Fungal spore transport through a building structure

Abstract

The study carried out laboratory measurements with a full-scale timber frame structure to determine penetration of inert particles with size distribution from 0.6 to 4 µm and spores of Penicillium and Cladosporium through the structure. Pressure difference over and air leakage through the structure were varied. Measurements at moderate pressure differences resulted in the penetration factors within the range of 0.05 to 0.2 for inert particles, and indicated also the penetration of fungal spores through the structure. The measurements showed that the penetration was highly dependent on pressure difference over the structure but not on holes in surface boards of the structure. The results show that surface contacts between the frames and mineral wool may have a significant effect on penetration. The penetration was approximately constant within particle size rage of 0.6-2.5 µm, but particles with diameter of 4.0 µm did not penetrate through the structure at all even at a higher-pressure difference of 20 Pa, except in the case of direct flow-path through the structure. Results have important consequences for practical design showing that penetration of fungal spores through the building envelope is difficult to prevent by sealing. The only effective way to prevent penetration seems to be balancing or pressurizing the building. In cold climates, moisture condensation risk should be taken into account if pressure is higher indoors than outdoors. Determined penetration factors were highly dependent on the pressure difference. Mechanical exhaust ventilation needs a special consideration as de-pressurizing the building may cause health risk if there is hazardous contamination in the building envelope exists. PRACTICAL IMPLICATIONSMeasurements at moderate pressure differences allowed determining penetration factors within the range of 0.05 to 0.2 for inert particles in a size range of 0.6-2.5 µm and indicative results with fungal spores confirmed the penetration through the wooden floor structure. Both measurements showed that the penetration was highly dependent on pressure difference and not dependent on holes in surface boards of the structure. The results are likely to show that surface contacts of mineral wool with other building elements may have an important role on the penetration.

Lateral fungal spore movement inside a simulated wall

“…Overall, spore migration may have been a function of air pressures inside the stud bays because pressure levels were similarly proportional to spore levels in both experiments. This finding is in agreement with Mosley et al (2001) and Airaksinen et al (2003) who determined that penetration factors for particles with diameters similar to those in our experiments were dependent upon pressure differences. Their analysis also showed that the bays were properly decontaminated between trials and that background spore levels did not influence spore levels inside the bays.…”

“…Buttner et al (1999) demonstrated that HVAC (heating, ventilating, and air conditioning) systems in a laboratory setting have the potential to allow the movement of airborne spores into a simulated room. Airaksinen et al (2003) found that spore movement was possible through residential flooring held vertically between two chambers inside a laboratory. Fazio et al (2005) examined spore exfiltration through simulated walls to test a new penetration procedure.…”

Mold spore penetration through wall service outlets: a pilot study

“…This estimation formula is similar to the one used by Airaksinen et al (2003) and is calculated from…”

“…Air sampling instruments inside the room recorded spore levels, and findings revealed that fungal spores had penetrated into the space. Airaksinen et al (2003) measured penetration factors for Penicillium spores and Cladosporium spores across an insulated residential floor held vertically between two chambers inside a laboratory. The wooden flooring contained holes that represented orifices associated with poor plumbing practices.…”

Moulds in floor dust – a particular problem in mechanically ventilated rooms? A study of adolescent schoolboys under the Danish moulds in buildings program

“…Possible mechanisms for this higher prevalence include: the systems may themselves be a source of pollution from dirty filters or ducts with or without recycling of the air, while an unbalanced system, with a lower pressure in the room than outside, can bring spores and other particles from constructions and crawl space/lofts etc into the room. Experiments have shown this both in chambers and in the field (21,22). The combined effect of moulds and ventilation might be the result of a higher airflow keeping the dust whirled up by the activity of the pupils, in the breathing zone for a longer time, and thereby increasing the exposure for the occupants of the classrooms.…”