EPNM2010 Blast and noise mitigation of open air explosions

Tuesday, June 13, 2006 Lay-out Blast introduction Blast mitigation Earlier experiments by others New experiments

Tuesday, June 13, 2006 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)

Tuesday, June 13, 2006 Blast

Tuesday, June 13, 2006 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)

Tuesday, June 13, 2006 Blast: Bare TNT charge in air TNT (internal and kinetic energy) Air (internal en kinetic energy) 100% 50% 0 1 ms 2 ms Energy Time

Tuesday, June 13, 2006 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)

Tuesday, June 13, 2006 Blast mitigation Container after internal explosion of 0.5 kg RDX Saw dust filled container

Tuesday, June 13, 2006 Blast mitigation : Water (in bags) 55 kg TNT covered using 114 kg water at 0.5 m distance M/W = 2; P max = 62% relative to free expansion 100% 50% 0 1 ms 2 ms TNT internal TNT kinetic Lucht internal Lucht kinetic Water internal Water kinetic Energie Tijd

Tuesday, June 13, 2006 Blast mitigation Water 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

Tuesday, June 13, 2006 Blast mitigation Water foam is a static water mist Foam exists of thin water films In the shockwave films break up into fine drops (micro-mist)

Tuesday, June 13, 2006 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

Tuesday, June 13, 2006 Blast mitigation Earlier water foam experiments 45 kg at 10 m Same charge Right-side using foam blast- mitigation

Tuesday, June 13, 2006 Blast mitigation Earlier water foam experiments Foam expansion ratio 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 dBA (at 2 km)

Tuesday, June 13, 2006 Practical application of blast mitigation for the cladding industry Effective? Costs? Safety? Cycling time increase? Site pollution? Static or dynamic system? Mitigating medium?

Tuesday, June 13, 2006 Out-door experiments at Burbach (D): set-up

Tuesday, June 13, 2006 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

Tuesday, June 13, 2006 Blast wave measurement example 50 kg ANFO at 10 m

Tuesday, June 13, 2006 Blast wave measurement example 20 kg RDX powder at 20 m

Tuesday, June 13, 2006 Video images of detonation of 20 kg RDX powder

Tuesday, June 13, 2006 Video of detonation of 20 kg RDX powder with water foam

Tuesday, June 13, 2006 Video images of detonation of 20 kg RDX powder without (left) and with water foam

Tuesday, June 13, 2006 Video images of detonation of 50 kg cladding explosive without (left) and with water foam

Tuesday, June 13, 2006 Video images of detonation of 50 kg ANFO explosive without (left) and with water foam

Tuesday, June 13, 2006 Experimental results: blast measurements

Tuesday, June 13, 2006 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 …….

Tuesday, June 13, 2006 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)

Tuesday, June 13, 2006 Blast mitigatie Waterdrops Massa water1kg Oppervlakte-energie0.073J/m2 Dichtheid1000kg/m3 snelheid1000m/s temperatuurtoename100K warmtecapaciteit4190J/kg*K verdampingswarmte2260kJ/kg molecuulmassa 18g/mol diameter druppels10micron druppel volume523ccmicron druppel oppervlak3.14E-10m^2 massa druppel5.2333E-13kg aantal druppels1.9108E+12 totaal oppervlak600m^2 n 55mol oppervlakte energie44J kinetische energie0.5MJ thermische energie0.4MJ verdampingswarmte2.26MJ TNT =4.5 MJ/kg

Tuesday, June 13, 2006 Blast mitigation water bags in detonation chamber (0.13 kg/m 3 ) 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 HE15 kPa (12%)