Indoor Formaldehyde Concentrations Research Articles

Indoor Formaldehyde Concentration, Personal Formaldehyde Exposure and Clinical Symptoms during Anatomy Dissection Sessions, University of Medicine 1, Yangon.

The formaldehyde (FA) embalming method, the world’s most common protocol for the fixation of cadavers, has been consistently used in medical universities in Myanmar. This study was designed to examine the indoor FA concentrations in anatomy dissection rooms, an exposed site, and lecture theater, an unexposed control site, and to access personal exposure levels of FA and clinical symptoms of medical students and instructors. In total, 208 second year medical students (1/2019 batch) and 18 instructors from Department of Anatomy, University of Medicine 1, participated. Thirteen dissection sessions were investigated from February 2019 to January 2020. Diffusive sampling devices were used as air samplers and high-performance liquid chromatography was used for measurement of FA. Average indoor FA concentration of four dissection rooms was 0.43 (0.09–1.22) ppm and all dissection rooms showed indoor concentrations above the occupational exposure limits and short-term exposure limit for general population. Personal FA exposure values were higher than indoor FA concentrations and the instructors (0.68, 0.04–2.11 ppm) had higher exposure than the students (0.44, 0.06–1.72 ppm). Unpleasant odor, eye and nose irritations and inability to concentrate were frequently reported FA-related symptoms, and the students were found to have significantly higher risks (p < 0.05) of having these symptoms during the dissection sessions than during lecture.

Impact of humidity on formaldehyde and moisture buffering capacity of porous building material

The aim of this article is to present a validated model to study the influence of humidity on formaldehyde sorption of building material and the effect of formaldehyde and moisture buffering capacity of hygroscopic porous material on indoor air environment. New empirical formulas proposed to describe the diffusion and partition coefficients as functions of humidity based on previous experimental data are incorporated in a coupled moisture and pollutants transport simulation model. The numerical model that takes into account the effect of RH (or moisture) in building materials on VOC diffusion can be used to simulate VOC emissions/sorption from building materials. The developed model is implemented in the environment SPARK (Simulation Problem Analysis and Research Kernel) using finite difference technique. The model is then applied to study the hygric and formaldehyde (FOR, a water soluble VOC) behavior of calcium silicate (CS) subjected to different dynamic conditions of RH and formaldehyde. The results obtained in this paper help to emphasize the importance of moisture and formaldehyde buffering capacity as a new key parameter when selecting clean and hygroscopic building materials in building design because they can contribute to dampen indoor RH and formaldehyde variations. In addition, the impact of RH variation is significant and needed to be taken into account in the simulation to correctly predict the indoor formaldehyde concentration. The model developed in this paper can also be used to optimize the hygric performance and IAQ in building.

Thermal, electrical and purification performance of a novel thermal-catalytic CdTe double-layer breathing window in winter

CdTe PV cell is one perfect candidate for window application because of its good daylighting performance, low-temperature coefficient and excellent electrical performance under weak light. In addition, thermal catalytic oxidation is an thermal driven air purification technology and the thermal energy can be easily obtained from PV window systems. Therefore, a novel thermal-catalytic CdTe double-layer breathing window was proposed. Firstly, the electrical, thermal and daylighting performances of proposed window were investigated experimentally. Secondly, the removal of formaldehyde was investigated using the verified coupled formaldehyde mass transfer and thermal-catalytic reaction kinetic model. Finally, the evolution of indoor formaldehyde concentration considering formaldehyde release source was calculated. Main results were: (1) The thermal and electrical efficiencies were respectively 0.297 and 0.0715, which were closed to the reported results. Also, the proposed window had better daylighting uniformity compared with conventional window. (2) The total generated clean air was 25.7 m3/(m2•day), with the equivalent formaldehyde degradation efficiency of 0.010 based on purification performances of various air purifiers in market. (3) The comprehensive thermal efficiency was 0.518, with increase of 9.28% considering the contribution from formaldehyde removal. (4) The proposed window could make the indoor concentration approach to standard concentration under most working conditions.

Indoor use of essential oil-based cleaning products: Emission rate and indoor air quality impact assessment based on a realistic application methodology

Cleaning is performed to increase hygiene, esthetics and material preservation. Despite its benefits, cleaning also poses risks, potentially contributing to nearly 20% of indoor pollution. As indoor air quality has become a major human health concern, “natural-scented” cleaning products, formulated with essential oils, have become market leaders among household products. However, these consumer products have benefitted from skillful marketing strategies based on the ambiguity of the words “green” and “natural”. The characterization of the emission processes studied through 1-m3 chamber experiments under a realistic scenario suggests variable maximum total terpene concentrations from 150 to 300 ppb. The estimated emission rate profiles confirm that the liquid-to-gas transfer of terpenes is driven by (i) the formulation of the product matrix inducing specific chemical affinities, (ii) the liquid content of individual terpenes, and (iii) the intrinsic volatility of terpenes. A unique formaldehyde emission kinetics profile was observed, suggesting the presence of a unique emission source: formaldehyde-releasers. Consequently, the use of essential-oil-based cleaning products might generate a long-term increase in the indoor formaldehyde concentration, and the maximum levels might be sustained for several hours after cleaning. Thus, essential-oil-based cleaners should be seriously considered as versatile and significant sources of fragrance molecules and formaldehyde.

Simulation of indoor pollutant diffusion concentration field in passive house based on CFD software

Due to the good air tightness of the passive house, once there are poor quality furniture materials in the room, it is easy to cause indoor formaldehyde pollution which do harm to people’s health as well as the quality of their life. This article introduces the CFD software to simulate the change of indoor formaldehyde concentration in the passive house when opening the fresh air system to ensure indoor air quality and to employ a new way to the better quality of life of residents. The function of CFD software and two fluid dynamics control equations are introduced in the essay, and the finite difference method of control equation discretization is studied as well. Based on CFD software, the case is analyzed, under which the indoor formaldehyde concentration changes, according to different fresh air system inlet locations. The simulation results show that when the two air outlets of the living room are on the side of the sofa and TV cabinet, and the air outlet of the bedroom is in the corner, the formaldehyde purification rate is better, which a more reasonable air supply method is.

Whole-House Emission Rates and Loss Coefficients of Formaldehyde and Other Volatile Organic Compounds as a Function of the Air Change Rate.

Whole-house emission rates and indoor loss coefficients of formaldehyde and other volatile organic compounds (VOCs) were determined from continuous measurements inside a net-zero energy home at two different air change rates (ACHs). By turning the mechanical ventilation on and off, it was demonstrated that formaldehyde concentrations reach a steady state much more quickly than other VOCs, consistent with a significant indoor loss rate attributed to surface uptake. The first order loss coefficient for formaldehyde was 0.47 ± 0.06 h-1 at 0.08 h-1 ACH and 0.88 ± 0.22 h-1 at 0.62 h-1 ACH. Loss rates for other VOCs measured were not discernible, with the exception of hexanoic acid. A factor of 5.5 increase in the ACH increased the whole-house emission rates of VOCs but by varying degrees (factors of 1.1 to 3.8), with formaldehyde displaying no significant change. The formaldehyde area-specific emission rate (86 ± 8 μg m-2 h-1) was insensitive to changes in the ACH because its large indoor loss rate muted the impact of ventilation on indoor air concentrations. These results demonstrate that formaldehyde loss rates must be taken into account to correctly estimate whole-house emission rates and that ventilation will not be as effective at reducing indoor formaldehyde concentrations as it is for other VOCs.

Study on the Characteristics of Formaldehyde Pollution in Typical Teaching Machine Room

This study focused on measuring the pollution characteristics, the monthly and seasonal variation rule of formaldehyde in the teaching machine room of Guangxi Normal University from March 2016 to February 2018, and the correlation between formaldehyde concentration and temperature or humidity were also analyzed. The results indicated that seasonal and monthly variation rule of formaldehyde changed with temperature and humidity in the teaching machine room. The concentration of formaldehyde was higher in summer and autumn, while was lower in winter and spring. Further analysis indicated that there was a strongly positive correlation (R2&gt;0.87, R2&gt;0.85, R2&gt;0.81, p&lt;0.01) between formaldehyde concentration and temperature, relative humidity or absolute humidity. It concluded that the formaldehyde concentration increased with the increase in the temperature and humidity. The maximum concentrations of formaldehyde in sitting breathing area and standing breathing area were 0.442mg/m3, 0.445mg/m3 and 0.184mg/m3, 0.213mg/m3 in July 2016, 2017, respectively. After eleven years, the formaldehyde in the teaching machine room was still seriously exceeded the standard (0.1mol/L), and decreased the temperature or humidity could effective alleviate the level of indoor formaldehyde concentration.

The role of simulation in preventing indoor air pollution: a foregone conclusion?

Indoor air pollution has become a broad problem due to various indoor or outdoor pollutant sources and limited ventilation. A performance-based approach, which is built upon accurate modelling and simulation of indoor air pollutant characteristics, has obvious advantages over the prescription-based method to achieve better indoor environment. Moreover, the simulation could play a key role in actively preventing indoor air pollution from happening in the first place. In this study, a mechanistic air quality simulation tool was introduced. To verify the reliability of simulation results, two actual field cases with different levels of complexity and time duration were discussed. One was performed in a full-scale experimental room with a single formaldehyde source of a medium density board, in which indoor formaldehyde concentrations varied naturally. Long-term (more than three years) comparison between the simulation results and measurement were conducted. Another occurred during the decoration process in an actual apartment. The formaldehyde concentration levels were well predicted at the design stage and later verified by the field data. Nevertheless, a lot more efforts are required to make indoor air quality (IAQ) simulation tools readily useful in actual engineering applications.

Exposure to benzene, toluene, ethylbenzene, xylene, formaldehyde, and acetaldehyde in and around gas stations in Japan

We investigated the personal exposure of gas station employees to benzene, toluene, ethylbenzene, xylene, formaldehyde, and acetaldehyde at three full-service gas stations in Okayama, Japan. We also assessed both the indoor (offices) and ambient background concentrations. The personal exposure, indoor, and ambient concentrations of benzene were 57.3, 6.11, and 1.31 μg/m3, respectively, in spring and 17.0, 2.04, and 0.603 μg/m3, respectively, in winter. Those for toluene were 196, 25.8, and 2.66 μg/m3, respectively, in spring and 30.6, 5.31, and 1.23 μg/m3, respectively, in winter. The personal exposure concentrations of benzene, toluene, ethylbenzene, and xylene for a gas station employee were significantly higher than those for indoors and the ambient air. However, the personal exposure, indoor, and ambient concentrations of formaldehyde were 5.08, 10.1, and 4.29 μg/m3, respectively, in spring and 11.6, 24.1, and 6.04 μg/m3, respectively, in winter. The indoor concentrations of formaldehyde were significantly higher than both the personal exposure concentrations for gas station employees and the ambient concentrations. The excess lifetime cancer risk from benzene exposure was estimated to be 2.22 × 10−5, 2.43 × 10−6, and 2.56 × 10−7 for full-service gas station employees, self-service gas station employees, and self-service gas station users who are assumed to use the station once a week, respectively. Assuming the occupational exposure to toluene, ethylbenzene, and xylene at the gas station were comparable to the maximum 2-h average exposure levels in the present study, the total hazard quotient for non-carcinogenic risk was calculated to be much lower than 1 (2.72–5.56 × 10−3) based on the TLV-TWA (8-h).

Efficiency and performance tests of the sorptive building materials that reduce indoor formaldehyde concentrations.

The adsorption of volatile organic compounds by building materials reduces the pollutant concentrations in indoor air. We collected three interior building materials with adsorption potentials—latex paint, micro-carbonized plywood, and moisture-buffering siding—used the sorptive building materials test (SBMT) to determine how much they reduced indoor formaldehyde (HCHO) concentrations, and then assessed the consequent reduction in human cancer risk from HCHO inhalation. Adsorption of HCHO by building materials significantly improved the effective ventilation efficiency. For example, the equivalent ventilation rate for Celite siding—used for humidity control—was 1.44 m3/(m2·h) at 25°C, 50% relative humidity (RH); the loading factor (L) was 0.4 m2/m3, and the HCHO concentration was 0.2 ppm; this effect is equivalent to a higher ventilation rate of approximately 0.6 air changes per hour in a typical Taiwanese dwelling. There was also a substantial reduction of risk in Case MCP-2 (Cin,te: 245 μg/m3, 30°C, 50% RH): males: down 5.73 × 10−4; females: down 4.84 × 10−4). The selection of adsorptive building materials for interior surfaces, therefore, significantly reduces human inhalation of HCHO. Our findings should encourage developing and using innovative building materials that help improve indoor air quality and thus provide building occupants with healthier working and living environments.

Evaluation of Indoor Air Pollution during Decorating Process and Inhalation Health Risks in Xi’an, China: A Case Study

ABSTRACT PM2.5, formaldehyde, and 8 volatile organic compounds (VOCs) were observed in 6 newly decorated apartment units to evaluate the effects of the decorating process on the indoor air quality in Xi’an, China. The comparison of indoor and outdoor formaldehyde and VOCs concentrations showed that the outdoor PM2.5 concentration exceeded the indoor one during the monitoring process, whereas the indoor formaldehyde and VOCs concentrations exceeded the outdoor ones. The levels of formaldehyde and VOCs in different rooms were investigated, and the concentrations in the bedroom were found to be the highest. Furthermore, the formaldehyde and VOCs concentrations were measured in 200 other rooms decorated within a 2-year period in Xi’an, and the results indicated that wallpapering, wooden flooring, and furniture were the major decorating processes emitting these compounds. In addition, a health risk assessment of the monitored formaldehyde and VOCs in the rooms 1 year after decorating showed that benzene posed the greatest health risk among the assessed VOCs.

Inhibitory effect of mould growth on formaldehyde emissions from medium-density fibreboards: Evidence from field observations in three experimental houses

The occurrence of mould and effect of formaldehyde emission on indoor air pollution has been widely reported. However, the potential effect of mould on formaldehyde emissions from building materials has been rarely examined. In this study, the formaldehyde emission from medium-density fibreboards was monitored in three full-scale unoccupied experimental houses for 24 months. Moulds were infested in two out of the three houses. Different indoor formaldehyde concentrations were observed accordingly. Three different stages of variation in concentrations were observed among the houses. In the first stage, when there was no mould growth in any of the houses, indoor formaldehyde concentrations varied in the same way. In the second stage, a large amount of mould was infested in one of the houses, and its formaldehyde concentration was reduced substantially and exhibited a trend opposite to those of the other two houses. In the third stage, 5% of the medium-density fibreboards were covered with mould in another house, and the difference in formaldehyde concentration compared to that in the house without mould growth was increased after that. The different indoor formaldehyde concentrations due to the presence of mould in these houses indicated the inhibitory effect of mould growth on formaldehyde emissions.

An investigation of formaldehyde concentration in residences and the development of a model for the prediction of its emission rates

Indoor air pollution caused by formaldehyde associated with building materials imposes a variety of acute and chronic adverse effects on people's health. The aim of this research is to investigate the concentrations of formaldehyde in residences and develop emission rate prediction model in residential buildings. On-site measurements including the indoor and outdoor concentrations of formaldehyde and CO2 were carried out in 42 urban residences in Chongqing. The people occupancy schedule in different functional rooms was obtained by observing the change in CO2 concentration. A robust model for the estimation of formaldehyde emission rates using CO2 as the tracer gas; associated with a Monte-Carlo simulation of occupant activities and the characteristics of residences; has been developed. It is revealed that the mean indoor formaldehyde concentration was 30.12 μg/m3, which was slightly higher than the outdoor concentration of 27.80 μg/m3. The emission rates of 61.82 ± 52.39 and 49.69 ± 42.13μg/h/m2 (mean ± SD) during the daytime and nighttime, respectively with a daily average of 57.20 ± 48.79μg/h/m2. The significant contribution to indoor formaldehyde concentration was from indoor sources. Indoor formaldehyde source control is suggested to be an efficient way to control the indoor concentration.

Change in Indoor Formaldehyde Concentration and Prevalence of Subjective Symptoms in Medical Students Exposed to Formaldehyde during Gross Anatomy Dissection Classes, and Effectiveness of Exposure Prevention by Wearing Personal Protective Equipment

In Japan, medical students are exposed to formaldehyde (FA) during gross anatomy dissection classes. Students complain various subjective symptoms such as mucous membrane irritation symptoms and unidentified complaints. We have taken ongoing measures to decrease FA exposure at our university. Wearing personal protective equipment (PPE) such as gas masks and safety glasses is effective in reducing exposure to FA, as shown by previous studies. This study evaluated correlation with FA concentration in an anatomy practical room and prevalence of 14 symptoms where students experienced during the anatomy practice. Furthermore, we evaluated the effectiveness of prevention by wearing PPE. We conducted brief questionnaire surveys after every practice with second-year students participating in an anatomy class in 2016, concerning 14 subjective symptoms, including eye, nose, and throat complaints, as well as unidentified complaints, and whether or not to wear PPE, their sleep duration of the previous night, the number of cigarettes smoked, and their physical condition during the day in question. And, we measured indoor levels of FA during every practice. Subjective symptoms were classified into four categories. Those answering &amp;#8220;very severe&amp;#8221; or &amp;#8220;severe&amp;#8221; were classified as having subjective symptoms. There were significant correlations between FA concentration in an anatomy practical room and prevalence of some symptoms where students experienced during anatomy practice. And we found a certain level of effectiveness of prevention by wearing PPE during the practice. We need to recommend to wearing PPE during the practice, especially at high level of indoor FA concentration.

Development of a multimedia model (IIAQ-CC) to assess climate change influences on volatile and semi-volatile organic compounds in indoor environments

An indoor air quality model (IIAQ-CC) was developed to assess climate change (CC) influences on indoor level of volatile or semi-volatile organic compounds. With IIAQ-CC, the CC influences is predicted in integrated manners by factors including fate/transport properties of pollutants, building characteristics, occupant behaviors, indoor emission sources, and outdoor air quality. IIAQ-CC was evaluated for the temperature sensitivity of indoor formaldehyde (FA) concentration at outdoor temperature below 20 °C. No significant difference (t-test, p < 0.05) was found between the predicted (3.9 ± 1.0%/oC) and the measured (5.0%/oC with a 95% confidence interval (3.7%/oC to 6.4%/oC)), demonstrating that IIAQ-CC can successfully predict CC influences driven by temperature change on VOCs of indoor environmental concern. IIAQ-CC predicts that the long-term FA concentration may slowly rise due to increase in the outdoor concentration or may decrease in the presence of strong indoor sources in RCP8.5 conditions of South Korea. In either case, the long-term change does not exceed 12% of the average FA concentration of the base period. Over a shorter period (e.g., a month), the FA level may noticeably rise (by about 4 times) when windows are closed due to exceedingly hot or cold weather. The FA concentration change is primarily governed by duration of windows kept open, which depends on outdoor temperature. That is, temperature manifests its effects on the indoor air quality essentially by change in window opening behavior rather than by changes in kinetics or equilibrium processes such as photo-degradation and sorption/desorption onto/from walls and floor.

Indoor air quality and occupants' ventilation habits in China: Seasonal measurement and long-term monitoring

It is very important to know the current level of indoor pollution and occupants' ventilation habits. With this aim, this study presents an investigative project that covered five climate zones in China. The project consisted of two parts: long-term monitoring and seasonal measurements. For the long-term monitoring, we installed indoor air quality (IAQ) sensors, window state sensors, and mechanical ventilation sensors inside homes. In regard to IAQ, The median indoor 24-h averaged PM2.5 concentration ranged from 18 to 49 μg/m3. The indoor and outdoor 24-h averaged PM2.5 concentrations were similar for most of the regions. The 24-h averaged indoor CO2 concentrations were lower than 1000 ppm for all regions in all four seasons. Northern China usually had higher indoor CO2 concentrations than did southern China. In regard to occupants' behavior, in naturally ventilated homes, both the window-opening probability and open-window duration per day increased from the north to the south of China in winter. According to the example of mechanically ventilated Apartments, where pressure sensors were used to monitor the relative pressure at the air outlet of a mechanical ventilation system, the occupants used the ventilation system mainly in winter and spring. For the seasonal investigation, indoor formaldehyde concentrations in 224 homes were measured in four seasons (sampling time: 20 min). In summer, the indoor formaldehyde concentration reached its peak for the year, with about 35% of homes having concentrations larger than 100 μg/m3 under closed conditions (doors and windows have been closed for more than 12 h).

Indoor air pollutant exposure and determinant factors controlling household air quality for elderly people in Hong Kong

This study investigated the levels and determinant factors of indoor air pollutants including fine particles (PM2.5), nitrogen dioxide (NO2), and formaldehyde (HCHO) in 55 households exclusively for the elderly in Hong Kong during summer and winter (Jul.–Sep. 2016 and Nov. 2016–Mar. 2017). The average concentrations of PM2.5, NO2, and formaldehyde were 25.3 ± 15.0, 40.5 ± 16.0, and 26.1 ± 22.8 μg/m3 in summer and 34.2 ± 19.0, 43.5 ± 17.0, and 15.4 ± 4.5 μg/m3 in winter, respectively. There were ~ 50.3% of households exceeding the World Health Organization indoor air quality standard for PM2.5 throughout the study, with ~ 40.6 and ~61.0% of the households in summer and winter, respectively. The determinant factors for indoor PM2.5 and NO2 concentrations were identified as from incense burning and cooking. Cooking with suitable ventilation is an important factor to ease indoor pollutant concentrations. Both of PM2.5 and NO2 indoor concentrations showed good correlations with outdoor concentrations. Winter was observed with higher pollutant concentrations than summer except for formaldehyde concentrations. Major factors controlling indoor formaldehyde concentrations are temperature and humidity. The outcome will be useful for the development of future indoor air quality guidelines for Hong Kong.

Differential Health Effects of Constant versus Intermittent Exposure to Formaldehyde in Mice: Implications for Building Ventilation Strategies

Formaldehyde, an air pollutant in the indoor environment, may have severe effects on human health. The aim of this study is to compare the health effects caused by intermittent exposure to formaldehyde (based on real monitoring) to those caused by exposures at constant concentration. Health effects explored in this study including the oxidative stress, histopathological changes, inflammatory responses, etc. Mice were divided into three groups and exposed to intermittent concentration formaldehyde (0.8 ppm for 12 h and 0 ppm for another 12 h), or constant concentration formaldehyde (0.4 ppm for 24 h) or zero concentration formaldehyde (reference) per day for 7, 14, and 28 days. Following these exposures, bronchoalveolar lavage fluid (BALF), lung tissue and lung tissue homogenate were prepared to measure biomarkers of oxidative stress (ROS, MDA, GSH), histopathological changes, inflammatory responses (EOS, NEU, LYM, IL-4, IL-5, IL-13, IL-6, IL-17A, NF-κB, IL-1β) and apoptosis (caspase-3). Compared to the constant exposure, intermittent exposure to fluctuating formaldehyde concentrations resulted in more profound increases in numbers of inflammatory cells in the BALF, greater biological alterations including apoptosis. The findings imply that with the same average indoor formaldehyde concentrations over the same time, a ventilation strategy to avoid higher peak concentrations would lead to lower health risks.

Spectral band decomposition combined with nonlinear models: application to indoor formaldehyde concentration forecasting

This paper proposes a new approach for forecasting continuous indoor air quality time series and in particular the concentration of a common air pollutant in offices like formaldehyde. Forecasting is achieved through the combination of the spectral band decomposition using fast Fourier transform and nonlinear time series modeling. Two nonlinear models have been tested: a threshold autoregressive (TAR) model and a Chaos dynamics-based modeling. This study shows the benefit of the Fourier decomposition coupled with nonlinear modeling of each extracted component, compared to forecasting applied directly on the raw data. Both TAR and Chaos dynamics models are able to reproduce nonlinearities, with slightly better performance in the case of the second model. These hybrid models provide good performance on forecast time horizon up to 12 h ahead.

Potential Exposure and Cancer Risk from Formaldehyde Emissions from Installed Chinese Manufactured Laminate Flooring.

Lumber Liquidators (LL) Chinese-manufactured laminate flooring (CLF) has been installed in >400,000 U.S. homes over the last decade. To characterize potential associated formaldehyde exposures and cancer risks, chamber emissions data were collected from 399 new LL CLF, and from LL CLF installed in 899 homes in which measured aggregate indoor formaldehyde concentrations exceeded 100μg/m3 from a total of 17,867 homes screened. Data from both sources were combined to characterize LL CLF flooring-associated formaldehyde emissions from new boards and installed boards. New flooring had an average (±SD) emission rate of 61.3 ±52.1μg/m2 -hour; >one-year installed boards had ∼threefold lower emission rates. Estimated emission rates for the 899 homes and corresponding data from questionnaires were used as inputs to a single-compartment, steady-state mass-balance model to estimate corresponding residence-specific TWA formaldehyde concentrations and potential resident exposures. Only ∼0.7% of those homes had estimated acute formaldehyde concentrations >100μg/m3 immediately after LL CLF installation. The TWA daily formaldehyde inhalation exposure within the 899homes was estimated to be 17μg/day using California Proposition 65 default methods to extrapolate cancer risk (below the regulation "no significant risk level" of 40μg/day). Using a U.S. Environmental Protection Agency linear cancer risk model, 50th and 95th percentile values of expected lifetime cancer risk for residents of these homes were estimated to be 0.33 and 1.2 per 100,000 exposed, respectively. Based on more recent data and verified nonlinear cancer risk assessment models, LL CLF formaldehyde emissions pose virtually no cancer risk to affected consumers.