Annals of Occupational Hygiene Advance Access originally published online on August 26, 2005
Annals of Occupational Hygiene 2005 49(8):719-725; doi:10.1093/annhyg/mei040
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© 2005 British Occupational Hygiene Society Published by Oxford University Press
Original Article |
Exposure to Low Molecular Weight Isocyanates and Formaldehyde in Foundries Using Hot Box Core Binders
1 Department of Occupational and Environmental Medicine, Örebro University Hospital, SE-701 85 Örebro, Sweden; 2 Department of Public Health Sciences, Division of Occupational Medicine, Karolinska Institutet, SE-171 77 Stockholm, Sweden; 3 TMV-Environmental Consultant, Box 506 SE-541 28 Skövde, Sweden; 4 Swedish Foundry Association, Box 2033 SE-550 02 Jönköping, Sweden
* Author to whom correspondence should be addressed. Tel: +46-19-6022493; fax: +46-19-120404; e-mail: hakan.westberg{at}orebroll.se
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIAL AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Emissions from a chemical core binder system (Hot Box) based on a formaldehyde–carbamide resin have been investigated. The binder is used in some Swedish die-casting foundries. During core-making and casting, low molecular monoisocyanates, in particular methyl isocyanate (MIC) and isocyanic acid (ICA), were identified. Exposure to air concentrations of MIC, ICA and formaldehyde were subsequently determined in all Swedish foundries using the Hot Box binder, and involved three brass and one grey iron foundry. The survey was carried out in the winter period of 2001, and involved core-makers, casters and fettlers in the brass foundries, whereas only core-makers were included in the grey iron foundry. For each worker, four to five short-term samples of isocyanates (n = 298) and one 8 h sample of formaldehyde (n = 64) were collected during one shift for 15 die-casters, 39 core-makers and 10 other workers in the foundry. The air concentrations of the MIC short-term samples varied between <4 and 68 µg m–3, with corresponding ICA levels between <4 and 280 µg m–3. Calculated 8 h time weighted average air concentrations of MIC, based on short-term samples for each individual, varied between <4 and 31 µg m–3; for ICA the corresponding levels varied from <4 to 190 µg m–3. The formaldehyde time weighted average concentration levels ranged from 14 to 1600 µg m–3, and the Swedish occupational exposure limit (600 µg m–3) was exceeded only in 3% of the samples. In general, the core-makers were exposed to higher average formaldehyde levels compared to the casters, the latter being more exposed to monoisocyanates. During core-making and die-casting, low molecular monoisocyanates, in particular MIC and ICA, were identified. Compared to the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value-time weighted average (TLV-TWA) for MIC, the exposures were low. The lack of toxicological and human data for ICA and the relatively high air concentrations call for medical examination and preventive measures in production, ventilation and the use of personal safety equipment in the investigated foundries.
Keywords: casting • core-making • exposure • foundries • isocyanic acid • methyl isocyanate
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIAL AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Exposure to isocyanates in iron, aluminium and metal foundries has historically been associated with the use of isocyanate based chemical binders for core production, the most common known as the Cold Box process, using core binders containing methylene bisphenyl diisocyanate (MDI; Archibald and Smith, 1988
). During the thermal degradation of this binder, monoisocyanates and diisocyanates could be formed, such as phenyl isocyanate and MDI (Renman et al., 1986). Lately this has become true also for carbamide containing binders like the Hot Box system, and here the monoisocyanates methyl isocyanate (MIC; CAS no 624-83-9) and isocyanic acid (ICA; CAS no 75-13-8) are emitted at high levels. In addition, monoisocyanates have been determined in a large number of new exposure situations in foundries, including the use of Hot Box core-binders in static die-casting foundries (Lilja et al., 1999).
To specifically determine low air concentrations of monoisocyanates, new analytical methods for the determination of low molecular isocyanates like ICA and MIC have been developed (Karlsson, 1998b; Spanne, 1999).
Isocyanates are a group of chemically very reactive agents; di-, poly- and prepolymerized isocyanates are used to form polyurethanes. The industrial use of polyurethanes has increased drastically during the last decades (IARC, 1999a,b) and the products cover a wide range of industrial applications. Adverse health effects have been studied almost exclusively for diisocyanates, the main effects are respiratory disorders and irritative effects on the mucous membranes (Baur et al., 1994). Little, if any knowledge exists on exposure to monoisocyanates (MIC and ICA) and adverse health effects in industrial settings (NIWL, 2002).
In this study the exposures to MIC and ICA in Swedish foundries using Hot Box binders are described. The study includes core-makers, die-casters and other workers in the foundry area. In parallel to the exposure investigation, a study of respiratory symptoms and lung function was conducted (reported elsewhere), and formaldehyde was, therefore, included in the monitoring programme of potentially harmful agents.
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MATERIAL AND METHODS |
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Study design
The exposures to MIC, ICA and formaldehyde were investigated in all four Swedish foundries using Hot Box binders, three small brass and one large grey iron foundry. The binder in use at all foundries was based on a carbamide–formaldehyde resin (<1% formaldehyde) and a curing agent containing ammonium nitrate (10–15%), urea and sodium hydroxide or water. The brass foundries were producing armatures for households, and the grey iron foundry spare parts for the automobile industry. During core production, both manual and enclosed automatic core machines were used, and during die-casting manually operated as well as enclosed robots were used. In the brass foundries, the alloy in use contained 62% copper, 32% zinc and 1–2% lead, in addition to smaller amounts of aluminium and tin. The corresponding grey iron alloy contained 94% iron, 3% carbon, 2% silicone, 0.7% manganese, 0.3% chromium, and 0.1% copper. The grey iron foundry was large, producing some 75 000 ton per year, in contrast to the smaller brass foundries producing between 500 and 1000 ton per year. In the brass foundries, all core-makers, die-casters and fettlers were included (in total 40 workers) and in the grey iron foundry 24 core-makers. Exposure measurements covering the whole shifts were performed for all included workers, mostly (>90%) as 4–5 short-term samples of MIC and ICA. Formaldehyde was determined with diffusive samplers (GMD) as full-shift samples.
Sampling and analysis
Sampling of isocyanates was performed by liquid chemosorption using impinger bottles, containing 0.01 M dibutylamine (DBA) dissolved in toluene (Tinnerberg et al., 1997; Karlsson et al., 1998b). To adsorb fine particulate aerosol normally passing through the adsorbing liquid, the impinger bottles were connected to a cellulose ester filter with a pore size of 0.3 µm. After the sampling, the filter was introduced into the impinger bottle. The sampling flow was 1 l min–1 and the sampling was performed with personal high-flow sampling pumps with flow-rates between 1 and 5 l min–1. We used SKC 224-PCXR-9, SKC 224-PCXR-3, GILIAN HFS-513 and -113, MSA FLOW-LITE 34RI sampling pumps, and the air flow was controlled with calibrated rotameters. Sampling of formaldehyde was carried out with diffusive samplers GMD, based on a reaction between aldehydes and dinitrophenylhydrazine (Levin et al., 1988).
The analysis of formaldehyde was performed with high performance liquid chromatography techniques, the corresponding analysis of monoisocyanates and diisocyanates with liquid chromatography mass spectrometry techniques (Karlsson et al., 1998a). The detection concentration level for formaldehyde during an 8 h sampling is 20 µg m–3, and for methyl isocyanate and ICA 4 µg m–3 for 15 min short-term sampling. All analyses were performed by the laboratory at the Department of Occupational and Environmental Medicine, Örebro University Hospital. The laboratory is accredited by the Swedish Board for Accreditation and Conformity Assessment (SBACA).
Statistical methods
The air concentrations for the individual ICA, MIC and formaldehyde samples were determined and 8 h time-weighted averages calculated for the total number of measurements, different jobs and foundries. The data included a number of measurements (n), and due to approximate log normal distributions of air concentrations, the parameters of the air concentration distributions were presented as the geometric mean (GM), and the corresponding geometric standard deviation (GSD). However, depending on the further use of air concentration data, the arithmetic mean and standard deviation were also presented (Seixas et al., 1988). Concentration values less than the detection limits were estimated by multiplying the detection limit by 
(Hornung and Reed, 1990). Univariate ANOVA with a post hoc test by Tukey (SPSS 12.0) was applied for ICA and MIC with the different foundries and job titles as the explaining variables. The determination of within- and between worker variability was carried out using variance component estimation (SPSS 12.0).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIAL AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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For a majority of the workers (>90%), 4–5 short-term samples of isocyanates, in all 298 samples, were taken, representing the exposures of 15 casters, 39 core-makers and 10 others. In addition, one full shift sample of formaldehyde was carried out.
Time-weighted averages (8 h TWA) of the air concentrations of MIC were calculated for each individual, based on the short-term samples, and varied between <4 and 31 µg m–3 (Table 2). No TWA exceeded the ACGIH TLV-TWA (ACGIH, 2004) for MIC (48 µg m–3). For ICA the corresponding levels varied from <4 to 190 µg m–3, and 27% exceeded the TLV for MIC.
For the short-term samples of MIC, the air concentrations varied between <4 and 68 µg m–3, and the corresponding ICA levels ranged from <4 to 280 µg m–3. For MIC, only 1% of the short-term samples exceeded 48 µg m–3, and 8% exceeded 24 µg m–3 (Table 1; Fig. 1). The corresponding figures for ICA were 26 and 47%, respectively.
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The GM of the total ICA concentrations was higher than that of the corresponding MIC concentrations, 24 versus 4.9 µg m–3, and this was also true for the different jobs such as core-makers (22 versus 4 µg m–3) and die-casters (48 versus 10 µg m–3; Table 1) and for other exposed workers present in the foundry area (Figs 2 and 3). A comparison between foundries revealed air concentrations of ICA and MIC for both core-makers and die-casters at
2–3 times higher in one of the foundries. Notably, high exposures to ICA, ranging up to 66 µg m–3, were determined for workers with secondary exposure to the Hot Box process emissions working in the foundry premises (Table 1).
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The formaldehyde levels ranged from 14 to 1600 µg m–3, but the ACGIH-TLV (600 µg m–3) was exceeded in only 3% of the samples (Table 2). These high levels were attributed to one particular foundry. The air concentrations of formaldehyde were higher for core-makers (GM = 200 µg m–3) than for die-casters (GM = 63 µg m–3).
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An ANOVA regarding determinant factors influencing variability of the air concentration levels showed for both ICA and MIC that different foundries (F = 7.50*** and 17.11***) and job titles (F = 41.40*** and 54.14***) had a significant effect (P < 0.001) on the variability of the air concentration, implying that no sole foundry or job title alone could represent the distribution of air concentrations for the whole group when used for compliance or epidemiology purposes. However, job titles explained most of the variability (Table 3).
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The overall and job title between-worker (GSDB) variability and the within-worker (GSDW) variability varied from 1.5 to 2.3, and the analysis also revealed slightly higher GSDB variability than variability GSDW for ICA, but not for MIC. The variance ratio (
) for the different variability measures range from 0.77 to 1.1. The ratio between 5 and 95% confidence limits for the GSDB variability (R0.95B) for all workers was higher or equal to those of the job titles (Table 4).
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When comparing core making for the grey iron and the three brass foundries, the average air concentrations of MIC (GM = 3.4 and 5.9 µg m–3, respectively) and ICA (GM = 24 µg m–3 for both types) were similar (Table 5).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIAL AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Comprehensive exposure measurements in Swedish brass and grey iron foundries using the Hot Box core binder system were performed. MIC, ICA and formaldehyde were analysed. The exposures to MIC were all below the TLV-TWA, however the ICA concentration levels were substantially higher. In general, the die-casters were more exposed to isocyanates than the core-makers. The formaldehyde concentrations were higher for the core-makers, although still below the ACGIH-TLV for most of the exposed workers.
All Swedish foundries using the Hot Box core binder system were included. The total work force included in the study for the brass foundries consisted of die-casters, core-makers and other workers, as for the grey iron foundry only the core-makers were included, whereas the casting area was left out. The grey iron foundry was actually using a blend of core binders like the Cold Box cores, Epoxy-SO2 cores and Hot Box cores as well as green sand moulding. Measurements of the casting process would most certainly include the emissions of thermal degradation products like isocyanates emanating from other binders than the binder under study, and therefore casters were excluded. The core-making and casting processes cover old and new techniques regarding the core machines, as well as different sizes and shapes of the cores, both manual and automatic die-casting techniques were used in each of the brass foundries. Notably, much lower ICA and MIC air concentrations were determined when the old and new techniques were compared, for ICA 49 versus 21 µg m–3 and for MIC 8.2 versus 5.2 µg m–3. The same pattern was seen for die-casting, the average ICA concentrations were reduced from 93 to 39 µg m–3, the corresponding MIC levels were reduced from 19 to 9.4 µg m–3. Between 80 and 90% of the core- and the die-casting machines were used during the time of our investigations.
Our sampling programme was initially based on measurements of different monoisocyanates and diisocyanates, in particular MIC and ICA. However, for practical and economical reasons, sampling of total dust (containing potential respirable quartz), phenol and mineral oil mist was left out. The measurement programme, originally designed to determine compliance with occupational exposure limits, was also intended to provide information in a parallel medical study on respiratory symptoms and lung function impairments, and phenol could then be ruled out. Due to its potential effect on the respiratory tract, formaldehyde was included. The sampling strategies for the short- and long-term samples as well as the number of samples for each job title followed developed theory and practice (Leidel et al., 1977).
For the sampling of isocyanates (in particular MIC and ICA) we used the latest developed analytical methods, an impinger sampling technique based on chemosorption with dibutylamine and liquid chomatography, and mass spectrometry analysis enabling the determination of a blend of isocyanates in each sample. No other isocyanates than the MIC and ICA were determined (Levin et al., 1988; Karlsson et al., 1998b) and during the course of this project, several interlaboratory controls regarding the DBA-method were performed. The sampling and analysis of formaldehyde was performed with an accredited method (Levin et al., 1988) at our laboratory, accredited by the SBACA.
When comparing core-making for different types of foundries using basically the same core-making techniques, the average air concentrations of MIC (GM = 3.4 and 5.9 µg m–3, respectively) and ICA (GM = 24 µg m–3 for both types) were similar, implying good internal validity.
Our measurements performed during the winter season, were likely to provide higher air concentrations than average thus representing a worst-case season sampling scenario. All Swedish foundries using the Hot Box core method were taking part in our survey, and the problem of external validity therefore did not exist. However, all potential exposures were not determined, but historical data exist. Dust and phenol measurements were performed by the company health services and their safety engineers at the three brass foundries. The total dust concentrations varied between 0.1 and 3 mg m–3 for the die-casters and between 0.1 and 1.5 mg m–3 for the core-makers. In the grey iron foundry, the corresponding respirable dust concentrations varied between 0.2 and 0.6 mg m–3.
The air concentrations of phenol were historically equally low, ranging from 0.09 to 0.17 mg m–3. The earlier measurements of formaldehyde in the grey iron foundry showed air concentrations ranging from 0.2 to 8 mg m–3; the same exposure pattern was seen in this study. Our survey was preceded by measurements of emissions during the thermal degradation of different nitrogen containing binders for cores and moulds carried out by the Swedish Foundry Association (Lilja et al., 1999). In this survey, the MIC levels for core-makers ranged from 2 to 8 µg m–3, and the ICA levels varied between 5 and 72 µg m–3. The corresponding MIC air concentrations for die-casters ranged from 2 to 29 µg m–3, the ICA levels from 13 to 190 µg m–3 (Lilja et al., 2000). These figures were in the same order of magnitude as in our study and the same patterns of exposures were seen. The overall within- and between-worker variabilities expressed as GSD were 2.2 for MIC and 2.7 for ICA, well reflecting normal variability in industrial settings (Rappaport, 1991).
The ACGIH TLV-TWA for MIC is 48 µg m–3 (ACGIH, 2004), the corresponding German occupational exposure limit (OEL) is 24 µg m–3 (DFG, 2004). In Sweden, the OELs for isocyanates are derived from the TLV for MDI (0.005 p.p.m.) and recalculated by molecular weight, giving TWA-TLVs for MIC and ICA of 12 and 9 µg m–3, respectively (NBOSH, 2000). Comparison with the Swedish OELs implies a large number of ICA air concentrations exceeding the threshold value-ceiling and TLV-TWA.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIAL AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Emissions from a chemical core binder system (Hot Box) based on a formaldehyde–carbamide resin have been investigated. During core making and casting, low molecular monoisocyanates, in particular ICA and MIC were identified. Compared to ACGIH TLV-TWA for MIC and formaldehyde, the exposures were low. The lack of toxicological and human data for ICA and the relatively high air concentrations calls for further medical examination and preventive measures in production, ventilation and personal safety equipment.
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ACKNOWLEDGEMENTS |
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TOPABSTRACTINTRODUCTIONMATERIAL AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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The authors thank the participating companies, employers and employees as well as company health services who helped us in our practical field work. We also thank Krister Berg and Lisbeth Viklund for the field measurements and Ing-Liss Bryngelsson and Cecilia Fedeli for the statistical analyses and data management. The study was financed by VINNOVA research fund, grant nos. 2001-03954 and 2001-03393.
Received April 7, 2005; in final form July 5, 2005
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIAL AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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ACGIH. (2004) Threshold limit values for chemical and physical agents and biological exposure indices. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.
Archibald JJ, Smith RL. (1988) Resin binder processes. In: Stefanescu DM, Davis JR, editors. Metals handbook. Vol. 15, Casting, 9th edn. Metals Park, OH: ASM International. pp. 214–21.
Baur X, Marek W, Ammon J et al. (1994) Respiratory and other hazards of isocyanates. Int Arch Occup Environ Health; 66: 141–52.[CrossRef][Web of Science][Medline]
DFG. (2004) List of MAK and BAT values. Deutsche Forschungsgemeinschaft, Bonn Germany.
Hornung RW, Reed LD. (1990) Estimation of an average concentration in the presence of nondetectable values. Appl Occup Environ Hyg; 6: 458–64.
IARC. (1999a) Toluene diisocyanates. IARC monographs on the evaluation of carcinogenic risks to humans. Vol. 71, part 2. Lyon: International Agency for Research on Cancer. pp. 865–79.
IARC. (1999b) 4,4'-methylenediphenyl diisocyanate and polymeric 4,4–methylene diphenyl diisocyanate. IARC monographs on the evaluation of carcinogenic risks to humans. Vol. 71, part 3. Lyon: International Agency for Research on Cancer. pp. 1049–58.
Karlsson D, Spanne M, Dalene M et al. (1998a) Determination of complex mixtures of airborne isocyanates and amines. Part 4. Determination of aliphatic isocyanates as dibutylamine derivatives using liquid chromatography and mass spectrometry. Analyst; 123: 117–23.[CrossRef]
Karlsson D, Dalene M, Skarping G. (1998b) Determination of complex mixtures of airborne isocyanates and amines. Part 5. Determination of low molecular weight aliphatic isocyanates as dibutylamine derivatives. Analyst; 123: 1507–12.[CrossRef][Medline]
Leidel N, Busch K, Lynch J. (1977) Occupational sampling strategy manual, NIOSH. Cincinnatti, OH: US Department of Health, Education and Welfare.
Levin JO, Lindahl R, Andersson K. (1988) High-performance liquid chromatographic determination of formaldehyde in air in the p.p.b. and p.p.m. range using diffusive sampling and hydrazone formation. Environ Technol Lett; 9: 1423–30.
Lilja BG, Westberg H, Nayström P. (1999) A survey of isocyanate exposure in Swedish foundries. Part I. Emission measurements. Jönköping, Sweden: Swedish Foundry Association. p. 31.
Lilja BG, Westberg H, Nayström P. (2000) A survey of isocyanate exposure in Swedish foundries. Part II Exposure measurements. Jönköping, Sweden: Swedish Foundry Association. p. 83.
NBOSH. (2000) Occupational exposure limits 2000:3. Stockholm, Sweden: National Board of Occupational Safety and Health.
NIWL. (2002) Scientific basis for Swedish Occupational Standards XXIII. Criteria group for occupational standards. Arbete och Hälsa, 2002:19. Stockholm, Sweden: National Institute of Working Life. pp. 1–63.
Rappaport SM. (1991) Assessment of long-term exposures to toxic substances in air. Ann Occup Hyg; 35: 61–121.
Renman L, Sangö C, Skarping G. (1986) Determination of isocyanate and aromatic amine emissions from thermally degraded polyurethanes in foundries. Am Ind Hyg Assoc J; 47: 621–8.
Seixas NS, Robins TG, Moulton LH. (1988) The use of geometric and arithmetic mean exposures in occupational epidemiology. Am Ind J Med; 14: 465–77.
Spanne M, Grzybowski G, Boghard M. (1999) Collection efficiency for submicron particles of a commonly used impinger. Am Ind Hyg Assoc J; 60: 540–4.
Tinnerberg H, Spanne M, Dalene M et al. (1997) Determination of complex mixtures of airborne isocyanates and amines. Part 3. Methylenediphenyl diisocyanate, methylendiphenylamino isocyanate and methylendiphenyldiamine and structural analogues after thermal degradation of polyurethane. Analyst; 122: 275–8.[CrossRef][Medline]
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