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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. 13
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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. 14
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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. 15
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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 16
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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 17
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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. 18
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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. 19
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