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UNPUBLISHED Security Engineering in Iraq
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Lessons Learned in Security Engineering in Iraq
by MAJ Bart Kemper, PE
Three years after the invasion of Iraq there are still lessons to be learned in security
engineering to counter the Anti Iraqi Forces (AIF). As the fight shifted from war fighting to
counter-insurgency, the primary security threat to bases and outposts shifted from coordinated
armed attacks to an adaptive insurgency currently using snipers, indirect fire, and Improvised
Explosive Devices (IEDs.) This has resulted in significant lessons learned, particularly in
material quality, ballistics and blast mitigation. These lessons must not only be understood, but
be the building blocks for future lessons as the enemy continues to adapt as well as carrying the
fight to other regions.
What is Security Engineering?
Security engineering is a fusion of security practices and engineering science. Just as the
combat engineer has to understand armor, infantry, and artillery tactics to be effective in a
combined arms battlespace, security engineering requires understanding some of the basic
premises of security:
*Given enough time and resources, any security system can be overcome. The AIF are
an adaptive enemy and try to develop countermeasures to our security measures. No security
measure should be considered the final answer to this threat and all security measures should be
continuously evaluated and improved upon.
*Successful security measures make it more difficult to breach than the opposition
perceives worth trying. This is a protective principle that doesn’t eliminate the threat, only shifts
it to a less protected target.
*Successful security measures forces the opposition to break their protective profile
before they can act. This is a pre-emptive principle that allows active measures to engage the
threat on better terms. Effective vehicle traffic controls makes it easier for overwatching forces
to identify Vehicle Borne IED drivers and engage the VBIED with greater standoff. Another
example is forcing the AIF to use more manpower and weapons to mount an effective attack
against a facility, as marshalling those resources can be detected and interdicted more easily than
a smaller force’s preparations.
These security concepts, once implemented, are bound by engineering principles:
*Understand the assumptions. All engineering solutions require assumptions, ranging
from the type of load, to strength of material, to the way the environment effects the final design.
Act outside of these assumptions and the design could fail.
*Know the project’s limitations and constraints. Engineering often requires a balancing
act of competing issues such as cost, durability, and effectiveness. It would be technically
possible to build a base as secure as Colorado’s nuclear-proof Cheyenne Mountain facility, but
the resources aren’t available. Understanding the resources available and the commander’s
priorities are critical for a successful engineering solution.
*All hazards cannot be eliminated by design. Warn the user of the residual risk so the
remaining hazards are understood and mitigated by other means if possible. For example, if it’s
determined it’s not cost effective to harden all structures on the FOB against VBIED attacks, the
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security planner mitigates the risk by using operational means such as searching vehicles to
prevent a VBIED from entering the FOB in the first place.
Standoff is your friend
There are three main threats by hostile action in Iraq: blast, fragments, and bullets.
Bullets generally require they see you to be effective, and if they can shoot you, usually you can
shoot them. Body armor, vehicle armor, concrete barriers, and sandbags can reduce most of the
threat from small arms. Most bases are secure from direct fire weapons by distance or T-barriers.
Fragments can be stopped with generally the same methods as small arms, whether the fragments
are due to indirect fire or IEDs. T-wall and sandbags are very effective in protecting billets,
offices, dining facilities, and other areas from fragments.
Blast, however, is more difficult to mitigate. Fragments may put holes in a concrete Twall, but blast can turn the entire T-wall into a giant buckshot burst. Body armor does little
against blast effects compared to bullets or fragments. Blast can cause damage even behind a
target. Different materials respond to blast differently.
However, blast also reduces exponentially as it travels. Fragments and bullets remain
deadly for far greater ranges, generally flying away from the blast until they hit something and
stop. For example, a 3.5 pound charge of TNT creates a 544 psi reflected pressure on a target at
5 feet. To have the same pressure at 20 feet, it would take 220 pounds of TNT.
These equivalent pressures do not result in equivalent damage. Blast is due to the charge
being converted into rapidly expanding gas. The larger the charge, the more energy released.
The 220 lbs of TNT at 20 feet can breach almost 9 inches of 4500 psi concrete, but the 3.5 lbs at
5 feet can only breach 1.5 inches, just as a tack hammer and a 10 pound sledge hammer hitting
same object at the same speed have different effects. Breaching concrete not only create a hole
through the structure but also a deadly shower of high velocity concrete fragments, potentially
creating a greater threat than the charge by itself depending on the charge, distance to the wall,
wall thickness and concrete strength.
The key is standoff. Double the distance of the 220 lbs of TNT to 40 feet and it can
breach less than 5.5 inches. At 300 feet away an inch thick slab of 4500 psi concrete would not
be breached. Close the standoff to six feet and the 220 lbs will breach over 19 inches and require
over 40 inches to prevent the wall from spalling, or having concrete break away, possibly
dangerously, from the non-blast side. Compare this to fragments or rifle bullets, which have
almost the same penetration at 300 feet as 6 feet. US Army Corps of Engineers Protective
Design Center (USACE PDC) provides the computer program CONWEP to calculate a wide
range of weapons effects on soils, concrete, wood, and other items.
Security engineering manuals, graphic training aids, and specialized software can provide
the needed standoff for a given charge. Unified Facilities Criteria 4-010-01, DoD AntiTerrorism for Buildings, provides guidelines for minimum standoff, including reduced standoff
distances if blast analysis shows it is acceptable. Understanding the assumed threat in this guide
is critical. UFC 4-010-02 is the addendum that specifies the threat charge or round. These threats
are less than the Central Command minimum threats. The local security professional should
specify the design threat based on local data, not less than the CENTCOM minimum threat. The
local engineer can then determine standoffs and other mitigations to provide the equivalent
protection in UFC 4-010-01. USACE PDC also provides the program BEEM to calculate
standoffs based on threat and type of structure.
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Standoff is not always available. For example, you need to get close to search a vehicle
for an IED. Therefore, in cases where standoff is not feasible for a task, the task should be
removed from other activities and a blast wall should be designed to absorb the blast and
shrapnel. Other times risk simply must be accepted, but it should be understood by the
commander and local personnel so contingencies for the risk are developed.
When sand isn’t sand
Sandbags are a common feature in Iraq. However, they are rarely filled with sand. The
silty soils common near most bases have anywhere between 1/3 and 1/5 the ballistic stopping
power of sand depending on the specific soil type, moisture, and projectile. For example, an
AK-47 has a muzzle velocity of 2330 feet/second. Allowing for some standoff and assuming an
impact velocity of 2250 feet/second, it takes a full foot of silty soil to stop the round while only
0.25 feet, or 3 inches, of sand to have the same effect. The need to account for soil properties is
true of any earthworks, including overhead cover, metal bins or HESCO concertainers.
Concrete is another common force protection material in Iraq. It is used in T-walls,
vehicle barriers, bunkers, guard towers, and other structures. Typical strength in the US, Europe,
and even Kuwait and Qatar is 4500 psi or greater after 28 days curing. Pre-Saddam Iraqi
structures also typically have comparable strengths. However, post-war issues with aggregates,
water, admixtures, and cement as well as weather effects often result in a fraction of strength.
This is particularly true if there are no military units or third party contractors testing concrete
batches using compresive strength machines and test cylinders. Based on material tests and field
tests, concrete strength is usually less than 2500 psi and can be as low as 500 psi.
Concrete strength is critical in force protection measures. Assume a single 155mm
artillery round, which is often used in IEDs and VBIEDs, at a distance of 10 feet. The 4500 psi
concrete must be five inches thick to prevent perforation and six inches thick to prevent spalling.
At 1500 psi, the wall must be 9.5 inches thick to prevent perforation and 10.75 inches thick to
prevent spalling. At 500 psi, which is very poor concrete with visible aggregate and rebar, it
would require over 19 inches to prevent perforation and over 22.5 inches to prevent spalling.
Large fragments perforating a 12 inch wall of this concrete would exit the other side traveling at
1890 feet per second, or 1290 mph.
Bricks, lumber, and steel also have quality issues affecting force protection. Some
batches of bricks turn to crumbs if dropped from shoulder level and would not stand up to even a
mild blast. Local construction often only put mortar in horizontal joints and not between the
sides of the bricks, weakening a structure against impact. Since the walls are often covered in a
smooth layer of mortar, this is not always apparent. If the lumber is rough cut and not marked, it
can have as little as a third of the strength of treated structural grade lumber. This affects
SEAHuts and wood-reinforced bunkers and roofs. This is particularly important using USACE
references and software since they use results based on testing these structures using structural
grade materials. Steel also has its challenges, with local welding typically having 70% to 25% of
the reliability of the unwelded section which could cause failure if subjected to blast loading.
Army Engineer Technicians (MOS 21T) are trained to evaluate construction materials.
They can develop quality control measures to test concrete and can work with local plants to
improve their strength. They can also perform field tests to estimate in-place concrete strength
and other materials.
As a rule of thumb for untested post-invasion concrete in Iraq, a 1500 psi strength can be
conservatively assumed if there are no visible defects. This can be checked by rapping the
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concrete with a hammer in several places. If the hammer consistently bounces back sharply with
no visible dents, its likely to be above 3000 psi. If it causes dents, chips, or small cracks, its
likely to be between 1500 and 3000 psi. If pieces containing several pieces of aggregate break
off it’s likely to be less than 1500. This test is an extremely rough field estimate and does not
take into account rebar design or strength, whether there are cracks or “soft spots” within the
structure, or other factors. The only way to reliably know the strength is by breaking sample
cylinders in a compressive test machine and inspecting the pours to ensure proper placement.
Protective Structures
Material property assumptions and design threat have to be considered when developing
protective structures using references such as the Joint Forward Operating Base (JFOB) Force
Protection Handbook or FM 5-34, Engineer Field Data. HESCO has their own construction
guidelines for use against different threats. These references have to make assumptions
regarding what materials are available. Summary tables and simplified Graphic Training Aids
do not state the assumptions. You have to read the references. It is up to the engineers to
understand these assumptions, know the local materials, and make the adjustments needed to
achieve the desired results or to advise the commander on what can be achieved and the
associated residual risk.
Overhead cover is a one of the common protective structures. Some of these are preengineered, such as the E-glass structures protecting large targets like dining facilities. Others
are field fortifications such as reinforcing bunker roofs against mortars using a bursting layer,
such as plywood, and a protective layer to stop the fragments. One of the assumptions, stated in
the JFOB handbook, is the incoming round is descending perfectly vertical and has a super-quick
fuse. This means there is no delay in detonating upon contact with the plywood and the majority
of the fragments are traveling to the sides and not down into the roof. Enemy rounds are usually
not well maintained, which can cause even what was a super-quick fuse to delay several
milliseconds. This would allow the round to penetrate the cover, increasing blast effects.
If the design protective layer is sand, more thickness is required for local soil. More soil
may require structural reinforcement to support the protective layer. Also, not all rounds have
super-quick fuses. Designs may need greater stand-off or thicker protection layers due to the
local threat and available materials. Many structures, such as billeting trailers and Containerized
Housing Units, simply cannot support enough sandbags to provide useful protection.
Rockets are another common threat. They do not come in vertically, but at an angle.
Because of this T-walls are required to be at least two feet taller than the protected structure in
order to intercept the rocket. The rocket will still detonate and endanger anyone on the impact
side of the wall. However, the wall prevents the rocket from striking the protected target and
causing catastrophic damage there. A development to address the two-level “stackable” trailers is
placing T-walls on bunkers. This elevates the T-wall so it can intercept the rocket, but it also
places the blast load in close proximity to bunker in addition to the tons of load from T-wall
itself. Analysis shows that the bunker is likely to fail due to the combined blast and structural
load, depending on the size of the rocket. These bunkers should not be used as shelters.
Costs
Cost is always a constraint. A sandbag may cost as little a 5 cents per bag in a pallet, but
local prices to have sandbags filled and emplaced by contractors is $1-$5 per sandbag using local
soils as fill. Importing sand is expensive and not often available, so more sandbags are needed to
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compensate for the silty soil. Sandbags also have a limited life, as little as 6 months in Iraq. A
possible solution is to use the Mil2 or Mil5 two-foot wide HESCOs. Two foot wide HESCOs
offer comparable protection as most sandbag walls with a much longer life. Another is using Twalls, which would also stop fragments. However, they may not be room for T-walls. The
distance between buildings and room available for emergency response and maintenance are also
constraints. Minimum clearances are specified in UFC 4-010-01.
T-walls may be commonplace, but not cheap. A single 13 foot tall by 10 foot wide Twall can cost $1100 at the plant, $500 to ship to the site, and $100 to emplace. Existing
substandard structures usually cannot be easily replaced due to budget constraints. Substandard
T-walls should be evaluated for what protection they can provide and placed accordingly.
Detailed engineering specification can improve the quality of new structures. If the
dimensions, rebar design, and concrete strength are specified in the contract and inspected, the
government can reject substandard items. Conversely, without detailed specifications the
government will have to continue to pay for whatever is delivered, even if it cannot perform as
needed. Specifications are not just to set the level of protection, but also to hold the contractor to
a measurable standard.
So how bad is it?
This seems like a lot of bad news. There have been cases where gravel and T-walls
produce more fragment than the incoming round itself. There have been VBIED attacks where
the vehicles broke through T-walls prior to detonation. Given the distance the truck had to
accelerate into the T-walls, the truck should not have broken through the walls if they were of the
USACE specification of 4500 psi or higher. These are real world problems..
However, the truth on the ground is the overall security engineering is working very well.
The AIF have been decisively defeated whenever they directly assault a base and now rarely try.
Indirect fires are sporadic with the enemy usually only having time to launch one or two rounds
due to effective counter-battery fire, air strikes, and reaction forces. Impacting rounds are
compartmentalized by T-walls and sandbag protection, isolating most of the damage to the
immediate vicinity of the point of impact where blast effects and high concentrations of
fragments are harder to mitigate. While there are many structures that do not meet the original
design intent, overall security is such the odds are a given wall or bunker will never be tested.
The question becomes what is the risk associated with that structure or system potentially failing.
Effective security engineering is a paradox. It’s difficult to tell the difference between
effective security that has discouraged enemy attack and ineffective security that simply hasn’t
been tested. Engineering is part of the entire security system. The engineers need design goals
and constraints from the security professionals, and the security professionals need solutions to
specific threats.
Three years in Iraq shows the AIF constantly adapts and seeks ways to exploit what is
already on the ground. Engineers have learned what’s in is not what was expected, particularly
in terms of materials. It is up to the security professionals and engineers to continually evaluate
their structures and systems against the evolving threat to ensure that they will be effective.
Knowing what a given threat can do and what the available resources can withstand are the
building blocks to make the most of what is on the ground and develop new counter-measures as
needed in Iraq and elsewhere.
-30-
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Resources (List or box insert)
HESCO Bastion (www.hescobastion.com)
DoD Anti-Terrorism Enterprise Portal (https://atep.dtic.mil/)
USACE Protective Design Center (https://pdc.usace.army.mil/)
Resources available from USACE PDC include:
UFC 4-010-01, -02 DoD Minimum AT Standards for Buildings
UFC 4-020-01 through -04 – Security Engineering (FOUO)
UFC 3-340-01 Design of Hardened Structures to Conventional Weapon Effects (FOUO)
Software tools such as CONWEP, BEEM, and others
MAJ Bart Kemper, PE is an Army Reserve engineer assigned to Det. 8, 412th ENCOM
supporting the 130th Engineer Brigade in Iraq. He has previously served in construction and
combat engineer units. Kemper has attended the USACE Security Engineering course and is the
detachment’s lead for structural, mechanical, and security engineering. He is also a civilian
consulting mechanical engineer whose practice includes mechanical design, blast analysis,
ballistic design, vehicle barrier design, and forensic engineering.
SECURITY ENGINEER CAPTIONS
All photos are Army photos by MAJ Bart Kemper
155mm 4500 psi – Output from CONWEP showing the velocity of a large shell fragment as it
passes through various thicknesses of 4500 psi strength concrete. The fragment is stopped about
5 inches.
155mm 1500 psi – Output from CONWEP showing the velocity of a large shell fragment as it
passes through various thicknesses of 1500 psi strength concrete. If the wall was only six inches
thick it would travel at over 1800 feet per second, or over 1200 mph. The fragment is stopped
about 9.5 inches.
AK-47 into silty soil – Output from CONWEP showing the how far a 7.62mm bullet from an
AK-47 would penetrate into silty soil based on impacted velocity. The AK-47 has a 2330 feet
per second muzzle velocity. With a 2250 feet per second impact velocity it would penetrate one
foot.
AK-47 into good sand – Output from CONWEP showing the how far a 7.62mm bullet from an
AK-47 would penetrate into dry granular sand based on impacted velocity. The AK-47 has a
2330 feet per second muzzle velocity. With a 2250 feet per second impact velocity it would
penetrate 0.25 feet, or 3 inches.
Blast 1 -- A rocket impacted in a living area, damaging several billets. The majority of the
fragments penetrating the trailer wall were gravel kicked up by the blast and pieces of concrete
from the t-wall. Point of impact is about where the airman with the camera is standing. The
crater had already been filled in.
blast 2 – Despite the degraded conditions of the sandbags, the sandbag wall prevented any
fragments from penetrating the trailer. The T-wall damage due to blast became fragments
striking the sandbags and trailer.
Brick wall1 – This wall was constructed on a Contingency Operating Base in 2004. The lack of
mortar in many of the vertical joints and poor quality of the horizontal joints weakens the wall
and makes it more vulnerable to blast effects.
Brick wall 2 – The inside of the building has been smoothed over with mortar, concealing the
poor quality of the brickwork and the potential hazard in the event of a blast.
Poor concrete (both) – This concrete has aggregate clearly visible with minimal cement holding
it together. Rebar is exposed. The concrete feels soft when struck with a hammer. The concrete
is estimated to have a 500 psi compressive strength and negligible tensile strength, indicating it
would shatter easily with a blast load. The poor cement/aggregate mixing gives the 12 inch wall
an effective thickness of 8 inches, further degrading its protective capacity.
Sandbags 1 year – These sandbags have deteriorated in about one year of exposure in Iraq. The
synthetic fibers in these sandbags deteriorate in direct sunlight and need to be replaced every six
months. Burlap bags tend to last longer but are more expensive. Sandbags were not meant for
long term use.
Sandbags – The sandbags are stacked to a minimum height of four feet above the floor of the
billets. This protects the soldier as they sleep. The sandbag wall was made wider to account for
the silty soil having less ballistic stopping power than sand, which was not available.
Sandbags-Hesco – Illustrates how a sandbag wall, designed to protect soldiers within their billets
from fragments, can be replaced by two-foot wide HESCO concerntainers.
Stacked – T-walls are placed on top of “SCUD Bunkers” to protect stacked billets from
incoming rocket attacks. T-walls are placed in front of the bunkers to prevent fragments from
entering the buckers. Due to the weight of the T-walls on top of the bunkers and the likely blast
loads if a rocket does strike the those T-walls, it is not recommended to shelter in these bunkers.
Twalls reinforcing sandbags. At this locations all of the billets are protected by two-foot thick
sandbag walls. These are sufficient to stop most bullets and fragments even with silty soil. The
T-walls further protect the billets and compartmentalize the area, primarily from fragments.
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