.

Stachybotrys, Penicillium/Aspergillus, Trichoderma are typical toxic moulds found in indoor air sampling and these can cause a variety of healthy symptoms from asthma, depression, skin irritation, flu like symptoms to liver or lung cancer with spontaneous abortion risk to foetus. Absenteeism or poor worker performance with Friday blues are typical symptoms of Sick Building Syndrome which, more often than not, are linked to mould or other IAQ Indoor air Quality problems. When you consider that mould (Penicillium) is used in medicine to kill bacteria, you should consider that pharmacy doses are minute in relationship to building exposure which may be thousands of times prescribed dose. Bio films of bacteria and mould regularly have localised battles to control moist growth areas within the building, often resulting in circular stains and odour or illness.

Where mould or bio films are found, cleaning and sanitation is required and decontamination controls may be similar to asbestos removal if clearance certification is required and therefore prevention rather than decontamination should be the watchword. Correct air exchanges and flow distribution is of course essential and should be measured with tracer gas especially when wall partitions have been added after the original HVAC installation.

Duct cleaning may be required but it should be recognised that sanitation from mould or indeed combative bacteria goes well beyond the standards or recommendations of HVCA TR2 standard and should always be accompanied by independent clearance and certification. Contractors may consider the installation of   in line Ultra Violet light sanitation which may be seen as a customer  benefit from the reduction of HVAC running costs and carbon footprint with the  added value of  “LEED” or “BREEAM” points from recognised  environmental benefits.

Toxic mould and its components are not usually identified by conventional SAS air sampling techniques because of culture agar/spore growth requirements, vector issues and most importantly non viable spores, a significantly greater health issue than viable spores, cannot be identified on culture plates. Mould spores contain a variety of chemicals which are slowly released to digest substrates they land on. When the spore is killed by desiccation or the application of sanitising agent such as bleach, they split open and release these chemicals which include mycotoxins, which  are responsible for  health hazards. For this reason bleach and  other chemical agents should not generally be used to destroy mould.
 
While health issues are the focus of this article it should be recognised that mould will destroy any cellulose material and can grow in mmmf and fibreglass, which although inorganic always has a bio film as a food source. This means insulated or bare duct work can become contaminated and other building materials or finishes can be destroyed. Spores can vary in size and may in some circumstances be trapped by Heppa filtration but mycotoxins are almost a gas and size can be as a small as .027 micron. It can be seen that prevention by design and measurement must be a first choice over degradation, poor health and associated absenteeism.

Professional HVAC contractors may consider the potential for additional work and client benefit from the measurement of air distribution, moisture control and air exchanges together with insulation and the potential presence of both viable and non viable mould. Air analysis for Volatile Organic Chemicals VOCs, dust and debris analysis should also accompany air make up for oxygen and carbon dioxide levels, and these results could influence decisions regarding additional work.