Healthy building, sick building syndrome (SBS), disinfecting, sterilising and dehumidification
 Renovation hygiene Development of safe repair methods for water damaged buildings
Ilpo Kulmala (1), Antti Souto (2), Vesa Mäkipää (2)
(1) VTT Automation, (2) Oy Lifa Air Ltd
Abstract
Efficient control methods are needed to prevent harmful microbes and other airborne contaminants from
spreading to adjacent areas during the renovation of water-damaged buildings. Such methods are important,
especially when exposure to microbes can create a severe risk to susceptible people, such as
immune-compromised patients. In this study safe repair and drying methods were evaluated during remediation
work in a hospital. The work area was sealed and maintained under negative pressure by a recently developed
air-handling unit that can clean and dry air. The microbe and dust concentrations were high in the
construction area during removal operations, about 10 4 - 10 5 cfu/m3 and 100 mg/m3, respectively.
The respective concentrations in the exhaust air of the air-handling unit were < 10 cfu/m3 and
0.002 mg/m3; therefore, with proper control techniques, very high control efficiencies can be achieved.
KEYWORDS: renovation, dust, mould, dehumidification, filtration
Intoroduction
Water damage occurs frequently in buildings. It is often caused by plumbing leaks, due to leaky foundation
walls, poor flashing details at wall junctions, inadequate foundation drainage, and other construction
defects. Prolonged moisture build-up often occurs when leaks go unnoticed within the wall itself even
though the moisture is not manifest itself on any interior surface. This moisture build-up often results
in microbial growth. Exposure to airborne spores of such microbes can cause several adverse health effects.
These effects depend on the fungal species and on the dose and duration of the exposure and include
respiratory infections, eye and mucous membrane irritation, allergic diseases, and organic dust
toxic syndrome. Another contributing factor to these adverse health effects is suspected to be
the metabolites produced by the microbes. The proper management of water damage includes eliminating
the water source, removing mouldy materials and drying the wet structures. Drying is usually expedited
with the aid of a dehumidifier, which reduces the relative humidity by removing moisture from the air.
If the removal work is done without any control methods, the airborne microbes can spread to the
surroundings of the site and cause potentially massive exposure of building occupants or residents [1].
Such exposure is a severe health risk to susceptible people, for example, transplant patients receiving
immune-suppressive therapy or cancer care patients in hospitals, especially when the microbes contain
fungi of the species Aspergillus fumigatus or Aspergillus flavus [2].
One control method currently used in the removal of mouldy materials involves sealing the area in enclosures
maintained under negative pressure by exhaust systems discharging to the surrounding or outside air
through efficient filter systems. The negative pressure is commonly created with air-handling units
that are equipped with HEPA filters rated at 99.97% for 0.3 µm particles and designed for asbestos
abatement work. These devices are not, however, particularly suitable for water-damage repairs.
For example, in damp and dusty environments microbial growth on HEPA filters can ruin the filters
and produce odours (Mäkipää, personal communication).
The objective of this study was to develop a safe repair method for demanding applications in areas
where very high control efficiency is needed, such as in hospitals and day-care centres. For this
purpose, a new innovative portable air-handling unit was designed and constructed. It combines a
dehumidifier with a filtration unit. It consists of a prefilter, dehumidifier, a HEPA filter and a
fan. An optional gas filter is available which removes the odours produced by the metabolism of the
moulds. The dehumidifier is of the refrigerant type that cools the air to a temperature below its dew
point so that water vapour condenses on the evaporator coils and is removed with an automatic pump-out
system. It is placed upstream of the HEPA filter so that the relative humidity of the air drawn through
the filter is so low that microbial growth is prevented
Methods
The efficiency of the developed control method was evaluated during water-damage repair work in a
hospital. Two washrooms were repaired. The evaluation included measurements of airborne microbes,
total dust and volatile organic compounds (VOC) during the removal and drying stages. Before any
renovation work was started, the doors to the washrooms were removed, and the space was isolated with
temporary plastic sheeting walls. To prevent the escape of airborne contaminants from the removal
area enclosure, a portable air-handling unit was installed to maintain a negative pressure of about
5 Pa within the working area. The exhaust air was discharged into a separate measurement chamber and
further into the indoor space. Therefore, the exhaust air was prevented from mixing with the
surrounding air so that the exhaust air samples could be taken accurately. With the aid of the
measurement chamber and a real-time aerosol photometer, the possible leaks and failures in the
filtration unit could be monitored and rapidly detected. Another portable air-handling unit was
adjusted at a slightly lower airflow rate and used to supply replacement air. Filtering the
incoming air, also helped minimize the effect of ambient air contaminant concentrations on
the results. The principle of the arrangements is shown in Figure 1.
Figure 1. Arrangement of the enclosures during the removal and drying operations. The air-sampling
points are identified by the following numbers: 1= washroom, 2=enclosure, 3=exhaust air chamber.
During the removal work, a pneumatic drill was used to break up the floor pavement. The tiles were
removed with a drill-hammer. All the removed material was bagged before transport to the disposal
site. The workmen entered the area through an airlock. Within the work site the workers wore protective
clothing and used powered positive-pressure filtration units.
After the demolition and clean-up, the plastic temporary walls were removed and the drying phase was
started. At this stage the portable air-handling units were placed inside the washroom to expedite the
drying process. The washroom to be dried was kept under slightly negative pressure by discharging part
of the exhaust air outside the washroom (Figure 1).
Measurement of airborne contaminants
The efficiency of the control method for various contaminants was evaluated by measuring the airborne
microbe, total dust and VOC concentrations, both in the washroom and in the exhaust air. In addition,
during the drying phase, the air temperature and humidity were measured.
The total dust concentration was measured using a standard filter method. The samples were collected
on open-face cassettes with a diameter of 37 mm. The exhaust air concentration was also continuously
monitored with an aerosol photometer to find possible leaks in the air handling unit (TSI Dust Trak,
model 8520).
The airborne microbe concentrations were determined by collecting the samples directly the cultivation
media with a six-stage cascade impactor. Three different media were used for culturing specific microbes:
Rose Bengal-malt-extract and dichloran glycerol agar (DG18) for mesophilic fungi and
Tryptone-yeast-glucose (TYG) agar for mesophilic bacteria. After the sampling, the fungal culture
plates were incubated at 25ºC for 7 days. The fungal colonies were calculated and the genus
identified with an optical microscope.
The VOC concentrations were measured by collecting samples on Tenax tubes. After the sampling, the
exposed tubes were thermally desorbed and analyzed by the gas chromatography - mass selective detection
method. The total VOC (TVOC) concentrations were determined as the toluene equivalent.
Results
The total dust concentrations are shown in Figure 2, and the microbe concentrations are presented in Figure 3.
From Figure 2 it can be seen that the total dust concentrations were very high during the removal
operations, the mean level being more than 100 mg/m3. The concentrations in the enclosure (measuring
point 2) were somewhat lower than in the washrooms, but they clearly exceeded the Finnish exposure
limits for in-organic dust (10 mg/m3 ). Thanks to the efficient filtration of the exhaust air, the
concentrations in the exhaust air of the air-handling unit were very low, on the average 0.002 mg/m3.
Figure 2. Mean total dust concentrations. The standard deviations are shown by vertical bars.
Figure 3. Measured microbe concentrations.
The microbe concentrations in the washroom were normal before the remediation work and the genus
consisted of typical species. During the demolition work the concentration levels increased and
the commonest isolated fungal genus became Aspergillus, followed by Pe-nicillium, and Acremonium.
Of the mesophilic bacteria, the commonest was Streptomycetes. In the exhaust chamber the concentrations
were low, below 10 cfu/m3. The microbe levels in the washroom were also lower during the drying phase
than before the renovation work began.
The TVOC concentrations in the washroom were 2050 µg/m3 before the remediation. The highest concentration
was detected for an aliphatic hydrocarbon solvent (880 µg/m3) that had been a component of the detergent
used in the washroom. During the removal work the TVOC concentration decreased to 240 µg/m3, and during
the drying phase it was further reduced to 70 µg/m3. This decrease is likely due to the removal of
contaminant sources and the filtration of the air.
During the drying phase the temperature and relative humidity (RH) were measured both in the washroom and
in the adjacent corridor. The drying phase took one week, and during it the temperature varied in the
corridor from 22 to 25ºC, and the RH ranged between 40% and 60%. The temperature in the washroom was
few degrees higher than in the corridor. When the dehumidifier was first put into operation, the RH in
the washrooms decreased rapidly, but after about eight hours it levelled off to between 30% and 35%.
Discussion
The results are in agreement with previous findings in that demolition inevitably disrupts loci or fungal
growth or the accumulations of spores and releases them into the indoor air [1]. The inorganic dust emission
rates can also be very high. Therefore effective control measures are needed to prevent these contaminants
from spreading to adjacent areas and causing potentially massive exposure among residents or occupants.
The developed work method was devised for critical applications in such places as hospitals, but it can
also be used on less demanding renovation sites.
The results show that, by carefully isolating of the work area, maintaining a negative pressure within it and
filtering the exhaust air, one can efficiently prevent the escape of contaminants, and thereby eliminate the
need to evacuate occupants during renovation work. However, the use of an asbestos-abatement type of negative
air unit during the handling of mouldy materials can cause significant problems. Professional experience has
shown that, under conditions in which both nutrients and high humidity are present, microbes can grow on HEPA
filters and cause potential exposure to the metabolites of the microbes. Moreover, the negative air units
designed for asbestos work do not remove gaseous contaminants. These drawbacks can be avoided with the
apparatus presented in this paper since it helps prevent conditions favourable for microbial growth and
amplification. Another benefit of the new apparatus is that only one air-handling device is needed in
place of a separate dehumidifier and filtration unit, and therefore the space required by the machinery
is reduced. These devices have been used for about a year, and so far no mould growth has been observed.
The selection of control strategies for renovation activities depends on the type and size of the project, the
type of contaminants and the consequences of occupant and equipment exposure. However, in many cases, water
damage is hidden, and the hazards due to microbial contamination cannot be predicted. Therefore, to avoid
fatal errors, renovation work should be done using effective control techniques, particularly in situations
in which exposure can have severe consequences.
The techniques and apparatus may also be used to reduce the curing time of paints and maintain a comfortable
work environment during finishing work, but additional studies are needed to verify this.
Acknowledgements
This study belongs to the Healthy Buildings technology programme and was financially supported by Tekes.
References
1. Rautiala, S., Reponen, T., Hyvärinen, A. et al. 1996. Exposure to airborne microbes
during the repair of moldy buildings. Am. Ind. Hyg. Assoc. J. Vol 57:279-284.
2. Kuehn, T., Cacek, B., Yang, C., et al. 1996. Identification of Contaminants, Exposures, Effects, and control
options for construction/renovation activities. AshraeTransactions. Vol. (2), pp. 89 - 101.
Measuring results of Healthy Building -project
Lifa Dry&CLean in use
1. Concentration inside the working area before renovation
2. Concentration inside the working area during renovation
3. Concentration in the Lifa Dry&Clean exhaust air during renovation
4. Concentrations of airborne fungi spores and bacteria (cfu/m3)
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