Jeff Charlton introduces us to the silent killer potentially lurking in the damp, dark corners of our homes and offices – toxic mould. One fact stands out: prevention is definitely better than cure.
THE HVCA industry may be facing its biggest opportunity - or 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 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 to 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 more than 100,000 species, but these are the species usually found in modern construction.

Stachybotrys, penicillium /aspergillus, trichoderma, are typical toxic moulds found in indoor-air sampling, and these can cause a variety of symptoms - from asthma, depression, skin
irritation, flu-like symptoms, to liver or lung cancer, with spontaneous abortion risk to a foetus.

Absenteeism, or poor worker performance, and Friday blues, are typical symptoms of sick building syndrome which, more often than not, are linked to mould, or other 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 the 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. Prevention, rather than decontamination is 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.

It should always be accompanied by independent clearance and certification. Contractors may consider the installation of in-line ultraviolet light sanitation. This 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. 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 chemicals - including 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 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, dust and debris analysis should also accompany air makeup for oxygen and carbon dioxide levels, and these results could influence decisions regarding additional work.

Building Science provides surveys, air sampling and laboratory assessments with clearance certification if required. See www.claimtech.­co.uk.