Design and Testing of Blast Shields for Different Blasting Applications.

Design and Testing of Blast Shields for Different Blasting Applications | 1

AbstractThe use of explosives bring countless benefits to our everyday lives in areas such as mining, oil and gas exploration, demolition or avalanche control. However, because of the potential destructive power of explosives, strict safety procedures must be an integral part of any explosives operation. The goal of this paper is to provide a solution against the hazards which unfortunately accompany the use of explosives. For this reason, a blast shield is specifically designed and tested for protect-ing personnel against these unpredictable effects. This document will develop a complete analysis answering the following questions: what are the potential hazards from an air blast; what are their effects; and how can we be protected against them. In order to answer these questions, theoretical, analytical, and numerical calculations are performed. Finally, a full blast shield prototype is tested under blasting conditions proving its effectiveness as a safety device while explosives are used.

Keywords: Hazards, composition B, casing, overpressure, fragmentation, ConWep, Autodyn.

By Eduardo Lozano1, Vilem Petr2, AXPRO Group, Colorado School of Mines, Colorado, USA

DESIGN AND TESTING OF BLAST SHIELDS FOR DIFFERENT BLASTING APPLICATIONS

1. IntroductionBlack powder, a low explosive, is the oldest type of explosive material known. While used for gun powder centuries earlier, it began to be used in mining and rock blasting for road construction in the 1600s and two centuries later, the devel-opment of nitroglycerin and dynamite led to ad-vancements such as the construction of road tun-nels. Nowadays, explosive materials are produced in numerous physical forms for their use in min-ing, engineering, or military applications. During 2013, 6.7 billion pounds of explosives were used only in the U.S. However, because of the inherent destructive power of explosives, strict safety pro-cedures must be an integral part of any explosives operation.

The hazards involving the use of explosives show the necessity of a reliable protection for the all the personnel involve in any blasting operations with a high risk of fatality. For this reason, AX-PRO Group decided to design and test a new blast shield according to all the safety requirements, in order to provide an operating solution for the pre-vention of any possible future accident.

This paper will determine guidelines for the bar-rier requirements and safety distances through theoretical, analytical, and numerical calculations. Next, testing will then be performed at the Ex-plosives Research Laboratory (ERL) by AXPRO Group utilizing the functional blast shield proto-type and their advanced explosives characteriza-tion equipment to determine the parameters of the detonation.

1 Eduardo Lozano, AXPRO Group, Colorado School of Mines, 1600 Illinois Street, Brown Building, Room 129, Golden, Colorado 80401, [email protected] Vilem Petr, AXPRO Group, Colorado School of Mines, 1600 Illinois Street, Brown Building, Room 120, Golden, Colorado 80401, [email protected].

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Blasting and FragmentationVol. 9, No. 1, 2015

2. Hazards to Personnel from Air BlastThe purpose of this blast shield is to protect per-sonnel from the effects produced by an explosion. The first factor to analyze is potential hazards to personnel from air blast so we can determine the level of safety required. For our calculations, the human body receiver is assumed to be standing in the free field on flat and level ground when con-tacted to by the blast wave. Excluding certain re-flected wave situation, this is the most hazardous body exposure condition [1]. Air blast effects can be divided into three categories: primary blast ef-fects, secondary blast effects and tertiary blast ef-fects.

2.1 Primary Blast DamagePrimary blast effects are associated with changes in environmental pressure due to the presence of an air blast. Humans are sensitive to the blast over-pressure, the duration of the blast wave, and the specific impulse of the blast wave. Since the specif-ic impulse is dependent on pressure as well as du-ration, pressure-impulse lethality or survivability curves are shown in figure 1. Each one represents percent survivability. Higher pressure and im-pulse combinations allow fewer survivors. Scaled Overpressure is calculated using the atmospheric pressure for a certain altitude and the impulse is

dependent of that atmospheric pressure and the mass of a human body [1]. As it will be shown in section 5.3, typical scaled impulse values for a 1 kilogram of composition B cylindrical charge will be between 0.25 and 1.35. The red line represents the limit scaled overpressure for these values of scaled impulse.

Elevation is a key factor to consider when blast overpressure is measured. With increasing altitude of both target and burst point, the over pressure at a given distance from an explosion of specified yield will generally decrease. At altitudes below 1,525 meters, the temperatures and pressures in the atmosphere do not change very much from the sea level values. If it is required to determine the air blast parameters at altitudes where the am-bient conditions are appreciably different from those at sea level, appropriate correction factors must be applied [2]. For the overpressure:

Where PS is peak overpressure at altitude and P1 is that at sea level. P0 is atmospheric pressure at alti-tude and Patm is that at sea level. The atmospheric pressure Patm at sea level is 101.35 kilopascals.

According to figure 1, the maximum value for scaled overpressure and any impulse with 100% survivability is 0.65. Additionally, it is recom-mended that a mass of 65 kilograms be used for adult males. It should be noted that the smallest bodies are the most susceptible to injury. Table 1 shows the overpressure values at different altitudes considering the atmospheric pressure.

Primary blast injuries occur most frequently in air-filled organs, and result from blast wave dynamic pressure changes at air-fluid interfaces. For this reason, peak overpressure values that a person can undergo decrease with altitude. However, accord-ing to equation (1), the overpressure generated by an air blast decreases with the altitude as well.For example, considering an elevation of 3,650

Figure 1. Pressure-Impulse percent survivability curves.


Blasting and FragmenationVol. 9, No. 1, 2015

meters, the estimated value for the atmospheric pressure is 60.05 kilopascals. According to these parameters, the estimated value for overpressure with 100% survivability is 39.02 kilopascals. Al-though the overpressure produced by an air blast decreases with altitude, peak overpressure values that a human can undergo decrease with altitude as well.

In conclusion, for ensuring 100% survivability, a ratio value between peak overpressure and atmo-spheric pressure under 0.65 is required.

2.2. Secondary Blast DamageSecondary injuries are caused by fragments pro-pelled by the explosion. These fragments can be divided into two categories: primary fragment and secondary fragment. Primary fragments are nor-mally small, high-speed fragments which cause injury by penetration and perforation. Secondary

fragments are normally larger and have less veloc-ity upon impact and can cause non-penetrating blunt trauma [1].

Figure 2 contains fragment impact damage crite-ria as presented by Ahlers 1969 [3]. The percent-age next to a particular curve denotes the percent of people (for a large sample) that would die if subjected to any of the impact conditions detailed in the curve. The serious injury threshold curves in figure 2 specify the debris velocity and weight combinations below which no serious injuries are expected to occur.

An estimation of possible fragment weights and velocities will be theoretically developed in section 3.2 so one can estimate the potential fragment hazard for different explosion situations.

Table 1. Peak overpressure with 100% survivability for different altitudes.

Figure 2. Personnel response to fragment impact.

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2.3. Tertiary Blast DamageTertiary blast damage involves whole-body dis-placement and subsequent decelerating impacts due to the interaction with blast overpressures and impulses. Although it depends on different factors such as type of surface impacted or the area of the body involved, the worst case scenario is assumed considering only impacts between the head and a hard surface such as concrete. Thus, translation damage criteria are based on skull fracture as it is shown in figure 3[1].

Figure 3 contains the pressure-scaled impulse combination required to produce the velocities for various expected percentages of skull fracture at sea level. Changes in the curves for other altitudes are negligible. Impact velocities fewer than 3 me-ters per second are considered mostly safe.

Limit overpressure values for 100% survivability at different altitudes are represented by the red lines. The green range represents typical scaled impulse values considering 1 kilogram composition B air burst and an adult male weight of 65 kilograms.

3. Blast Shield CalculationsIt is critical for the design of the shield to consider all possible loads that it may be subjected to. The loads in our analysis will be those resulting from

the detonation of a 1 kilogram charge of Compo-sition B with a number 8 detonator. These blast loads will be divided into pressure loading and fragmentation loading. The first one will be de-termined according to analytical prediction per-formed by ConWep and the second one will be calculated using theoretical equations.

3.1. Pressure Range EstimationThe pressure range estimation is calculated using ConWep which performs a variety of conventional weapons effects calculations, including an assort-ment of airblast routines, fragment and projectile penetrations, cratering, and ground shock [4].

Figure 4 shows the pressure values originated by a spherical free-air burst of 1 kilogram of Composi-tion B at sea level. This situation represents the charge resting on the ground and it is the worst case scenario for the overpressure analysis which is no casing that would absorb part of the explosion energy.

According to table 1 and figure 4, a person placed 5 meters away from the 1 kilogram Composition B charge has a percent of survivability of 100% against the blast load at sea level. This distance re-mains invariant for all altitudes because the peak

Figure 3. Pressure – Impulse skull fracture curves.



overpressure produced by the air burst and the overpressure that a human can undergo decreases at the same rate according to equation (1) and table 1.

Although a blast shield is designed for worst case scenario, hearing and eye protection are always mandatory according to OSHA 29 CFR Part 1910 regulations. In the following sections, the attenua-tion provided by the blast shield will be estimated according to the numerical model.

3.2. FragmentationSignificant damage in accidental explosions is caused by the impact of fragments which were generated during the explosion and hurled against receivers at high speed. Fragments from equip-ment or machinery in contact with or very near

a detonation explosive charge can be acceler-ated to very high velocities and pose a threat to nearby personnel and equipment.

3.2.1. Fragment Initial VelocityThe Gurney Equations are a range of formulas used in explosives engineering to predict how fast an explosive will accelerate a surrounding layer of metal or other material when the ex-plosive detonates. This determines how fast primary fragments are released on detonation. This initial fragment velocity can then be used with other ballistic equations to predict either danger areas or fragment penetration [5]. The

equation for cylindrical charge is as follows (2):Two different types of casing are considered in or-der to compare their effects in the fragmentation loading. First, a 13.5 kilograms steel casing re-ferred as “heavy casing” and second, 0.7 kilograms aluminum casing referred as “light casing.”

Calculations using equation (2) are performed for 1 kilogram cylindrical charge of Composition B using the two types of casing discussed above. The Gurney constant for Composition B is 2774 m/s.

Figure 4. Pressure vs. Range in a spherical free-air burst of 1 kilogram of Composition B at sea level.

Table 2. Estimated initial fragment velocity for heavy and light casings.

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3.2.2. Fragment Mass DistributionUpon detonation of an encased explosive, the cas-ing breaks up into a large number of high velocity fragments. The destructive potential of these frag-ments is a function of their kinetic energy distri-bution. Therefore, through testing or analysis of the velocity and weight of the worst case fragment must be determined and utilized as a design crite-rion for fragment shields [1].

The Mott equation yields estimates of the frag-ment mass distribution resulting from the high order detonation of an evenly distributed explo-sive within a uniform thickness and naturally frag-menting cylindrical casings. The average fragment weight derived from Mott equation is as follows:

The Mott scaling constant for Composition B is 8.5678e-4. The casing thickness is 16.08 millime-ters for heavy casing and 3.18 millimeters for light casing. The average fragment weight for both cas-ings is calculated as follows:

According to the Mott equation, the average frag-ment weight calculated implies that 75.7% of all primary fragments generated by the detona-tion have weight less than the overall average. For design purposes, a confidence level (CL) where 0<CL<1 can be defined as the probability that the weight, Wf, is the largest weight fragment released. For CL<0.9999, the equation is as follows:

A confidence level of 0.9 is employed and the maximum fragment weights for heavy and light casings:

3.2.3. Fragment Size DistributionIn order to determine the damage potential of primary fragments, it is necessary to evaluate the caliber, density, and shape of the fragments, as well as the previously described weight and velocity. From the mass of the fragment and shape of the containment vessel, one can estimate the size of in-dividual fragments. The influence of the fragment weight to the fragment diameter ratio is expressed in terms of the caliber density (D) of the fragment which is defined as the total fragment weight Wf

divided by the fragment diameter (d). Addition-ally, a standard fragment with mild nose shape is used for the calculations. The standard fragment is generally considered appropriate for use in design since: (a) only a small number of fragments will strike the structure nose-on: and (b) only a small fraction of these fragments will have more severe nose shape than the standard fragment [1].

Figure 5 shows the shape and parameters for a standard fragment shape where n is the caliber ra-dius of tangent ogive of fragment nose; N is the nose shape factor; Wf is the total fragment weight; D is the caliber density for a standard fragment; and A is the cross sectional area.

According to figure 5, estimations of the fragment cross sectional area A are performed using the pre-



vious fragment weights estimations. The average fragment cross sectional area for both casings is calculated:

Additionally, the same calculations are performed for the estimation of the maximum fragment cross sectional area using the maximum fragment weight estimation for heavy and light casings:

3.2.4. Fragment Range EstimationThe fragment dispersion generated by an explo-sion may have a lethal effect. For this reason, the fragment range prediction is performed and ap-plied as design factor. This prediction is performed

according to the previous fragment hazard analy-sis. Figure 6 represents the limit fragment impact velocity below the serious injury threshold for the maximum fragment masses estimated before for heavy and light casings.

Considering the information provided by figure 6 about the fragment damage, 45 meters per second impact fragment velocity with no serious risk is estimated for the heavy casing and 74 meters per second for the light casing. A reduction in frag-ment velocity will result from the drag applied by the medium though which the fragment travels. This velocity attenuation can be calculated from:

Figure 5. Standard fragment shape.

Figure 6. Limit impact fragment velocity for non-serious injuries.

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According to equation (5), one can estimate the distance at which a fragment cannot produce seri-ous injuries. Figure 7 shows the fragment velocity attenuation from drag for both types of casing and table 3 shows the hazard range for a maximum estimated fragment generated by the heavy and light casings.

Figure 7. Fragment velocity attenuation from drag.

3.3 Factor of Safety AnalysisThe factor of safety is a term describing how much stronger the system is than it usually needs to be for an intended load. Loading may be static, impact, fatigue, wear, etc. The purpose of using a safety factor is to assure that the design does not fail in the event of unexpectedly high loads or the presence of material defects. Examples of unexpected high loads might be higher fragment

mass than predicted or sharp nose fragments with higher penetration capacity. Additionally, materi-als defects as micro cracks might be produced due to a continue exposure to extreme weather condi-tions or accidental impacts against the design dur-ing the operations.

In our particular case, this factor of safety will be estimated according to a possible fragment pen-etration. Its value will be predicted on the basis of estimated variations of four different measures that are involved in the process: shield material, shield geometry, blast loads, and desired reliability [6]. The better known the material properties of the shield and the fragmentation loads, the closer the factor of safety should be to 1. The simplest way to present this technique is to associate a value greater than 1 with each of the measures and de-fine the factor of safety as the product of these four values:

FS + FSmaterial · FSgeometry · FSloads · FSreliability

Ullman 1986 [6] developed a guideline by break-ing down the rules given in textbooks and hand-books into the four measures and cross checking the values with those from statistical methods. Ac-cording to those criteria, the next factors of safety are chosen for the shield calculations:

Table 3. Serious injury range for heavy and light casing.

Table 4. Factor of safety values.



The resultant factor of safety is:

Factor of Safety = 1.98 ≈ 2

Considering this value and according to the defi-nition of factor of safety, the fragment resistant capacity of the blast shield must be always at least two times bigger than the possible fragment load. This means that the allowed fragment penetra-tion will be always less than half of the shield total thickness. This phrase in terms of ratio would be expressed as follows:

Blast Shield ThicknessFactor of Safety = ≈ 2 Fragment Penetration

3.4. Barrier Thickness RequirementsBarrier thickness requirements are performed based on fragment penetration. Fragment penetra-tion is calculated using ConWep. Different curves are obtained depending on fragment weight; frag-ment initial velocity and impacted material. For our studies, hardened steel will be used as barrier material.

Each type of casing generates different fragment sizes with different initial velocities. Thus, we pro-ceed to analyze the penetration produced by the average fragment and the maximum fragment es-timated for each case. Considering a 12.7 millime-ters hardened steel shield, one can determine the range at which the blast shield must be placed. A recommended safety factor of 2 is applied, allow-ing maximum penetrations of 6.35 millimeters for the shield. These limits will be represented as a green line in each of following graphs. According to the Gurney Equation (2), the initial velocity of the fragments generated by steel heavy casing is 740.9 meters per second.

According to the Gurney Equation (2), the initial velocity of the fragments generated by light alumi-num casing is 2,528 meters per second.

The steel heavy casing shows a lower initial frag-ment velocity but higher fragment weight. The light aluminum casing shows a higher initial frag-ment velocity but lower fragment weight. In both cases, the same energy from the explosion is trans-

Figure 8. Heavy Casing - Penetration in millimeters into hardened steel by average fragment 4.094 g at 740.9 m/s.

Figure 9. Heavy Casing - Penetration in inches into hardened steel by maximum fragment of 10.85 g at 740.9 m/s.

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ferred to the casings but the differences in frag-ment velocities and weights can be observed due to the different thicknesses and failure modes of the steel and aluminum.

4. Blast Shield Design Geometry. The geometry for this design was select-ed in order to direct possible overpressure away from the persons sheltered behind the blast shield. When designing the angles of the blast shield, it is

critical to consider the constructive interference that can form from refraction of a shock wave off a surface. The blast shield weighs approximately 1,590 kilograms. Additionally, the shield could be attached to the trailer using angle iron with multi holes at the bottom of the frame for bolting to the trailer.

Materials. The blast shield is constructed primar-ily of 12.7 millimeters AR400F plate. AR400F is a through-hardened, abrasion-resistant plate with

Figure 11. Light Casing. Penetration in inches into hardened steel by maximum fragment of 0.5458 g at 2,528 m/s.

Figure 10. Light Casing. Penetration in inches into hardened steel by average fragment of 0.2059 g at 2,528 m/s.

Figure 12. Blast shield mounted on a trailer.



a nominal hardness of 400HBW. This product is intended for applications where a good combina-tion of abrasion resistance, formability, and weld-ability is desired. The window of the blast shield is made of 25.4 millimeters thick LEXGARD® MP1000 laminate. LEXGARD® MP1000 lami-nate is a four-ply polycarbonate laminate primar-ily developed for security protection. It combines dependable ballistic protection and exceptional abrasion resistance. Material shall have a flexural strength not less than 93,080 kPa (ASTM D790); 72% light transmission (ASTM D1003). Material shall be a total thickness of 25.4 mm ± 5%. Mate-rial shall have an abrasion resistance surface to im-prove service life performance, and must conform with ICBO, BOCA, and SBCCI Model Building Codes as an Approved Light-Transmitting Plastic with a C1 (CC-1) flammability.

5. TestingA total of eight tests were conducted at the Explo-sive Research Laboratory (ERL) site of the Colora-do School of Mines on November 10th and 11th, 2014. The ERL is a 2000 acre property in Idaho Springs, Colorado. The laboratory consist in one primary test site for up to 20 kilograms of explo-sives per delay; and four secondary test sites for charges of 0.5 to 2.5 kilograms per delay. Support facilities include type I & type III magazines with

multiple explosives and initiation systems avail-able. Data collection capabilities include: fiber optic VOD measurement, high speed imagery, air overpressure measurement, strain measurement, x-ray radiography, and ground vibration and air blast monitoring.

All testing was conducted in ERL blasting pit at an elevation of 2,450 meters. The weather condi-tions were cloudy with light snow, temperatures between -12 to -6 degrees Celsius, and humidity from 20 to 90 percent. In the experimental design, 4 transducers where placed offset from the detonation source. Trans-ducer 2 and 4 where placed 5 meters from the point of initiation, transducer 1 at 7.5 meters, and transducer 3 was placed 9 meters from the detona-tion source. The blast shield was placed 7 meters from the detonation site. Blast data was collect-ed by the pressure gauges to determine the peak overpressure and the duration of the shockwave acting upon the blast shield. A total of eight test where performed using 1 kilogram Composition B placed within two different types of cylindrical projectiles: CIL Orion [7] and DeltaLancer [8]. These two projectiles were tested using four dif-ferent configurations: bare projectile, cased pro-jectile, tilted projectile, and cased and tilted. A 3.2 millimeters aluminum tube was used as light

Figure 13. Blast shield interior.



casing in all the experiments. Future testing will be performed using steel heavy casing in order to determine its effects.

5.1. Test SetupFigure 14 and figure 15 show the position of the blast shield, pressure transducers, and cameras relative to Ground Zero (GZ) in the test arena. The charge was hung 1 meter above the ground by a rope hanging from a metal support struc-ture. The pressure transducers were placed one

meter above the ground and pointed towards GZ. A steel blast shield was placed in the arena in or-der to observe its performance during the tests. A Phantom V711 camera was used for the close-up views of the charge detonating while a Photron High Speed Camera was used for an overview of the entire arena. The pressure transducers were PCB 137 series free air pressure transducers.

Tests 1 through 4 were the CIL Orion type with the axis oriented vertically. Test 5 was the Delta-Lancer type also with the axis oriented vertically. Test 6 had the CIL Orion tilted in the plane par-allel to the face of the shield. Test 7 and 8 had the DeltaLancer projectiles similarly tilted. Tests 4 and 8 had a 0.7 kilograms aluminum casing around the charge.

Figure 15. Experimental test site.

Figure 16. DeltaLancer (left) and CIL Orion (right) suspended 1 meter above the ground.

Figure 17. DeltaLancer suspended 1 meter above the ground with 45 degrees elevation and cased within an aluminum tube.

Figure 14. Experimental test setup.



5.2. Test ExecutionA Phantom V711 camera was used for the close-up views of the charge detonating while a Photron high speed camera was used for an overview of the entire arena. The pressure transducers were PCB 137 series free air pressure transducers. Figures 18 to 20 show different instants captured by the high speed camera during the test execution.

Figure 18. Test execution with casing (instant 1).



A particular effect is observed on the shield in fig-ures 19 and 20. When aluminum fragments from the casing impact the shield, the oxidation of the aluminum takes place. The surface of aluminum metal is covered with a thin layer of oxide that helps protect the metal from attack by air. So, nor-mally, aluminum metal does not react with air. If the oxide layer is damaged, the aluminum metal is exposed to attack. Aluminum will burn in oxygen with a brilliant white flame to form the trioxide aluminum (III) oxide, Al2O3. Future testing will be conducted in order to validate fragment ve-locities and masses for heavy and light casing, as well as penetration depths reached by both type of fragments.

Figure 21. Aluminum fragment imprints after the test with casing.

Figure 22. Aluminum fragment imprints after the test with casing.



5.3. Data CollectionTable 5 shows the values of peak overpressure and impulse obtained in the eight different tests per-formed with different projectiles, casing and ori-entations.

6. Numerical ModelA numerical simulation is performed using AN-SYS Autodyn in order to predict the pressure at-tenuation provided by the blast shield. ANSYS Autodyn software is an explicit analysis tool for modeling nonlinear dynamics of solids, fluids and gases as well as their interaction. It is a versatile explicit numerical tool providing advanced capa-bilities backed by first-class support [9].

6.1. Model SetupA 1 kilogram cylindrical charge is built in order to emulate the DeltaLancer projectile used during

the test executions. The initiation point is placed at one of the ends of the charge.

Figure 23. Cylindrical charge model (top) and Del-taLancer (bottom).

Table 5. Test data collection sorted by distance.



An Euler space is built and filled with atmospheric air and the cylindrical charge in order to simulate a cylindrical air burst and create a remapping file.

Figure 25 shown the importance of the orienta-tion of the charge in the case of cylindrical charg-es. The higher values of overpressure are radially produced from the charge axis. For this reason, the charge will be placed with its axis parallel to the shield front surface in order to model the worst case scenario for the overpressure loads.

Next, a new Euler space is created and filled with atmospheric air, the geometry of the shield and the air burst remapping file. The shield geometry

constitutes an unused lagrangian body which suf-fers the overpressure generated by the cylindrical airburst.

The center of the explosion is placed 1 meter over the ground level with the axis of the charge ori-ented vertically. The blast shields are placed 5 me-ters away from the center of the explosion with 3 theoretical gauges inside the shield and one extra gauge outside the shield. The three interior gauges are placed at different elevations in order to mea-sure the overpressure suffered by the critical body parts for this type of blast loading: head, lungs, and intestines.

Figure 24. Cylindrical charge setup.

Figure 25. Pressure contour generated by the cylindrical charge (cycle 449).



Figure 26. Numerical model general setup.

Figure 27. Detailed view of different setup parameters.

Figure 28. Conceptual overpressure view before impacting the shield (cycle 389).



6.2. Simulation ResultsThe results of the four different gauges are pre-sented in the following graph. Notice that the ver-tical scale represents total pressure:

Figure 29. Pressure vs. time lectures provided by the five gauges.

The higher overpressure value is measured by gauge number 3 which is placed at an approxi-mately intestine location. As it is shown in fig-ure 29, the difference between the overpressure outside and inside the shield is 60.2 kPa, which means that, according to the numerical model, the blast shield provide an attenuation of approxi-mately 75 percent at 5 meters from the center of the explosion.

6.3. Model ValidationIn order to validate the information provided by this numerical model, one can compare the over-pressure measured at 5 meters in the experimental test and the numerical model. Future testing will be conducted in order to validate experimentally the attenuation provided by the shield placing pressure sensors within it. In this analysis, the ac-curacy of the numerical model versus the experi-mental results is measured using the percent error between the experimental and theoretical gauges at 5 meters from the air burst. The percent er-ror in some data is the discrepancy between an

exact value and some approximation to it [10]. Given some value pexperiment and its approxi-mation pmodel, the percent error (6) is as follows:

The percent error is calculated using average val-ues from the experiment and the predicted value from the model. These average values are obtained by the arithmetic mean [11] which formula (7) is as follows:

The average experimental overpressure measured during the experimental testing by transducers 2 and 4 placed located at 5 meters from the charge is 55.65 kPa. Considering an elevation of 2,450 meters at the ERL, the corrected overpressure at sea level is:

According to the gauge number 4 placed at 5 me-ters in the model, the value of pressure measured during the simulation is:

The percent error of the numerical model at 16 feet obtained using the equation (6) with average experimental values is:

7. ConclusionsEach accident situation has its own unique envi-ronment with trees, buildings, hills, and various topographical conditions which may dissipate the energy of the blast wave or reflect it and amplify its effects on individuals. Therefore, this paper shows how a blast shield is able to provide the lev-el of safety required against the hazards involved during blasting operations according to worst case scenarios.



Even though, all the calculations are performed for a specific weight of high explosive (1 kilogram of Composition B), the analysis developed within this document can constitute a reference for simi-lar estimations considering variations in the net weight of explosives, casings and environmental conditions.

Future work will be performed by the AXPRO Group in order to study the fragmentation phe-nomena and shield attenuation through experi-mental testing. This work will implemented in the Explosive Research Laboratory (ERL) and it will be focused on the validation of theoretical, analyt-ical and numerical calculations developed in this document.

8. AcknowledgmentsThe recommendations and conclusions contained in this report are the result of a collaborative ef-fort by members of the AXPRO group and other recognized authorities in the explosives field. The following individuals provided input, technical oversight and reviewed and approved this paper:

• Dr. Vilem Petr, AXPRO Team leader and Re-search Associate Professor. • Tyler Weldon P.E., CDOT Avalanche Control Administrator.• Amanullah Mommandi P.E., Head of CDOT Research.• David Reeves P.E., CDOT Research.• Steve Beggs, Program Manager AT-Solutions, Inc.• Scott Narreau, CO State Explosives Inspector.• Matthew Traver, Senior Special Agent, ATF.

This project would not have been possible without the support of Kyle Lester, Tyler Weldon, James Walker and the rest of the CDOT team. Special thanks also go to Ray Johnson, Susan Rainey, Bob Lynch, and the rest of the AXPRO team. Last, we appreciate the support provided by the Min-ing Engineering Department at Colorado School

of Mines for the use of the Explosives Research Laboratory at Idaho Springs.

9. References[1] U.S. Department of Energy, Albuquerque Operations Office, Amarillo Area Office, 1981, “Manual for the predic-tion of blast and fragments loadings on structures”.

[2] United States Department of Defense and the Energy Re-search and Development Administration, 1977, “The Effects of Nuclear Weapons”, Chapter III, Air Blast Phenomena in Air and Surface Bursts.

[3] Ahlers, E.B., ”Fragment Hazard Study”, Minutes of Elev-enth Explosives Safety Seminar, Vol.1, Armed Services Explo-sives Safety Board , Washington DC, September 1969.

[4] Hyde, David W. ARMY ENGINEER WATERWAYS EXPERIMENT STATION VICKSBURG MS STRUC-TURES, “Microcomputer Programs CONWEP and FUN-PRO, Applications of TM 5-855-1, Fundamentals of Protec-tive Design for Conventional Weapons”.

[5] UN SAFER GUARD, 2013, “International Ammunition Technical Guideline”, Formulae for ammunition manage-ment.

[6] David G.Ullman, 1986, “The Mechanical Design Pro-cess”, Second Edition, The classical rule-of-thumb for Factor of Safety.

[7] CIL Orion, 2014, “Classic Snowlauncher System Load-ing Procedures”.

[8] http://www.delta-k.co.uk/Pages/DeltaLancerProjectileT-mp.aspx

[9] ANSYS Autodyn, http://www.esss.com.br/pdf/auto-dyn-11.pdf

[10] Merigo, Jose M.; Cananovas, Montserrat (2009). “The Generalized Hybrid Averaging Operator and its Applica-tion in Decision Making”. Journal of Quantitative Meth-ods for Economics and Business Administration 9: 69–84. ISSN 1886-516X

[11] Golub, Gene; Charles F. Van Loan (1996). “Matrix Computations – Third Edition. Baltimore: The Johns Hop-kins University”, Press. p.53. ISBN 0-8018-5413-X.

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Design and Testing of Blast Shields for Different Blasting Applications.

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