Applications In Indoor Environments Research Articles

Potential of wood fiber/polylactic acid composite microperforated panel for sound absorption application in indoor environment

This study introduces a novel approach using wood fiber/PLA composite microperforated panel (WFCMPP) for indoor sound absorption purposes. WFCMPP, comprising rubber tree chip-derived fibers and a polylactic acid (PLA) matrix, with the dimensions of the rubber tree chip-derived fibers ranging from 0.5 to 1 mm, demonstrated promising sound absorption coefficients comparable to other natural fiber composite microperforated panels. The maximum sound absorption coefficient was recorded at 0.989 with a resonance frequency of 1416 Hz when the wood fiber composition was 30 %. The study also investigates the impact of wood fiber composition on sound absorption, revealing a linear relationship between fiber content and both porosity and sound absorption. The peak sound absorption coefficient of WFCMPP remained almost identical at different air gap thicknesses, showcasing the versatility and effectiveness of the samples. Additionally, the performance remained robust even with variations in air gap size. Scanning electron microscope analysis confirms the irregular porous structure and complexity contributing to enhanced sound absorption. WFCMPP presents a sustainable and effective alternative for acoustic applications, combining sound absorption performance with environmental considerations.

Monitoring and Predicting African Rural Household Air Pollution Using Internet of Things and Artificial Intelligence

Abstract According to a 2020 report from the World Health Organization (WHO), household air pollution has led to over 3 million deaths globally, with recent statistics showing a worsening situation in Africa. Integrating Internet of Things (IoT) and Artificial Intelligence (AI) technologies can help address this global challenge. IoT enables real-time data collection for monitoring pollution levels, while AI algorithms predict pollution before it reaches hazardous levels. However, existing solutions are not tailored to the African context, where wood fuel is a primary pollutant, and they predominantly focus on monitoring rather than prediction. This study presents the design and implementation of an IoT-based solution for monitoring and predicting indoor air pollution in rural African households. The system collects data in real time and transmits it to the cloud for storage, processing, and analysis, with alerts to users when pollution is detected. An AI model was successfully trained and tested to predict indoor air pollution based on the collected data. The results indicate that this approach significantly improves the accuracy and timeliness of pollution alerts, potentially reducing health risks associated with indoor air pollution. The successful implementation and testing of the system demonstrate its potential for broader applications in various indoor environments.

Fire Fighting Robot- The Fire Extinguisher

This study presents the design and implementation of a fire fighting robot using an Arduino UNO microcontroller as the central control unit. The robot is equipped with a flame sensor for detecting fires, a motor driver for precise motor control, and a water pump for extinguishing flames. Additionally, an ultrasonic sensor is integrated for obstacle detection and navigation, enhancing the robot's mobility in complex environments. A Bluetooth module allows for remote control and monitoring of the robot's operation, while a buzzer provides audible feedback during emergency situations. The performance of the fire fighting robot is evaluated under various conditions, demonstrating its effectiveness in autonomously detecting and extinguishing fires. Overall, the developed robot offers a promising solution for automated fire fighting tasks, with potential applications in both indoor and outdoor environments

Analysis of a Fuzzy Based Intrusion Detection System in Wireless Ad Hoc Networks

Technology and its growth is considerably enormous. This massive growth allows the opening of new fields of application in the domain of wireless networking and mobile ad-hoc networks (MANET) is one of its kinds. Mobile ad hoc network is widely used from collaborative computing to time critical applications in indoor and outdoor environment. Mobility of ad hoc network makes very attractive in all areas of mobile applications. Nodes participating in mobile ad hoc networks are autonomous, self-configurable and act as a router as well. These types of networks are dynamic in nature and have sort life time. Dynamic nature and limitations of the wireless transmission medium make MANET unsecured and vulnerable to various attacks. It is very tough to implement security for this networks and it opens up doors for further research work on this area. There is a great scope for designing a system to identify attacks and take countermeasures to minimize it and keep the performance of the network within acceptable limits. Intrusion detection system is one of its kinds and considered as security mechanism for MANET. This thesis explores different types of intrusion detection system like misuse detection and anomaly detection for mobile ad hoc networks. Anomaly detection techniques for ad hoc networks depend on the characterization of normal behavior pattern of wireless nodes. This research work focuses on wireless node behavior based detection technique. Most of anomaly intrusion detection systems are focusing on upper layer traffic to a profile normal behavior of wireless node. This research work focus on media access control (MAC) layer and network layer of wireless node. It is inefficient to use a large feature set of MAC layer and network layer due to energy limitation in ad-hoc network. A minimal feature set from MAC layer and network layer were proposed. This research work proposed an anomaly intrusion detection system for mobile ad hoc network using fuzzy logic and weighted average method. The network performance of mobile ad hoc network with intrusion detection system was analyzed using various network parameters. Further the performance of the performance of the intrusion detection system was analyzed using detection rate and false alarms. Results show good improvement in detection rate and other performance metrics

The effect of verbal instructions while using digital indoor wayfinding devices on gender, performance, and self-reported strategies

Studies indicate that verbal instructions may impact associations between gender and wayfinding performance (measured via relative direction pointing accuracy and walking pace). Following the increasing use of digital navigation applications in indoor environments, and their implications on acquiring and processing spatial information, the aim of this study is to evaluate the stability of previously established associations. The study included 34 participants (16 females) aged 24–34 and was conducted in an indoor hospital setting. In addition to using a navigation application, one of three types of verbal instructions (route, survey, or none) were given in each wayfinding scenario. Self-reported wayfinding strategies were also assessed. The findings indicate that male participants made fewer pointing accuracy errors and walked faster than females, regardless of the type of instructions given, implying that the impact of naturally employed wayfinding strategies by gender (route for females; survey for males) on wayfinding performance may be more dominant than that of navigational devices. In addition, when males and females were exposed to their unnatural wayfinding strategy, no significant differences were seen in either group's self-reported wayfinding strategies. These findings may suggest that applying survey knowledge to females may improve their indoor wayfinding.

MagLoc-AR: Magnetic-based Localization for Visual-free Augmented Reality in Large-scale Indoor Environments.

Accurate localization of a display device is essential for AR in large-scale environments. Visual-based localization is the most commonly used solution, but poses privacy risks, suffers from robustness issues and consumes high power. Wireless signal-based localization is a potential visual-free solution, but its accuracy is not enough for AR. In this paper, we present MagLoc-AR, a novel visual-free localization solution that achieves sufficient accuracy for some AR applications (e.g., AR navigation) in large-scale indoor environments. We exploit the location-dependent magnetic field interference that is ubiquitous indoors as a localization signal. Our method requires only a consumer-grade 9-axis IMU, with the gyroscope and acceleration measurements used to recover the motion trajectory, and the magnetic measurements used to register the trajectory to the global map. To meet the accuracy requirement of AR, we propose a mapping method to reconstruct a globally consistent magnetic field of the environment, and a localization method fusing the biased magnetic measurements with the network-predicted motion to improve localization accuracy. In addition, we provide the first dataset for both visual-based and geomagnetic-based localization in large-scale indoor environments. Evaluations on the dataset demonstrate that our proposed method is sufficiently accurate for AR navigation and has advantages over the visual-based methods in terms of power consumption and robustness. Project page: https://github.com/zju3dv/MagLoc-AR/.

The clinical and environmental effects of an advanced air purification technology in multiple healthcare settings

Many facility acquired infection (FAI) causing pathogens are airborne and controlling them is critical to preventing illness. An advanced air purification technology (AAPT) was designed to inactivate the genetic material of pathogens and remediate volatile organic compounds (VOCs). This study explores the effect of the AAPT on critical metrics in multiple healthcare settings. The AAPT was installed in the heating, ventilation, and air conditioning (HVAC) ductwork of a hospital’s medical surgical floor (ACH-MSF), a second hospital’s post-anesthesia care unit (PACU), intensive care unit (ICU), and medical surgical (MS) unit, and in a senior living facility’s (SLF) memory support unit. In all installations, the control area(s) were protected only by high efficiency particulate air (HEPA) filtration. The measured airborne fungal levels, airborne and surface bacterial levels, and VOC levels decreased with the installation of AAPT. The AAPT removed infectious airborne pathogens and reduced surface pathogens and VOCs. The ACH-MSF and SLF protected by the AAPT documented improved clinical and economic metrics including a 39.5% decrease in patient length of stay, 23% in cost savings improvement, and a 39.6% decrease in FAIs. The current findings support the hypothesis that indoor environmental quality impacts wellness and has potential applications in diverse indoor environments.

Performance of photocatalytic oxidation surface with new geometry for indoor environment application: experimental and simulation

Abstract Many studies of the photocatalytic oxidation process investigated on the removal efficiency and other variables of the input and output photoreactor. In the laboratory scale, it’s impossible, examination of the removal efficiency details, such as mass and energy transfer with air flow rate. Also, experimental methods request time consumption and money. For this reason, the simulation method can be used. The aim of this study was to prove that the validation of modeling approach in the photocatalytic oxidation process in the removal of toluene from air. Investigation of bed surface morphology, with FESEM, BET and TGA, shows acceptable monotonous of TiO2 nanoparticles on the ss plate. Furthermore, it was observed good adherence of nanoparticles on it. Experimental results on photocatalytic bed surface exhibited in the toluene concentration range of 10–40 ppm and flow rate of 2–5 l/min, with increasing flow and decreasing concentration, removal efficiency increased. The optimum removal point was 59% and 25 g/m3 min for 3.75 ppm and 5.61 l/min. For bed surface performance, the correlation between experimental results and simulation data was obtained 98%. According to the results, the photocatalytic oxidation process performed well for removal of low concentration of toluene from air. In addition, the obtained simulation method eliminated the random factors which can be affected by photocatalytic bed surface and it can show dependence of results based on reality.

Comparing Efficiency and Performance of IoT BLE and RFID-Based Systems for Achieving Contract Tracing to Monitor Infection Spread among Hospital and Office Staff.

COVID-19 is highly contagious and spreads rapidly; it can be transmitted through coughing or contact with virus-contaminated hands, surfaces, or objects. The virus spreads faster indoors and in crowded places; therefore, there is a huge demand for contact tracing applications in indoor environments, such as hospitals and offices, in order to measure personnel proximity while placing as little load on them as possible. Contact tracing is a vital step in controlling and restricting pandemic spread; however, traditional contact tracing is time-consuming, exhausting, and ineffective. As a result, more research and application of smart digital contact tracing is necessary. As the Internet of Things (IoT) and wearable sensor device studies have grown in popularity, this work has been based on the practicality and successful implementation of Bluetooth low energy (BLE) and radio frequency identification (RFID) IoT based wireless systems for achieving contact tracing. Our study presents autonomous, low-cost, long-battery-life wireless sensing systems for contact tracing applications in hospital/office environments; these systems are developed with off-the-shelf components and do not rely on end user participation in order to prevent any inconvenience. Performance evaluation of the two implemented systems is carried out under various real practical settings and scenarios; these two implemented centralised IoT contact tracing devices were tested and compared demonstrating their efficiency results.

Cascade filter system tests for airborne nano‐ and microplastic particle analytics in a laboratory dust chamber

AbstractMeasuring nano‐ and microplastic particle (NMP) loads in air requires suitable analytical filter systems that allow a size‐selective separation of airborne nano‐ and microplastic (NMP) fractions. Previously, various filter materials and setups including nano/micro cascade filtration stacks have been presented (P.‐T. Miclea, 2022). To evaluate these novel filter systems, implementing reliable sampling procedures and instrumentation, as well as sample handling, well‐defined test setups, NMP reference materials, and procedures are of major interest. In this study, a novel triple‐stage silicon (Si) and aluminum oxide (Al2O3) cascade filter system for airborne NMP particles is tested in a laboratory environment. Special focus is put on its ability for size‐selective analytical filtration of airborne NMP particles based on a well‐defined mixture of poly‐ and monodisperse NMP reference materials. For this purpose, a laboratory dust test chamber has been adapted for the dispersion of NMP particles in air as well as the vacuum air extraction through the cascade filter system. A defined NMP test material was fabricated from polydisperse polyethylene (PE) and PE terephthalate, and monodisperse polystyrene, polymethylmethacrylate, spanning a size region from 130 nm to >22 µm. Dispersion and filtration experiments are performed by vacuum extraction under defined temperature, pressure, and humidity conditions on single and triple filtration stages. NMP particle analytics are performed with polydisperse PE particles on a single‐stage filter system with subsequent optical microscopy. Here, the aim is to detect the filtration cutoff for retained particles and transmitted particles referring to initial distribution. A second experiment is run on a triple filtration cascade with mixed poly‐ and monodisperse NMP test material. The different filter stages are equipped with analytical Si and Al2O3 filters with pore sizes of 10 µm, 1 µm, and 100 nm, to test the size selectivity and sealing of the complete cascade setup. The NMP particle size distribution on the individual analytical filter substrates is analyzed by optical and scanning electron microscopy to assess size selectivity performance of the triple‐stage setup. The obtained results in our laboratory NMP dust‐dispersion test chamber demonstrate requirements and limitation of size‐selective NMP cascade filter systems and the involved analytical procedures. Future applications in real indoor and outdoor environments will be discussed.

AN INDOOR LOCALIZATION METHOD FOR MOBILE ROBOT USING CEILING MOUNTED APRILTAGS

Localization is one of the most important functions for autonomous mobile robots (AMRs). For indoor applications, the localization problem faces some difficulties such as lightning variation, dynamic objects or highly reflective surfaces that generate measurement noises for the perceptive sensor systems. Recently, tags-based pose estimation has become a popular and efficient solution for AMRs. In this article, we also ultilize ceiling mounted AprilTags for our AMR application in indoor environment. The advantage of AprilTags is their invariance to uncertainty of the environment such as lightning conditions, providing robust pose measurements with a fairly large range of measuring distances from the camera to fiducial markers. By integrating AprilTags in the SLAM package, we have solved several problems such as robot pose-recovery problem and improving the accuracy of the robot localization. Experiments with an AMR robotic system, the Vibot-2 robot, are carried out in two cases: under day-light condition and night-time condition to verify the accuracy of the method. In addition, we also discuss our solution of tag positioning in order to increase the stability of the robot navigation in global map. Experiment results show that the accuracy in pose estimation is less than 20 cm in terms of position and less than 5° in terms of heading angle. Furthermore, the pose measurements from the camera are quite stable under different lightning conditions.

Interpretable Passive Multi-Modal Sensor Fusion for Human Identification and Activity Recognition.

Human monitoring applications in indoor environments depend on accurate human identification and activity recognition (HIAR). Single modality sensor systems have shown to be accurate for HIAR, but there are some shortcomings to these systems, such as privacy, intrusion, and costs. To combat these shortcomings for a long-term monitoring solution, an interpretable, passive, multi-modal, sensor fusion system PRF-PIR is proposed in this work. PRF-PIR is composed of one software-defined radio (SDR) device and one novel passive infrared (PIR) sensor system. A recurrent neural network (RNN) is built as the HIAR model for this proposed solution to handle the temporal dependence of passive information captured by both modalities. We validate our proposed PRF-PIR system for a potential human monitoring system through the data collection of eleven activities from twelve human subjects in an academic office environment. From our data collection, the efficacy of the sensor fusion system is proven via an accuracy of 0.9866 for human identification and an accuracy of 0.9623 for activity recognition. The results of the system are supported with explainable artificial intelligence (XAI) methodologies to serve as a validation for sensor fusion over the deployment of single sensor solutions. PRF-PIR provides a passive, non-intrusive, and highly accurate system that allows for robustness in uncertain, highly similar, and complex at-home activities performed by a variety of human subjects.

Qualitative and quantitative determination of butanol in latex paint by fast gas chromatography proton transfer reaction mass spectrometry

Butanol is a common organic solvent used in latex paint, and one of its isomers, tert-butanol, is toxic and can cause potential harm to the human body. Therefore, it is of great significance to develop a qualitative and quantitative detection method for butanol isomers. In this study, we combined the advantages of rapid detection of proton transfer reaction mass spectrometry (PTR-MS) with the separation and qualitative capabilities of gas chromatography-mass spectrometry (GC-MS) to achieve the detection of isomers, building a fast gas chromatography proton transfer reaction mass spectrometry (FastGC-PTR-MS) equipment. Firstly, the developed technology was optimized using standard samples of several common volatile organic compounds. The retention times of acetonitrile, acetone, and alcohols were less than 50 s, and the retention times of the benzene series were less than 110 s, on the premise that these isomers could be basically separated (resolution R > 1.0). Compared with a commercial GC-MS equipment, the detection times were shortened by 5-6 times and 2-4 times, respectively. Then the FastGC-PTR-MS was applied to detect the isomers of butanol in latex paint. The results showed that the headspace of brand D latex paint mainly contained five substances: tert-butanol, n-butanol, acetaldehyde, methanol, and acetone. Tert-butanol and n-butanol could be completely separated (R > 1.5). The concentration of tert-butanol was 4.41 ppmv, far below the 100 ppmv maximum allowable workplace concentration. The developed FastGC-PTR-MS can be used for rapid qualitative and quantitative detection of butanol isomers in latex paint. The new equipment has the potential to play an important role in indoor environmental safety applications.

Development of Functional Composite Cu(II)-Polyoxometalate/PLA with Antimicrobial Properties.

Novel composite self-disinfecting films of polylactic acid (PLA) filled with nanosized particles of double sodium–copper(II) paratungstate B Na2Cu3(CuOH)2[W12O40(OH)2]·32H2O (POM) were developed. The solvent casting (POM/PLA film) and solvent-free melt extrusion methods (Extr. POM/PLA film) were applied for film preparation. The copper (II) ion release to water from both types of the films after 10 days at different temperatures demonstrated that the PLA matrix acts as a diffusion barrier, and the resulting concentration of released copper in water at room temperature remained low, at 0.79% for POM/PLA film and 0.51% for Extr. POM/PLA film. The POM-containing films reveals a significant inhibitory effect against E. coli ATCC 25922 in the agar diffusion test. The numbers of CFUs in washes of the films after incubation for 24 h were found to be 3.6 log CFU mL–1 (POM/PLA film) and 4.1 log CFU mL–1 (Extr. POM/PLA film). The films combine the antibacterial properties of POM and a bio-based polymer matrix, which makes them a prospective coating material for applications in hospital indoor environments. Excellent thermal stability of POM gives a technological advantage for industrial manufacturing to allow the processing of novel composite material in the solvent free (molten) state.

Tunable Graphene/Nitrocellulose Temperature Alarm Sensors.

Tunable temperature alarm sensors were prepared using multilayer graphene and nitrocellulose (NC) to reliably monitor early high temperature risks. The graphene/NC alarm sensor keeps in a state of electrical insulation, however, turns electrically conductive at high temperatures, such as encountering a flame attack. Its response time is limited to only a few seconds because of a quick chemical reaction of NC. The 90% graphene/NC (wt % ratio 1:9) composite alarm sensor stably remains insulated at an ambient temperature of 200 °C, resulting in a satisfactory responsive temperature (232 °C), instant response time (4.4 s), and sustained working time in the flame below the ignition temperature of most combustibles. Furthermore, the response temperature and time of the alarm sensor can be tuned by graphene/NC ratios to reduce the fire risk of various combustible materials in different fire-prone scenarios and thus has promising applications in both indoor and outdoor environments. The sensor has also proven to work in the form of paint, wallpaper, and other composites due to its superior flame retardancy property, as well as under extreme conditions (i.e., underwater and vacuum).

Node Calibration in UWB-Based RTLSs Using Multiple Simultaneous Ranging.

Ultra-wideband (UWB) networks are gaining wide acceptance in short- to medium-range wireless sensing and positioning applications in indoor environments due to their capability of providing high-ranging accuracy. However, the performance is highly related to the accuracy of measured position and antenna delay of anchor nodes, which form a reference positioning system of fixed infrastructure nodes. Usually, the position and antenna delay of the anchor nodes are measured separately as a standard initial procedure. Such separate measurement procedures require relatively more time and manual interventions. This paper presents a system that simultaneously measures the position and antenna delay of the anchor nodes. It provides comprehensive mathematical modeling, design, and implementation of the proposed system. An experimental evaluation in a line-of-sight (LOS) environment shows the effectiveness of the anchor nodes, whose position and antenna delay values are measured by the proposed system, in localizing a mobile node.

Numerical Investigation on the Effect of Ventilation on the Distribution of Phthalate Esters in the Residential Environment

Semi-volatile organic compounds (SVOCs), such as phthalates and brominated flame retardants, is a kind of emerged pollutants due to wide application in indoor environment. Certain indoor SVOCs have been found to be associated with various adverse health effects, attracting large attentions of researchers. Due to relatively low vapor pressure, SVOCs are easily adsorbed on various surfaces including particles. Therefore, airborne SVOCs are always simultaneously presented in the gas-phase and particle-phase. Ventilation is an important means to improve indoor air quality. Different forms of indoor air distribution will affect the distribution of indoor pollutants and further affect the exposure to the human body. Therefore, in this paper, we selected Di (2-ethylhexyl) phthalate (DEHP) as the target compound and employed computational fluid dynamics (CFD) technique to simulate the emission of DEHP and the concentration distribution with different phases in a modeled room. Euler-Lagarian model is applied to simulate flow field, particle tracks and UDF (user defined function) was implemented to describe the dynamic adsorption of DEHP by the suspended particles. Furthermore, the effect of location of vent and airflow rate on indoor fate of DEHP were discussed and the effect of particle age on indoor fate of DEHP was also investigated.

Hydrophobic cellulose-based and non-woven fabrics coated with mesoporous TiO2 and their virucidal properties under indoor light

Antiviral hydrophobic cellulose-based cotton or non-woven fabrics containing mesoporous TiO2 particles were developed for potential use in healthcare and in other contaminated environments. Hydrosols made with the sol-gel method using two different amounts of the Ti precursor were applied to cotton and non-woven fabrics and their virucidal effect on Murine Coronavirus (MHV-3) and Human Adenovirus (HAdV-5) was evaluated under indoor light irradiation. The results show 90% reduction of HAdV-5 and up to 99% of MHV-3 in non-woven fabric, and 90% reduction of MHV-3 and no reduction of HAdV-5 in cotton fabric. The antiviral activity was related to the properties of the TiO2 powders and coatings characterized by BET surface area, DRX, DLS, FTIR, DRS, SEM, TEM and water contact angle. The hydrophobic characteristic of the treated fabrics and the high surface area of the TiO2 particles favor interaction with the virus, especially MHV-3. These results demonstrate that non-woven fabric and cotton, coated with TiO2, can be highly effective in preventing contamination with MHV-3 and HAdV-5 viruses, particularly for applications in healthcare indoor environments.

High Water Adsorption MOFs with Optimized Pore-Nanospaces for Autonomous Indoor Humidity Control and Pollutants Removal.

The indoor air quality is of prime importance for human daily life and health, for which the adsorbents like zeolites and silica-gels are widely used for air dehumidification and harmful gases capture. Herein, we develop a pore-nanospace post-engineering strategy to optimize the hydrophilicity, water-uptake capacity and air-purifying ability of metal-organic frameworks (MOFs) with long-term stability, offering an ideal candidate with autonomous multi-functionality of moisture control and pollutants sequestration. Through variant tuning of organic-linkers carrying hydrophobic and hydrophilic groups in the pore-nanospaces of prototypical UiO-67, a moderately hydrophilic MOF (UiO-67-4Me-NH2 -38 %) with high thermal, hydrolytic and acid-base stability is screened out, featuring S-shaped water sorption isotherms exactly located in the recommended comfortable and healthy ranges of relative humidity for indoor ventilation (45 %-65 % RH) and adverse health effects minimization (40-60 % RH). Its exceptional attributes of water-uptake working capacity/efficiency, contaminants removal, recyclability and regeneration promise a great potential in confined indoor environment application.

High Water Adsorption MOFs with Optimized Pore‐Nanospaces for Autonomous Indoor Humidity Control and Pollutants Removal

AbstractThe indoor air quality is of prime importance for human daily life and health, for which the adsorbents like zeolites and silica‐gels are widely used for air dehumidification and harmful gases capture. Herein, we develop a pore‐nanospace post‐engineering strategy to optimize the hydrophilicity, water‐uptake capacity and air‐purifying ability of metal‐organic frameworks (MOFs) with long‐term stability, offering an ideal candidate with autonomous multi‐functionality of moisture control and pollutants sequestration. Through variant tuning of organic‐linkers carrying hydrophobic and hydrophilic groups in the pore‐nanospaces of prototypical UiO‐67, a moderately hydrophilic MOF (UiO‐67‐4Me‐NH2‐38 %) with high thermal, hydrolytic and acid‐base stability is screened out, featuring S‐shaped water sorption isotherms exactly located in the recommended comfortable and healthy ranges of relative humidity for indoor ventilation (45 %–65 % RH) and adverse health effects minimization (40–60 % RH). Its exceptional attributes of water‐uptake working capacity/efficiency, contaminants removal, recyclability and regeneration promise a great potential in confined indoor environment application.