Stability of Isocyanates Sampled in Fire Smokes

Annals of Work Exposures and Health, 2018, Vol. 62, No. 9, 1171–1175 doi: 10.1093/annweh/wxy072 Advance Access publication 11 August 2018 Short Communication Short Communication Stability of Isocyanates Sampled in Fire Smokes Centre for Fire and Hazards Sciences, School of Physical Sciences & Computing, University of Central Lancashire, Preston, Lancashire PR1 2HE, UK; 2Present address: Department of Health and Life Sciences, Leicester School of Pharmacy, Faculty of Health Sciences, De Montfort University, The Gateway, Leicester LE1 9BH, UK 1 *Author to whom correspondence should be addressed. E-mail: Submitted 13 February 2018; revised 12 June 2018; editorial decision 2 July, 2018; revised version accepted 7 August, 2018. Abstract Inhalation of airborne isocyanates is associated with acute asthma attacks and inflammation in the respiratory tract as well as cancer. These highly reactive compounds are used as monomers in various applications such as foams for insulation materials and upholstery furniture and are therefore commonly found in fire smoke from insulation materials, such as rigid polyisocyanurate (PIR) foams. Consequently, there is an increasing concern regarding the potential adverse health effects they may cause during this type of exposure. The aim of this study was to investigate the stability of generated isocyanates from aerobic pyrolysis of PIR after sampling in the derivatization solution as well as after sample preparation to establish the optimal storage conditions and rate of degradation. Both airborne and particle-bound isocyanates were collected, using dibutylamine as derivatization agent in a midget impinger and impregnated filter after the impinger. The rapid degradation of the generated isocyanates after sampling emphasizes the need for a prompt sample preparation and analysis, in particular for the collected mono-isocyanates, as the concentration decreased by 50% within 4–8 h. Keywords: fire; fire toxicity; foam; HPLC-MS/MS; isocyanates; polyisocyanurate Introduction Isocyanates are highly reactive compounds used extensively as monomers and polymers in the production of rigid polyisocyanurate (PIR) building insulation materials (Avar et al., 2012). Previous studies have shown that burning PIR foams release airborne isocyanates (Blomqvist et al., 2003; Stec and Hull, 2011), indicating that human exposure may occur during fires. Isocyanate exposure, through inhalation or absorption through the skin, can cause acute asthma attacks, respiratory tract sensitization and is also associated with cancer (Wisnewski et al., 1999; Redlich and Karol, 2002; Bello et al., 2007; Lockey et al., 2015). Due to their reactivity, isocyanates need to be derivatized during sampling in order to stabilize them and minimize losses prior to analysis (Spanne et al., 1996; Gylestam et al., 2014). One of the most commonly used derivatization agent nowadays is dibutylamine (DBA) (Karlsson et al., 2005; Marand et al., 2005; Gylestam et al., 2014). © The Author(s) 2018. Published by Oxford University Press on behalf of the British Occupational Hygiene Society. Linda Bengtström1,2, , Mariëlle Salden1 and Anna A. Stec1,* 1172 Materials and methods Chemicals Acetonitrile (HPLC grade, 99.9%) and toluene (HPLC grade, 99.9%) was purchased from Fischer Scientific (Loughborough, UK). Mobile phase A was prepared using ultrapure water obtained from a Millipore Milli-Q Gradient A10 system (Millipore, Bedford, MA, USA). Formic acid (≥95%), DBA (≥99.5%), and non-deuterated as well as deuterated labelled (d9- or d18-labelled) isocyanate standard mixtures, see Supplementary Material (available at Annals of Work Exposures and Health online), were purchased from Sigma-Aldrich (Steinheim, Germany). Insulation materials The insulation material used was rigid PIR foam at 33 kg m−3. The sample used was commercially available and purchased at local vendors, with an estimated organic content of 100%. Sample generation and collection The NFX 70–100 static tube furnace (Fig. 1) is a benchscale furnace in which the sample is introduced to the furnace and thermally decomposed. Immediately prior to the sampling, the glass fibre filter (25 mm, Whatman Grade GF/C, Sigma-Aldrich) mounted behind a midget impinger, was impregnated by the derivatization solution (0.01 M DBA in toluene) at an air flow of 1 l min −1 for 4 min. The midget impinger was put in an ice bath throughout the experiment. After that, the insulation foam (0.25 g) was introduced into the middle of the NFX 70–100 tube furnace set at 400°C. No ignition for any samples was observed. The samples were aerobically pyrolysed in an air flow of 2 l min−1, and a subset of the effluent, 1 l min−1, was collected for 10 min after sample introduction. Blank samples were collected before and after sample runs. Isocyanate stability optimization Nine different time intervals (0, 1, 2, 4, 8, 24, 48, 120, and 240 h) after sample collection were analysed and duplicate samples were stored at either room temperature or in a refrigerator (6–8°C). The stability of the isocyanates after the vaporization step was also investigated at four different time intervals (0, 24, 120, and 240 h). The samples were stored at 8°C between the different HPLC-MS/MS analyses and analysed in triplicates. Sample preparation After isocyanate sampling, both the impinger solution and filter were transferred to a 25-ml glass vial. The vials Figure 1. Schematic figure of the NFX 70–100 static tube furnace set-up used in this study. Collection methods for airborne isocyanates include impingers (UK Health and Safety Executive 2014), filters or denuders (Gylestam et al., 2014), or a combination of both (UK Health and Safety Executive, 2014). The main advantage of using impingers is the favourable kinetic conditions for quantitative isocyanate collection (Henneken et al., 2007). However, the impinger method does not efficiently collect particles between 0.01 and 1.5 µm (Spanne et al., 1999) leading to potential losses in adsorbed isocyanates on airborne particles. Therefore in-line impregnated filters after the impinger are often used for the collection of isocyanates absorbed on particle matter (Karlsson et al., 2000; Creely et al., 2006; BS ISO 17734-1:2013, 2013; Health and Safety Executive HSE, 2014). Yet, fire smoke could contain compounds capable of interfering with isocyanate analysis, either by reacting with them or causing matrix effects during analysis (Woolley et al., 1975; Blomqvist et al., 2003). There is currently a very limited amount of studies for the stability of isocyanates generated in fires after sampling. We present an investigation to establish the optimal storage conditions and rate of degradation of isocyanates generated from the aerobic pyrolysis at 400°C of rigid PIR insulation foam at 400°C, collected by impingerfilter sampling and analysed by high-performance liquid chromatography coupled to a tandem mass spectrometer (HPLC-MS/MS). The t (...truncated)