Risk assessment during explosion severity tests of carbon black and MWCNT in a laboratory
Résumé
Risk assessment has been conducted by quantitative and qualitative methods during explosion severity tests for two nanomaterials (NMs) in a laboratory. First a quantitative assessment was performed in order to assess the exposure of the operator during explosiveness testing in the 20 L sphere for carbon black (N990) and MWCNT (NC7000TM). The methodology was based on general recommendations for exposure measurement assessment (e.g. [1]), and an easy-to-use operational sampling approach [2]. Exposure was measured with a Condensation Particle Counter (CPC) in background field as well as in the immediate vicinity of the operator. The operator was also equipped with a portative particle counter DiscMini. Samples for Transmission Electron Microscopy (TEM) analysis were collected with a Mini Particle Sampler (MPS) system. The testing procedure was clearly split into different steps to allow identifying the emitting activities. Background concentrations were monitored using a scanning mobility nanoparticle sizer (SMPS). The measurements campaign enabled to assess the air flow in the laboratory, the performance of the local exhaust ventilation and to monitor the particle number concentration, nature and morphology both in the immediate vicinity of the operator and in the background. The measurements allowed to identify a few sources of NMs emission during the tests and to come up with recommendations to reduce the operator exposure. It led also to the finding that the dynamic barrier provided by the local exhaust ventilation system can be temporarily weakened during overpressure events. Second, a qualitative assessment was performed using two control banding tools, i.e. CB Nanotool 2.0 and the StoffenManager Nano 1.0. The risk levels assessed by the control banding tools are not in full agreement. The subjectivity associated with some input parameters for the risk assessment and the lack of information in the safety data sheets (SDS) and literature are discussed for several parameters. Third, the results from measured versus estimated exposure to NMs were compared. The results from comparing airborne nanoparticles concentrations are in line with estimated exposure. However risk assessment with control banding tools remains questionable in some cases. Causes and consequences are investigated.