Abstract
This paper reports results obtained from a surface (both visually clean and dirty/dusty surfaces) and active (aggressive or activated) air testing scheme on 140 residential rooms in England, without visible water damage or mould growth, along with a few rooms with visible mould growth/water damage tested for comparison purposes. The aim was to establish normal background levels of mould in non-water-damaged interiors to benchmark a 'normal' indoor environment, and in turn when there is a need for further investigation, and, possibly, remediation. Air and surface mould was quantified based on the activity of β-N-acetylhexosaminidase (EC 3.2.1.52; NAHA). The obtained readings showed a log-normal distribution. Ninety-eight percent of the samples obtained from visually clean surfaces were equal to or less than 25 relative fluorescence units (RFU), which is suggested to be the higher bound for the range which can be used as a success criterion for surface cleaning/remediation. Of samples obtained from visually dirty/dusty surfaces, around 98% were below 450 RFU, which is suggested to define the lower-bound for abnormally high levels of mould, rare even on dirty/dusty surfaces. Similarly, around 98% of the air samples were found to have 1700 RFU or below. Values above 1700 RFU are therefore deemed unlikely in a non-problem indoor environment and can be indicative of a possible problem inducing mould growth. The samples with values below 1700 were further divided into three proposed sub-categories. Finally, the obtained RFU values and the suggested benchmarks were compared to those obtained from 17 non-residential indoor environments tested previously in Copenhagen, and the benchmarks that are currently used in Danish national standards, and they were both found to be highly congruent, suggesting that local climate regimes and room functions might not be as influential on indoor mould levels as commonly thought, or that the nuances between England and Denmark in terms of these factors are not strong enough to lead to sizable changes in the typical indoor mould levels in these countries' building stocks.
Highlights
Mould growth is one of the most persistent problems affecting the indoor built environment and the UK is among those countries where it is claimed that this problem is especially pronounced [1] with an estimated >1 million properties considered to have a significantly higher than average risk of harm due to seasonal or continuous mould and damp in England alone [2]
The identification of normal background surface mould concentrations was undertaken in two stages: (1) surface samples taken from visually clean surfaces were used to benchmark the upper threshold for the level of mould concentration to target following a cleaning/remediation work, 1These data have been collected by Mycometer A/S between 2008 and 2011, and not been published elsewhere but partly form the basis of the current Danish national benchmarks
In order to identify when a surface is to be considered in need of remediation, those 316 samples from visually dirty/dusty surfaces with heightened NAHA readings were filtered through microscopy analysis
Summary
Mould growth is one of the most persistent problems affecting the indoor built environment and the UK is among those countries where it is claimed that this problem is especially pronounced [1] with an estimated >1 million properties considered to have a significantly higher than average risk of harm due to seasonal or continuous mould and damp in England alone [2]. An already limited number of suggested values for acceptable indoor mould levels are based on institutional consensus or professional judgement rather than concrete data obtained by means of well-established, transparent testing protocols, and are often contradictory. The differentiation between a ‘problem’ indoor environment and a ‘normal’ indoor environment has been the subject of many scholarly publications. Richards, in his early review [9], defines a damp/ problem home as one where there is visible mould, which is in broad agreement with the findings of Hyvärinen et al [10]. The guidelines either have no specific criteria, or use visible mould growth (or water damage, or musty odours) as the remediation triggering event The guidelines either have no specific criteria, or use visible mould growth (or water damage, or musty odours) as the remediation triggering event (e.g. [13, 14]), which are of little use when high mould concentrations have not (yet) manifested in the form of visible mould, when there is no obvious water damage or when the mould is hidden inside cavities
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