Airborne methylene diphenyl diisocyanate (MDI) concentrations associated with the application of polyurethane spray foam in residential construction

The primary objectives of this study were (a) to measure potential exposures of applicators and assistants to airborne methylene diphenyl diisocyanate (MDI), (b) to measure airborne concentrations of MDI at various distances from the spray foam application, and (c) to measure airborne MDI concentrations as a function of time elapsed since application. Other study objectives were, (a) to compare the results from filter and impinger samples; (b) to determine the particle size distribution in the spray foam aerosol; (c) to determine potential exposures to dichlorofluoroethane; and (d) to measure any off-gassing of MDI after the foam had fully cured. This study was conducted during application of spray polyurethane foam inside five single-family homes under construction in the United States and Canada.Spray foam applicators and assistants may be exposed to airborne MDI concentrations above the OSHA permissible exposure limit. At these concentrations, OSHA recommends appropriate respiratory protection during spray foam application to prevent airborne MDI exposures above established limits and to protect against exposure to dichlorofluoroethane (HCFC-141b). Airborne MDI concentrations decrease rapidly after foam application ceases. The highest airborne concentrations measured after 15 min and 45 min were 0.019 mg/m3 and 0.003 mg/m3, respectively. After 45 min, airborne concentrations were below the limit of quantitation (LOQ) of 0.036-microg per sample. For samples taken 24 hours after completion of foaming, results were also below the LOQ. Approximately two-thirds of the total mass of the airborne particles in the spray foam aerosol was greater than 3.5 microns in diameter. Airborne MDI concentrations determined by filter sampling methods were 6% to 40% lower than those determined by impinger methods.     

Center for the Polyurethanes Industry summary of unpublished industrial hygiene studies related to the evaluation of emissions of spray polyurethane foam insulation

Spray polyurethane foam (SPF) insulation is used as thermal insulation for residential and commercial buildings. It has many advantages over other forms insulation; however, concerns have been raised related to chemical emissions during and after application. The American Chemistry Council's (ACC's) Center for the Polyurethanes Industry (CPI) has gathered previously unpublished industrial hygiene air sampling studies submitted by member companies that were completed during an eight-year period from 2007–2014. These studies address emissions from medium density closed cell and low density open cell formulations. This article summarizes the results of personal and area air samples collected during application and post application of SPF to interior building surfaces in both laboratory and field environments. Chemicals of interest included: Volatile Organic Compounds (VOCs), methylene diphenyl diisocyanate (MDI), flame retardants, amine catalysts, blowing agents, and aldehydes. Overall, the results indicate that SPF applicators and workers in close proximity to the application are potentially exposed to MDI in excess of recommended and governmental occupational exposure limits and should use personal protective equipment (PPE) consisting of air supplied respirators and full-body protective clothing to reduce exposure. Catalyst emissions can be reduced by using reactive catalysts in SPF formulations, and mechanical ventilation is important in controlling emissions during and after application.     

Occupational asthma related to low levels of airborne methylene diphenyl diisocyanate (MDI) in orthopedic casting work

Orthopedic plaster casts contain methylene diphenyl diisocyanate (MDI). A few case reports have suggested occupational asthma to MDI in casting work. However, the knowledge of the exposure levels related to the occupational asthma cases is lacking. We report on two occupational asthma cases due to MDI in nurses irregularly applying orthopedic plaster casts, verified with placebo controlled specific inhalation challenge. The levels of MDI in the air were measured in the exposure chamber during the specific inhalation challenges with a quantitative method including filter collection and subsequent liquid chromatography-mass spectrometry (LC-MS) analysis of the isocyanate groups. In order to estimate the level of airborne MDI in casting work, measurements were conducted also in two hospitals during the application and removal of synthetic plaster casts using the same method. The concentrations were well below the occupational exposure limit in both specific inhalation challenge and hospital measurements. Based on our findings, even minor exposure to airborne MDI in casting work can cause an asthmatic reaction in some patients.     

Assessment and control of exposures to polymeric methylene diphenyl diisocyanate (pMDI) in spray polyurethane foam applicators

In this work we characterize personal inhalation and dermal exposures to diphenyl methane diisocyanate (MDI) and other species in polymeric MDI (pMDI) formulations during spray polyurethane foam (SPF) insulation at 14 sites in New England. We further assess the adequacy of current workplace practices and exposure controls via comparative urinary biomonitoring of the corresponding methylene diphenyl diamine (MDA) pre- and post-shift. MDI and pMDI are potent dermal and respiratory sensitizers and asthmagens, strong irritants of the skin, eyes, and the respiratory tract, and may cause skin burns. This study is the first comprehensive report to-date on the work practices, inhalation and dermal exposures to isocyanates and effectiveness of existing controls during SPF applications.Breathing zone exposures to 4,4′ MDI (n = 31; 24 sprayers, 7 helpers) ranged from 0.9 to 123.0 μg/m3 and had a geometric mean (GM) of 13.8 μg/m3 and geometric standard deviation (GSD) of 4.8. Stationary near field area samples (n = 15) were higher than personal exposures: GM, 40.9 (GSD, 3.9) μg/m3, range 1.4–240.8 μg/m3. Sixteen percent of personal air samples and 35% of area samples exceeded the National Institute for Occupational Health and Safety's (NIOSH) full shift recommended exposure limit (REL) of 50 μg/m3, assuming zero exposure for the unsampled time. 4,4′ MDI load on the glove dosimeters had a GM of 11.4 (GSD 2.9) μg/glove pair/min, suggesting high potential for dermal exposures. Urinary MDA had a GM of 0.7 (GSD, 3.0) μmol MDA/mol creatinine (range, nd-14.5 μmol MDA/mol creatinine). Twenty-five % of urine samples exceeded the Health and Safety Executive (HSE) biological monitoring guidance value (BMGV) of 1 μmol MDA/mol creatinine. We further report on field observations regarding current exposure controls, discuss implications of these findings and opportunities for improving work practices to prevent isocyanate exposures during SPF insulation.     

Physical and mathematical simulation of gasoline component migration in ground water systems.

Results are presented from a research study examining the transport and fate of gasoline components in ground water systems. A two-phased modeling approach is described: first, physical laboratory pilot scale models of aquifer systems are constructed and second, mathematical models are constructed to simulate the data generated in the laboratory studies. In general, single-component batch studies overpredicted the degree of retardation shown by multi-component column experiments.     

Modeling breathing-zone concentrations of airborne contaminants generated during compressed air spray painting

This paper presents a mathematical model to predict breathing-zone concentrations of airborne contaminants generated during compressed air spray painting in cross-flow ventilated booths. The model focuses on characterizing the generation and transport of overspray mist. It extends previous work on conventional spray guns to include exposures generated by HVLP guns. Dimensional analysis and scale model wind-tunnel studies are employed using non-volatile oils, instead of paint, to produce empirical equations for estimating exposure to total mass. Results indicate that a dimensionless breathing zone concentration is a nonlinear function of the ratio of momentum flux of air from the spray gun to the momentum flux of air passing through the projected area of the worker's body. The orientation of the spraying operation within the booth is also very significant. The exposure model requires an estimate of the contaminant generation rate, which is approximated by a simple impactor model. The results represent an initial step in the construction of more realistic models capable of predicting exposure as a mathematical function of the governing parameters.     

Evaluation of the SureSpot direct-reading instrument for the determination of polymeric MDI aerosols

Recent studies in our laboratories have focused on the reliability of direct-reading instruments for the determination of airborne isocyanate concentrations. The evaluation of airborne isocyanates is complicated because these substances exist as diisocyanate monomers and polyisocyanate oligomers, both in the vapor and aerosol phases. The studies showed that a number of direct-reading instruments, including the SureSpot test kit, do not allow an accurate determination of isocyanates in the aerosol phase. Using a test chamber, concentrations of various commercial polymeric methylenediphenyl diisocyanates (PMDI) were generated in the aerosol phase to examine the correlation between the SureSpot monitor and two laboratory methods. The results obtained with the SureSpot and laboratory methods correlated poorly. More precisely, the results indicated that the SureSpot direct-reading instrument had a distinctive response to each commercial PMDI and, in addition, it was not accurate for the determination of total PMDI in the aerosol phase. It seemed that the analytical response of the SureSpot is based on a calibration curve only reliable for MDI and not for the determination of PMDIs in the aerosol phase. Further investigation also indicated that the calibration provided by the manufacturer could not be converted into a linear curve over the suggested MDI concentrations range. An appropriate calibration procedure was developed in our laboratories for the SureSpot to accurately determine all commercial PMDIs without great variability.     

Indoor air quality index for preoccupancy assessment

The purpose of this study is to document the potential impacts on indoor air quality associated with different types of building materials (wall and floor finishes) through the development of an Indoor Air Quality index. The study first identifies pollutant sources and their corresponding health impacts due to short-term and long-term exposures. The study also quantifies levels of certain pollutants within a steady-state controlled environment, comparing the results of this study with previous studies conducted in different regions. It also proposes an IAQ index as an assessment tool which can be utilized preoccupancy. The field studies were conducted in residential buildings during January and February in Cairo to monitor volatile organic compounds (VOCs), formaldehyde (HCHO), ammonia (NH₃), radon gas, and particulate matter (PM). The indoor air was monitored in nine locations: four during the construction process and five following completion of construction. For this investigation, three rooms under construction within a Cairene building site were utilized to test the finishing materials. Chemical analysis and direct reading devices were used for air sampling and monitoring. The results revealed that the concentration of some pollutants decreased within the first year of construction, while others remained above target limits. The results of this study offer recommendations for engineers regarding the selection of appropriate materials through the implementation of source control strategies and an IAQ index which can be used as an assessment tool to ensure that the Indoor Air Quality meets recommended standards. Based on the conclusions and limitations of this study, recommendations for future work are documented such as the screening of materials and monitoring of Indoor Air Quality.     

The agricultural dispersal-valley drift spray drift modeling system compared with pesticide drift data

The coupling of the valley drift (VALDRIFT) atmospheric dispersion/deposition model with the agricultural dispersal (AGDISP) aircraft wake model generates a modeling system for predicting the off-target drift of pesticides sprayed in a mountain valley. The approach uses the AGDISP near-field spray model to estimate the mass fraction of pesticide remaining airborne after initial application, then the VALDRIFT complex terrain model to estimate the drift of pesticide from the target area. The modeling system inputs include detailed spray information, a measure (or estimate) of winds in the valley, and the valley topographic characteristics; the results are pesticide concentrations throughout the valley atmosphere and pesticide deposition to the valley surface. The AGDISP and VALDRIFT models are operated independently, with the results from AGDISP being used as input to VALDRIFT through user-created data files. The modeling system was evaluated using pesticide drift data from spray trials conducted in the Mill Creek Canyon of Utah's Wasatch Mountains, USA, during the late spring of 1993. The predicted deposition compared within a factor of three of the observations (70% of the time) at all sampling locations extending several kilometers down-valley from the spray treatment block. The overall average ratio of predicted-to-observed deposition was 0.9.     

Experimental evaluation of a mathematical model for predicting transfer efficiency of a high volume-low pressure air spray gun

The transfer efficiency of a spray-painting gun is defined as the amount of coating applied to the workpiece divided by the amount sprayed. Characterizing this transfer process allows for accurate estimation of the overspray generation rate, which is important for determining a spray painter's exposure to airborne contaminants. This study presents an experimental evaluation of a mathematical model for predicting the transfer efficiency of a high volume-low pressure spray gun. The effects of gun-to-surface distance and nozzle pressure on the agreement between the transfer efficiency measurement and prediction were examined. Wind tunnel studies and non-volatile vacuum pump oil in place of commercial paint were used to determine transfer efficiency at nine gun-to-surface distances and four nozzle pressure levels. The mathematical model successfully predicts transfer efficiency within the uncertainty limits. The least squares regression between measured and predicted transfer efficiency has a slope of 0.83 and an intercept of 0.12 (R2 = 0.98). Two correction factors were determined to improve the mathematical model. At higher nozzle pressure settings, 6.5 psig and 5.5 psig, the correction factor is a function of both gun-to-surface distance and nozzle pressure level. At lower nozzle pressures, 4 psig and 2.75 psig, gun-to-surface distance slightly influences the correction factor, while nozzle pressure has no discernible effect.     

Exposure to airborne nano-titanium dioxide during airless spray painting and sanding

The objectives of the study were to measure and characterize exposure to airborne nanoscale titanium dioxide during airless spraying and sanding of a nano-enabled paint, and to evaluate the effectiveness of dust capture methods in reducing airborne nanoparticle concentrations. A tradesperson performed the work activities in an environmentally controlled chamber. Samples were collected in the tradesperson's breathing zone and in surrounding areas to assess bystander exposure. Filter-based samples were analyzed using gravimetric methods, scanning electron microscopy, and energy dispersive spectroscopy. Differential particle count data were obtained by means of a scanning mobility particle sizer. Local exhaust ventilation provided statistically significant reductions of airborne nanoparticle concentrations during sanding. Sanding the paint after drying with a handheld power sander generated relatively low levels of airborne titanium dioxide. In contrast, task-based exposure measurements collected during the initial airless spray application of the nano-enabled paint suggested a potential for occupational exposures to exceed the time-weighted average exposure limit for ultrafine titanium dioxide recommended by the National Institute for Occupational Safety and Health. Painters applying nano-enabled coatings may have little recourse but to rely, in some instances, on lower tiers of the hierarchy of controls, such as personal protective equipment. In light of these findings, employers and industrial hygienists should characterize exposures and implement the hierarchy of controls to ensure painters are sufficiently protected.     

MDI Exposure for Spray-On Truck Bed Lining

Worker exposure to MDI (methylenediphenyl isocyanate) in the sprayed-on truck bed lining industry was assessed by examining Washington State OSHA inspection files and industrial insurance records. The industry uses MDI to form a protective urethane coating on pick-up truck beds. The lining is applied by a worker using a handheld spray gun with application equipment at temperatures and pressures specified by the urethane supplier. Inspections with MDI sampling were initially identified by searching the agency's laboratory database and were further screened for the targeted process. Data for 13 employers was found and extracted from the inspection records. All were small companies with only 1 to 2 workers exposed to MDI; 10 of the 13 employers had started the bed lining service within the last 4 years. The process was found in truck bed lining specialty shops as well as in other truck-related businesses. Six different urethane products were used with reported MDI monomer concentrations of up to 75 percent along with varying concentrations of MDI pre-polymers and other reactants and solvents. Sampling for MDI by inspectors found 7 worksites with worker exposure in excess of the state and OSHA ceiling limit of 0.200 mg/M(3). Deficiencies in respirator programs and engineering controls for MDI were cited. A review of the industrial insurance records found a total of five MDI-related claims at 4 inspected worksites, two for new-onset asthma. It was concluded that workers in the urethane sprayed-on truck bed lining industry are at an increased risk of developing illnesses associated with isocyanate exposure. Interventions are needed to further assess the hazard as well as motivate and assist franchisers, distributors, and retailers to implement effective engineering controls and respiratory protection programs in this nationally emerging small employer industry.     

Assessment of isocyanate exposure during the spray application of polyurethane foam

This survey examined the air concentrations of diphenylmethane 4,4' diisocyanate (MDI) produced during the spray application of polyurethane foam at both indoor and outdoor locations. The sprayer, his helper(s), and fixed distances from the spray operation were sampled. The sprayers had the highest exposure levels, followed by outdoor helpers, then by indoor helpers. Area sample results showed that levels at a distance greater than 3 m (10 ft) outdoors and 8 m (25 ft) indoors were negligible, thereby supporting the establishment of a "work zone" around the spray operation.     

Identification of methylene diphenyl diisocyanate thermal degradation products in a generation chamber by liquid chromatography coupled with tandem mass spectrometry

Isocyanate thermal degradation characterization by liquid chromatography coupled with electrospray tandem mass spectrometry has been performed to elucidate the methylene diphenyl diisocyanate (MDI) thermal degradation structure emitted in a generation chamber using a temperature between 50°C and 180°C to produce MDI vapors. [M+H]⁺ ions containing an isocyanate functional group were studied by tandem mass spectrometry. The [M+H]⁺ ion analyses based on the combination of full scans and precursor ion scans were useful for identifying all structures. The compounds emitted were identified and validated as a mixture of compounds containing amine and isocyanate functions. Residual MDI, methylene diphenyl amino-isocyanate, and methylene diphenyl diamine were identified. Polymerized forms of these structures were also observed because amine and isocyanate chemical functions react rapidly to polymerize. These results must be used with special care by scientists establishing sensitization diagnostics and developing sampling devices using generation chambers as they must be related to MDI behavior in workplaces. Even if pure MDI is introduced in the generation chamber, several different compounds are generated when the MDI is heated at a high temperature. This can result in some misleading interpretations for non-specific isocyanate sampling device development and sensitization diagnostics as MDI is present in the chamber with other compounds with known adverse effects.     

Modeling dermal exposure--an illustration for spray painting applications

This article presents a conceptual, mathematical model of dermal exposure resulting from aerosol deposition on human forearm hair. The model is applicable to exposure scenarios where dermal deposition is governed by aerosol impaction, interception, and diffusion mechanisms. The model employs filtration theory, single fiber efficiency equations, and a modified potential airflow approximation. The results are extended, using previously published results, for application to dermal deposition on the forearm during spray painting. The average (N = 8) predicted dermal deposition of 1,6-hexamethylene diisocyanate as collected on a 10-cm(2) tape strip is 108.9 (+/- 70.3) pmol, whereas field measurements indicated an average of 168.6 (+/- 82.0) pmol per strip. The corresponding measured average dermal flux was 3.63 pg/cm(2)s (+/- 1.34); the prediction was 2.24 pg/cm(2)sec (+/- 1.25). The study calls attention to the importance of body hair both for modeling and measuring dermal exposures.     

Application of the RICEWQ-VADOFT model for simulating the environmental fate of pretilachlor in rice paddies

No validated models in Europe are capable of simulating the environmental fate of pesticides under the specific conditions of rice fields. Rice water quality--vadose zone flow and transport (RICEWQ-VADOFT) is a model developed from the coupling of a surface runoff model (RICEWQ) and a vadose zone flow and transport model (VADOFT) for determining predicted environmental concentrations in paddy water and sediment, runoff, and groundwater. This study is intended to evaluate the capability of this model to simulate effectively the environmental fate of the herbicide pretilachlor in the paddy environment. A two-year field study conducted in a representative rice-cultivated area of northern Italy provided measured concentrations of pretilachlor in paddy water and sediment and also a limited number of observations on runoff losses. The model successfully predicted the water balance in the paddy field in both years. After limited calibration, the model predicted the fate of pretilachlor in paddy water and sediment with high accuracy. Agreement between predicted and measured concentrations of pretilachlor in both years was assessed statistically using several statistical indicators. For example, modeling efficiency (EF) values of 0.867 to 0.935 and 0.702 to 0.718 in paddy water and sediment, respectively, document the strong agreement between predicted and measured pesticide concentrations. The model predictions showed high agreement with the limited amount of measured runoff data in 2002. The model predicted that no significant amounts of pretilachlor would leach below the top 25 cm of the soil, although no measured data were available to evaluate the predicted results. A sensitivity analysis of the model to variables controlling pesticide partitioning to paddy sediment (VBIND, depth for direct partitioning of pesticide to bed sediment; VMIX, mixing velocity by molecular diffusion) revealed that the predictions of pesticide leaching were influenced strongly by those variables. Generally the RICEWQ-VADOFT model is a useful modeling tool for pesticide risk assessment in rice paddies.     

Development of the spray drift task force database for aerial applications

This article is part of a series describing the development of the Spray Drift Task Force (SDTF) database and its application to agricultural chemical exposure risk assessment modeling. The series describes the development of a large generic database (assuming that active ingredient rate is not a factor affecting physical drift) and its use in estimating spray movement immediately following application by aerial methods. The components of the database are described. In agreement with field trials in the open literature, the database shows that the major variables affecting off-target spray deposition are droplet size, spray release position (boom height and length), and wind speed and direction. In addition, secondary parameters that can affect these variables and drift are also discussed.     

Geographic exposure modeling: a valuable extension of geographic information systems for use in environmental epidemiology

Geographic modeling of individual exposures using air pollution modeling techniques can help in both the design of environmental epidemiologic studies and in the assignment of measures that delineate regions that receive the highest exposure in space and time. Geographic modeling can help in the interpretation of environmental sampling data associated with airborne concentration or deposition, and can act as a sophisticated interpolator for such data, allowing values to be assigned to locations between points where the data have actually been collected. Recent advances allow for quantification of the uncertainty in a geographic model and the resulting impact on estimates of association, variability, and study power. In this paper we present the terminology and methodology of geographic modeling, describe applications to date in the field of epidemiology, and evaluate the potential of this relatively new tool.     

Inhalation exposure during spray application and subsequent sanding of a wood sealant containing zinc oxide nanoparticles

Nano-enabled construction products have entered into commerce. There are concerns about the safety of manufactured nanomaterials, and exposure assessments are needed for a more complete understanding of risk. This study assessed potential inhalation exposure to ZnO nanoparticles during spray application and power sanding of a commercially available wood sealant and evaluated the effectiveness of local exhaust ventilation in reducing exposure. A tradesperson performed the spraying and sanding inside an environmentally-controlled chamber. Dust control methods during sanding were compared. Filter-based sampling, electron microscopy, and real-time particle counters provided measures of exposure. Airborne nanoparticles above background levels were detected by particle counters for all exposure scenarios. Nanoparticle number concentrations and particle size distributions were similar for sanding of treated versus untreated wood. Very few unbound nanoparticles were detected in aerosol samples via electron microscopy, rather nano-sized ZnO was contained within, or on the surface of larger airborne particles. Whether the presence of nanoscale ZnO in these aerosols affects toxicity merits further investigation. Mass-based exposure measurements were below the NIOSH Recommended Exposure Limit for Zn, although there are no established exposure limits for nanoscale ZnO. Local exhaust ventilation was effective, reducing airborne nanoparticle number concentrations by up to 92% and reducing personal exposure to total dust by at least 80% in terms of mass. Given the discrepancies between the particle count data and electron microscopy observations, the chemical identity of the airborne nanoparticles detected by the particle counters remains uncertain. Prior studies attributed the main source of nanoparticle emissions during sanding to copper nanoparticles generated from electric sander motors. Potentially contrary results are presented suggesting the sander motor may not have been the primary source of nanoparticle emissions in this study. Further research is needed to understand potential risks faced by construction workers exposed to mixed aerosols containing manufactured nanomaterials. Until these risks are better understood, this study demonstrates that engineering controls can reduce exposure to manufactured nanomaterials; doing so may be prudent for protecting worker health.