Mitigation of TNT and Destex explosion effects using water mist

Experimental research on explosion suppression affected by ultrafine water mist containing different additives

The suppression effects of pure ultrafine water mist and 5% mass fraction alkali metal (NaCl, Na₂CO₃, KHCO₃, KCl and K₂CO₃) solutions ultrafine water mist on methane explosion were conducted under five mist concentrations in a sealed visual vessel. Mist diameters of different additive solutions were measured by a phase doppler particle analyzer. Pressure data and dynamic flame pictures were recorded respectively by a high-frequency pressure sensor and a high-speed camera. Results indicate that alkali metal compound can enhance the suppression effect of ultrafine water mist and it was related to the additive type. The suppression order of alkali metal compound for methane explosion was K₂CO₃>KCl > KHCO₃>Na₂CO₃>NaCl. Meanwhile, additive radicals can obviously affect explosion intensity and it mainly reflected in the reduction of explosion pressure under different mist conditions (K⁺>Na⁺, Cl^- >HCO₃^-). The pressure generated from combustion wave accelerating propagation underwent two accelerating rises and was affected by additive type and mist amount. The effect of additive type on explosion intensity (maximum explosion overpressure (ΔP_max), two peak values of pressure rising rate) was similar with flame propagation velocity and were decreased evidently with increasing mist concentration. The enhancement in explosion suppression was due to the combination of improved physical and chemical effects.

Inhibition of aluminum dust explosion by NaHCO3 with different particle size distributions

NaHCO₃ with three particle size distributions was employed to determine the minimum inerting concentration (MIC, g/m³) for the explosion of 5μm and 30μm aluminum dust in a standard 20L spherical chamber and thus examine the effect of particle size on the inhibition efficiency. Results showed that the MIC significantly increases as the aluminum particle size decreases from 30μm to 5μm. For 30μm aluminum, the MIC dramatically decreased with the reduction in the NaHCO₃ particle size. By contrast, for 5μm aluminum, the MIC was nearly independent of the particle size of NaHCO₃ in the range studied. Time-scale analysis indicated that the decomposition of NaHCO₃ must be faster than the aluminum combustion reaction for effective chemical inhibition. Scanning electron microscopy showed that the particles of the explosion residues of a NaHCO₃/Al mixture were considerably larger than those of pure aluminum explosion residues. A diameter ratio β_mix was defined to evaluate the degree of incomplete reaction promoted by NaHCO₃. The composition of the explosion products was analyzed by X-ray photoelectron spectroscopy, and the data revealed that Na₂CO₃ and Al₂O₃ are the major species of the products. An inhibition mechanism was proposed based on these results.

Experimental study of fuel sootiness effects on flashover

Previous fire safety studies have demonstrated that flashover can result in severe injure and death and heat radiating back to a fuel is an important mechanism. Fuel sootiness dominates in radiative heat transfer. However, empirical correlations from previous investigations did not consider the fuel sootiness but nevertheless generated reasonably good predictions of flashover. In this study, a series of experiments was employed to examine fuel sootiness effects on flashover. The fuels used, in the order of their sootiness, were gasoline, n-hexane, iso-propanol and methanol. These fuels were filled in circular pans 100-320 mm in diameter to generate fires with different heat release rates and levels of sootiness. The pans were in 1/3 the size of the ISO 9705 test chamber. After ignition, the heat release rate (HRR), temperature inside the chamber, as well as heat flux on the floor and time to flashover (t(fo)) were determined. Experimental data show that HRR at flashover and t(fo) were strongly corrected and their relationship was independent of the fuel burned. Although heat feedback to the floor increased as fuel sootiness increased, consequently enhancing the burning of sooty fuels, flashover occurs only when the HRR at flashover criterion is reached.