A Method to Ensure Occupational Safety for Employees Using Personal Head Protection Equipment in Explosive and Fire-Hazardous Media

To ensure the safety of employees, protective helmets that have been proven as reliable personal head protective equipment against mechanical impacts are widely used. However, these have one significant flaw, which is a low electric conductivity of the material they are made from, which conditions a potential generation and accumulation of electric charges on their surface during a contact electrification «protective helmet – scalp hair». Electric charges accumulated on the surface of a protective helmet can cause, as a result of electrostatic discharge, the ignition of many combustible substances and volatile liquids considered explosive and fire-hazardous that are used in production premises. The study addresses the problem of selecting a method to prevent electric charge accumulation resulting from contact of scalp hair with elements of protective helmets. A calculation method determines a minimum metallized (grounded) area of internal surface of a protective helmet that, in case of grounding, will ensure the flow of charges to the grounded poles. The first condition under which no electric charge generated due to the electrification of the employee's scalp hair when contacting the integral harness of the helmet can become an inflammation source, has been obtained for a specific combustible substance with minimum ignition energy and a specific ungrounded surface of a protective helmet. The dynamics of electrostatic potential of preliminarily charged elements of the internal harness of a protective helmet in relation to the ground from the moments of their connection to a grounding device, with registration of the time of charge flow to the one-tenth of initial values, has been studied by a non-contact method, and its results have been provided. As a result, the dependence of the rate of charge flow on the area of grounded conducting coating on the internal surface of a protective helmet has been determined. The results of the study refer to the necessity to develop a methodology for protective helmet tests during their production and to introduce amendments into their test programs.