Effectiveness of Various Concentrations of an Inert Gas Mixture for Preventing and Suppressing Mining Equipment Cab Fires: Development of a Dual Cab Fire Inerting System

The National Institute for Occupational Safety and Health (NIOSH/PRL) conducted a series of large-scale experiments to evaluate the effectiveness and safety of various concentrations of an inert gas mixture (CO₂, 8%; N₂, 50%; Ar, 42%) for preventing and suppressing cab fires. Comparison of concentrations effectiveness in yielding safe times has led to the choice of an optimum gas mixture concentration, discharged in the cab through a muffled nozzle system, for the development of a dual cab fire inerting system. Of note is that safety training programs, including the synchronization of performed tasks, need to accompany this technology to enhance operator’s efficiency and safety during fire emergencies within the safe times yielded by the cab fire inerting system. Cab fires are caused by the ignition of flammable vapors and mists (ball of fire) that penetrate the cab during prolonged hydraulic fluid and fuel fires, and electrical malfunctions involving other cab combustible materials. Often, these fires force the operator to exit the cab under hazardous conditions during a time needed to perform emergency tasks. Hence, it is important to provide the operator, not only with an engine fire suppression system (dry chemical powder), but also with a cab fire protection system, effective both in preventing the ignition of flammable vapors in the cab, and suppressing cab material fires. This paper details the results of the experiments, and presents the development of a dual cab fire inert system, using an optimum gas mixture concentration discharged in the cab through a muffled nozzle system. Of note is that the design of a gas mixture concentration volume according to cab volumes, and system fabrication/installation have been undertaken by cooperating industries. Disclaimer: This information is distributed solely for the purpose of pre-dissemination peer review under applicable information quality guidelines. It has not been formally disseminated by NIOSH. It does not represent and should not be construed to represent any agency determination or policy.