Ignition potential of transient sparks produced by abrasive waterjet cutting in explosive environments

Abstract

Explosive atmospheres are a significant hazard in many mining, mineral processing, and industrial workplaces. These workplaces often require hot work for maintenance, repairs, or production activities. If the workpiece cannot be removed from the potential explosive atmosphere, the hazard must be mitigated through engineering and administrative controls. The hazards must be identified, explosive atmospheres evacuated from the work area, sources of gases removed, and appropriate measure taken to prevent hazards from reentering the area during hot work. Despite these measures, fatalities and significant losses still occur. The ideal solution is to move up the hierarch of controls to substitution.Abrasive waterjet (AWJ) cutting is a potential substitute for hot drilling and cutting processes. At the macroscopic level, AWJ cutting of steel is a cool process. The scientific literature and industry experts have demonstrated that transient sparks can occur during AWJ cutting. No model of AWJ ignition potential is presently available in the literature. The spark generation process and sparks have not been characterized. A single published data set exists with ignitions reported at 300MPa (43.5kpsi) and is not representative of field cutting parameters that represent a potential hot work substitute.The AWJ ignition process was characterized and a model of AWJ ignition was developed. Energy transfer and spark generation were calculated from the model and the maximum potential spark was characterized. Based on the model, it was hypothesized that reducing the operating pressure would reduce the ignition rate. Experiments were conducted with AWJ parameters representative of field cutting applications. Drilling and linear cutting tests were conducted at 69MPa (10kpsi) in a hydrogen-oxygen atmosphere. No ignitions occurred during the drilling and cutting experiments. It is concluded that AWJ cutting is a promising potential hot work substitute for cutting and drilling steel in a subset of explosive atmospheres. Further parametric analysis is recommended.