Introduction |
|
Millions
of acres of property in the world contain unexploded ordnance (UXO),
most of which is a result of weapons system testing and troop training
activities conducted. This property includes active military, formerly
used defense sites, post, pre-war, and battle area clearance sites.
The risks posed by property containing UXO could be great depending
on the types and amount of UXO present and how the property is or
may be used.
Those who use and manage property with UXO, as well as those responsible
for making decisions regarding the property, need information on
the risks presented by UXO, options for eliminating or reducing
the risks, and factors to be considered in the decision-making process.
This document summarizes the characteristics of UXO, safety procedures
which can be used on property that contains UXO, UXO risks and risk
assessments, options and technologies for reducing the risks, and
factors that should be considered.
|
Overview
of UXO |
|
"Explosive
ordnance" is any munition, weapon delivery system, or ordnance
item that contains explosives, propellants, and chemical agents.
UXO consists of these same items after they (1) are armed or otherwise
prepared for action, (2) are launched, placed, fired, or released
in a way that they cause hazards, and (3) remain unexploded either
through malfunction or design.
A person's ability to recognize a UXO is the first and most important
step in reducing the risk posed by a UXO hazard. This section presents
information on the most common types of UXO and how it may be found
in the field. |
Types
of UXO |
|
In
the past century, all shapes, sizes, and types of explosive ordnance
have been used in the world for weapons system testing and troop
training activities.
The following types of UXO are those most likely to be encountered:
• Small arms munitions
• Hand grenades
• Rockets
• Guided missiles
• Projectiles
• Mortars
• Projected grenades
• Rifle grenades
• Submunitions
• Bombs
Ordnance is color-coded during manufacturing for identification
purposes. However, color markings cannot be relied upon to identify
UXO — markings can be altered or removed by weather or exposure
to the environment. Instead, other features should be used to identify
UXO. The following sections describe the basic features and characteristics
associated with each general type of UXO. |
Small
Arms Munitions |
|
Small
arms munitions contain projectiles that are 0.5 inches or less in
caliber and no longer than approximately 4 inches. They are fired
from various sizes of weapons, such as pistols, carbines, rifles,
automatic rifles, shotguns, and machine guns.
Generally, the shell casings of small arms munitions are made from
brass or steel. Although the hazards associated with these UXO are
much less than for other munitions, unexploded small arms munitions
may explode if thrown into a fire or struck with a sharp object
such as a nail. Figure 1 illustrates various small arms munitions. |
 Figure
1. Small Arms Munitions |
Hand
Grenades |
|
Hand
grenades are small explosive- or chemical-type munitions that are
designed to be thrown at short range. Various classes of grenades
may be encountered as UXO, including fragmentation, smoke, and illumination
grenades.
All grenades have three main parts: a body, a fuze with a pull ring
and safety clip assembly, and a filler. Figure 2 shows typical grenades. |
 Figure
2. Typical Grenades |
Fragmentation
grenades are the most common type of grenade used. They have a metal
or plastic body filled with an explosive material. When the filler
explodes, the body of the grenade or a metal fragmentation sleeve
breaks into small, lethal, high velocity fragments. These grenades
use a burning delay fuze that functions 3 to 5 seconds after the
safety lever is released.
Other grenades may be made of metal, plastic, cardboard, or rubber
and may contain explosives, white phosphorus, chemical agents, or
illumination flares, depending on their intended use. Most use a
burning delay fuze that functions 3 to 5 seconds after the safety
lever is released, but some are activated instantly when the lever
is released (smoke grenades). |
Rockets |
|
A
rocket uses gas pressure from rapidly burning material (propellant)
to transport a payload (warhead) to a desired location. Rockets
can range from 11/2 to more than 15 inches in diameter, and they
can vary from 1 foot to over 9 feet in length. All rockets consist
of a warhead section, a motor section, and a fuze. They are unguided
after launch and are stabilized during flight by canted nozzles
at the base of the motor or fins attached to the motor. |
 Figure
3: Rocket Parts |
The
warhead section of the rocket is the portion that produces the intended
effect; it can be filled with explosives, toxic chemicals, white
phosphorus, submunitions, riot-control agent, or illumination flares.
Fuzes may be located in the nose of the rocket or internally between
the warhead and motor. The fuzing on rockets can be impact, time-delay,
or proximity fuzing. Impact fuzes function when they hit the target.
Delay fuzes contain an element that delays explosion for a fixed
time after impact. Proximity fuzes are intended to function when
the rockets reach a predetermined distance from the target.
Caution: Do not approach—proximity
fuzing may activate, causing the rocket warhead to explode. Also,
fired rockets may still contain residual propellant that could ignite
and burn violently. |
Guided
Missiles |
|
Guided
missiles are similar to rockets (see Figure 4); however, they are
guided to their target by various systems. Some are wired-guided,
and others are guided by internal or external radar or video. Guided
missiles are usually stabilized by fins controlled by internal electronics.
Internal proximity fuzes are used in guided missiles, which makes
approaching them extremely dangerous. Also, fired guided missiles
may still contain residual propellant that could ignite and burn
violently. |
 Figure
4. Guided Missile |
Projectiles |
|
Projectiles can range from approximately 1 inch to 16 inches in
diameter and from 2 inches to 4 feet in length. Projectile fuzes
can be located in the nose or in the base, as shown in Figure 5.
Like rockets, projectiles may be stabilized during flight by fins
or bands fixed around the circumference of the projectile. |
 Figure5.
Typical Projectiles |
Mortars |
|
Mortars
range from approximately 1 inch to 11 inches in diameter and can
be filled with explosives, toxic chemicals, white phosphorus, or
illumination flares. Mortars generally have thinner metal casing
than projectiles, but use the same types of fuzing and stabilization.
Figure 6 shows various types of mortars. |
 Figure
6. Typical Mortars |
Projected
Grenades |
|
The
most commonly used projected grenade is the 40 millimeter (40mm)
grenade. This grenade is also among the most commonly found UXO
items. The 40mm grenade is about the same size and shape as a chicken
egg, as shown in Figure 7. It contains high explosives and uses
a variety of fuzes, including some of the most sensitive internal
impact fuzing systems.
Because of their relatively small size, 40mm grenades are easily
concealed by vegetation. They are extremely dangerous and can explode
if moved or handled. |
 Figure
7. 40mm Grenades |
Rifle
Grenades |
|
Rifle
grenades look like mortars and range from about 9 to 17 inches in
length. They may be filled with high explosives, white phosphorus,
riot-control agent, illumination flares, or chemicals that produce
colored screening smoke. Rifle grenades are fired from standard
infantry rifles. They have an opening at the far end of a tube near
the fin assembly that allows the rifle grenade to be placed on the
barrel of a rifle.
Rifle grenades rely on impact fuzing, which is located on the nose
or internally behind the warhead. Figure 8 shows various types of
rifle grenades. |
 Figure
8. Rifle Grenades |
Submunitions |
|
Submunitions
include bomblets, grenades, and mines filled with explosives or
chemical agents. They may be antipersonnel, antimateriel, antitank,
dual-purpose, incendiary, or chemical submunitions. Submunitions
are typically spread over a large area by dispensers, missiles,
rockets, or projectiles. Each of these delivery systems disperses
the submunitions while still in flight, scattering the submunitions
over an area.
Submunitions are activated in a variety of ways, depending on their
intended use. Some are activated by pressure, impact, or movement
or disturbance. Others are activated in flight or when they come
near metallic objects. Some submunitions contain a self-destruct
fuze as a backup. The self-destruct time can vary from a couple
of hours to several days. Warning: Submunitions are extremely
hazardous because even very slight disturbances can cause them to
explode.
Some types of submunitions require stabilization to hit the target
straight on. Stabilization can be provided through an arming ribbon,
parachute, or fin assembly. Figure 9 shows a variety of submunitions. |
 Figure
9. Typical Submunitions |
Bombs |
|
Bombs
range in weight from 1 to 3,000 pounds (some specialised bombs may,
however, be larger) and in length from 3 to 10 feet. Generally,
all bombs have the same components—a metal container, a fuze,
and a stabilizing device (see Figure 10). The metal container, or
bomb body, holds the
explosive or chemical filler and may consist of one piece or multiple
pieces. |
 Figure
10: Low Drag Bombs |
Bombs
use either mechanical or electrical fuzes, typically located in
the nose or tail section, either internally or externally. Mechanical
fuzes are generally armed by some type of arming vane. The arming
vane operates like a propeller to line up all the fuze parts and
thus arm the fuze. The fuzes may be configured as impact, proximity,
or delay fuzes.
Bombs are stabilized during flight by fin or parachute assemblies
attached to the rear section of the bomb. These assemblies often
detach from the bomb after impact. |
Encountering
UXO |
|
UXO
is found in the environment in many different ways depending in
part on the specific type of ordnance, when and where it was deployed,
how it was deployed, and activities that may have taken place at
the location since deployment. For example, UXO can be at the ground
surface, can be partially buried, or can be fully buried. In fact,
UXO may be found at depths in excess of 30 feet below the ground
surface. Ordnance stabilized by parachute may be completely buried,
but the parachute may appear at the surface. UXO may also be found
fully intact or in parts or fragments. All UXO, whether intact or
in parts, presents a potential hazard and should be treated as such.
In addition, the UXO casing may have deteriorated depending on the
type of material used, the length of time since deployment, and
the elements to which it was exposed. UXO that has deteriorated
presents a particular hazard because it may contain chemical agents
that could become exposed.
UXO may be encountered as an isolated munition or as one of many
in a given area. The density and type of UXO in an area depends
on the intensity and proximity of troop training and weapons testing
activities, the degree of UXO cleanup already conducted, and the
types of ordnance used. For example, UXO such as dispensers, missiles,
rockets, or projectiles may still contain submunitions, or those
submunitions may have been scattered across a large area. If any
UXO is found, one should assume that other UXO is in the area. |
UXO
Safety and Reporting Procedures |
|
UXO,
whether present in an area by design or by accident, poses the risk
of injury or death to anyone in the vicinity. To lessen the danger
of UXO hazards and to help prevent placing others at future risk,
certain precautions and steps should be
taken by anyone who encounters UXO.
|
IF
YOU DID NOT DROP IT, DO NOT PICK IT UP! |
Safety
Procedures |
|
A
person can lessen the danger of UXO hazards by being able to recognize
the hazard and by adhering to the following basic safety guidelines:
-
After identifying potential UXO, do not move any closer to it.
Some types of ordnance have magnetic or motion-sensitive proximity
fuzing that may detonate when they sense a target. Others may
have self-destruct timers built in.
-
Do not transmit any radio frequencies in the vicinity of a suspected
UXO hazard. Signals transmitted from items such as walkie talkies,
short-wave radios, citizens' band (CB) radios, or other communication
and navigation devices may detonate the UXO.
-
Do not attempt to remove any object on, attached to, or near
a UXO. Some fuzes are motion-sensitive, and the UXO may explode.
-
Do not move or disturb a UXO because the motion could activate
the fuze, causing the UXO to explode.
-
If possible, mark the UXO hazard with a standard UXO marker
or with other suitable materials, such as engineer tape, colored
cloth, or colored ribbon. Attach the marker to an object so
that it is about 3 feet off the ground and visible from all
approaches. Place the marker no closer than the point where
you first recognized the UXO hazard.
-
Leave the UXO hazard area.
-
Report the UXO to the proper authorities (see Section 2.2).
-
Stay away from areas of known or suspected UXO. This is the
best way to prevent accidental injury or death.
|
|
UXO SAFETY WARNINGS
 When
you see UXO, stop. Do not move closer.
Never
transmit radio frequencies (walkie talkies, citizens' band radios).
Never
attempt to remove anything near a UXO.
Never
attempt to touch, move, or disturb a UXO.
Clearly
mark the UXO area.
Avoid
any area where UXO is located.
|
Reporting
Procedures |
|
Any
UXO discovered in the field should be immediately reported to site
Explosive Ordnance Disposal (EOD) personnel. If EOD personnel are
not present at the site, the military provost marshal or local law
enforcement agency should be notified. The appropriate authority
should initially be notified by telephone, with a written report
submitted later to document the UXO hazard. Ideally, the exact location
should be noted along with the type, condition, estimated size,
and distinctive features of the ordnance. |
UXO
Risks and Risk Assessments |
|
All
sites that contain UXO present some degree of risk. Furthermore,
many UXO sites are not marked or identified. Use caution in all
areas that are suspected of containing UXO. Do not rely on warning
signs and physical barriers. UXO risks may be evaluated in terms
of three main components or events: (1) UXO encounter, (2) UXO detonation,
and (3) consequences of UXO detonation (PRC 1996b). The first component,
UXO encounter, considers the likelihood that a person will come
across a UXO and will influence the UXO through some level of force,
energy, motion, or other means.
The second component, UXO detonation, is the likelihood that a UXO
will detonate once an encounter has occurred. Risk factors associated
with these two components are discussed below.
The third component, consequences of UXO detonation, encompasses
a wide range of possible outcomes or results, including bodily injury
or death, health risks associated with exposure to chemical agents,
and environmental degradation caused by the actual explosion and
dispersal of chemicals nuclear materials to air, soil, surface water,
and groundwater.
Generally, UXO risk evaluations take a conservative approach and
assume that the consequences of UXO detonation are serious injury
or death. |
Risk
Factors |
|
The
following factors influence the degree of acute risk associated
with UXO, particularly in terms of the likelihood of an encounter
and the likelihood of detonation: |
Factors
Affecting the Likelihood of an Encounter |
•
Amount or density of UXO on the property
• Depth of the UXO
• Size of the UXO
• Current and potential property use
• Accessibility of the property
• Topography
• Vegetation or ground cover
• Soil type
• Climate
|
Factors
Affecting the Likelihood of Detonation |
|
•
UXO fuze type and sensitivity
• Activities of individuals frequenting the property
|
These
factors are interrelated and cannot be evaluated singly to assess
risk. Each of the factors is discussed below. |
| Density
of UXO. |
The
greater the number of UXO in a given area, the greater the possibility
that a person will encounter UXO. Conversely, a low UXO density
decreases the possibility that a person will encounter UXO. Density
is mainly determined by the type and quantity of ordnance used
in a particular area. For example, areas with submunitions may
have a higher UXO density than areas with other types of UXO.
Density can also be affected by soil type and climate, as discussed
later.
|
| Depth
of UXO. |
Individuals
are usually more likely to encounter UXO that is on the ground
surface or is partially buried than UXO that is fully buried.
For buried UXO, the
likelihood of an encounter depends on the activities conducted
at the site. Activities that could disturb the subsurface UXO
include shallow digging, trenching, plowing, and construction,
among others. Furthermore, UXO that is buried above the frost
line may eventually migrate to the surface (see climate).
|
| Size
of the UXO. |
The
size of a UXO influences whether it will be seen. Because large
UXO is more visible than small UXO, a person would be more likely
to see and avoid contact with large UXO.
|
| Current
and potential property use. |
Property use that increases the number of individuals on a property
increases the likelihood of a UXO encounter. For example, UXO
is more likely to be encountered by a person on property used
for recreational purposes (such as hiking, hunting, or camping)
than on property used for grazing or as a wildlife preserve. In
general, the larger and deeper the area disturbed by property
use activities, and the greater the force associated with those
activities, the greater the likelihood that a UXO will be encountered
and detonated.
|
| Accessibility
of the property. |
The
accessibility of an area will affect the number of people who
would enter the property and encounter UXO. For example, an unfenced
area near a road would be more accessible than a remote, fenced
area, increasing the likelihood of an encounter with UXO.
|
| Topography.
|
Topography
also influences the number of people likely to access a site,
as well as the amount and type of property use. People are more
likely to enter flat property near populated areas than remote
property with a rugged terrain. In addition, topography influences
where UXO may concentrate. UXO is more likely to migrate to valleys
and depressions through surface water movement and soil erosion.
|
|
Vegetation and ground cover. |
Heavy
vegetation and ground cover may conceal even large surface UXO;
however, it may also limit access to an area, preventing potential
UXO encounters.
|
| Soil
type. |
Soil
type influences the depth to which UXO may penetrate as well as
whether the fuze will activate. Some fuze types require a substantial
impact before they will activate. If the munition lands in mud
or fine soil, the fuze may not activate as designed. Site conditions
such as these may in turn increase the likelihood and density
of UXO. Some soils are also more easy to penetrate than others,
and as a result, UXO in soft soils may be found at greater depths
than expected.
|
| Climate.
|
Climate
affects the surface migration of UXO, the visibility of UXO, and
the migration of buried UXO to the surface. Climates with heavy
precipitation and high winds are more likely to cause UXO to migrate
through surface water movement and soil erosion, and snow cover
may conceal surface UXO. Finally, climate affects the depth of
the frost line and freeze-thaw cycles. In general, the colder
the climate, the deeper the frost line and the greater number
of UXO that may migrate to the surface. Similarly, the greater
the number of freeze-thaw cycles over an extended period of time,
the sooner UXO may migrate to the surface.
|
| UXO
fuze type and sensitivity. |
In
very general terms, magnetic and proximity fuzes are considered
the most sensitive, and pull-friction and pressure-type fuzes
are considered the least sensitive (Lantzer and others, 1995).
The fuze sensitivity, together with other factors such as whether
the fuzes are armed and the fuze's location on the munition influence
the likelihood of detonation.
|
| Activities
of individuals frequenting the area. |
The
activities of individuals in areas containing UXO, combined with
the fuze type, may increase the likelihood of detonation. For
example, UXO with impact fuzes would more likely detonate in areas
of heavy excavation than in wildlife areas.
|
Risk
Assessment Initiatives |
|
There
are several initiatives to assess risks posed by UXO. These efforts
include (1) conducting risk assessments at specific military bases,
(2) developing a standardized methodology to assess occupational
and residual risks in areas containing UXO (Mulvihill and others
1996), and (3) developing a methodology for ranking ordnance and
explosive waste sites based on life cycle cost and public risks
(QuantiTech 1994). The results of any site-specific risk assessment
effort, however, are limited by the amount and reliability of data
available about the site.
The first step in determining site-specific risks is to conduct
a site assessment. Typical site assessments involve collecting existing
information on such factors as soils and geology, terrain, vegetation,
climate, and current and predicted land use.
The assessment may also require a visual inspection or sampling
of soil, water, or air. The results are used to determine whether
risks can be readily managed or whether more detailed study and
analysis is required.
If more detailed study and analysis is required, a site evaluation
is conducted to assess the level of risk posed by the site and to
make an informed risk management decision. Information is collected
on the types of munitions used in the area, materials associated
with those munitions, and the environmental setting.
The information collected is more specific than that collected during
a site assessment. The results of the site evaluation are used to
estimate the overall risk, determine whether a site- specific response
is required, and evaluate the effectiveness of response options
for a specific risk. |
UXO
Management, Characterization, and Remediation |
|
Several
options and technologies are available to manage, characterize,
and remediate property containing UXO so that the hazards and risks
are reduced or eliminated. The applicability of the options and
technologies depends on various factors such as type and density
of UXO present, depth of UXO, topography, land use, and degree of
risk posed by the UXO. In addition, existing technologies are being
improved and new technologies are being developed to increase the
effectiveness of UXO characterization and remediation. The following
sections discuss management options and remediation options, and
UXO characterization and excavation technologies. |
Management
Options |
|
Management
options provide a means of reducing immediate risks by controlling
potential encounters with UXO. However, they do not eliminate the
risk because the UXO remains in place. Management options include
restricting property access, limiting property uses or activities
that can occur on the property, conducting community education and
awareness programs, and conducting surface sweeps for UXO. These
options are typically used as a readily available, proven method
of addressing risk when UXO characterization and removal cannot
be conducted in a safe, efficient, or cost-effective manner. Two
management options commonly used include restricting access to the
property and limiting the activities that can occur on the property. |
| Restricting
access. |
Access
to areas containing UXO can be limited by installing fencing or
barriers to reduce the number of people who may enter the property
and encounter a UXO. This option might be applicable as a short-term
measure, particularly for remote property that is not used or
for property with extremely rugged terrain.
|
| Limiting
activities. |
Activities
that can take place on property with UXO can be limited through
deed restrictions or through other means. For example, a deed
restriction may prohibit property development or may prohibit
excavation and other earthmoving activities. In addition, notices
of prohibited activities and UXO warning signs can be posted throughout
the area. A typical warning sign may state "Danger-UXO. Do
Not Enter." This option might be applicable for private property.
|
Remediation
Options |
|
Unlike
management options, remediation options reduce risks from UXO by
removing all or some of the UXO present in an area. DoD policies
and procedures regarding remediation of property containing UXO
are defined in DoD Ammunition and Explosives Safety Standards (DoD
1995). The standards specify procedures for UXO characterization
and control at active installations, UXO remediation of property
that is to be transferred or leased to another entity, and remediation
of FUD sites.
DoD procedures for remediating property with UXO include the following
steps:
- Determine
the ultimate land use
- Determine
the boundaries of the areas to be investigated and remediated
- Determine
the type of known or suspected UXO
- Define
the locations and depths of UXO
- Remove
or neutralize the UXO
- Document
the process
- Provide
continued surveillance of areas where UXO is above the frost line
but below the remediation depth
In cases when site-specific planning is not possible, DoD policies
and procedures specify remediation depths based on land use. The
remediation depths listed in Table 1 are to be used for interim
planning. Although the table provides guidance on remediation depths,
remediation to those depths does not assure that all UXO has been
removed. Residual UXO may exist. |
| Planned
End Use |
Remediation
Depth |
| Unrestricted:
Commercial, residential, utility, subsurface recreational, and
construction |
10
feet* |
| Public
Access: Farming, agricultural, surface recreational, vehicle
parking, and surface supply storage |
4
feet |
| Limited
Public Access: Livestock grazing and wildlife preserve |
1
foot |
| Not Yet
Determined |
Surface |
Table 1
Note: *If construction
will occur, the presence of UXO must be determined to a depth of
4 feet below the planned excavation depths. Any UXO should be remediated
to those depths. |
Characterization
Technologies |
|
Once
a remediation depth is selected, the appropriate technologies can
be implemented to characterize UXO. The technologies available to
detect and characterize UXO vary in terms of the types and depths
of UXO they can detect, the topography for which they can be used,
and their overall effectiveness. The various technologies currently
in use are discussed below. |
| Magnetometry.
|
Magnetometry,
which involves the use magnetometers and gradiometers, is designed
to locate buried ordnance by detecting irregularities in the earth's
magnetic field caused by ferrous (iron-based) materials in the
ordnance.
Gradiometers typically consist of two magnetometers configured
to measure the spatial rate of change in the magnetic field. There
are numerous types of magnetometers, many of which were developed
to improve detection sensitivity under varying soil conditions.
The components of a typical magnetometer include a detection sensor,
a power supply, a computer data system, and a means to record
the locations of detected anomalies. More advanced magnetometers
incorporate a navigation system, such as a differential global
positioning system (GPS), to determine location. Magnetometers
can be hand-held, man-portable, towed by a vehicle, or mounted
on aircraft.
|
 Figure
11. Typical Magnetometer System |
The
effectiveness of magnetometers depends on their sensitivity, the
distance between the sensor and UXO, the amount of ferromagnetic
material in the UXO, background magnetic noise, and site-specific
soil properties. For optimal performance, magnetometers must be
placed close to the ground surface. Recent technology demonstrations
of commercially available magnetometry technology showed that hand-held
and vehicle-towed magnetometers detected between 50 to 83 percent
of the ordnance present (PRC 1996a). The number of false alarms
generated for each UXO item detected (false alarm ratio) was 10
for the 50 percent detection rate and 4 for the 83 percent detection
rate. Airborne magnetometers showed little or no capability to detect
UXO. |
| Ground
Penetrating Radar. |
Ground
penetrating radar (GPR) has been used for many years as a remote
sensing technology. The main elements of any GPR system are the
transmitter unit, the receiving unit or antenna, the control unit,
and the display and recorder unit. The transmitter produces short
pulses of electromagnetic energy that are directed toward the
ground. As the energy pulses travel into the ground, buried objects
reflect the signals back to the receiving unit, where they are
recorded and processed into an image. Figure 12 shows a typical
GPR system.
|
 Figure
12. Typical GPR system |
Many
environmental factors significantly affect the ability of GPR
systems to produce accurate images. Important factors include
the density and type of vegetative cover, water content of the
vegetation and soil, and topography. For optimal performance,
the antenna should be positioned perpendicular to the ground and
the soil should be dry. In general, GPR is not effective in saturated
soils and wet areas because water absorbs GPR energy. Of nine
GPR systems evaluated during recent technology demonstrations,
none of the systems could effectively detect UXO, primarily because
of the wet clay soils at the test site. For the systems that detected
ordnance, the detection rate ranged from 1 to 5 percent of the
ordnance present. The false alarm ratio was 28 and 3, respectively
(PRC 1996a).
|
| Electromagnetic
Induction. |
Electromagnetic
(EM) induction can be used to detect both ferrous and on ferrous
metallic UXO. EM induction systems transmit electric current into
the soil to detect metallic objects. The systems measure either
the secondary magnetic field induced in metal objects or the difference
between the electrical conductivity of the soil and the electrical
conductivity of buried objects such as UXO.
Components of an EM induction system include transmitting and
receiving units, a power supply, a computer data acquisition system,
and a means of recording locations of anomalies. More advanced
systems typically incorporate a navigation system such as GPS
to determine locations. Most EM induction systems are man-portable
units consisting of a small, wheeled cart to transport the transmitter
and receiver, a backpack containing the system's electrical components,
and a hand-held data recorder. Figure 13 shows a typical EM Induction
system.
|
 Figure
13. Typical EM Induction System |
EM
induction systems are most effective in detecting metallic objects
near the soil surface. The performance of EM induction systems
depends on the distance between the transmitter- receiver assembly
and the UXO and the size of the UXO. For optimal performance,
the assembly must be positioned close to the ground. Like magnetometers,
EM induction systems experience high background magnetic noise
levels when they are used to survey areas with high concentrations
of surface ordnance fragments. EM induction systems evaluated
during recent technology demonstrations were capable of detecting
between 11 and 85 percent of the ordnance present. The corresponding
false alarm ratio for these EM systems were 13 and 5, respectively
(PRC 1996a).
|
| Infrared
Sensors. |
Infrared
(IR) sensor technologies can be used to identify objects by measuring
their thermal energy signatures. UXO on or near the soil surface
may have a different heat capacity or heat transfer properties
than the surrounding soil; theoretically, this temperature difference
can be detected and used to identify UXO. For optimal performance
of IR sensor technologies, a sharp thermal contrast must exist
between the UXO and its surroundings—usually the soil surface.
IR sensor results also depend on the type and density of vegetative
cover, weather conditions, time of day, and specific size and
properties of the UXO. In practice, IR sensor technologies can
be used to detect UXO located on an unvegetated soil surface.
However, they have shown a minimal ability to characterize UXO.
|
| Multiple
Sensors. |
Combining
two or more sensor technologies into a multisensor approach has
been demonstrated to improve UXO detection and characterization.
For example, during technology demonstrations of commercially
available sensor technologies, magnetometers combined with an
EM sensor were capable of detecting between 65 to 72 percent of
the ordnance present. The false alarm ratios were 9 and 21, respectively.
|
| Other
Technologies. |
Other
technologies are currently being developed for detecting UXO,
but have not been successfully demonstrated. These include nuclear
technology, acoustic sensors, and biological sensors. Nuclear
technology is based on the premise that some chemicals in explosive
compounds respond in a unique way, such as emitting gamma particles,
when exposed to radiation. However, nuclear technology cannot
penetrate soils well, and if the soils have been treated with
fertilizers, the number of false alarms may be high (Heckelman
1995). Acoustic sensors transmit sound waves through the soil;
the sound waves then bounce off or echo back from any object encountered
in the soil. However, acoustic sensors cannot discriminate UXO
from other objects, and the relatively long wave lengths used
by the acoustic sensors cannot detect small UXO. Finally, dogs
(biological sensors) have been trained to detect vapors given
off by explosives in munitions, but they find it difficult to
detect UXO more than 6 inches below the ground surface. Wind direction
and terrain type can affect dog detection performance.
|
Excavation
Technologies |
|
Historically,
the UXO excavation phase primarily involved manual methods that
were very labor-intensive. Research and development efforts over
the last 20 years have focused on increased mechanization to improve
efficiency and enhance operator safety. The effectiveness of any
excavation technology, however, depends on the effectiveness of
the technology used to detect UXO. If a detection system generates
a high number of false alarms over a large area, that area will
require otherwise unnecessary excavation.
Available UXO excavation technologies are grouped into three categories—manual
methods, mechanized systems, and remote- controlled systems. |
Manual Methods.   |
Manual
UXO excavation methods are performed entirely without mechanized
equipment. Standard manual excavation methods include using shovels
and other digging tools to excavate soil and expose potential
UXO targets. Manual excavation methods require that additional
UXO detection activities be conducted to confirm target removals
and increase the probability of removing all UXO present. Manual
methods work best for near-surface and shallow subsurface UXO.
They are also more effective in excavating small UXO (such as
small arms munitions and grenades) than large munitions (such
as bombs). Manual methods present significant safety risks to
workers. In heavily vegetated areas, vegetation should be removed
to increase worker safety.
In 1985, DoD estimated that the cost to manually excavate UXO
to 0.5 meter below the surface may range from $140 to $315 per
item cleared, based on an economic model for clearing 1,000 acres
of hilly terrain with medium overgrowth (NAVEODTECHCEN 1985).
|
Mechanical
Systems.  |
Mechanical
UXO excavation systems include the use of excavators, bulldozers,
front-end loaders, and other heavy construction equipment. Historically,
backhoe-type excavators have been the most commonly used mechanized
system. Vacuum excavators use high-speed air to penetrate and
dislodge the soil, a vacuum to extract the dislodged soil, and
a conveyor belt to transport the soil away from the excavation.
A vacuum e excavator evaluated during recent demonstrations of
commercially available excavation technologies was capable of
excavating to 3 meters below ground surface in soft, silty soil.
The use of mechanized systems is generally faster and more efficient
than the use of only manual systems. In addition, mechanized systems
offer a higher degree of worker safety because the machine separates
the UXO and the operator. Mechanized systems operate less efficiently
in remote areas, in areas with muddy or saturated soils, or in
areas with shallow water tables. Mechanized excavation methods
may require that additional UXO detection activities be conducted
to confirm target removals and increase the probability of removing
the UXO.
In 1985, it is estimated that the cost to mechanically excavate
UXO to 0.5 meter below the surface may range from $35 to $450
per item cleared, based on an economic model for clearing 1,000
acres of hilly terrain with medium overgrowth.
|
 Remote-Controlled
Systems. |
Remote-controlled
UXO excavation systems include telerobotic and autonomous systems.
In general, the capabilities, effectiveness, and implementability
of remote-controlled systems are the same as those for mechanized
systems. The primary difference is that the operator of a remote-controlled
system remains outside the immediate hazard area. Of the three
categories of UXO excavation methods, remote-controlled systems
offer the highest degree of safety.
Remote-controlled systems typically include a navigation and positioning
component—usually a GPS. However, GPS satellite signals
can be obstructed by tall trees and dense vegetation, limiting
the system's accuracy and applicability. GPS can be integrated
with an inertial navigation system to increase the capability
of the navigation system.
Remote-controlled excavation systems evaluated during recent technology
demonstrations had difficulty exposing small targets in fine,
silty soil. In some cases, the remote-controlled systems required
the use of man-portable UXO detection systems to search the excavated
soil for UXO targets. In addition, the process can be relatively
slow. For example, one system demonstrated excavated only five
ordnance items per day. The equipment operates best in relatively
flat grassy or unvegetated areas where the equipment can be easily
maneuvered (PRC 1994 and 1996a).
|
Decision-Making
Factors |
|
Making
a correct assessment for the clearance/destruction or remediation
of sites is important to gauge the effects of any actions taken.
Decisions will have to be made regarding appropriate procedures
and personnel.
Intended
use for the site needs to be considered when making decisions on
remediation. Will the site be used by the public? Will it be made
accessable to the public? Will it remain barren? For instance, greater
clearance and safety procedures will be required if the site is
to be used for future construction of housing/ factories/ or hospitals,
etc.
The
effectiveness of characterisation and excavation technologies is
also a limiting factor. Although many charactarisation systems are
capable of detecting and locating UXO, they are generally unable
to discriminate between ordnance and non-ordnance items. Factors
that effect technologies are: a) depth of excavation, b) time requirements
or restraints, c) environmental impacts from UXO clearance.
The
impact on local residents and local customs are also important considerations
when making decisions on clearance/ remediation techniques. Social
and economic impacts need to be considered when scheduling operations.
Environmental
concerns include soil erosion, wildlife habitats, potential loss
of species and loss of flora and fauna. Decisions on technologies
and equipment used will be based on these factors.
All
these factors will affect the cost and the actions to be undertaken. |
Glossary
of UXO Terminology |
|
antimateriel:
|
Designed
to cause deterioration of or damage to selected materiel.
|
antipersonnel: |
Designed
to kill, wound, or obstruct personnel. |
antitank: |
Designed to be used against tanks.
|
arming
device: |
A
device designed to perform the electrical and/or mechanical
alignment necessary to initiate an explosive train. |
caliber: |
The diameter of a projectile or the diameter of the bore of
a gun or launching tube. Caliber is usually expressed in millimeters
or inches.
|
casing:
|
The
fabricated outer part of ordnance designed to hold an explosive
charge and the mechanism required to fire this charge. |
dispenser: |
An item designed to be mounted, but not permanently fixed,
on aircraft to carry and eject small ordnance.
|
electromagnetic
induction: |
Transfer of electrical power from one circuit to another by
varying the magnetic linkage.
|
explosive: |
A substance or mixture of substances that can undergo a rapid
chemical change generating large quantities of energy generally
accompanied by hot gases.
|
fragmentation:
|
Term
applied to ordnance indicating that it is primarily intended
to produce a fragmentation effect. |
fuze: |
1. A device with explosive components designed to initiate
a train of fire or detonation in ordnance.
2. A nonexplosive device designed to initiate an explosion
in ordnance.
|
fuze,
delay: |
Any impact fuze incorporating a means of delaying its action
after contact with the target. Delay fuzes are classified
by the length of time of the delay. |
fuze,
impact: |
A fuze in which detonation is initiated by the force of impact
and that usually functions instantaneously or after a short
delay.
|
fuze,
proximity: |
A fuze wherein primary initiation occurs by remotely sensing
the presence, distance, and/or direction of the target through
the characteristics of the target itself or its environment. |
fuze,
self-destruct: |
A fuze designed to burst a projectile before the end of its
flight.
|
gradiometer: |
Magnetometer for measuring the rate of change of a magnetic
field.
|
ground
penetrating radar: |
A system that uses pulsed radio waves to penetrate the ground
and measure the distance and direction of subsurface targets
through radio waves that are reflected back to the system. |
illumination: |
Term applied to ordnance indicating that it is primarily intended
to produce light of high intensity. Such ordnance usually
contains a flare and may contain a parachute for suspension
in the air. |
incendiary: |
Any flammable material that is used as a filler in ordnance
intended to destroy a target by fire.
|
magnetometer: |
An instrument for measuring the intensity and direction of
magnetic fields.
|
materiel: |
All items necessary for the equipment, maintenance, operation,
and support of military activities without distinction as
to their application for administrative or combat purposes;
excludes
ships or naval aircraft. |
munition: |
1. Ordnance.
2. Any and all supplies and equipment required to conduct
warfare. |
ordnance: |
1. Military weapons collectively, along with ammunition and
the equipment to keep them in good repair.
2. Explosives, chemicals, pyrotechnics, and similar stores,
e.g., bombs, guns and ammunition, flares, smoke, napalm. |
projectile: |
An object projected by an applied force and continuing in
motion by its own inertia, as a bullet, bomb, shell, or grenade.
Also applied to rockets and to guided missiles.
|
propellant: |
An agent such as an explosive powder or fuel that can be made
to provide the necessary energy for propelling ordnance. |
smoke: |
1. Filling for ordnance such as bombs, projectiles, and grenades.
2. Term applied to ordnance indicating that it is primarily
intended to produce smoke of the types or colors specified.
|
unexploded
ordnance (UXO): |
Explosive ordnance that has been primed, fuzed, armed, or
otherwise prepared for action, and that has been fired, dropped,
launched, projected, or placed in such a manner as to constitute
a hazard, and that remains unexploded by malfunction, design,
or any other cause. |
warhead: |
That part of a missile, projectile, rocket, or other munition
that contains the explosive system, chemical or biological
agents, or inert materials intended to inflict damage. |
white
phosphorous: |
A chemical that when exposed to air, burns spontaneously,
producing dense clouds of white smoke. |
|
|
