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2
Safety
As with all chemical and industrial processes, the destruction of the separated
rocket motors1 from the M55 rockets will present inherent safety risks. Working with
energetic materials safely requires carefully devised and approved safe operating
procedures, processes, and equipment. M55 rockets were manufactured in 19611965
(CMA, 2008). The M28 propellant in the rockets was therefore 4751 years old when this
report was prepared. Disposing of the separated rocket motors will require additional
consideration given that the M28 propellant includes aged and degraded materials. And
the propellant contains lead compounds that must be taken into account in considering
disposal options.
A well-designed process for disposal of the separated rocket motors will provide
physical safety for the workers controlling or performing the work activities, protect the
community and local environment, minimize risks to the physical infrastructure and
capital equipment required to perform the work, and produce a manageable waste stream
that is minimized to the greatest extent possible. The Blue Grass Chemical Agent-
Destruction Pilot Plant (BGCAPP) will use extensive automation to minimize employee
exposure to agent and explosive hazards associated with the handling and destruction of
M55 rockets in the plant. However, M55 rocket processing in BGCAPP will result in the
need to dispose of about 70,000 intact rocket motor assemblies2 outside BGCAPP. For
more information on the important topic of process safety, the reader is referred to NRC,
2011.
ENERGETICS SAFETY ISSUES
Because the rocket motor propellant presents an energetic hazard, explosives
safety precautions must be taken in all handling and storage operations. Such operations
are governed by Department of Defense (DoD) Ammunition and Explosives Safety
Standards (DoD, 2008) and within the Army by the current version of the Army's
Ammunition and Explosives Safety Standards (U.S. Army, 2011). Guidance in those two
documents must be followed in any treatment program.
1
See Appendix A for how the committee defines separated rocket motor.
2
These assemblies include the rocket motor in its steel case, aluminum fins, ignition system and
wires, fins and miscellaneous parts, and fore closure--all in the rear half of the shipping and firing tube.
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The composition of M28 propellant used in the M55 rocket is listed in Table 2-1.
It is a double-base3 propellant with a lead stearate burn-rate modifier. The propellant is
contained within a cellulose acetate inhibitor that has been plasticized with
dimethylphthalate. The purpose of the inhibitor is to limit propellant burning along the
outer surface of the propellant during motor firing. The hazard classification of the
separated rocket motors as determined by following the Department of Defense
Ammunition and Explosives Hazard Classification Procedures, TB 7002 (DoD, 1998),
affects the packaging requirements for the rocket motors, the number of rocket motors
that may be transported off-site in a given shipment configuration, and the number of
rocket motors that may be stored in a given location before disposal. The hazard
classification of the assembled M55 rockets in their shipping and firing tubes (SFTs) for
storage and transportation is currently 1.2.1, which means that they present a nonmass
explosion and fragment-producing hazard. BGCAPP intends to apply for a 1.3 hazard
classification, which would mean that they present a mass fire and minor blast or
fragmentation hazard, to cover shipping and handling of the separated rocket motors
(DoD, 1998).Table 2-2 lays out the hazard classifications that are applied to explosive
materials.
Table 2-1 Nominal Composition of M28 Propellant
Component Weight Percent Purpose
Nitrocellulose 60 Energy source
Nitroglycerin 23.8 Energetic plasticizer
Triacetin 9.9 Casting solvent
Dimethylphthalate 2.6 Plasticizer
Lead stearate 2.0 Burn-rate modifier
2-Nitrodiphenylamine 1.7 Stabilizer
SOURCE: CMA, 2005.
Table 2-2 Hazard Classifications Applied to Explosive Materials
Hazard Classification Hazard
1.1 Mass explosion
1.2 Nonmass explosion, fragment-producing
1.3 Mass fire, minor blast, or fragment
1.4 Moderate fire, no blast, or fragment
1.5 Explosive substance, very insensitive
(with mass explosion hazard)
1.6 Explosive article, extremely insensitive
SOURCE: DoD, 1998.
Finding 2-1. The hazard classification of the rocket motors has not been determined. The
classification will directly affect packaging, transportation, and storage requirements for
off-site disposal options.
3
The term double-base connotes that there are two active constituents in the propellant. In the case
of the M28 propellant, they are nitrocellulose and nitroglycerin.
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Recommendation 2-1. Blue Grass Chemical Agent-Destruction Pilot Plant program staff
should expedite the process required to provide the hazard classification of the separated
rocket motors.
The aging and degradation of the M28 propellant could cause it to have increased
sensitivity to impact, shock, and thermal conditions. There were four pressure-pulse
events when the motors of M55 rockets were cut at the Umatilla Chemical Agent
Disposal Facility. There have also been over 20 fires when rocket motors were cut at
incineration-based chemical agent disposal facilities (CDC, 2006). Although the
separated rocket motors at the Blue Grass Army Depot will not be cut, those incidents
indicate some sensitivity of the propellant, which could be a factor in disposing of the
separated rocket motors. Because of the potential severity of incidents arising from
propellant sensitivities, the Department of Defense (DoD, 2008) and the Department of
Transportation (49 CFR 173.56) have instituted policies for handling these types of
materials.
Nitrate esters, such as the nitrocellulose in the M28 propellant, degrade slowly
and liberate nitrogen dioxide (NO2).4 One mechanism for that is the breaking of the
carbon monoxidenitrogen dioxide (CONO2) bond in the nitrocellulose, which is
thermally labile and can be broken under storage-temperature conditions. If liberated NO2
does not react with the nitrate ester (the propellant), it can react with water in air to form
acids, which will degrade nitrate esters further. For instance, NO2 is a strong oxidizer and
can react with the nitrocellulose or abstract hydrogen from the nitrocellulose to produce
nitrous acid (HONO). The CONO2 bond may also be hydrolyzed to form nitric acid
(HNO3). And the degradation of the propellant can be catalyzed by the presence of bases
and metals. Finally, the overall chemical reaction is exothermic (it generates heat), and
can catalyze degradation further. In other words, the degradation of the nitrate esters in
the M28 propellant is accelerated by its own degradation product (NO2). If the
degradation reaction rate becomes high enough, the nitrate ester will self-initiate, and this
can lead to ignition, deflagration, or detonation.
Standard practice is to avoid the undesirable consequences of the runaway
reaction by adding an NO2 scavenger, commonly referred to as a stabilizer. The stabilizer
does not contribute substantially to the energy delivered by the propellant when used for
its intended purpose, so quantities of stabilizer used in propellants are limited. Over time,
the stabilizer becomes depleted, and the undesirable reactions can become dominant.
Surveillance programs are instituted to ensure that sufficient stabilizer remains in
propellants to minimize the risk of autoignition. Such a program consists of accelerated-
aging estimations of stabilizer content combined with occasional monitoring of the rocket
motor inventory. Conventionally, both evaluations require the extraction of a piece of
propellant, followed by chemical analysis of that piece. In 2002, the Army determined
that the M28 propellant inside an intact M55 rocket assembly, in its current
configuration, could be handled with minimal risk (U.S. Army, 2002). In the 10 years
that have elapsed since the 2002 assessment, the propellant has degraded further. If the
4
Stephanie E. Leach and Bruce P. Thomas, Naval Air Warfare Center Weapons Division, China
Lake, California, "Assessment of Alternative Strategies to Determine Solid Rocket Motor Stability,"
meeting poster presented at the 2012 Pittsburgh Conference, March 16, 2012, Orlando, Florida.
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propellant has followed the degradation rate projected in 2002, the risk of autoignition
should not have increased appreciably. To the committee's knowledge, the propellant has
not been assessed since 2002, so it does not know whether the propellant has degraded as
projected.
However, cutting the fiberglass SFT and separating the rocket motor from the
warhead changes both the system configuration and the storage environment of the rocket
motor. For instance, the propellant will have greater exposure to environmental factors,
such as heat and humidity, via an air pathway between the rocket motor case and the SFT
and up through the nozzle than when it was been sealed in an SFT as a whole rocket. The
chemical reactions in the propellant generate heat on an ongoing basis, and the storage
box in which the separated rocket motors will be placed will influence heat transfer to
and from a given rocket motor and the others boxed with it and heat exchange between
ambient air and the propellant. The design of the box, including its ability to dissipate
heat generated in the propellant grains and its ability to maintain a dry storage
environment, will determine the validity of the previous safety studies vis-à-vis the new
configuration of the cut rocket motors.
Other aging-related phenomena that may not correlate directly with the stabilizer
content include migration of nitroglycerin into the inhibitor and changes in mechanical
properties, such as softening and hardening of the propellant. The M28 propellant
contains nitroglycerin, which is used as a plasticizer to tailor the propellant's mechanical
properties (to increase its flexibility) and to increase energy content. The nitroglycerin
can diffuse and migrate within the bulk propellant, form small accumulations at the
propellant surface, be absorbed into the inhibitor layer, or lead to propellant brittleness.
Those physical effects can lead to a reduction in propellant stability and an increase in
propellant sensitivity, both of which warrant careful consideration in handling aged M28
propellant. Propellant softening is often exhibited as slumping, and propellant hardening
can be exhibited as cracking. On initiation, as in some disposal technologies, those
phenomena change the surface area being burned and can increase the inner pressure of
the motor case. If that pressure exceeds maximum limits for the nozzle or the case, a
catastrophic failure will occur and potentially can cause serious damage to personnel and
facilities. The phenomena can thus pose a safety risk during rocket motor disposal.
A hazards analysis working group (HAWG) is a useful and important tool for
addressing energetics safety (DoD, 2012). A HAWG comprises operators, safety experts,
industry experts, vendor representatives, and regulators at BGCAPP could examine in
great detail all the possible actions and activities that involve the M55 rocket with
specific focus on the energetic material components during demilitarization. A HAWG
assessment may reveal safety risks in a process or procedure that are otherwise not
readily apparent.
Finding 2-2. The Army's 2002 M55 Rocket Assessment Summary Report for the intact
M55 rocket may not be directly applicable to the separated rocket motors. New not-
readily-apparent safety risks could emerge during demilitarization operations involving
the M55 rocket containing energetic materials.
Finding 2-3. Among the vitally important approved safety practices and procedures that
need to be followed in handling energetic materials are the assessment and approval of
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standard operating procedures and hazard analyses. They will account for potential new
safety risks that emerge during the demilitarization process.
Finding 2-4. The design of the storage and shipping box will significantly influence the
storage environment of the M28 propellant.
Recommendation 2-2. Blue Grass Chemical Agent-Destruction Pilot Plant program staff
should ensure that the storage and shipping containers minimize the exposure of rocket
motors to environmental conditions that will accelerate propellant degradation, such as
heat and humidity, and allow adequate heat dissipation from the separated rocket motors.
For example, desiccant could be added to the storage and shipping containers to reduce
humidity.
Recommendation 2-3. Blue Grass Chemical Agent-Destruction Pilot Plant program staff
should establish a hazards analysis working group to assess, analyze, and develop risk
mitigation practices and procedures with specific attention to energetic materials in the
overall demilitarization of the M55 rocket.
ELECTRICAL SAFETY
The hazards of electromagnetic radiation to ordnance (HERO) and electrostatic
discharge (ESD) need to be considered as they apply to the separated rocket motors. The
rocket-cutting operation will produce a rocket motor with an ignition system
configuration that is different from that of an intact M55 rocket. The cutting operation
may also damage the igniter leads and shunting as the installed rocket motor ignition
system is integrated with the bottom half of the cut fiberglass SFT. Although the rocket-
cutting operation is designed not to damage the rocket motor, unintended damage to the
igniter leads and the safety shunting may occur when the rocket is cut because the SFT
will be clamped at the rear end for this operation, which is where much of the ignition
system is. In addition, because the steel rocket motor case will be exposed along the cut,
a new electrically conductive path that was not envisioned when the rockets were
designed will be created. That may change the system's sensitivity to ESD.
Regarding HERO, the current electromagnetic radiation environment is substantially
different from when this ordnance was produced. For example, personal electronic
devices and cellular-telephone towers did not exist when the M55 rockets were designed
and produced. They can produce local electromagnetic fields that could affect the
separated rocket motors and cause electrical safety problems, including possibly ignition.
Finding 2-5. The current hazards to the separated rocket motors posed by
electromagnetic radiation and the potential for electrostatic discharge may require
verifying the condition of the igniter system after cutting before placement in the storage
and shipping box.
Recommendation 2-4. Blue Grass Chemical Agent-Destruction Pilot Plant program staff
should address the condition of the ignition system after cutting. If it is warranted by the
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changed configuration of the separated rocket motors, the design of the storage and
shipping box should provide protection from hazards of electromagnetic radiation to
ordnance and from electrostatic discharge.
LEAD
As shown in Table 2-1, the M28 propellant contains 2 percent lead stearate by
weight. The weight of the propellant in each motor is about 20 lb, so the propellant in
each motor contains about 0.4 lb of lead. Lead released from burning propellant will be in
the form of respirable particulate matter (PM2.5).5 Releases are likely to be in the form of
lead metal and lead oxides. Unpublished data on static-fired rocket motors indicate that a
substantial fraction (2-10 percent) of the lead may remain in the motor carcass after
firing. Any technology used to dispose of the separated rocket motors would need to
ensure minimal redistribution of lead through the environment and protection of
employees and the public.
Finding 2-6. Thermal and chemical processes that destroy the propellant will produce a
lead waste stream that will present challenges from worker, public health, and
environmental exposure perspectives.
REFERENCES
CDC (Centers for Disease Control and Prevention). 2006. M55 Rocket Fire/Explosion
Concerns, March 1. Aberdeen Proving Ground, Md.: U.S. Army Chemical Materials
Agency.
CMA (Chemical Materials Agency). 2005. Fact Sheet: M28 Propellant Grain. Available
online at http://www.cma.army.mil/fndocumentviewer.aspx?docid=003674658. Last
accessed September 12, 2012.
CMA. 2008. Fact Sheet: M55 Rockets, March 5. Available online at
http://www.cma.army.mil/fndocumentviewer.aspx?docid=003677976. Last accessed
July 5, 2012.
DoD (Department of Defense). 1998. Joint Technical Bulletin: Department of Defense
Ammunition and Explosives Hazard Classification Procedures, TB 7002, January 5.
Available online at http://www.ddesb.pentagon.mil/. Last accessed August 7, 2012.
DoD. 2008. DoD Ammunition and Explosives Safety Standards, DoD Number 6055.09-
M, February 29. Available online at http://www.dtic.mil/whs/directives/corres/html/
605509m.html. Last accessed June 8, 2012.
5
PM2.5 is Environmental Protection Agency nomenclature for particulate matter that has an
aerodynamic particle size equal to or less than 2.5 µm. That particle size is important because such particles
can travel into the alveoli in the lungs.
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DoD. 2012. Department of Defense Standard Practice, System Safety, MIL-STD-882E,
May 11. Available online at http://www.everyspec.com/MIL-STD/MIL-STD-0800-
0899/MIL-STD-882E_41682/. Last accessed July 3, 2012.
NRC (National Research Council). 2011. Assessment of Approaches for Using Process
Safety Metrics at the Blue Grass and Pueblo Chemical Agent Destruction Pilot Plants.
Washington, D.C.: The National Academies Press.
U.S. Army. 2002. M55 Rocket Assessment: Summary Report, July. Aberdeen Proving
Ground, Md.: U.S. Army Program Manager for Chemical Demilitarization.
U.S. Army. 2011. Department of the Army Pamphlet 385-64: Ammunition and
Explosives Safety Standards. Available online at http://armypubs.army.mil/epubs/
pdf/p385_64.pdf. Last accessed June 8, 2012.
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