Air quality surveys in a residential home in London

In this episode, we look at a case where we were called to carry out a property inspection and microbiological sampling. The purpose of the investigation was to evaluate the levels of fungal elements in the indoor air and evaluate the risk to health of the property occupants. The property itself was a two-storey detached building with rendered external brick walls and a pitched tiled roof. The building was situated in a dense woodland area surrounded by thick and mature vegetation. At the time of our inspection we found signs of penetrating damp in the living room and first floor bedrooms of the property. However, no visible contamination was observed on the internal surfaces.

Indoor air quality investigation methodology 

The sampling of total mould spores and fungal fragments was carried out in strict accordance with methods outlined in our specialist procedure manual. Based on a review of existing scientific publications, we set out a number of guideline values for the assessment of the fungal bio-burden in the indoor environment. In order to conduct a reliable assessment, it was vital to consider the outdoor concentration of fungal spores against those indoors.

In Non-viable samples, indoor concentration of fungal elements expressed as cnt/m3 indicates a problem, just as the presence of any one fungal species in high concentration indicates a problem. In contact samples, samples should always be less than 200 CFU a strip for areas to be judged as clean. Likewise, fungal element counts per cm2 higher than a non-problem area indicates a problem. Throughout our analysis, moisture mapping was carried out using a Hydrometter HB30 moisture meter and Tramax Moisture Encounter Plus.

Mould Survey Conclusions 

 After conducting our mould investigation, the fungal spore trap samples showed that the overall concentration of airborne fungal spores in the indoor areas was lower in comparison to the existing environmental background. The overall concentration of fungal spores in the indoor area ranged between 1458 and 2840 counts per cubic meter. Qualitatively, the spore trap samples collected in habitable areas of the property were dominated by Penicillium/Aspergillus type spores followed by Cladosporium and undifferentiated spores.

The distribution of fungal genera indoors indicates a marginal elevation of Penicillium/Aspergillus type of spores in comparison to the existing environmental background. The Penicillium/Aspergillus moulds are closely associated with water damage in buildings and are considered to allergenic to sensitive individuals. Overall, the assessment of the indoor air quality indicates that the air quality is good. However, marginally elevated Penicillium/Aspergillus spores are indicative of water damage in the property, so we advised the owner to keep an eye on dampness in case of future problems.

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