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Monitored Indoor Environmental Quality of a Mass Timber Office Building: A Case Study

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A broad range of building performance monitoring, sampling, and evaluation was conducted periodically after construction and spanning more than a year, for an occupied office building constructed using mass timber elements such as cross-laminated timber (CLT) floor and roof panels, as well as glue-laminated timber (GLT) beams and columns. This case study contributes research on monitoring indoor environmental quality in buildings, describing one of the few studies of an occupied mass timber building, and analyzing data in three areas that impact occupant experience: indoor air quality, bacterial community composition, and floor vibration. As a whole, the building was found to perform well. Volatile organic compounds (VOCs), including formaldehyde, were analyzed using multiple methods. Formaldehyde was found to be present in the building, though levels were below most recommended exposure limits. The source of formaldehyde was not able to be identified in this study. The richness of the bacterial community was affected by the height of sampling with respect to the floor, and richness and composition was affected by the location within the building. Floor vibration was observed to be below recognized human comfort thresholds.
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buildings
Article
Monitored Indoor Environmental Quality of a Mass
Timber Oce Building: A Case Study
Jason Stenson 1, 2, *, Suzanne L. Ishaq 2, Aurélie Laguerre 3, Andrew Loia 1, Georgia MacCrone 2,
Ignace Mugabo 4, Dale Northcutt 1,2, Mariapaola Riggio 5, Andre Barbosa 4, Elliott T. Gall 3
and Kevin Van Den Wymelenberg 1,2
1Energy Studies in Buildings Laboratory, Department of Architecture, University of Oregon, Eugene,
OR 97403, USA; andrewloia@gmail.com (A.L.); tdnorth@uoregon.edu (D.N.);
kevinvdw@uoregon.edu (K.V.D.W.)
2Biology and the Built Environment Center, University of Oregon, Eugene, OR 97403, USA;
sueishaq@uoregon.edu (S.L.I.); gmaccro5@uoregon.edu (G.M.)
3Mechanical and Materials Engineering, Portland State University, Portland, OR 97201, USA;
aurelie@pdx.edu (A.L.); gall@pdx.edu (E.T.G.)
4School of Civil & Construction Engineering, Oregon State University, Corvallis, OR 97331, USA;
nkurikim@oregonstate.edu (I.M.); Andre.Barbosa@oregonstate.edu (A.B.)
5Department of Wood Science & Engineering, Oregon State University, Corvallis, OR 97331, USA;
mariapaola.riggio@oregonstate.edu
*Correspondence: jstenson@uoregon.edu
Received: 14 May 2019; Accepted: 11 June 2019; Published: 13 June 2019


Abstract:
A broad range of building performance monitoring, sampling, and evaluation was
conducted periodically after construction and spanning more than a year, for an occupied oce
building constructed using mass timber elements such as cross-laminated timber (CLT) floor and
roof panels, as well as glue-laminated timber (GLT) beams and columns. This case study contributes
research on monitoring indoor environmental quality in buildings, describing one of the few studies of
an occupied mass timber building, and analyzing data in three areas that impact occupant experience:
indoor air quality, bacterial community composition, and floor vibration. As a whole, the building
was found to perform well. Volatile organic compounds (VOCs), including formaldehyde, were
analyzed using multiple methods. Formaldehyde was found to be present in the building, though
levels were below most recommended exposure limits. The source of formaldehyde was not able
to be identified in this study. The richness of the bacterial community was aected by the height of
sampling with respect to the floor, and richness and composition was aected by the location within
the building. Floor vibration was observed to be below recognized human comfort thresholds.
Keywords: mass timber; cross laminated timber; air quality; bacterial community; vibration
1. Introduction
Mass timber wood products are gaining adoption in US buildings through changes to
building codes and standards [
1
,
2
], as well as specialized manufacturing facilities coming on-line.
Prefabricated panelized products like Cross-Laminated Timber (CLT), Dowel-Laminated Timber (DLT),
Nail-Laminated Timber (NLT) and Mass Plywood Panels (MPP) are now able to be used as structural
floor, roof and wall assemblies. These structural elements impact the type and distribution of major
materials used throughout a mass timber building as compared to other construction types. They
often take the place of concrete or steel, and their relatively lightweight may impact floor vibrational
performance (serviceability). They often remain exposed as interior finished surfaces, changing the
Buildings 2019,9, 142; doi:10.3390/buildings9060142 www.mdpi.com/journal/buildings
Buildings 2019,9, 142 2 of 15
makeup of surface to air volume of interior materials, and possibly impacting indoor air chemistry and
indoor microbial community dynamics.
Indoor Environmental Quality (IEQ) of buildings include aspects of the built environment that
aect occupant health and well-being, and commonly includes factors such as indoor air quality, thermal
comfort, visual comfort and acoustic comfort [
3
]. Occupant satisfaction and productivity are common
metrics of IEQ, with short-term and long-term health eects for occupants being more challenging
to quantify, and understanding of source characterization and exposure assessment continuing to
evolve [
4
]. The contribution of wood in creating healthy environments is discussed in several studies,
many of which are based on occupant feedback rather than on quantitative monitoring data (acoustic
comfort in residential timber buildings [
5
], thermal comfort and air quality [
6
], general ‘perceived’
IEQ [
7
]). Most quantitative IEQ studies are limited to measurements in a laboratory environment or in
unoccupied buildings (acoustic performance of assemblies [
8
], floor vibration performance [
9
,
10
]). In a
few exceptions IEQ data were collected in occupied buildings, however, in most cases these full-scale
studies monitored data related to one single IEQ performance indicator (thermal comfort [
11
,
12
];
contribution of wood nonstructural elements to air quality [13]).
This case study contributes to research on monitoring IEQ in buildings, describing one of the few
studies of an occupied mass timber building, and using exposure measurement methods for three
important factors: indoor air quality, indoor bacterial community and vibrational comfort. Other IEQ
indicators such as acoustic performance and occupant response were investigated in the study, but
data were too limited; therefore, these indicators are omitted in this paper.
A newly constructed and occupied building oers layers of building performance complexity.
Simply adding finishes and furnishings to a wood structure successively changes the Volatile organic
compound (VOC) profile and concentrations, with barrier and sink eects reducing or delaying some
emissions [
14
]. Introducing occupants, occupant behavior, and variable environmental conditions
such as temperature and humidity fluctuations also aect indoor air quality. Monitoring indoor air
quality of an occupied mass timber building, including characterizing VOCs that are present, will help
to inform future research on primary emissions from CLT and secondary reaction products in indoor
air that may be sourced in part from CLT.
The indoor microbial community is primarily sourced from indoor occupants and from outdoor
microbial communities which are dispersed indoors from outdoor-sourced ventilation or occupant
trac [
15
]. It is unknown whether the use of CLT building materials would directly contribute to the
indoor microbial community, either by direct deposition of microorganisms from materials into general
dust, or through the contribution of solid or gaseous chemicals which might aect microorganisms.
Due to the unique combination of occupants, building materials, local environmental conditions,
and geographic location, the microbial communities in buildings tend to be highly variable between
dierent structures. Thus, we sought to compare passive sampling height and open oce location for
the implications each may have on indoor microbial community.
The mass of CLT buildings, when compared to conventional concrete buildings, might pose a
challenge for vibrational serviceability design. Some design criteria for controlling floor vibrations are
dicult to incorporate in general design guides, as they are dependent on variable conditions, such as
live loads [
16
]. Monitoring floor vibration of mass timber systems is therefore important to inform
serviceability design criteria for new types of construction systems.
This case study investigates performance of a mass timber building; how building materials
and assemblies impact indoor air quality, indoor bacterial community, and vibration in an oce
environment of an occupied mass timber building. The case study site is Albina Yard, which was
constructed in Portland, Oregon in 2016 and was the first mass timber oce building in the U.S. to use
domestically sourced and produced CLT [
17
]. It is a 1500 m
2
, four-story building with a footprint of
approximately 14 m
×
26 m and is comprised of oce and ground floor retail space. Its rectangular
building form is elongated in the east-west direction with predominately glazed east and west façades.
Floor and roof assemblies at Albina Yard use 105 mm thick three-lamella (3-lam) CLT as structural
Buildings 2019,9, 142 3 of 15
diaphragm with panels spanning in the E-W direction, and are supported by glue-laminated timber
(GLT) beams and columns. GLT beams are 171 mm
×
610 mm and 171 mm
×
457 mm, and columns
are 222 mm
×
305 mm and 222 mm
×
229 mm, with larger cross-sections of both occurring at the
perimeter of the building. All three structural components are left unfinished and exposed at the
ceiling. Light-framed shear walls constitute the lateral load resisting system. East and west exposures
are floor to ceiling structural GLT window walls with small operable awning units at the floor level.
The majority of the fourth floor is an open-plan oce layout with computer workstations, a kitchen
area and an adjacent alcove housing server, copier and printer equipment. Other spaces include large
and small conference rooms, a laser cutter room and restrooms. Finish surface materials found on this
level include painted gypsum wall board, carpet floor covering and exposed unfinished CLT ceiling.
The floor assembly is comprised of 105 mm 3-lam CLT, 25 mm gypcrete topping, and carpet squares
without a pad.
2. Materials and Methods
2.1. Indoor Air Quality
A range of direct-measurement continuous monitoring air quality sensors were deployed during
four week-long periods spread over more than a year and capturing predominantly heating season
building operation in December 2016 (week 1), March 2017 (week 2), October 2017 (week 3) and
January 2018 (week 4). Sensors were deployed as a contained air quality monitoring kit at two indoor
locations, in the northeast and southwest corners of the fourth-floor open oce space (Figure 1), to
capture potential influence of window operation as well as dierences in solar orientation. Indoor air
quality monitoring kits included sensors measuring the following: air velocity, barometric pressure,
carbon dioxide, carbon monoxide, formaldehyde, ozone, particulate matter, radon, relative humidity,
solar radiation, temperature, and total volatile organic compounds. A similar air quality monitoring
kit, excluding radon and including wind speed and direction sensors was deployed in an outdoor
ground-level patio location onsite. Table 1lists air quality sensors and samplers with results reported
in this study.
Table 1. Air quality monitoring and sampling instrumentation used in reported results.
Make Model Parameter(s)
Entech BLV1A & HDS-F03 Bottle-Vac Helium Diusion Whole Air Sample (1 L)
Entech BLV1A & RS-QTS1 Evacuated Bottle-Vac Whole Air Grab Sample (1 L)
Entech CS1200ES7 Evacuated Canister Whole Air Outdoor Sample (6 L)
GrayWolf FM-801 Formaldehyde (<20–1000 ppb, +/4 ppb <40 ppb,
+/10% of reading 40 ppb)
TSI Velocicalc IAQ Probe 986 Carbon Dioxide (0–5000 ppm, +/3% of reading or
50 ppm whichever is greater)
During sampling weeks 3 and 4, passive whole air helium diusion sampling (HeDS) for analysis
of VOCs was added to the indoor kits [
18
]. 1-liter canisters (Entech, Bottle-Vac) filled with helium to a
slight positive pressure were deployed in triplicate at each location. A calibrated orifice exchanged a
portion of the helium in each canister with ambient air over the week, providing, in theory, a near
constant sampling rate. After the collection period, canisters were again filled with helium to the initial
pressure and weighed to calculate helium dilution factors. An outdoor whole air sample was captured
on the roof using a 6-liter evacuated canister (Entech, Silonite Canister) and flow controller. Additional
one-minute grab samples were also captured at various indoor locations using 1-liter evacuated
canisters with a calibrated orifice. In the laboratory, proton transfer reaction-time of flight-mass
spectrometry (PTR-TOF-MS) [
19
,
20
] was used for quantification of VOCs following a described method
with specific operational parameters described elsewhere [
21
,
22
], connecting canisters directly to the
PTR-TOF-MS (PTR-TOF 1000, Ionicon Analytik GmbH, Innsbruck, Austria) inlet for analysis.
Buildings 2019,9, 142 4 of 15
Buildings 2019, 9, x FOR PEER REVIEW 4 of 15
(Figure 1). One location, the northeast corner of the open office, was a location common to the sample
weeks with full monitoring equipment. A storage closet with no mechanical ventilation was
monitored, as was the laser cutter room with additional dedicated mechanical exhaust.
Figure 1. Annotated Level 4 Plan of Albina Yard showing air quality and microbial, monitoring and
sampling locations.
2.2. Bacterial Community
Dust was collected from the indoor open office environment in three locations and from one
outdoor ground-level patio location with passive sampling integrated into the air quality monitoring
kits. Samples were collected using 150 mm × 15 mm sterile polystyrene petri dishes. Both petri dish
lids and bases were used as settling dishes, with 6 collection plate surfaces per sample. At each indoor
monitoring kit, plates were deployed at three heights: on top of the kit at 1.12 m above finish floor,
on a shelf within the kit enclosure at 0.88 m above finish floor, and below the kit at finish floor level.
Only the shelf within the kit was used for sampling at the outdoor location. Plates were allowed to
sit at ambient conditions for a period of one week, then sealed with parafilm and stored in sampling
bags for transport to the laboratory.
Plates were stored at 20 °C in the laboratory until DNA extraction was performed, at which
point, dust from all six plate surfaces per sample was collected using sterile nylon-flocked swabs and
100 µL of phosphate-buffered solution per dish surface. Swab tips and PBS solution were added
directly to bead tubes for extraction. Nucleic acids were extracted using the MoBio PowerSoil DNA
Extraction Kit (MoBio, Carlsbad, CA, USA) following kit instructions.
The V3 and V4 (319F-806R) regions of the 16S rRNA gene were polymerase chain reaction (PCR)
-amplified following a previously described protocol [23], and amplicons were purified with a bead-
based clean-up using Mag-Bind RxnPure Plus (Omega Bio-tek, Norcross, GA, USA). Cleaned DNA
was quantified using Quant-iT dsDNA assay kit, and pooled with equal concentrations of amplicons
for Illumina Miseq ver 4 paired-end sequencing using a 250-cycle kit. Sequence data is available from
Figure 1.
Annotated Level 4 Plan of Albina Yard showing air quality and microbial, monitoring and
sampling locations.
Outside of these four weeks of intensive monitoring, GrayWolf FM-801 formaldehyde monitors
were also deployed for longer periods in three indoor locations that varied in use and ventilation
rate (Figure 1). One location, the northeast corner of the open oce, was a location common to the
sample weeks with full monitoring equipment. A storage closet with no mechanical ventilation was
monitored, as was the laser cutter room with additional dedicated mechanical exhaust.
2.2. Bacterial Community
Dust was collected from the indoor open oce environment in three locations and from one
outdoor ground-level patio location with passive sampling integrated into the air quality monitoring
kits. Samples were collected using 150 mm
×
15 mm sterile polystyrene petri dishes. Both petri dish
lids and bases were used as settling dishes, with 6 collection plate surfaces per sample. At each indoor
monitoring kit, plates were deployed at three heights: on top of the kit at 1.12 m above finish floor, on
a shelf within the kit enclosure at 0.88 m above finish floor, and below the kit at finish floor level. Only
the shelf within the kit was used for sampling at the outdoor location. Plates were allowed to sit at
ambient conditions for a period of one week, then sealed with parafilm and stored in sampling bags
for transport to the laboratory.
Plates were stored at
20
C in the laboratory until DNA extraction was performed, at which
point, dust from all six plate surfaces per sample was collected using sterile nylon-flocked swabs
and 100
µ
L of phosphate-buered solution per dish surface. Swab tips and PBS solution were added
Buildings 2019,9, 142 5 of 15
directly to bead tubes for extraction. Nucleic acids were extracted using the MoBio PowerSoil DNA
Extraction Kit (MoBio, Carlsbad, CA, USA) following kit instructions.
The V3 and V4 (319F-806R) regions of the 16S rRNA gene were polymerase chain reaction
(PCR) -amplified following a previously described protocol [23], and amplicons were purified with a
bead-based clean-up using Mag-Bind RxnPure Plus (Omega Bio-tek, Norcross, GA, USA). Cleaned
DNA was quantified using Quant-iT dsDNA assay kit, and pooled with equal concentrations of
amplicons for Illumina Miseq ver 4 paired-end sequencing using a 250-cycle kit. Sequence data is
available from the National Center for Biotechnology Information (NCBI)’s Sequence Read Archive
(SRA) under BioProject Accession PRJNA532899.
DNA sequence filtering, noise reduction, dereplication, sequence variant picking, chimera removal
and taxonomic identification were performed within the DADA2 package [
24
] of the R statistical
platform (R Core Team 2018). The first and last 10 bases were trimmed from sequences, with an
additional 10 bases trimmed from the ends of reverse sequences to remove low-quality bases. Max
expected errors were 2 for forward and 3 for reverse sequences, with no ambiguous bases accepted,
and any residual phiX DNA removed. The Silva ver. 132 database was used for taxonomy [
25
], and
both DNA extraction and PCR negative controls were used to identify potential contaminants and
remove sequence variants from samples [
26
]. Sequences were rarified to 4450 per sample. Analysis
was performed with R packages phyloseq [
27
], vegan [
28
], DESEQ2 (on non-rarefied data) [
29
], and
visualized with ggplot2 [
30
]. Species’ richness was compared using generalized linear mixed eects
model via the lme4 package [31], with the year collected as a fixed eect.
2.3. Vertical Vibration
A floor vibration study was conducted during week 4 and focused on a section of the fourth-floor
open oce area subject to footfall and various impacts from oce activities, and followed a dynamic
monitoring study [
32
]. The purpose was to measure the vertical floor accelerations, capturing the
floor response to passersby. Acceleration response time-series were collected to measure peak vertical
floor acceleration responses associated with regular oce activities and to understand the frequency
content of the response within the range of human comfort for comparison with existing design
standards [3335].
Figure 2shows the northwest portion of the floor plan with locations where accelerometers were
installed. To measure the vertical accelerations triggered by footfall, four uniaxial accelerometers were
installed on the floor, which were placed close to the mid-span of three consecutive structural bays.
The accelerometers were secured in access points to the base of floor boxes that were fixed to the CLT
floor panels and then connected to a data acquisition system through BNC cables, and data stored in a
laptop computer. The laptop was remotely accessible, allowing for data to be monitored and stored.
Table 2below contains a summary of the equipment used.
A data-recording trigger was set for recording events of interest. When the floor vertical
acceleration at any of the accelerometers reached a value of +/
0.02 g (g =9.81 m/s
2
), all accelerometers
would record for a total duration of 10 seconds, starting 0.125 s before the triggering event to ensure
that the triggering signal was included in the data. The threshold value was selected by recording
normal walking at distances similar to the estimated distances between the on-site pathways and the
locations of accelerometers. An event was considered relevant if its time domain profile matched
the profile of a normal walk at approximately two steps per second. This was determined in a lab
environment and confirmed onsite during installation. Data collection was performed at 2048 Hz, over
a one-week period, totaling 1130 events.
To evaluate the frequency content of the signals collected, power spectral densities (PSDs) of
the signals were evaluated using the pwelch algorithm in MATLAB’s signal processing toolbox
(MathWorks, 2018). In the pwelch function, a data window size of two seconds and overlap size of
half-second was used for averaging purposes. The following processing steps were conducted before
the PSDs were evaluated: Band-pass finite impulse response (FIR) filter with cutorange of 0.5–20 Hz
Buildings 2019,9, 142 6 of 15
and filter order of 4098; Down-sampling from the original sampling frequency of 2048 Hz to a sampling
frequency of 256 Hz.
Buildings 2019, 9, x FOR PEER REVIEW 5 of 15
the National Center for Biotechnology Information (NCBI)’s Sequence Read Archive (SRA) under
BioProject Accession PRJNA532899.
DNA sequence filtering, noise reduction, dereplication, sequence variant picking, chimera
removal and taxonomic identification were performed within the DADA2 package [24] of the R
statistical platform (R Core Team 2018). The first and last 10 bases were trimmed from sequences,
with an additional 10 bases trimmed from the ends of reverse sequences to remove low-quality bases.
Max expected errors were 2 for forward and 3 for reverse sequences, with no ambiguous bases
accepted, and any residual phiX DNA removed. The Silva ver. 132 database was used for taxonomy
[25], and both DNA extraction and PCR negative controls were used to identify potential
contaminants and remove sequence variants from samples [26]. Sequences were rarified to 4450 per
sample. Analysis was performed with R packages phyloseq [27], vegan [28], DESEQ2 (on non-
rarefied data) [29], and visualized with ggplot2 [30]. Species’ richness was compared using
generalized linear mixed effects model via the lme4 package [31], with the year collected as a fixed
effect.
2.3. Vertical Vibration
A floor vibration study was conducted during week 4 and focused on a section of the fourth-
floor open office area subject to footfall and various impacts from office activities, and followed a
dynamic monitoring study [32]. The purpose was to measure the vertical floor accelerations,
capturing the floor response to passersby. Acceleration response time-series were collected to
measure peak vertical floor acceleration responses associated with regular office activities and to
understand the frequency content of the response within the range of human comfort for comparison
with existing design standards [33–35].
Figure 2 shows the northwest portion of the floor plan with locations where accelerometers were
installed. To measure the vertical accelerations triggered by footfall, four uniaxial accelerometers
were installed on the floor, which were placed close to the mid-span of three consecutive structural
bays. The accelerometers were secured in access points to the base of floor boxes that were fixed to
the CLT floor panels and then connected to a data acquisition system through BNC cables, and data
stored in a laptop computer. The laptop was remotely accessible, allowing for data to be monitored
and stored. Table 2 below contains a summary of the equipment used.
Figure 2. Uniaxial accelerometer layout. The dashed lines represent GLT beams and girders.
Dimensions refer to the center of the accelerometers.
Figure 2.
Uniaxial accelerometer layout. The dashed lines represent GLT beams and girders. Dimensions
refer to the center of the accelerometers.
Table 2. Description of vibrational test equipment used.
Item Description
Accelerometers 4–PCB 393B04
Data acquisition 1–NI cDaq 9178
Connectors 4–BNC cables
Data storage 1–Laptop equipped with NI LabVIEW SignalExpress 2014
3. Results & Discussion
3.1. Indoor Air Quality
Carbon dioxide (CO
2
) levels in indoor air are tied to occupancy and ventilation, as humans
exhale CO
2
and ventilation rate reduces indoor concentrations by exchanging indoor air with outdoor
air. A workplace exposure limit of 5000 ppm as an 8-hour time-weighted average (TWA) set by the
Occupational Safety and Health Administration (OSHA) has been the standard commonly referenced.
More recently CO
2
has been investigated as a direct indoor air pollutant and not just an indicator of
ventilation rate required for the dilution of other human associated indoor air pollutants in buildings.
It has been shown that CO
2
concentrations as low as 1000 ppm impact occupant decision making
performance [36] and demonstrated declines in cognitive test scores of oce workers [37].
In reviewing week 1 of collected air quality monitoring data from this study, CO
2
levels were safe
and typical for an oce. However, one-minute trend data revealed that the mechanical ventilation
system may not be operating as intended. It was discovered that an outside air damper for the ERV
was closed. The issue was remedied and the result can be seen in Figure 3, where weekday average
CO2concentrations are reduced from week 1 levels in subsequent monitored weeks.
Buildings 2019,9, 142 7 of 15
Figure 3.
Weekday average indoor CO
2
and HCHO by time of day monitored in the northeast corner
of the fourth-floor open oce area. Formaldehyde reported using GrayWolf FM-801.
Formaldehyde (HCHO) is a common indoor air pollutant that has been classified as a known
human carcinogen [
38
]. Indoor air sources include emissions from building materials, particularly in
new construction, as emission rates from new materials decrease over time. Secondary formation of
HCHO can also occur in indoor air, for example, from ozone-initiated reaction with terpenes [
39
,
40
].
There are numerous potential indoor as well as outdoor sources of HCHO, these include the use of
consumer products and human activities indoors, industrial and vehicle emissions are among urban
atmospheric sources outdoors. The 2010 World Health Organization (WHO) Guidelines for Indoor Air
Quality recommend a 30-minute exposure limit of 0.1 mg/m
3
(81 ppb) for formaldehyde to prevent
both short-term and long-term health eects [
41
]. Permissible and recommended exposure limits do
vary by agency, ranging both higher and lower than the WHO guideline. However, the WHO guideline
continues to be supported, even found to be “highly precautionary” [42].
HCHO results from week 3 & 4 captured with a GrayWolf FM-801 formaldehyde meter are
reported in Figure 3as weekday average values by time of day and the maximum 30-minute value
recorded by time of day for both monitored periods. The overall maximum was 30 ppb in the open
oce for these two weeks, below the WHO guideline.
The same sensors were deployed for longer monitoring periods in two additional spaces along
with the open oce: the laser cutter room with additional exhaust ventilation and a storage closet
with no mechanical exhaust. No attempts were made to control access to either space or influence
occupant behavior and both rooms were accessed and used as required of normal business operations.
The laser cutter room, with dedicated exhaust ventilation, saw slightly lower HCHO on average than
the open oce, and the storage closet saw higher values, with a maximum 30-minute reading of 63 ppb
recorded in the storage closet.
VOCs were also analyzed from various locations throughout the building using one-minute
grab samples captured with evacuated canisters. Grab samples oered a quick method of collecting
additional samples beyond the weeklong time-integrated HeDS samples collected at the monitoring
kit locations. They were also useful for sampling locations where monitoring equipment could not
be deployed for the week. Locations included the ground floor lobby which has some additional
natural ventilation from building occupants entering and exiting the building, the top of the main stair
constructed of CLT and without mechanical ventilation and the storage closet mentioned above.
Buildings 2019,9, 142 8 of 15
Six common VOCs were selected for analysis: acetone, formaldehyde, methanol, benzene, toluene
and monoterpenes. All have outdoor and indoor sources and all of them except benzene and toluene
are known to be emitted from wood products, but each one has other possible sources and secondary
reactions also complicate identifying a specific source for any of them within the scope and methods of
this study. Monoterpenes are emitted from wood products [
43
] and also derived from the biosynthesis
of plants, as are acetone, formaldehyde and methanol [
44
,
45
]. Acetone and methanol are also often
related to urban and industrial activities [
46
] with many dierent sources. Formaldehyde is also known
to be among the VOCs emitted by cleaning products and detergents [
47
]. Benzene and toluene are
known as BTEX and mainly emitted from vehicle exhaust [
48
] but also from some detergents, rubbers,
resins, and cigarettes [
49
,
50
]. Figure 4shows results for toluene and monoterpenes, compounds with
indoor and outdoor sources, as each canister is connected and disconnected from the PTR-TOF-MS for
analysis. A field blank was also analyzed. Again, the storage closet with no intended ventilation, was
found to have the highest levels of both compounds (30 ppb Monoterpenes, 17 ppb Toluene).
Buildings 2019, 9, x FOR PEER REVIEW 8 of 15
Six common VOCs were selected for analysis: acetone, formaldehyde, methanol, benzene,
toluene and monoterpenes. All have outdoor and indoor sources and all of them except benzene and
toluene are known to be emitted from wood products, but each one has other possible sources and
secondary reactions also complicate identifying a specific source for any of them within the scope
and methods of this study. Monoterpenes are emitted from wood products [43] and also derived
from the biosynthesis of plants, as are acetone, formaldehyde and methanol [44,45]. Acetone and
methanol are also often related to urban and industrial activities [46] with many different sources.
Formaldehyde is also known to be among the VOCs emitted by cleaning products and detergents
[47]. Benzene and toluene are known as BTEX and mainly emitted from vehicle exhaust [48] but also
from some detergents, rubbers, resins, and cigarettes [49,50]. Figure 4 shows results for toluene and
monoterpenes, compounds with indoor and outdoor sources, as each canister is connected and
disconnected from the PTR-TOF-MS for analysis. A field blank was also analyzed. Again, the storage
closet with no intended ventilation, was found to have the highest levels of both compounds (30 ppb
Monoterpenes, 17 ppb Toluene).
Figure 4. Results for toluene and monoterpenes over PTR-TOF-MS analysis time for one-minute grab
samples from various building locations and one field blank canister.
HeDS is not an established sampling method for indoor air quality and further inter-comparison
with established methods is needed. This preliminary investigation of the method, paired with PTR-
TOF-MS analysis, was selected because it provided a low-cost, simple to deploy, silent method of
collecting a whole air sample [18]. Replicate samples were, on average, within 34% for five of six
VOCs selected: acetone, formaldehyde, methanol, benzene, and monoterpenes. Figure 5 shows HeDS
results from week 3 for the two open office monitoring kit locations as well as an outdoor sample
taken with an evacuated canister on the roof.
0.1 1 10 100 1000
m59.0439 (acetone H+)
m31.01783 (formaldehyde H+)
m33.03230 (methanol H+)
m79.05478 (benzene H+)
m137.1325 (terpenes H+)
Corrected average mixing ratio (ppb)
21402 (SW building) Avg. 21408 (NE building) Avg. Outdoor Avg.
Figure 4.
Results for toluene and monoterpenes over PTR-TOF-MS analysis time for one-minute grab
samples from various building locations and one field blank canister.
HeDS is not an established sampling method for indoor air quality and further inter-comparison
with established methods is needed. This preliminary investigation of the method, paired with
PTR-TOF-MS analysis, was selected because it provided a low-cost, simple to deploy, silent method
of collecting a whole air sample [
18
]. Replicate samples were, on average, within 34% for five of six
VOCs selected: acetone, formaldehyde, methanol, benzene, and monoterpenes. Figure 5shows HeDS
results from week 3 for the two open oce monitoring kit locations as well as an outdoor sample taken
with an evacuated canister on the roof.
3.2. Bacterial Community
The mean number of bacterial species observed in dust was aected by the sampling location
within the room as well as the height of sampling, although there was a large amount of variation
among samples (Figure 6). The interior of the building hosted significantly fewer bacterial species than
either the northeast or southwest corners (glmer, p =0.001), and the northeast corner had a higher
number than the southwest corner. This may reflect both occupant usage and window ventilation
patterns, as both contribute to adding microorganisms to the indoor environment [
15
,
51
]. On average,
settled dust at the shelf level (0.88 m high) contained more bacterial species (p =0.001) than either the
floor or the top (1.12 m high) of the sampling unit (Figure 6).
Buildings 2019,9, 142 9 of 15
Buildings 2019, 9, x FOR PEER REVIEW 8 of 15
Six common VOCs were selected for analysis: acetone, formaldehyde, methanol, benzene,
toluene and monoterpenes. All have outdoor and indoor sources and all of them except benzene and
toluene are known to be emitted from wood products, but each one has other possible sources and
secondary reactions also complicate identifying a specific source for any of them within the scope
and methods of this study. Monoterpenes are emitted from wood products [43] and also derived
from the biosynthesis of plants, as are acetone, formaldehyde and methanol [44,45]. Acetone and
methanol are also often related to urban and industrial activities [46] with many different sources.
Formaldehyde is also known to be among the VOCs emitted by cleaning products and detergents
[47]. Benzene and toluene are known as BTEX and mainly emitted from vehicle exhaust [48] but also
from some detergents, rubbers, resins, and cigarettes [49,50]. Figure 4 shows results for toluene and
monoterpenes, compounds with indoor and outdoor sources, as each canister is connected and
disconnected from the PTR-TOF-MS for analysis. A field blank was also analyzed. Again, the storage
closet with no intended ventilation, was found to have the highest levels of both compounds (30 ppb
Monoterpenes, 17 ppb Toluene).
Figure 4. Results for toluene and monoterpenes over PTR-TOF-MS analysis time for one-minute grab
samples from various building locations and one field blank canister.
HeDS is not an established sampling method for indoor air quality and further inter-comparison
with established methods is needed. This preliminary investigation of the method, paired with PTR-
TOF-MS analysis, was selected because it provided a low-cost, simple to deploy, silent method of
collecting a whole air sample [18]. Replicate samples were, on average, within 34% for five of six
VOCs selected: acetone, formaldehyde, methanol, benzene, and monoterpenes. Figure 5 shows HeDS
results from week 3 for the two open office monitoring kit locations as well as an outdoor sample
taken with an evacuated canister on the roof.
0.1 1 10 100 1000
m59.0439 (acetone H+)
m31.01783 (formaldehyde H+)
m33.03230 (methanol H+)
m79.05478 (benzene H+)
m137.1325 (terpenes H+)
Corrected average mixing ratio (ppb)
21402 (SW building) Avg. 21408 (NE building) Avg. Outdoor Avg.
Figure 5.
VOC results for five compounds from PTR-TOF-MS analysis of week 3 HeDS canisters from
southwest and northeast indoor monitoring kit locations and from the outdoor evacuated canister
location on the roof.
Buildings 2019, 9, x FOR PEER REVIEW 9 of 15
Figure 5. VOC results for five compounds from PTR-TOF-MS analysis of week 3 HeDS canisters from
southwest and northeast indoor monitoring kit locations and from the outdoor evacuated canister
location on the roof.
3.2. Bacterial Community
The mean number of bacterial species observed in dust was affected by the sampling location
within the room as well as the height of sampling, although there was a large amount of variation
among samples (Figure 6). The interior of the building hosted significantly fewer bacterial species
than either the northeast or southwest corners (glmer, p = 0.001), and the northeast corner had a
higher number than the southwest corner. This may reflect both occupant usage and window
ventilation patterns, as both contribute to adding microorganisms to the indoor environment [15,51].
On average, settled dust at the shelf level (0.88 m high) contained more bacterial species (p = 0.001)
than either the floor or the top (1.12 m high) of the sampling unit (Figure 6).
(a) (b)
Figure 6. Bacterial species’ richness in indoor settled-dust from different (a) locations within the
building; (b) heights relative to the floor.
Disturbance of floor surfaces can resuspend settled or tracked-in microorganisms [52], which
distribute within a space based on air currents and thermal plumes, which can pose a differential
exposure to occupants relative to height above the floor and particle size [52,53]. The shelf level is
covered and minimally screened, though is otherwise quite similar in sampling location to the top of
the monitoring kit, suggesting this geometry may contribute to the sample collected. The increase in
species richness may reflect the positioning between two microbial populations; larger particles
which settle out of air to floor surfaces and are resuspended during traffic, and smaller particles
which are more apt to stay airborne but were less likely to be disturbed from the shelf settling dish,
leading to a combined accrual of more bacterial species. The bacterial community collected at shelf-
height was trending towards having fewer bacteria sourced from outdoor air than the floor (Figure
7), but only the top samples had significantly fewer bacterial species that were likely sourced from
outdoor air.
Figure 6.
Bacterial species’ richness in indoor settled-dust from dierent (
a
) locations within the
building; (b) heights relative to the floor.
Disturbance of floor surfaces can resuspend settled or tracked-in microorganisms [
52
], which
distribute within a space based on air currents and thermal plumes, which can pose a dierential
exposure to occupants relative to height above the floor and particle size [
52
,
53
]. The shelf level is
covered and minimally screened, though is otherwise quite similar in sampling location to the top of
the monitoring kit, suggesting this geometry may contribute to the sample collected. The increase in
species richness may reflect the positioning between two microbial populations; larger particles which
settle out of air to floor surfaces and are resuspended during trac, and smaller particles which are
more apt to stay airborne but were less likely to be disturbed from the shelf settling dish, leading to a
combined accrual of more bacterial species. The bacterial community collected at shelf-height was
trending towards having fewer bacteria sourced from outdoor air than the floor (Figure 7), but only the
top samples had significantly fewer bacterial species that were likely sourced from outdoor air.
Buildings 2019,9, 142 10 of 15
Buildings 2019, 9, x FOR PEER REVIEW 10 of 15
Figure 7. Similarity of indoor air bacterial communities to on-site outdoor air bacterial communities.
Communities sampled from the top of the unit were significantly less like outdoor bacterial
communities than those from the floor or shelf height.
The bacterial community in buildings is not often connected to the occupant experience with
several exceptions: visible microbial growth and building damage or odor complaints, triggering of
asthma or allergy symptoms or facilitating the spread of infectious disease. Due to the recency of this
building’s construction, microbial overgrowth was not a concern, and due to lacking occupant health
data, we are unable to comment. However, microbial communities may impact building occupants
in positive, neutral or negative ways which we are largely unaware of. Exploring these spatial
patterns can be used to form hypotheses about microbial accrual or transit in spaces, and determine
the potential for interaction with occupants.
3.3. Vertical Vibration
Figure 8 displays a ten second segment of footfall-triggered data. Accelerometers A1 through
A3 show the response of a person walking at an approximate pace corresponding to 1.7 Hz. The
recurring footfall signal is not as distinctly visible in accelerometer A4 data. The peak acceleration
measured in this data set is approximately 0.05 g at accelerometers A2, which is indicative that the
person was walking nearest to that accelerometer. In addition, it can be seen that as the amplitude of
the motion in A2 is reduced, at approximately t = 3 s, and increased at A3, indicating the direction of
the movement of the passerby from west to east.
Figure 7.
Similarity of indoor air bacterial communities to on-site outdoor air bacterial communities.
Communities sampled from the top of the unit were significantly less like outdoor bacterial communities
than those from the floor or shelf height.
The bacterial community in buildings is not often connected to the occupant experience with
several exceptions: visible microbial growth and building damage or odor complaints, triggering of
asthma or allergy symptoms or facilitating the spread of infectious disease. Due to the recency of this
building’s construction, microbial overgrowth was not a concern, and due to lacking occupant health
data, we are unable to comment. However, microbial communities may impact building occupants in
positive, neutral or negative ways which we are largely unaware of. Exploring these spatial patterns
can be used to form hypotheses about microbial accrual or transit in spaces, and determine the potential
for interaction with occupants.
3.3. Vertical Vibration
Figure 8displays a ten second segment of footfall-triggered data. Accelerometers A1 through A3
show the response of a person walking at an approximate pace corresponding to 1.7 Hz. The recurring
footfall signal is not as distinctly visible in accelerometer A4 data. The peak acceleration measured
in this data set is approximately 0.05 g at accelerometers A2, which is indicative that the person was
walking nearest to that accelerometer. In addition, it can be seen that as the amplitude of the motion in
A2 is reduced, at approximately t =3 s, and increased at A3, indicating the direction of the movement
of the passerby from west to east.
Figure 9shows the corresponding PSDs plots to the data records shown in Figure 8, in the
frequency range of 0 to 30 Hz. A major frequency peak is observed at a frequency of 9.90 Hz, and
smaller amplitudes for the frequency peaks in the range of 10–20 Hz, while the amplitudes in the
frequency ranging 0–8 Hz shows amplitudes at approximately 1.7 ×105g2/Hz and below.
Murray (1999) presented an extensive review of research aimed at quantifying the response of
humans to floor vibration [
54
]. The following factors, aecting the perception and tolerance level
of the human were identified: (a) the frequency of vibration, (b) the magnitude of vibration, (c) the
duration of motion, (d) the occupant’s body orientation and (d) the occupant’s activity. Procedures
for evaluation of the eect of vibrations on humans are presented in documents such as ISO 2631
(2003) and ISO 10137 (2007), where the peak acceleration is used as the threshold for human comfort
in oces or residences subjected to vibration frequencies between 4 Hz and 8 Hz is 0.005 g, or 0.5%
of gravity [
55
,
56
]. The lower threshold within the frequency range of 4 to 8 Hz can be explained by
studies showing that humans are particularly sensitive to vibrations with frequencies in the 5-8 Hz
range [54].
Buildings 2019,9, 142 11 of 15
Buildings 2019, 9, x FOR PEER REVIEW 10 of 15
Figure 7. Similarity of indoor air bacterial communities to on-site outdoor air bacterial communities.
Communities sampled from the top of the unit were significantly less like outdoor bacterial
communities than those from the floor or shelf height.
The bacterial community in buildings is not often connected to the occupant experience with
several exceptions: visible microbial growth and building damage or odor complaints, triggering of
asthma or allergy symptoms or facilitating the spread of infectious disease. Due to the recency of this
building’s construction, microbial overgrowth was not a concern, and due to lacking occupant health
data, we are unable to comment. However, microbial communities may impact building occupants
in positive, neutral or negative ways which we are largely unaware of. Exploring these spatial
patterns can be used to form hypotheses about microbial accrual or transit in spaces, and determine
the potential for interaction with occupants.
3.3. Vertical Vibration
Figure 8 displays a ten second segment of footfall-triggered data. Accelerometers A1 through
A3 show the response of a person walking at an approximate pace corresponding to 1.7 Hz. The
recurring footfall signal is not as distinctly visible in accelerometer A4 data. The peak acceleration
measured in this data set is approximately 0.05 g at accelerometers A2, which is indicative that the
person was walking nearest to that accelerometer. In addition, it can be seen that as the amplitude of
the motion in A2 is reduced, at approximately t = 3 s, and increased at A3, indicating the direction of
the movement of the passerby from west to east.
Figure 8. Accelerometers time records triggered by footfall.
Buildings 2019, 9, x FOR PEER REVIEW 11 of 15
Figure 8. Accelerometers time records triggered by footfall.
Figure 9 shows the corresponding PSDs plots to the data records shown in Figure 8, in the
frequency range of 0 to 30 Hz. A major frequency peak is observed at a frequency of 9.90 Hz, and
smaller amplitudes for the frequency peaks in the range of 10–20 Hz, while the amplitudes in the
frequency ranging 0–8 Hz shows amplitudes at approximately 1.7 × 10
5
g
2
/Hz and below.
Figure 9. PSDs plots of footfall triggered responses. Human discomfort critical range in red.
Murray (1999) presented an extensive review of research aimed at quantifying the response of
humans to floor vibration [54]. The following factors, affecting the perception and tolerance level of
the human were identified: (a) the frequency of vibration, (b) the magnitude of vibration, (c) the
duration of motion, (d) the occupant’s body orientation and (d) the occupant’s activity. Procedures
for evaluation of the effect of vibrations on humans are presented in documents such as ISO 2631
(2003) and ISO 10137 (2007), where the peak acceleration is used as the threshold for human comfort
in offices or residences subjected to vibration frequencies between 4 Hz and 8 Hz is 0.005 g, or 0.5%
of gravity [55,56]. The lower threshold within the frequency range of 4 to 8 Hz can be explained by
studies showing that humans are particularly sensitive to vibrations with frequencies in the 5-8 Hz
range [54].
Eurocode 5 (2004) [34], which is viewed to be more stringent on floor vibrations than American
standards [55], places a serviceability limit for wood structures with a vertical natural frequency of
less than 8 Hz. HIVOSS (2008), although geared for footbridges, identifies the critical range for
vertical vibrations that produce discomfort, which includes frequencies in the range of 1.25 Hz to 4.6
Hz [35]. The measured floor vibrations at Albina Yard place the fundamental frequency at 9.90 Hz,
outside of the human discomfort range presented in [34,55,56]. The findings provide confidence in
the floor design solution and span lengths.
4. Conclusions
This case study investigated performance aspects of a mass timber building that relate to
occupant experience. Exposure measurements were conducted for three indoor environmental
quality (IEQ) factors to better understand how cross-laminated timber (CLT) and glue-laminated
timber (GLT) wood products and systems impact indoor air quality, indoor bacterial community,
and vibrational comfort in an office environment of a mass timber building.
Indoor air quality was analyzed using both direct-measurement continuous monitoring and
passive air sampling techniques. Indoor and outdoor concentrations were collected and compared.
Multiple data collection periods and locations in the building were considered. In locations with low
or no ventilation, like a storage closet, we observed elevated monoterpene levels compared to well-
Figure 9. PSDs plots of footfall triggered responses. Human discomfort critical range in red.
Eurocode 5 (2004) [
34
], which is viewed to be more stringent on floor vibrations than American
standards [
55
], places a serviceability limit for wood structures with a vertical natural frequency of less
than 8 Hz. HIVOSS (2008), although geared for footbridges, identifies the critical range for vertical
vibrations that produce discomfort, which includes frequencies in the range of 1.25 Hz to 4.6 Hz [
35
].
The measured floor vibrations at Albina Yard place the fundamental frequency at 9.90 Hz, outside
of the human discomfort range presented in [
34
,
55
,
56
]. The findings provide confidence in the floor
design solution and span lengths.
4. Conclusions
This case study investigated performance aspects of a mass timber building that relate to occupant
experience. Exposure measurements were conducted for three indoor environmental quality (IEQ)
Buildings 2019,9, 142 12 of 15
factors to better understand how cross-laminated timber (CLT) and glue-laminated timber (GLT) wood
products and systems impact indoor air quality, indoor bacterial community, and vibrational comfort
in an oce environment of a mass timber building.
Indoor air quality was analyzed using both direct-measurement continuous monitoring and
passive air sampling techniques. Indoor and outdoor concentrations were collected and compared.
Multiple data collection periods and locations in the building were considered. In locations with
low or no ventilation, like a storage closet, we observed elevated monoterpene levels compared to
well-ventilated areas like an entryway. We speculate this dierence is likely due to accumulation of
monoterpenes emitted from materials and potentially indoor chemistry occurring in these spaces.
Follow-up studies deploying real-time volatile organic compound instrumentation, like chemical
ionization - time of flight - mass spectrometry, in CLT buildings would shed light on the VOC sources
and chemistry occurring in buildings using substantial CLT structural elements. CO
2
data collected
during the first sampling week was used to initiate further investigation of the mechanical ventilation
system and correct a damper position issue. Formaldehyde, toluene and monoterpenes were observed
to vary in concentration across spaces that also varied by ventilation rate.
The height of passive bacterial sampling and the sampling location within the building had a
small but measurable eect on the bacterial communities in settled dust, confirming the eect of
localized conditions on the accrued microbial community. It also suggests the capacity to intentionally
select a microbial community by integrating environmental conditions (i.e. outdoor air), and holds
implications for individual occupant exposure to indoor microbial communities based on location
within a building.
Footfall triggered vibrational accelerations were observed in monitored data to be within the
serviceability range for human comfort. While it is well known that floor dynamic response depends
on both structural and non-structural components, the satisfactory vibration performance of the
studied floor mainly relies on structural features, such as relative short spans and thickness of the CLT
floor panels.
Author Contributions:
Conceptualization, M.R., A.B, E.T.G. and K.V.D.W.; methodology, J.S., S.L.I., A.L.
(Andrew Loia), D.N., I.M., M.R., A.B., E.T.G. andK.V.D.W.; validation, S.L.I., M.R., E.T.G. andK.V.D.W.; formal analysis,
J.S., S.L.I., A.L. (Aur
é
lie Laguerre), I.M. and D.N.; investigation, J.S., A.L. (Aur
é
lie Laguerre), A.L. (Andrew Loia), G.M.,
I.M., D.N., M.R. and A.B.; resources, M.R., A.B., E.T.G. and K.V.D.W.; data curation, J.S., S.L.I., A.L. (Aur
é
lie Laguerre),
I.M. and D.N.; writing—original draft preparation, J.S., S.L.I., A.L. (Aur
é
lie Laguerre) and I.M.; writing—review and
editing, J.S., S.L.I., A.L. (Aur
é
lie Laguerre), A.L. (Andrew Loia), G.M., I.M., D.N., M.R., A.B, E.T.G. and K.V.D.W.;
visualization, J.S., S.L.I., A.L. (Aur
é
lie Laguerre), I.M. and D.N.; supervision, M.R., A.B, E.T.G. and K.V.D.W.; project
administration, M.P. and K.V.D.W.; funding acquisition, M.R., A.B, E.T.G. and K.V.D.W.
Funding:
This work was funded by a grant with the U.S. Department of Agriculture’s Agricultural Research
Service [USDA ARS Agreement No. 58-0202-5-001], a grant to the Biology and the Built Environment Center
from the Alfred P. Sloan Foundation [grant no. G-2015-14023], and by start-up funds provided by Portland
State University.
Acknowledgments:
The authors wish to acknowledge the building owner, Reworks Inc., for providing access
to the building; the building architect and fourth-floor occupant, Lever Architecture, for providing access to
their oce and occupant survey feedback. The authors would like to thank Leslie Dietz and Susie Nunez at the
University of Oregon for their contribution to molecular biology laboratory work; Mark Fretz, Alejandro Manzo,
and Daniel Roth at the University of Oregon for their contribution to fieldwork.
Conflicts of Interest:
The authors declare no conflict of interest. The funders had no role in the design of the
study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to
publish the results.
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... A further two studies evaluated prefabricated or modular/relocatable school classrooms [40,41]. A wooden apartment in a prefabricated wooden building was the focus of one study [42], and a mass timber office building in another [43]. Two model rooms constructed from mass timber materials (OSB, CLT) were also studied [44]. ...
... For passive sampling of VOCs, a sampling duration of 1-5 days was reported [40]. Furthermore, one-minute whole air grab samples were collected by [43] using an evacuated "bottle-vac" whole air grab sample (BLV1A & RS-QTS1) or a "bottle-vac" helium diffusion whole air sample ( Table 2). For aldehydes, sampling techniques included short-term active sampling for 30 min using sorbent media [38,39] or an electronic formaldehyde sensor [43]. ...
... Furthermore, one-minute whole air grab samples were collected by [43] using an evacuated "bottle-vac" whole air grab sample (BLV1A & RS-QTS1) or a "bottle-vac" helium diffusion whole air sample ( Table 2). For aldehydes, sampling techniques included short-term active sampling for 30 min using sorbent media [38,39] or an electronic formaldehyde sensor [43]. An additional two studies utilised active sampling for a duration between 60-75 min [18,42], and one study used low flow rate active sampling over 7-8 h [41]. ...
Article
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Prefabricated timber buildings offer a low-carbon approach that can help reduce the environmental impact of the building and construction sectors. However, construction materials such as manufactured timber products can emit a range volatile organic compounds (VOCs) that are potentially hazardous to human health. We evaluated 24 years (2000–2024) of peer-reviewed publications of VOCs within prefabricated timber buildings. Studies detected hazardous air pollutants such as formaldehyde, benzene, toluene, and acetaldehyde (indoor concentration ranges of 3.4–94.9 µg/m3, 1.2–19 µg/m3, 0.97–28 µg/m3, and 0.75–352 µg/m3, respectively), with benzene concentrations potentially exceeding World Health Organization indoor air quality guidelines for long/short term exposure. Most studies also detected terpenes (range of 1.8–232 µg/m3). The highest concentrations of formaldehyde and terpenes were in a prefabricated house, and the highest of benzene and toluene were in a prefabricated office building. Paradoxically, the features of prefabricated buildings that make them attractive for sustainability, such as incorporation of manufactured timber products, increased building air tightness, and rapid construction times, make them more prone to indoor air quality problems. Source reduction strategies, such as the use of low-VOC materials and emission barriers, were found to substantially reduce levels of certain indoor pollutants, including formaldehyde. Increasing building ventilation rate during occupancy is also an effective strategy for reducing indoor VOC concentrations, although with the repercussion of increased energy use. Overall, the review revealed a wide range of indoor VOC concentrations, with formaldehyde levels approaching and benzene concentrations potentially exceeding WHO indoor air quality guidelines. The paucity of evidence on indoor air quality in prefabricated timber buildings is notable given the growth in the sector, and points to the need for further evaluation to assess potential health impacts.
... It remains an open question whether a smaller quantity of adhesive used, relative to the amount of wood in CLT panels, and the overall exposed surface area relative to the space will have a meaningful effect on IAQ [26]. However, the development of an adhesive free of potentially toxic species would help to alleviate concerns over deleterious impacts on IAQ. ...
... Formaldehyde has also been shown to persist in the indoor air of an occupied building constructed with CLT floor and roof panels, exposed as the finish ceiling, and supported by GLT columns and beams. Stenson et al. found a 30-min maximum formaldehyde concentration of 37 µg/m 3 (30 ppb) in a ventilated and occupied open office space, and up to 77 µg/m 3 (63 ppb) in an adjacent storage room with no mechanical ventilation, both at more than a year after construction [26]; however, explicit source tracking is difficult in occupied buildings. ...
Article
Full-text available
Volatile organic compound (VOC) emissions from indoor sources are large determinants of the indoor air quality (IAQ) and occupant health. Cross-laminated timber (CLT) is a panelized engineered wood product often left exposed as an interior surface finish. As a certified structural building product, CLT is currently exempt from meeting VOC emission limits for composite wood products and confirming emissions through California Department of Public Health (CDPH) Standard Method testing. In this study, small chamber testing was conducted to evaluate VOC emissions from three laboratory-produced CLT samples: One bonded with a new soy-based cold-set adhesive; a second bonded with a commercially available polyurethane (PUR) adhesive; and the third assembled without adhesive using dowels. A fourth commercially-produced eight-month-old sample bonded with melamine formaldehyde (MF) adhesive was also tested. All four samples were produced with Douglas-fir. The test results for the three laboratory-produced samples demonstrated VOC emissions compliance with the reference standard. The commercially-produced and aged CLT sample bonded with MF adhesive did not meet the acceptance criterion for formaldehyde of ≤9.0 µg/m3. The estimated indoor air concentration of formaldehyde in an office with the MF sample was 54.4 µg/m3; the results for the soy, PUR, and dowel samples were all at or below 2.5 µg/m3.
... Another problem related to wood is the growth of microorganisms and fungi. Solid wood buildings can present microbial charge by direct dust deposition due to a complex combination of local environmental conditions Stenson et al., 2019). Old buildings must be monitored to minimize health risks and optimize maintenance costs, especially if they are historical and of tourist interest. ...
Conference Paper
Wood is a very versatile building material. For centuries it has been used in construction. The use of wood declined as the use of reinforced concrete increased. Wood is a renewable material capable of storing CO2, which is helpful for the struggle against climate change. Thus, starting from proper forest management, it is possible to have a building material that suits indoor climate conditions, allowing the improvement of structural response, good thermal and acoustic insulation, excellent olfactory perception, and easy humidity control. This versatility makes it a great material to ensure the well-being and comfort of the user. Well-being and comfort are people's perceptions of their environmental conditions. People's expectations and experiences are vital to the success of bio-economy business strategies, even if the inclusion of the human dimension is often not considered in the resolution of problems relating to housing. The focus of this paper is the encouragement of using wood, notably engineered woods like cross-laminated timber (CLT), glued laminated timber (glulam), nail laminated timber (NLT) and dowel laminated timber (DLT), because it favors the relationship between people and spaces, and it guarantees an excellent response in structural terms. This triggers a virtuous mechanism that enhances the entire wood supply chain that starts from forest management and reaches the benefits of the user both in the residential dimension and in the global space.
... One of the more versatile applications from this addition is for mass timber floors, including crosslaminated timber (CLT). Under these new code provisions, mass timber floors must have a noncombustible topping for increased fire protection and improved vibration performance (Frangi et al. 2010;Stenson et al. 2019). The topping also improves the acoustic performance of CLT floors (Van den Wymelenberg et al. 2019). ...
... CLT exhibits a greater bidirectional performance benefited by the perpendicular combination of dimension lumber [10]. Ringhofer et al. [11] investigated the nail-holding performance of GLT and CLT and concluded that CLT had the better ductility. ...
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Full-text available
Fiber reinforced polymer (FRP) has been proved to be effective to improve the structural strength and ductility for column structures. An experimental study was conducted to investigate the compressive performance of FRP confined glued-laminated timber (GLT) and cross-laminated timber (CLT) columns. A total of 60 column specimens of two dimensions in height using different FRP types, FRP thickness, and laminate types were tested under cyclic axial compression loads. This study focuses on the compressive capacity and ductility of the new FRP composited timber structure. For this purpose, a loading protocol was designed, including a force-dependent pre-load and an amplitude-increasing displacement-dependent cyclic compression load. The results showed that the ultimate compression load of specimens was considerably promoted by the FRP sheets. Wrapping FRP sheets led to an average improvement of 29% and 24% for the FRP confined CLT and GLT specimens, respectively, compared to the initial stiffness of unreinforced specimens. Using the FRP sheets, the energy dissipation capacity of CLT and GLT specimens was increased by 358% and 266%, respectively. In general, GLT specimens had a higher energy dissipation rate compared to the CLT specimens, while CLT specimens showed a better potential for sustained energy consumption if confined with sufficient FRP sheets.
... Cowsheds buildings can present microbial load by means of direct dust settlement due to a complex combination of local environmental conditions, large crowding of animals and airflow when serving food, milking, hygienic procedures or the expulsion and return of cattle to and from pastures (Gnat et al., 2018;Łagowski et al., 2020). All parameters related to the indoor microclimate are consistent with those recorded for human environments (Marcu et al., 2021;Shelton et al., 2002;Stenson et al., 2019;Tseng et al., 2021), although it seems that the aerosol load with potentially pathogenic microorganisms for livestock is much higher. Moreover, these conidia or dermatophyte hyphae tend to proliferate from air to other organic compounds, such as food, milk, litter and dust, among others (Tseng et al., 2021;van Rhijn & Bromley, 2021). ...
Article
Aims: Indoor air quality in stables, cowsheds or henhouses has recently become in interest due to the potential risks of zoonotic infections. Cowsheds are commonly known to have high fungal loads, particularly if insufficient attention is paid to the monitoring and control of the indoor microclimate around three elements, that is heating, ventilation and lighting. The aim of this study was to determine the concentrations and spectrum of dermatophyte propagules in the indoor air of cowsheds. Methods and results: Air samples were collected on five farms, and the dermatophyte species were identified using MALDI-TOF MS analysis. The quantitative analysis of the fungal pollutants showed an average of 0.084 dermatophyte propagules (CFU) per m3 of flowing air in spring and 0.0239 CFU/m3 in the summer. Dermatophyte species were identified in case of 64.6% of the obtained colonies. Trichophyton verrucosum as dominant species was isolated on all five farms. In turn, Nannizzia gypsea was isolated on four farms and Trichophyton mentagrophytes as well as Paraphyton cookei were isolated on two farms. Conclusions: This study demonstrated that indoor aerosol appears to be one of the underestimated risks of dermatophyte infections. Moreover, the risk of zoonotic infections is posed by airborne zoophilic dermatophytes, especially T. verrucosum, whose prevalence of infections has been increasing in recent years. Significance and impact of the study: The ability of dermatophytes to infect animals and humans is thought to be a consequence of not only their adaptation to new ecological niches but also occurring as an aerosol component, which we demonstrate for the first time in this study. The microclimate of the cowshed may be an underestimated reservoir of zoophilic dermatophytes, which pose a zoonotic threat to farmers, animal breeders and veterinarians.
... Additional problems are caused by the construction material (especially wood), which forms a culture medium for the growth of microorganisms and fungi. Solid wood buildings can present microbial load by means of direct dust settlement due to a complex combination of local environmental conditions [3,4]. Arguably, old heritage buildings must be monitored in order to minimize the risks to the health of visitors and employees, to optimize the maintenance costs, and prior to their inclusion in sightseeing tours. ...
Article
Full-text available
Monitoring the indoor microclimate in old buildings of cultural heritage and significance is a practice of great importance because of the importance of their identity for local communities and national consciousness. Most aged heritage buildings, especially those made of wood, develop an indoor microclimate conducive to the development of microorganisms. This study aims to analyze one wooden church dating back to the 1710s in Romania from the microclimatic perspective, i.e., temperature and relative humidity and the fungal load of the air and surfaces. One further aim was to determine if the internal microclimate of the monument is favorable for the health of parishioners and visitors, as well as for the integrity of the church itself. The research methodology involved monitoring of the microclimate for a period of nine weeks (November 2020–January 2021) and evaluating the fungal load in indoor air as well as on the surfaces. The results show a very high contamination of air and surfaces (>2000 CFU/m3). In terms of fungal contamination, Aspergillus spp. (two different species), Alternaria spp., Cladosporium spp., Mucor spp., Penicillium spp. (two different species) and Trichopyton spp. were the genera of fungi identified in the indoor wooden church air and Aspergillus spp., Cladosporium spp., Penicillium spp. (two different species) and Botrytis spp. on the surfaces (church walls and iconostasis). The results obtained reveal that the internal microclimate not only imposes a potential risk factor for the parishioners and visitors, but also for the preservation of the wooden church as a historical monument, which is facing a crisis of biodeterioration of its artwork.
... It is also important to note that terpenes are highly reactive and, while exposure to terpenes themselves may not constitute a health issue, oxidation reactions involving terpenes can generate byproducts that are irritating to the respiratory system (Nazaroff and Weschler, 2004;Wolkoff et al., 2000). On the other hand, formaldehyde emission from adhesives used in some engineered wood products, such as cross-laminated timber (CLT), as well as from the wood itself, may also because for concern (Stenson et al., 2019;Knowles et al., 2011;Alapieti et al., 2020). Finally, while some materials may emit VOCs, others may be able to sequester them (Niedermayer et al., 2013;Won et al., 2001). ...
Article
Full-text available
Indoor environmental quality is a paramount concern among architects. Exposure to VOCs and microorganisms impacts occupant health, yet the role of materials on these exposures remains poorly understood. In this study, we placed four material types in individual microcosms to test whether material type influences bacterial community structure and VOC emission. We used culture-independent methods to characterize bacterial communities and TD-GC-MS to measure VOC emission. We found that viable bacterial communities had different patterns of abundance, diversity, and composition, in comparison with total (viable plus dead cells) bacterial communities. Examining viable bacteria only, Earth had the highest abundance and diversity, unique community composition, and overall negative VOC emission. Timber had the lowest bacterial abundance, composition similar to Gypsum and Concrete, and the highest VOC emission rate. Our research provides further evidence that architects’ decisions about building materials can influence chemical and microbial exposures indoors.
... In particular, bacteria that can survive frequent, harsh cleanings may be better able to withstand variations in environmental conditions within patient rooms (Velazquez et al., 2019). While the unique design and occupancy of individual buildings make it difficult to compare indoor microbial communities between structures, it is important to note that many observational studies of microbial communities within the built environment, such as office spaces and homes, identify thousands of unique taxa (Kembel et al., 2012;Stenson et al., 2019). The present study identified approximately 1000 taxa, despite the high occupancy and activity level typical of a hospital, lending credence to the idea that patient rooms with regular cleaning are a harsh environment for bacteria, and that this cleaning regime is a stronger selection force than sunlight exposure. ...
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Previous studies demonstrate an exchange of bacteria between hospital room surfaces and patients, and a reduction in survival of microorganisms in dust inside buildings from sunlight exposure. While the transmission of microorganisms between humans and their local environment is a continuous exchange which generally does not raise cause for alarm, in a hospital setting with immunocompromised patients, these building-source microbial reservoirs may pose a risk. Window glass is often neglected during hospital disinfection protocols, and the microbial communities found there have not previously been examined. This pilot study examined whether living bacterial communities, and specifically the pathogens Methicillin-resistant Staphylococcus aureus (MRSA) and Clostridioides difficile (C. difficile), were present on window components of exterior-facing windows inside patient rooms, and whether relative light exposure (direct or indirect) was associated with changes in bacterial communities on those hospital surfaces. Environmental samples were collected from 30 patient rooms in a single ward at Oregon Health & Science University (OHSU) in Portland, Oregon, USA. Sampling locations within each room included the window glass surface, both sides of the window curtain, two surfaces of the window frame, and the air return grille. Viable bacterial abundances were quantified using qPCR, and community composition was assessed using Illumina MiSeq sequencing of the 16S rRNA gene V3/V4 region. Viable bacteria occupied all sampled locations, but was not associated with a specific hospital surface or relative sunlight exposure. Bacterial communities were similar between window glass and the rest of the room, but had significantly lower Shannon Diversity, theorized to be related to low nutrient density and resistance to bacterial attachment of glass compared to other surface materials. Rooms with windows that were facing west demonstrated a higher abundance of viable bacteria than those facing other directions, potentially because at the time of sampling (morning) west-facing rooms had not yet been exposed to sunlight that day. Viable C. difficile was not detected and viable MRSA was detected at very low abundance. Bacterial abundance was negatively correlated with distance from the central staff area containing the break room and nursing station. In the present study, it can be assumed that there is more human traffic in the center of the ward, and is likely responsible for the observed gradient of total abundance in rooms along the ward, as healthcare staff both deposit more bacteria during activities and affect microbial transit indoors. Overall, hospital window components possess similar microbial communities to other previously identified room locations known to act as reservoirs for microbial agents of hospital-associated infections.
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The European energy policy pushes the member states to transform building stock into nearly Zero-Energy Buildings (nZEB). This paper is focused on data collected from existing nZEB day-care centres,in order to be able to assess possible differences between predicted and actual energy and indoorenvironmental performance. Building structures, service systems and the indoor climate and energyperformance of five day-care centres were investigated in Estonia, Finland and Norway.Indoor climate condition measurements showed that in general, the thermal environment and indoor airquality corresponded to the highest indoor climate categories I and II (EN 15251). Building heating andventilation systems in studied buildings are working without major problems. Good indoor climate conditions were also reflected in the occupant satisfaction questionnaires. For most of the studied buildings, over 80%of the people marked all indoor environment condition parameters (thermal comfort, indoor air quality,acoustics, odour and illuminance) acceptable. The thermal environment in the cooling season was reportedproblematic because it was lower than the minimum temperature for indoor climate category II.Energy consumption analysis showed that measured real energy use was higher, or even significantlyhigher, than the energy use calculated during the design phase. Potential causes of the higher actualenergy consumption are caused by differences of measured and designed solutions, methodology of theenergy calculations, and the differences in user behaviour.Lessons learnt from previously constructed day-care centres can be utilised in the planning and designof new nZEBs.
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This article presents parts of a wide survey on acoustic comfort in Swedish family buildings, specificallywith focus on timber light-weight buildings. The scope of the whole research is to investigate acousticcomfort dimensions after collecting and combining data from standardized acoustic measurements andsubjective responses from a questionnaire survey. Certain noise sources were reported as dominantwithin living environments, impact noise from neighbors being the most important. Installation noisefrom inside the building and outdoor low-frequency noise disturb also a lot. However, the overall levelof acoustic comfort in contemporary wooden buildings seems satisfactory.
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Until recently, plant-emitted methanol was considered a biochemical by-product, but studies in the last decade have revealed its role as a signal molecule in plant-plant and plant-animal communication. Moreover, methanol participates in metabolic biochemical processes during growth and development. The purpose of this review is to determine the impact of methanol on the growth and immunity of plants. Plants generate methanol in the reaction of the demethylation of macromolecules including DNA and proteins, but the main source of plant-derived methanol is cell wall pectins, which are demethylesterified by pectin methylesterases (PMEs). Methanol emissions increase in response to mechanical wounding or other stresses due to damage of the cell wall, which is the main source of methanol production. Gaseous methanol from the wounded plant induces defense reactions in intact leaves of the same and neighboring plants, activating so-called methanol-inducible genes (MIGs) that regulate plant resistance to biotic and abiotic factors. Since PMEs are the key enzymes in methanol production, their expression increases in response to wounding, but after elimination of the stress factor effects, the plant cell should return to the original state. The amount of functional PMEs in the cell is strictly regulated at both the gene and protein levels. There is negative feedback between one of the MIGs, aldose epimerase-like protein, and PME gene transcription; moreover, the enzymatic activity of PMEs is modulated and controlled by PME inhibitors (PMEIs), which are also induced in response to pathogenic attack.
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In 2010, the World Health Organization (WHO) established an indoor air quality guideline for short- and long-term exposures to formaldehyde (FA) of 0.1 mg/m(3) (0.08 ppm) for all 30-min periods at lifelong exposure. This guideline was supported by studies from 2010 to 2013. Since 2013, new key studies have been published and key cancer cohorts have been updated, which we have evaluated and compared with the WHO guideline. FA is genotoxic, causing DNA adduct formation, and has a clastogenic effect; exposure-response relationships were nonlinear. Relevant genetic polymorphisms were not identified. Normal indoor air FA concentrations do not pass beyond the respiratory epithelium, and therefore FA's direct effects are limited to portal-of-entry effects. However, systemic effects have been observed in rats and mice, which may be due to secondary effects as airway inflammation and (sensory) irritation of eyes and the upper airways, which inter alia decreases respiratory ventilation. Both secondary effects are prevented at the guideline level. Nasopharyngeal cancer and leukaemia were observed inconsistently among studies; new updates of the US National Cancer Institute (NCI) cohort confirmed that the relative risk was not increased with mean FA exposures below 1 ppm and peak exposures below 4 ppm. Hodgkin's lymphoma, not observed in the other studies reviewed and not considered FA dependent, was increased in the NCI cohort at a mean concentration ≥0.6 mg/m(3) and at peak exposures ≥2.5 mg/m(3); both levels are above the WHO guideline. Overall, the credibility of the WHO guideline has not been challenged by new studies.
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For the first time a high mass resolution thermal desorption proton transfer reaction mass spectrometer (hr-TD-PTR-MS) was deployed in the field to analyze the composition of the organic fraction of aerosols. We report on measurements from the remote Mt. Sonnblick observatory in the Austrian alps (3108 m a.s.l.) during a 7 week period in summer 2009. A total of 638 mass peaks in the range 18–392 Da were detected and quantified in aerosols. An empirical formula was tentatively attributed to 464 of these compounds by custom-made data analysis routines which consider compounds containing C, H, O, N, and S atoms. Most of the other (unidentified) compounds must contain other elements – most likely halogenated compounds. The mean total concentration of all detected compounds was 1.1 μg m−3. Oxygenated hydrocarbons constitute the bulk of the aerosol mass (75%) followed by organic nitrogen compounds (9%), inorganic compounds (mostly NH3, 8%), unidentified/halogenated (3.8%), hydrocarbons (2.7%), and organic sulfur compounds (0.8%). The measured O/C ratios are lower than expected and suggest a significant effect from charring. A significant part of the organic nitrogen compounds is non volatile. Organic carbon concentrations measured with TD-PTR-MS were about 25% lower than measurements on high volume filter samples.
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Building insulation materials can affect indoor air by (i) releasing primary volatile organic compounds (VOCs) from building enclosure cavities to the interior space, (ii) mitigating exposure to outdoor pollutants through reactive deposition (of oxidants, e.g., ozone) or filtration (of particles) in infiltration air, and (iii) generating secondary VOCs and other gas-phase byproducts resulting from oxidant reactions. This study reports primary VOC emission fluxes, ozone (O3) reaction probabilities (γ), and O3 reaction byproduct yields for eight common, commercially available insulation materials. Fluxes of primary VOCs from the materials, measured in a continuous flow reactor using proton transfer reaction-time of flight-mass spectrometry, ranged from 3 (polystyrene with thermal backing) to 61 (cellulose) μmol m-2 h-1 (with total VOC mass emission rates estimated to be between ∼0.3 and ∼3.3 mg m-2 h-1). Major primary VOC fluxes from cellulose were tentatively identified as compounds likely associated with cellulose chemical and thermal decomposition products. Ozone-material γ ranged from ∼1 × 10-6 to ∼30 × 10-6. Polystyrene with thermal backing and polyisocyanurate had the lowest γ, while cellulose and fiberglass had the highest. In the presence of O3, total observed volatile byproduct yields ranged from 0.25 (polystyrene) to 0.85 (recycled denim) moles of VOCs produced per mole of O3 consumed, or equivalent to secondary fluxes that range from 0.71 (polystyrene) to 10 (recycled denim) μmol m-2 h-1. Major emitted products in the presence of O3 were generally different from primary emissions and were characterized by yields of aldehydes and acetone. This work provides new data that can be used to evaluate and eventually model the impact of "hidden" materials (i.e., those present inside wall cavities) on indoor air quality. The data may also guide building enclosure material selection, especially for buildings in areas of high outdoor O3.
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The assessment of the dynamic properties and vibration performance of two full-scale timber floor specimens is presented. The specimen set comprised a Timber-Concrete Composite floor and a Cross Laminated Timber floor. The floors, which are characterized by the same length and mass, are located in two separate five-storey timber buildings constructed in the urban area of Trento (Italy). The assessment was conducted by adopting analytical and numerical methods as well as by performing onsite experimental tests. Mock up samples of the floor specimens were also made and tested in laboratory. Multiple analytical methods that are available in literature were evaluated and compared. The Vibration Dose Value (VDV) method, as proposed by ISO 10137 and BS 6472, was used as reference method for the numerical modelling and the laboratory testing. To determine the VDV, loading associated to human walking was simulated. Dynamic identification tests, where the floors were excited by a modal hammer, were also performed in order to investigate the dynamic properties (i.e. natural frequencies, damping and mode shapes) of the floors. Discussion on the vibration performance of the timber floor typologies studied herein and on the effectiveness of the different assessment approaches (i.e. analytical, numerical and experimental) is provided.
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Human-induced resuspension of floor dust is a dynamic process that can serve as a major indoor source of biological particulate matter (bioPM). Inhalation exposure to the microbial and allergenic content of indoor dust is associated with adverse and protective health effects. This study evaluates infant and adult inhalation exposures and respiratory tract deposited dose rates of resuspended bioPM from carpets. Chamber experiments were conducted with a robotic crawling infant and an adult performing a walking sequence. Breathing zone (BZ) size distributions of resuspended fluorescent biological aerosol particles (FBAPs), a bioPM proxy, were monitored in real-time. FBAP exposures were highly transient during periods of locomotion. Both crawling and walking delivered a significant number of resuspended FBAPs to the BZ, with concentrations ranging from 0.5 to 2 cm^–3 (mass range: ∼50 to 600 μg/m^3). Infants and adults are primarily exposed to a unimodal FBAP size distribution between 2 and 6 μm, with infants receiving greater exposures to super-10 μm FBAPs. In just 1 min of crawling or walking, 10^3–10^4 resuspended FBAPs can deposit in the respiratory tract, with an infant receiving much of their respiratory tract deposited dose in their lower airways. Per kg body mass, an infant will receive a nearly four times greater respiratory tract deposited dose of resuspended FBAPs compared to an adult.
Conference Paper
Wood is a commonly used interior material in private housing in Northern Europe. However, the use is still marginal in public buildings. This study describes findings on human perception and experiences of wood in care buildings. Human well-being is particularly important in such environments. Therefore, focus is on the relationship between human comfort indoors and spatial design. The buildings and user experiences are evaluated using qualitative study methods, questionnaires, interviews and observation. The aim is to increase the understanding of how wood-based building materials influence human experience of and well-being in indoor environments. Design criteria for care environments, like nursing homes, day-care centres and educational facilities, are evaluated. The results of the ongoing study are used to identify means to improve human well-being indoors and care-building design. Abstract. In: WCTE 2016 World Conference on Timber Engineering August 22-25, 2016, Vienna, Austria Participant`s Handbook, Vienna University of Technology, p. 216 The paper presents a study on human perception and experiences of wood in care buildings including a comparison to quantitative data like LCA analysis.