Blast and noise mitigation
of open air explosions
EPNM2010
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)
Energy
100%
50%
0
2 ms
1 ms
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
Saw dust filled container
of 0.5 kg RDX
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; Pmax = 62% relative to free expansion
100%
Energie
TNT internal
TNT kinetic
Lucht internal
Lucht kinetic
50%
Water internal
Water kinetic
0
2 ms
1 ms
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
Same charge
Right-side using
foam blastmitigation
45 kg at
10 m
Tuesday, June 13, 2006
Blast mitigation
Earlier 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)
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
P5 (±200m)
de
Vi
am
c
o
a
er
R
oa
d
Hill / rocks
P4 (23m)
P3 (20m)
P2 (10m)
P1 (5m)
ad
Ro
Hill / rocks
Charge
Sound
(up hill
? ±300m)
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
P2_10m_ANFO50kg_foam_3
81.90
kPa
15.0
ms
0.205
kPa.s
21.7
ms
P2_10m_ANFO50kg_4
88.20
kPa
13.2
ms
0.238
kPa.s
22.4
ms
Blast wave measurement example
50 kg ANFO at 10 m
P2_10m_ANFO50kg_foam_3
P2_10m_ANFO50kg_foam_3_impulse
zero
P2_10m_ANFO50kg_4
P2_10m_ANFO50kg_4_impulse
kPa
kPa.s
100
0.50
90
0.45
80
0.40
70
0.35
60
0.30
50
0.25
40
0.20
30
0.15
20
0.10
10
0.05
0
0.00
-10
-0.05
-20
-0.10
12
14
16
18
20
22
24
26
28
30
32
ms
Tuesday, June 13, 2006
P3_20m_RDX20kg_foam_5
27.87
kPa
46.4
ms
0.077
kPa.s
59.7
ms
P3_20m_RDX20kg_6
38.89
kPa
41.8
ms
0.150
kPa.s
59.0
ms
Blast wave measurement example
20 kg RDX powder at 20 m
P3_20m_RDX20kg_foam_5
P3_20m_RDX20kg_foam_5_impulse
P3_20m_RDX20kg_6
P3_20m_RDX20kg_6_impulse
kPa
kPa.s
40
0.40
35
0.35
30
0.30
25
0.25
20
0.20
15
0.15
10
0.10
5
0.05
0
0.00
-5
-0.05
-10
-0.10
40
42
44
46
48
50
52
54
56
58
60
ms
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
Distance Peak pressure reduction
[m]
[kPa]
%
ANFO 50 kg - Foam
P1
5
P2
10
P3
20
P4
23
P5
200
ANFO 50 kg
P1
5
P2
10
P3
20
P4
23
P5
200
RDX 20 kg -Foam
P1
5
P2
10
P3
20
P4
23
P5
200
RDX 20 kg
P1
5
P2
10
P3
20
P4
23
P5
200
Clad 50 kg - extra Foam
P1
5
P2
10
P3
20
P4
23
P5
200
Clad 50 kg
P1
5
P2
10
P3
20
P4
23
P5
200
time
[ms]
av. shock velocity
[m/s]
Impulse max. reduction
[kPa.s]
%
at time
[ms]
146.42
54.83
48
38
7.1
18.9
704
529
0.276
0.206
0
13
13.7
26.8
21.74
1.04
17
17
51.7
530.7
445
377
0.103
0.012
18
20
64.4
549.5
4.29
13.25
37.69
46.09
523.73
1166
755
531
499
382
0.276
0.238
0.17
0.126
0.015
8.05
19.46
46.36
55.52
536.34
621
514
431
414
373
0.156
0.116
0.077
0.058
0.007
6.46
16.36
41.8
50.73
527.59
774
611
478
453
379
0.202
0.207
0.15
0.113
0.012
12.65
25.6
52.01
61.33
541.84
395
391
385
375
369
0.179
0.117
0.078
0.062
0.007
8.92
19.8
45.54
54.06
535.72
561
505
439
425
373
0.192
0.147
0.094
0.074
0.009
282.85
88.2
33
26.1
1.25
95.05
32.7
18.5
15.23
0.74
25
44
29
21
33
126.97
58.74
26
19.4
1.11
51.07
28.61
15
13.27
0.62
114.69
48
23
16.84
0.86
55
40
35
21
28
6.9
22.42
52.89
62.36
544.67
23
44
49
49
42
14.2
27.61
59.74
66.86
549.81
10.2
32.49
59
71.05
546.86
7
20
17
16
22
20.37
34.16
65.18
73
555.88
13.55
28.31
59.09
65.47
549.96
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 water
kg
Oppervlakte-energie
0.073
J/m2
Dichtheid
1000
kg/m3
snelheid
1000
m/s
temperatuurtoename
TNT =4.5 MJ/kg
1
100
K
warmtecapaciteit
4190
J/kg*K
verdampingswarmte
2260
kJ/kg
18
g/mol
molecuulmassa
diameter druppels
druppel volume
druppel oppervlak
10
523
3.14E-10
micron
ccmicron
m^2
massa druppel
5.2333E-13
kg
aantal druppels
1.9108E+12
totaal oppervlak
600
m^2
n
55
mol
oppervlakte energie
44
J
kinetische energie
0.5
MJ
thermische energie
0.4
MJ
verdampingswarmte
2.26
MJ
Tuesday, June 13, 2006
Blast mitigation
water bags in detonation chamber (0.13 kg/m3)
•
•
•
•
•
QSP after 1 kg PETN in bunker
QSP with 0.5 kg water on HE
QSP with 1 kg water on HE
QSP with 3 kg water on HE
QSP with 6 kg water on HE
130 kPa (100%)
60 kPa (46%)
45 kPa (35%)
25 kPa (20%)
25 kPa (20%)
• QSP 5 kg water at 50 cm from HE
15 kPa (12%)
Tuesday, June 13, 2006