HVAC Filters Research Articles

Quantitative filter forensics for allergens and semivolatile organic compounds in residential buildings in Toronto, Canada

Quantitative filter forensics (QFF) is a method for estimating the time-averaged concentration of particle-bound containments using filter metadata and its extracted dust. In this study, QFF was applied to dust samples extracted from four types of HVAC filters deployed in 20 homes from December 2016 to December 2017 in Toronto, Canada. The analysis covered six allergens, eight phthalates, and 12 polycyclic aromatic hydrocarbons (PAHs). The allergen results from four homes showed elevated concentrations of cat and dog allergens (Fel d 1 and Can f 1) in homes with cats or dogs. All eight phthalates were detected, dominated by diisononyl phthalate (DiNP) and bis(2-ethylhexyl) phthalate (DEHP), with median concentrations of 4.27 ng/m³ and 4.20 ng/m³, respectively. All PAHs, except anthracene, were detected in over 50 % of the homes, with benzo[a]pyrene being the most abundant (median concentration of 0.067 ng/m³). Median concentrations of all semivolatile organic compounds (SVOCs) were lower in winter 2016 compared to spring 2017, potentially due to losses of more volatile SVOCs from filters because of higher filtration volumes in winter, in addition to differences in sources and ventilation rates. All phthalate and most PAH concentrations were one to two orders of magnitude lower compared to those found from QFF in apartments in Toronto social housing multi-unit residential buildings (MURB), indicating those with lower socio-economic status (SES) were exposed to higher SVOC concentrations. Occupant density was positively related to most phthalate and specific PAH concentrations, while environmental factors including room temperature, relative humidity, and supply air temperature were not.

Comprehensive analysis of model parameter uncertainty influence on evaluation of HVAC operation to mitigate indoor virus: A case study for an office building in a cold and dry climate

Simulation-based studies of HVAC operation to mitigate indoor virus have been conducted to understand tradeoffs between indoor air quality (IAQ) and energy consumption. However, the influence of model parameter uncertainty in these studies has not been systematically quantified, which is critical when providing guidance to building operators. To address this gap, we identify 20 model parameters for a typical medium office building system in a cold and dry climate that can influence IAQ and energy consumption for indoor virus scenarios. Next, the distributions of the parameter values are estimated from literature and a set of simulation samples for three representative days is generated that simultaneously sample all of the parameters from their distributions. Two HVAC virus mitigation strategies are studied: increased filtration using MERV 13 filters and increased ventilation, via supply of 100% outdoor air into buildings. The model parameter uncertainty leads to significant variability in the results, particularly for the IAQ because of the highly uncertain virus generation rate. Use of 100% outdoor air can be beneficial for some uncertain scenarios on the hot day, but shows less IAQ improvement and/or significant energy increases on the other days. The virus removal efficiency and pressure drop of the HVAC filter, fan efficiency, and internal heat gain are the most important parameters to determining the tradeoffs of the two strategies. The results demonstrate how this model parameter uncertainty analysis methodology can provide practical guidance to building operators.

Optimization of electro‐blown polysulfone nanofiber mats for air filtration applications

AbstractDurable, robust, and hydrophobic air filtration media was produced via electro‐blow spinning (EBS) technique using polysulfone (PSU) due to its superior properties. To our knowledge, this is the first optimization study of PSU nanofiber production via EBS technique for air filtration applications. Concentration, air pressure, and voltage were determined as independent variables for the optimization based on “smaller is the better” approach of Taguchi Design of Experiment. The optimized values which supplied the smallest average fiber diameter (AFD) possible were obtained as 13 wt% PSU, 3 bar, and 7.5 kV. The AFD of the sample obtained from the confirmation experiment was calculated as 105 ± 34 nm. Surface morphologies, porosity values, and wettability behaviors of the samples were investigated by using scanning electron microscopy, gravimetric method, and water contact angle measurements, respectively. PSU nanofiber mats exhibited superhydrophobic behavior (water contact angle values up to 159.8°) which is important for various separation processes. Samples prepared at different deposition times (15, 30, 45, and 60 min) were investigated in terms of particle capture efficiency and pressure drop. The 0.3 μm particle filtration efficiency was found to be 98.09% at an expense of 202 Pa pressure drop which would be suitable for various respiratory and HVAC filter applications.

An evaluation of the risk of airborne transmission of COVID-19 on an inter-city train carriage.

Experiments were conducted in an UK inter-city train carriage with the aim of evaluating the risk of infection to the SARS-CoV-2 virus via airborne transmission. The experiments included in-service CO2 measurements and the measurement of salt aerosol concentrations released within the carriage. Computational fluid dynamics simulations of the carriage airflow were also used to visualise the airflow patterns, and the efficacy of the HVAC filter material was tested in a laboratory. Assuming an infectious person is present, the risk of infection for a 1-h train journey was estimated to be 6 times lower than for a full day in a well-ventilated office, or 10-12 times lower than a full day in a poorly ventilated office. While the absolute risk for a typical journey is likely low, in the case where a particularly infectious individual is on-board, there is the potential for a number of secondary infections to occur during a 1-h journey. Every effort should therefore be made to minimize the risk of airborne infection within these carriages. Recommendations are also given for the use of CO2 sensors for the evaluation of the risk of airborne transmission on train carriages.

Dose Calculation for Emergency Control Room HVAC Filter

NPP Krsko is introducing Emergency Control Room (ECR) as part of safety upgrades. According to 10CFR50 Appendix A, GDC 19, both main control room and emergency control room should have adequate radiation protection to permit operators to shutdown the plant and keep it in safe shutdown conditions without receiving more than 50 mSv effective whole body dose, within 30 days from accident initiation. One of the important prerequisites to achieve that is proper operation of control room HVAC. In this work we are focused to calculation of gamma doses from radioactive materials accumulated in HEPA and charcoal filters during 30 days of HVAC operation. The dose at selected points around the filter was calculated using Microshield 10.0 point kernel code. The radioactive gamma source is calculated using RADTRAD 3.03 for plant's severe accident SGTR sequence calculated with MAAP 4.0.7 code. Calculated dose rates at peak filter activity are compared against results obtained with SCALE 6.2 MAVRIC shielding sequence (Monaco Monte Carlo functional module and CADIS methodology). The reasonable agreement between point kernel and hybrid Monte Carlo results was obtained.

Single-pass wind tunnel testing for recirculating virus aerosol control technologies

A number of recirculating flow aerosol control technologies have been commercialized to mitigate aerosol-transmitted virus infections. Many of these technologies incorporate filters for particle collection and some may also incorporate technologies for virus inactivation. Given the wide variety of commercially available aerosol control technologies to consumers, it is extremely important to develop standardized methods to characterize their performance in bioaerosol removal and inactivation, such that technologies can be compared on an “equivalent-test” basis. However, no standard procedures have been established to evaluate the effectiveness of bioaerosol removal and inactivation in recirculating aerosol control technologies. We propose the use of a single-pass tunnel to assess the performance of bioaerosol control technologies, as single-pass wind tunnels can be sealed with well-controlled velocity and particle concentration profiles. Here, we specifically describe the construction of a single-pass wind tunnel and apply it to three recirculating aerosol control technologies, incorporating UV-C sources, filters, and electrostatic precipitators, respectively. We utilize a porcine respiratory coronavirus (PRCV) challenge aerosol, generated via pneumatic nebulization of a high titer (∼107 TCID50 mL−1) viral suspension. Following guidelines similar to those used in the ANSI/ASHRAE Standard 52-2 test procedure for HVAC filters, in single-pass wind tunnel tests, velocity uniformity and particle uniformity are first monitored across the cross-section of the tunnel. The size distribution of viable particles is additionally determined in advance of tests by the collection of particles in the wind tunnel using a cascade impactor, with both RT-qPCR and titration used to quantify viruses collected on each impaction stage. We show that the viable particle size distribution follows the volumetric size distribution of the nebulized virus-laden suspension, and that this distribution can be tuned to be similar in shape to the observed distribution of aerosol from human respiratory activities. Following tunnel and virus aerosol characterization, for each tested technology, using triplicate tests, the single-pass log reduction based on RT-qPCR and viable virus titration is determined by simultaneously collecting virus aerosol particles upstream and downstream of the control technology. The tested technologies in this study have titration-based single-pass log reductions in the 1.5–4.0 range.Overall, design and testing suggest that the single-pass wind tunnel approach is a tractable method to examine the efficacy of aerosol control technologies in removing and inactivating viruses in aerosols, and suggest that such technologies should be described by their single-pass log reduction and operating flow rate, with the test virus size distribution reported alongside test results. In addition, we examine the limits of detection in single-pass wind tunnel tests in comparison to chamber tests, and in doing so find that for most control technologies, the wind tunnel test will yield higher concentrations downstream or during sampling, and hence clearer results for the log reduction.

SARS-CoV-2 on Surfaces and HVAC Filters in Dormitory Rooms

SARS-CoV-2 on Surfaces and HVAC Filters in Dormitory Rooms

Investigation of HVAC operation strategies for office buildings during COVID-19 pandemic

To minimize the indoor transmission of contaminants, such as the virus that can lead to COVID-19, buildings must provide the best indoor air quality possible. Improving indoor air quality can be achieved through the building’s HVAC system to decrease any concentration of indoor contaminants by dilution and/or by source removal. However, doing so has practical downsides on the HVAC operation that are not always quantified in the literature. This paper develops a temporal simulation capability that is used to investigate the indoor virus concentration and operational cost of an HVAC system for two mitigation strategies: (1) supplying 100% outdoor air into the building and (2) using different HVAC filters, including MERV 10, MERV 13, and HEPA filters. These strategies are applied to a hypothetical medium office building consisting of five occupied zones and located in a cold and dry climate. We modeled the building using the Modelica Buildings library and developed new models for HVAC filtration and virus transmission to evaluate COVID-19 scenarios. We show that the ASHRAE-recommended MERV 13 filtration reduces the average virus concentration by about 10% when compared to MERV 10 filtration, with an increase in site energy consumption of about 3%. In contrast, the use of 100% outdoor air reduces the average indoor concentration by about an additional 1% compared to MERV 13 filtration, but significantly increases heating energy consumption. Use of HEPA filtration increases the average indoor concentration and energy consumption compared to MERV 13 filtration due to the high resistance of the HEPA filter.

Evaluation of Antimicrobial Effect of Zinc Pyrithione against Airborne Fungi and Bacteria Growth Collected onto New and Loaded HVAC Fibrous Filters

Microbial growth onto HVAC filters was observed in real conditions with possible degradation of the indoor air quality. The filtration performance of marketed antimicrobial filters containing zinc pyrithione was tested under laboratory conditions and compared to that of similar filters with the same classification, F7 (EN779:2002). The filtration performance of the two tested filters during loading with PM10 particles was quantified in an experimental setup with filter pressure drop measurement and particle counting upstream and downstream of the filters. The microbial growth on the new and loaded filters, both contaminated with a microbial airborne consortium composed of two bacteria (Gram-positive and -negative) and fungi, was quantified by colony-forming units after conditioning the filters for a few days under controlled temperature (25 °C) and humidity (50% or 90% relative humidity). The results reveal that there was no degradation of the filtration performance of the filters treated with the antimicrobial agent. The efficiency of the antimicrobial treatment, i.e., the ability to inhibit the growth of microorganisms during the incubation period, was significant with the new filters regarding the fungal growth, but the results demonstrate that the antimicrobial treatment became inefficient with the loaded filters.

Dust and microbial filtration performance of regular and antimicrobial HVAC filters in realistic conditions

Two polypropylene HVAC electret filters: a regular filter and an antimicrobial filter containing zinc pyrithione (ZPT), were compared for filtration performance. The study was conducted over 7 months in realistic conditions with semi-urban outdoor air. Several parameters were monitored over the study period: the average temperature was about 20 °C and relative humidity about 60%, the average inlet concentration of cultivable microorganisms was 50 CFU m-3, the average inlet concentration of particles was 10 μg m-3, the filter pressure drop increased moderately by about 30 Pa, and the particle collection efficiency of soda fluorescein (median diameter 0.35 μm) decreased in the first half of the study period by about 30% and then stabilized. The microbial concentration on the filters was quantified every 2 months using an innovative methodology based on media coupons in conjunction with microorganism quantification by CFU counting, with 5 culture media favorable to bacteria and/or fungi growth. The microbial concentrations on the filters were between 100 and 2000 CFU cm-2. The antimicrobial effect of zinc pyrithione was confirmed by the fungi cultivated with DRBC agar: no effects in the level of filter clogging were revealed in the range studied. The high statistical deviation in the results regarding the inhibiting effect of zinc pyrithione on bacteria prevents any conclusion.

Distribution of SARS-CoV-2 RNA signal in a home with COVID-19 positive occupants.

Although many COVID-19 patients isolate and recover at home, the dispersal of SARS-CoV-2 onto surfaces and dust within the home environment remains poorly understood. To investigate the distribution and persistence of SARS-CoV-2 in a home with COVID-19 positive occupants, samples were collected from a household with two confirmed COVID-19 cases (one adult and one child). Home surface swab and dust samples were collected two months after symptom onset (and one month after symptom resolution) in the household. The strength of the SARS-CoV-2 molecular signal in fomites varied as a function of sample location, surface material and cleaning practices. Notably, the SARS-CoV-2 RNA signal was detected at several locations throughout the household although cleaning appears to have attenuated the signal on many surfaces. Of the 24 surfaces sampled, 46% were SARS-CoV-2 positive at the time of sampling. The SARS-CoV-2 concentrations in dust recovered from floor and HVAC filter samples ranged from 104 to 105 N2 gene copies/g dust. While detection of viral RNA does not imply infectivity, this study confirms that the SARS-CoV-2 RNA signal can be detected at several locations within a COVID-19 isolation home and can persist after symptoms have resolved. In addition, the concentration of SARS-CoV-2 (normalized per unit mass of dust) recovered in home HVAC filters may prove useful for estimating SARS-CoV-2 airborne levels in homes. In this work, using the quantitative filter forensics methodology, we estimated an average integrated airborne SARS-CoV-2 concentration of 69 ± 43 copies/m3. This approach can be used to help building scientists and engineers develop best practices in homes with COVID-19 positive occupants.

Concentrations and size-resolved I/O ratios of household airborne bacteria and fungi in Nanjing, southeast China

This work quantitatively investigated the concentration relationships between indoor and outdoor bioaerosols in residence. We measured bacteria and fungi from air in 28 residential homes throughout Nanjing, southeast China during summer and winter. The culture-based method was applied and the ratios of indoor to outdoor concentrations, expressed in I/O, were calculated. Results revealed that concentrations of indoor bioaerosols were significantly associated with outdoor bioaerosols, and their size distributions showed similar single-peak pattern. Spearman correlation analysis indicated that I/O ratios were positively related to indoor microbial concentration. The I/O ratios differed insignificantly from seasons, but significantly higher I/O ratios were observed in airborne bacteria rather than airborne fungi during the same season. For bacteria, as much as 89% of homes in summer and 67% of homes in winter have I/O ratios >1, while for fungi, more than half of homes have I/O ratios <1, i.e. 50% in summer and 73% in winter. The different size distribution of bacteria and fungi could make a difference in I/O ratios. The greater percentage of I/O > 1 was observed in smaller size of bacteria and greater percentage of I/O < 1 was observed in larger size of fungi. The significant difference of I/O ratios between bacteria and fungi revealed that airborne bacteria being mainly originated from indoor sources, but airborne fungi dominantly from outdoor sources. Among various housing operations, the window opening period per day, the usage of air cleaner, and indoor planting played significant roles on I/O ratios, but the frequency of HVAC filter cleaning and the housing cleaning as well as the occurrence of mold played insignificant roles in this study.

Filtering Out Microbes

Abstract A new HVAC filter, developed through a collaboration of Houston-based medical real estate developer Medistar and researchers at the University of Houston and Texas A&amp;M University, uses a heated filter made of nickel foam that traps and kills 99.8 percent of the virus.

Distribution and comparison of bacterial communities in HVAC systems of two university buildings: Implications for indoor air quality and public health.

The installation of HVAC systems in building is meant to enhance indoor air quality as well as increase comfort to occupants. However, HVAC systems have also become a vehicle of contamination of indoor air with potentially pathogenic microorganisms. DNA was extracted from ten HVAC filter dust samples collected from two buildings and subjected to high throughput sequencing analysis to determine the bacterial community structure. Further, the Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt2) software was used to predict the potential functional capabilities of the bacterial communities. Sequencing analysis led to the identification of five major bacterial phyla, including Proteobacteria, Cyanobacteria, Actinobacteria, Firmicutes and Bacteroidetes. At genus level, Mycobacterium, Bacillus, Cupriavidus, Hyphomicrobium and Mesorhizobium were the most dominant. With the exception of the later two bacterial genera, the first three are potential pathogens whose presence in HVAC systems poses a significant public health risk, especially among immunocompromised individuals. Nine pathways associated with antibiotics resistance and bacterial pathogenicity were identified, including polymyxin resistance and peptidoglycan biosynthesis pathways. Further, investigation of the relationship between the detected bacterial meta-communities and predicted potential virulence factors (antibiotic resistance and pathogenic genes) led to the detection of 350 positive associations among 43 core bacteria, 2 pathogenic genes (sitA and uidA) and 14 resistance genes. Overall, the heterogeneous nature of microorganisms found in HVAC systems observed in this study shows that HVAC systems are the origin of airborne infections in indoor environments, and must be periodically cleaned and disinfected to avoid the build-up of pathogens, and the subsequent exposure of human occupants of these pathogens.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10661-020-08823-z.

Multi-scenario and multi-criteria approach to evaluate prediction techniques used to recognise failure patterns

Predicting the next failure of a specific component in a machine results in higher performance of the equipment in terms of its reliability. This study examines the five most applicable prediction methods used to predict HVAC filter blockage. Considering different scenarios that use design of experiment (DOE), a multiple criteria decision making (MCDM) tool, known as TOPSIS, is utilised to compare the performance of each predictive technique according to their performance in various contexts. The results show that the performance of the system is improved when the best predictive method has been selected not only on the premises of a purely mathematical approach, but also when the solid mathematical prediction is supplemented by the judgments of experts and edited data. In addition, the empirical data is retrieved and a new method to evaluate the prediction techniques based on the applications of DOE and MCDM tools is illustrated.

Development of a Method to Determine the Fractional Deposition Efficiency of Full-Scale HVAC and HEPA Filter Cassettes for Nanoparticles ≥3.5 nm

Novel methods have been developed to measure the fractional deposition efficiency for nanoparticles of full-scale HVAC and HEPA filter cassettes down to a particle size of 3.5 nm. The methods use a flame spray nanoparticle generator to produce NaCl test aerosols with narrow size distributions and very high concentrations. While the efficiency curves of lower efficiency filters of classes F7 and E10 were still able to be determined by measuring the size distributions of the polydisperse test aerosols upstream and downstream of the filter, two new testing procedures were developed for high efficiency filters of class H13. One considers the narrow size distributions of the test aerosols as quasi-monodisperse and follows a similar approach like EN 1822 for flat sheet media. The second one evaluates mobility classified fractions of the quasi-monodisperse test aerosols. A dedicated multiple charge correction scheme was developed to account for the effect of multiply charged particles. While the latter procedure allows to extend the particle size range, the prior significantly reduces the measurement time. All tests delivered meaningful results, which were very comparable with the results from flat sheet media tests.

Characterization of a thermal aerosol generator for HVAC filtration experiments (RP-1734)

HVAC filters are exposed to a diverse mixture of aerosols during their service life. Aerosol physiochemical properties can have a significant impact on the removal efficiency and loading behavior of a filter. New aerosol generation techniques are needed to age HVAC filters with particle size distributions (PSDs) representative of those found in outdoor (urban) and indoor environments. This study evaluated the physical characteristics of salt aerosol produced by a newly designed commercially available thermal aerosol generator. The thermal aerosol generator produced a high mass output of sub-micron (≤ 1,000 nm) sodium chloride (NaCl) and potassium chloride (KCl) particles by burning a salt stick in an oxygen-propane flame. The shape of the number and mass PSDs is similar to those found in outdoor (urban) and indoor air and can be modulated by varying the rate at which the salt stick is fed into the flame. The morphology of the NaCl and KCl particles varied with size, with compact spherical or cubic structures observed below 100 nm and agglomerates observed above 100 nm. The thermal aerosol generator is a cost-effective technique for rapid ageing of HVAC filters with a PSD that more accurately represents, compared to conventional loading dusts, what filters encounter in real HVAC installations.

In-situ effectiveness of residential HVAC filters.

In this study, we explore different filter and contextual characteristics that influence effectiveness of high-efficiency filters in 21 residences in Toronto, Canada. The in situ effectiveness was assessed with decay tests at the beginning andthe end of filter life with four different filters (MERV 8-14 from ASHRAE Standard 52.2) installed in operational HVAC systems, compared with either the system off or with no filter installed. There was considerable difference between median PM2.5 effectiveness of the non-electret filters when compared to electret filters (16% vs. 36%) of the same nominal efficiency (MERV 8). However, median PM2.5 effectiveness of electret filters only slightly improved (between 5% and 9% absolute increase) as MERV increased from 8 to 14. There was more variation in filter effectiveness between the same filter in different homes than there was between different filters in the same home. Variations in filter performance arose because home-specific particle loss rates (eg, ventilation rate) vary greatly in different buildings. The higher the loss rates due to non-filter factors, the lower the effectiveness of a filter. Given the relatively large variation in effectiveness for a given filter over time and in different homes, increasing system runtime may be a productive way to improve filter performance in many homes.

Exposure assessment in one central hospital: A multi-approach protocol to achieve an accurate risk characterization

The bioburden in a Hospital building originates not only from patients, visitors and staff, but is also disseminated by several indoor hospital characteristics and outdoor environmental sources. This study intends to assess the exposure to bioburden in one central Hospital with a multi-approach protocol using active and passive sampling methods. The microbial contamination was also characterized through molecular tools for toxigenic species, antifungal resistance and mycotoxins and endotoxins profile. Two cytotoxicity assays (MTT and resazurin) were conducted with two cell lines (Calu-3 and THP-1), and in vitro pro-inflammatory potential was assessed in THP-1 cell line. Out of the 15 sampling locations 33.3% did not comply with Portuguese legislation regarding bacterial contamination, whereas concerning fungal contamination 60% presented I/O > 1. Toxigenic fungal species were observed in 27% of the sampled rooms (4 out of 15) and qPCR analysis successfully amplified DNA from the Aspergillus sections Flavi and Fumigati, although mycotoxins were not detected. Growth of distinct fungal species was observed on Sabouraud dextrose agar with triazole drugs, such as Aspergillus section Versicolores on 1 mg/L VORI. The highest concentrations of endotoxins were found in settled dust samples and ranged from 5.72 to 23.0 EU.mg−1. While a considerable cytotoxic effect (cell viability < 30%) was observed in one HVAC filter sample with Calu-3 cell line, it was not observed with THP-1 cell line. In air samples a medium cytotoxic effect (61–68% cell viability) was observed in 3 out of 15 samples. The cytokine responses produced a more potent average cell response (46.8 ± 12.3 ρg/mL IL-1β; 90.8 ± 58.5 ρg/mL TNF-α) on passive samples than air samples (25.5 ± 5.2 ρg/mL IL-1β and of 19.4 ± 5.2 ρg/mL TNF-α).A multi-approach regarding parameters to assess, sampling and analysis methods should be followed to characterize the biorburden in the Hospital indoor environment. This study supports the importance of considering exposure to complex mixtures in indoor environments.

Bioburden in health care centers: Is the compliance with Portuguese legislation enough to prevent and control infection?

This study intends to assess the bioburden in ten Portuguese health care centers (PHCC) with a multi-approach protocol using active (air sampling by impaction and impinger) and passive (surface swabs and air-conditioning filters) sampling methods, and compare the results with compliance levels of IAQ Portuguese legislation for the assessment of bioburden. The fungal burden in the PHCC was also characterized through molecular detection of toxigenic species, antifungal resistance and mycotoxins profile. Concerning legal compliance criteria for bacteriota the first criteria [indoor] + 350 CFU. m−3 < [outdoor] was not complied in all PHCC analyzed. Regarding fungal load, 60% did not comply with the quantitative guideline (I/O < 1). Growth of four fungal genera (Chrysosporium, Cladosporium, Mucor and Penicillium) was observed in HVAC filter samples collected from 6 out of 10 assessed PHCC when using azole-supplemented SDA media. Overall, Aspergillus/Penicillium/Paecilomyces levels were above the detection limits, except in one PHCC. The presence of mycotoxins was found both in air and HVAC filter samples. From the air samples analyzed, nine were contaminated (ng/ml) with 1–5 different mycotoxins within the same sample, whereas in HVAC filters, four samples contained 1 or 2 mycotoxins in the same filter. Overall, it was possible to conclude that Portuguese legislation is not enough to ensure IAQ in health care settings. The multi-approach sampling protocol used in this study allowed to unveil a more real scenario regarding exposure to bioburden. Detection of mycotoxins reinforces the relevance of studying mycotoxins in the clinical environment.