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EPNM2010

Blast and noise mitigation of open air explosions. EPNM2010. Lay-out. Blast introduction Blast mitigation Earlier experiments by others New experiments. Cladding industry practice. Large metal surfaces (5x5 m or 3x8 m) Large amounts of explosive (hundreds of kg) Large flat charges

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EPNM2010

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  1. Blast and noise mitigation of open air explosions EPNM2010

  2. Lay-out • Blast introduction • Blast mitigation • Earlier experiments by others • New experiments

  3. Cladding industry practice • Large metal surfaces (5x5 m or 3x8 m) • Large amounts of explosive (hundreds of kg) • Large flat charges • In open air (enormous noise/bang) • Inside a tunnel (erosion/maintenance/safety)

  4. Blast

  5. Directed blast due to flat shape of explosive • Simulation of the blast wave form a Ø 2 m plate of detonating TNT (0.1 m thick)

  6. Blast: Bare TNT charge in air • TNT (internal and kinetic energy) • Air (internal en kinetic energy) 100% Energy 50% 0 2 ms 1 ms Time

  7. Blast mitigation = redistribution of energy • Kinetic energy in other media than air • Mass; solids (metal, stone) or liquids (water) • Dissipation of energy (plastic deformation/heat) • Compressible media (sand, saw dust, fibers) • Heat transfer (heating another medium) • Huge surface needed (small particles or water drops/mist) • Water damp generation takes 2.5 MJ/kg (4.5 MJ/kg TNT)

  8. Blast mitigation Container after internal explosion of 0.5 kg RDX Saw dust filled container

  9. Blast mitigation :Water (in bags) • 55 kg TNT covered using 114 kg water at 0.5 m distance • M/W = 2; Pmax = 62% relative to free expansion 100% TNT internal TNT kinetic Lucht internal Lucht kinetic Water internal Water kinetic Energie 50% 0 2 ms 1 ms Tijd

  10. Blast mitigationWater canon/sprinkler • Water drops 50% blast reduction • Mass (kinetic energy) • Cooling capacity (surface area) • Drawback is continuous water flow Characteristic diameter: 5 mm 0.2 mm < 10 μm

  11. Blast mitigationWater foam is a static water mist • Foam exists of thin water films • In the shockwave films break up into fine drops (micro-mist)

  12. Blast mitigation • Relation between blast and noise intensity: • Sound pressure level (SPL) • 20 log ( Y Pa/20 μPa) • If Y = 200 Pa for a blast wave SPL = 140 dB • Blast mitigation could be used for noise reduction! • Kill the monster while it is “small” • TNO Defense, Safety and Security core-business! • Protection of ship (internal explosion) • Safety of munition storage • Large blast measuring experience (Australia, Canada, Sweden) • Mitigation knowledge and techniques developed could be used for blast/noise-reduction of open air explosions

  13. Blast mitigation Earlier water foam experiments Same charge Right-side using foam blast-mitigation 45 kg at 10 m

  14. Blast mitigationEarlier water foam experiments • Foam expansion ratio 60-200 reduced the distance to a impulse level of 10 psi-ms with a factor 3 (compared to air). • Peak pressure reduced by an order of magnitude • Noise reduction 12-15 dBA (at 2 km)

  15. Practical application of blast mitigation for the cladding industry • Effective? • Costs? • Safety? • Cycling time increase? • Site pollution? • Static or dynamic system? • Mitigating medium?

  16. Out-door experiments at Burbach (D): set-up

  17. Water foam using fire-brigade equipment • Foam in container • Foam layer thickness about 80 cm • no optimization of foam or layer thickness • Foaming agent is biodegradable

  18. Blast wave measurement example 50 kg ANFO at 10 m

  19. Blast wave measurement example 20 kg RDX powder at 20 m

  20. Video images of detonation of 20 kg RDX powder

  21. Video of detonation of 20 kg RDX powder with water foam

  22. Video images of detonation of 20 kg RDX powderwithout (left) and with water foam

  23. Video images of detonation of 50 kg cladding explosive without (left) and with water foam

  24. Video images of detonation of 50 kg ANFO explosive without (left) and with water foam

  25. Experimental results: blast measurements

  26. Conclusions • Water foam seems an useful blast mitigation medium • Cheap • Effective • Environmentally friendly • No large influence on production time-cycle • Eight shots (4 with water foam) in 3 hours • Blast reduced both in peak pressure and impulse • ~25% for cladding explosive • ~40% for RDX (no after-burning) • ~20% for ANFO • Tests are indicative only • No optimization of foam type and thickness • No noise/acoustic measurements yet …….

  27. Acknowledgements • Chubb-Ajax is thanked for providing the foaming agent • DMC-Dynaplat was a great help in this TNO project: • Allowing TNO to perform these test at their shooting range • Providing much of the explosives used • Providing the fire-truck for foam generation • Enthusiastic help during the tests (on a rainy day)

  28. Blast mitigatieWaterdrops TNT =4.5 MJ/kg

  29. Blast mitigationwater bags in detonation chamber (0.13 kg/m3) • QSP after 1 kg PETN in bunker 130 kPa (100%) • QSP with 0.5 kg water on HE 60 kPa (46%) • QSP with 1 kg water on HE 45 kPa (35%) • QSP with 3 kg water on HE 25 kPa (20%) • QSP with 6 kg water on HE 25 kPa (20%) • QSP 5 kg water at 50 cm from HE 15 kPa (12%)

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