Suppressing flame over electrical wire in confined space by oscillatory airflow

Abstract

Electric wires installed in confined spaces, such as underground tunnels and false ceilings, represent a prevalent source of fire occurrences. Such a hidden fire is hard to be extinguished by traditional firefighting techniques. This paper proposes using oscillatory airflow for suppressing wire fire hazards in confined environments. A horizontal wire with polyethylene insulation and copper core is selected as the target, combined with an electromagnetic piston developed to generate airflows oscillating at frequencies from 50–70 Hz and velocities up to 0.28 m/s. Results confirm that, compared to steady wind, oscillatory airflow can achieve extinction at a lower velocity while consuming less electrical power. The heat transfer involving oscillatory flows between the flame and the fuel is analyzed, revealing that augmented fuel cooling and diminished flame radiation are the primary contributors to its improved extinguishing performance. Unsteady flame stretch under oscillatory airflow is also analyzed, providing a mechanistic explanation for the superior extinction performance observed for lower-frequency flows. An extinction criterion based on fuel heat loss and airflow perturbation is formulated to explain the extinction limits. This work introduces a low-carbon firefighting technique that employs normal air as an extinguishing agent, and it helps expand the channel for fire safety design in constrained environments.