The Army’s quantitative risk assessment (QRA) for the Tooele Chemical Agent Disposal Facility (TOCDF) estimates the risk to the public and to workers from accidental releases of chemical agent associated with all activities during storage and throughout the disposal process (U.S. Army, 1996a). Activities associated with the disposal process include:
munitions handling in preparation for transport to the disposal facility
transport of munitions to the disposal facility
the disposal processes
The QRA includes all identified potential causes of release, except for intentional acts, such as sabotage and terrorism. Releases resulting from both internal initiating events (events that originate inside the facility or that result directly from activities during the disposal process) and external events (such as earthquakes, aircraft crashes, and tornadoes) are included.
The factors in developing a QRA for a chemical agent and munitions storage and destruction site are shown in Figure E-1, which shows as the two primary sources of risk (1) the stockpile itself (storage risk) and (2) the destruction of the stockpile (processing risk). The actual risk posed by either or both sources depends on whether or not risk-initiating events occur.
Stockpile-related risks from sabotage, terrorism, and war are reportedly evaluated and managed by specific government agencies and are not considered in publicly available site-specific risk assessments.
The stockpile is hazardous principally because of the inherent toxicity of the anti-cholinesterase nerve agents, GB and VX, and mustard agents, H, HD, and HT. Because of its toxicity and volatility, agent GB presents the greatest hazard offsite. The risks associated with stockpile storage are almost all related to releases of agent as a result of either internal events—such as handling accidents during stockpile manipulation and maintenance, the deterioration of containment systems, the spontaneous detonation of munitions, or the spontaneous ignition of propellant—or external events such as natural disasters and airplane crashes.
Agent destruction imposes risks above and beyond the inherent risks associated with the existence and maintenance of the chemical agent and munitions stockpile. The transportation of chemical agent from storage to the destruction facility, the unpacking and disassembly of munitions and containment systems, and the actual process of agent destruction are activities during which agent could potentially be released. Like the storage risk, the predominant processing risk is associated with agent toxicity, although the quantities of agent being processed at any given time are small compared with the original inventories in the stockpile and are much better protected than in the stockpile.
Potential hazards other than agent toxicity that can contribute to processing risk include the toxic effects of products of incomplete combustion of agent and other hazardous materials used in the disposal process, as well as the effects of fire or explosion. (Because the quantity of the products of incomplete combustion is substantially smaller than the original quantity of agent, combustion products generally represent a lesser hazard.) Release of toxic by-products can occur during process upsets, a possibility allowed for in an
NOTE: This appendix is adapted from NRC (1997).
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Appendix E Additional Information Concerning Risk QUANTITATIVE RISK ASSESSMENT Storage Risk The Army’s quantitative risk assessment (QRA) for the The stockpile is hazardous principally because of the Tooele Chemical Agent Disposal Facility (TOCDF) esti- inherent toxicity of the anti-cholinesterase nerve agents, GB mates the risk to the public and to workers from accidental and VX, and mustard agents, H, HD, and HT. Because of its releases of chemical agent associated with all activities dur- toxicity and volatility, agent GB presents the greatest hazard ing storage and throughout the disposal process (U.S. Army, offsite. The risks associated with stockpile storage are al- 1996a). Activities associated with the disposal process in- most all related to releases of agent as a result of either inter- clude: nal events—such as handling accidents during stockpile manipulation and maintenance, the deterioration of contain- • munitions handling in preparation for transport to ment systems, the spontaneous detonation of munitions, or the disposal facility the spontaneous ignition of propellant—or external events • transport of munitions to the disposal facility such as natural disasters and airplane crashes. • the disposal processes Processing Risk The QRA includes all identified potential causes of re- lease, except for intentional acts, such as sabotage and ter- Agent destruction imposes risks above and beyond the rorism. Releases resulting from both internal initiating inherent risks associated with the existence and maintenance events (events that originate inside the facility or that result of the chemical agent and munitions stockpile. The trans- directly from activities during the disposal process) and ex- portation of chemical agent from storage to the destruction ternal events (such as earthquakes, aircraft crashes, and tor- facility, the unpacking and disassembly of munitions and nadoes) are included. containment systems, and the actual process of agent de- The factors in developing a QRA for a chemical agent struction are activities during which agent could potentially and munitions storage and destruction site are shown in Fig- be released. Like the storage risk, the predominant process- ure E-1, which shows as the two primary sources of risk (1) ing risk is associated with agent toxicity, although the quan- the stockpile itself (storage risk) and (2) the destruction of tities of agent being processed at any given time are small the stockpile (processing risk). The actual risk posed by ei- compared with the original inventories in the stockpile and ther or both sources depends on whether or not risk-initiat- are much better protected than in the stockpile. ing events occur. Potential hazards other than agent toxicity that can con- Stockpile-related risks from sabotage, terrorism, and tribute to processing risk include the toxic effects of prod- war are reportedly evaluated and managed by specific gov- ucts of incomplete combustion of agent and other hazardous ernment agencies and are not considered in publicly avail- materials used in the disposal process, as well as the effects able site-specific risk assessments. of fire or explosion. (Because the quantity of the products of incomplete combustion is substantially smaller than the original quantity of agent, combustion products generally represent a lesser hazard.) Release of toxic by-products can occur during process upsets, a possibility allowed for in an NOTE: This appendix is adapted from NRC (1997). 97
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98 EVALUATION OF CHEMICAL EVENTS AT ARMY CHEMICAL AGENT DISPOSAL FACILITIES Normal and upset emissions Initiators (analyzed in HRA) Receptors Processing Internal events Workers Accidental emissions Public (analyzed in QRA) External Environment events DCD Storage FIGURE E-1 Schematic illustration of risk elements at a chemical agent and munitions storage and destruction site. SOURCE: Adapted from NRC (1997). upper-bound calculation in the QRA. External events such Risks to the public stem primarily from releases of agent as earthquakes could cause the release of dangerous materi- caused by external events, although the public could also be als, such as propane or sodium hydroxide, from on-site stor- put at risk by long-term exposure to the products and by- age tanks, as well as shutdown of the disposal process and products of agent destruction, if they were released into the possible one-time release of products of incomplete com- environment as a result of chemical agent destruction pro- bustion from a furnace at shutdown. cesses. Environmental risk is associated almost exclusively with the release of agent and the products and by-products of agent destruction beyond site engineering controls. Risk Receptors There are three potential risk receptors: workers, the Risk Measures public, and the environment. Because of their proximity to the stockpile and agent-processing operations, workers are For humans (both workers and the public), the three po- at risk from exposure to the acute lethal (and nonlethal) haz- tential consequences of the risk posed by either stockpile ards associated with agent releases, regardless of the initiat- storage or agent destruction are acute lethality, acute and ing event. They are also potentially at risk from long-term latent noncancerous health effects, and latent cancer. The exposure to agent at very low concentrations and to the prod- potential adverse consequences for the environment are the ucts and by-products of agent destruction. The only known contamination of land and water, and adverse effects suf- latent effects are cancers following exposure to mustard fered by native or endangered species. (NRC, 2001a).1 Risk Mitigation 1 Workers are also susceptible to injury from ordinary industrial acci- Risk is most effectively mitigated or prevented before a dents (e.g., falls, burns, eye injuries, overheating in protective clothing), but hazardous material is released. However, after a hazardous such risks, which are not included in the Army’s QRAs, can be better under- material has been released, but before it reaches a receptor, stood through safety inspections and analyses of injury rates and can be the consequences of the release can be reduced. Risk mitiga- managed by adhering to safety practices proven in many industries.
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99 APPENDIX E Risk to the Public from Stockpile Storage tion can include measures taken at the spill site (e.g., contain- ing the spill) or at the receptor site (e.g., using protective masks), and emergency response measures (e.g., sheltering, The risk-dominant initiating event for release of agent evacuation). The Army’s 1996 site-specific QRA takes into stored in the chemical stockpile at DCD is an earthquake account some of these measures (U.S. Army, 1996a). How- (U.S. Army, 1996a). Although earthquakes are infrequent, ever, the primary purpose of the QRA is to calculate a realis- they have widespread effects and could cause the release of tic estimate of risk to the public. The analysis is not struc- much more chemical agent than other types of accidents. tured to measure the effectiveness of the local Chemical Seismic events that would contribute to storage risk are Stockpile Emergency Preparedness Program (CSEPP). those with mean accelerations above 0.2 g and recurrence intervals of 1,000 years or more. Such earthquakes signifi- cantly exceed normal building code design values and thus Uncertainty can lead to failures of equipment and structures. Overall, To provide the most realistic representation of risk, all according to the Army’s 1996 QRA for TOCDF, earth- forms of uncertainty are considered. Rather than assuming quake-initiated events account for 82 percent of the average the existence of some representative condition prior to the public fatality risk associated with continued storage of the accident scenario, a study models the full range of condi- stockpile; of the remaining 18 percent of the average public tions and other uncertainties that can affect the scenario. fatality risk, leaks of agent GB from ton containers account Results include uncertainties in the frequency and conse- for 11 percent (Figure E-2). quences of each scenario. The upper uncertainty bound An aircraft crash into storage structures and the electro- shown for the QRA risk estimates is a measure of the ana- magnetic effects of lightning (which could cause a fire in a lysts’ confidence in the results. There is a 95 percent chance storage igloo or cause an M55 rocket to ignite) were also that the risk is less than the upper bound. considered in the Army’s 1996 QRA. The results (see Figure For those readers desiring more details on risk assess- E-2) indicated that the impact of these initiators is only 2 ment and risk management, Appendix A of the National percent and 4 percent, respectively, of the total storage risk. Research Council (NRC) report Risk Assessment and Man- Risks from normal stockpile maintenance, such as isolating agement at Deseret Chemical Depot and the Tooele Chemi- leaking munitions, account for about 1 percent of the storage cal Agent Disposal Facility (NRC, 1997) develops the bases risk. These maintenance activities are infrequent, and the for the presentations of risk (risk profiles and expected fa- potential for a significant release is small because the num- talities), explains how to interpret the results, and discusses ber of munitions handled at any given time is limited. various measures according to which risks can be compared. Risk to the Public from Disposal Operations QRA RESULTS: THE ARMY’S 1996 ANALYSIS The risk to the public from processing of chemical weap- Results from the published QRA for the Tooele Chemi- ons is compared with the risk of continued storage in Figure cal Agent Disposal Facility (TOCDF) (U.S. Army, 1996a) E-3. The 1996 QRA put the risk level for the first campaign are used below to illustrate the form of QRA results. of GB disposal at about 0.00006 fatalities per year with a Lightning 4% Aircraft crash 2% Seismic events 82% GB TC leak 11% Handling accident/ lgloo fire 1% FIGURE E-2 Contributors to the average public fatality risk from continued storage at Deseret Chemical Depot. SOURCE: Adapted from U.S. Army (1996a).
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100 EVALUATION OF CHEMICAL EVENTS AT ARMY CHEMICAL AGENT DISPOSAL FACILITIES 0.0014 key: Continued storage, no processing TC ton containers 0.0012 MC-1 mines 1:GB Average number of estimated acute 105s 105 mm projectile Rockets 155s 155 mm projectile and public fatalities (per year) TC Numbers preceding colons refer 0.0010 to the disposal campaign number. Stockpile risk at DCD during TOCDF processing 0.0008 2:VX Rockets and 0.0006 spray tanks 3:GB 9:VX TC 0.0004 MC-1 and mines 4:GB 10:HD Weteyes TOCDF TC 12:HD 8:VX processing 0.0002 5:GB TC 155s 4.2" risk 11:HD 7:GB 6:GB 13:HD 155s 155s 105s TC 0.0000 1.00 2.00 3.00 4.00 6.00 7.00 8.00 0.00 5.00 Time from start of processing (years) FIGURE E-3 Comparison of risks to the public during processing at Deseret Chemical Depot and the Tooele Chemical Agent Disposal Facility. All risks on these curves are shown on a per-year-of-operation basis so that they are directly comparable. The risks of continued storage, assuming no processing takes place, are indicated by the broken line. The vertical axis shows average public fatality risk per year, and the horizontal axis shows the time line for disposal. SOURCE: Adapted from U.S. Army (1996a). processing duration of about 9 months (U.S. Army, 1996a). Handling All other Note, however, that the stockpile storage risk decreases at accidents disposal 0.76% the end of that time by two-thirds because the agent posing activities 0.04% the greatest risk would be removed from the stockpile during Aircraft crash 1.7% the first disposal campaign. By the end of the fifth campaign at TOCDF (GB ton containers nearly 3 years into disposal operations), the risk of both storage and processing have essentially disappeared. Nevertheless, although the risk is small, it is clear that stor- age risk is still much greater than processing risk and that accepting the processing risk for 3 years dramatically re- Seismic events duces the total risk. 97.4% Using the information shown in Figure E-3, risk manag- ers at TOCDF ascertained the relative effects of various agent destruction campaigns. This information was used to reorder the disposal campaigns to minimize the total overall risk. For disposal processing at TOCDF, the 1996 QRA re- sults show that the risk of public fatalities is dominated by earthquakes (97.4 percent) as the most dangerous risk-initi- FIGURE E-4 Contributors to the average public fatality risk from disposal operations at DCD and TOCDF. SOURCE: Adapted from ating event (Figure E-4). A structural failure in the unpack U.S. Army (1996a). area of the container handling building area caused by an
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101 APPENDIX E earthquake stronger than the building is designed to with- risks to the public, as would be expected because of the prox- stand could have severe consequences partly because muni- imity of the workers to the chemical agent. Small releases tions are unpacked in this area and are not protected by trans- that would not have an impact at a significant distance could port containers. The same earthquake would undoubtedly still be lethal to workers in the immediate area. According to lead to the release of much more agent from the DCD stor- the QRA, for the workforce of about 500 workers at TOCDF, age area next to TOCDF. if the 0.13 expected fatalities per 7.1 years of operation are The QRA results shown in Figure E-4 also indicate that dominated by single-fatality accidents, then the individual disposal-worker risk at TOCDF is about 4 x 10–5 per year. internal events associated with processing account for less than 1 percent (i.e., 0.8 percent) of the risk at TOCDF and that The risk for other on-site workers (outside the TOCDF nearly all of this risk is associated with handling rather than and DCD storage area) is evaluated in the same manner as with actual agent destruction. The 1996 study credits the low the risk to the public. The probability of one or more fatali- risk of processing to the safety and mitigation features of the ties for other on-site workers during the 7.1 years of disposal processing is 5 x 10–4 (1 in 2,000). With about 100 workers baseline system and the limited quantities of agent available for release during processing (U.S. Army, 1996a). in this category, and assuming that most accidents cause a single fatality, the individual annual risk is 1 x 10–6 (1 in 1 million per year) for other on-site workers. Risk to Workers from Disposal Operations Workers at TOCDF, including all support and adminis- QRA: RECENT ADVANCES trative staff at the facility or in nearby buildings and muni- tion handlers responsible for removing munitions from the The recent, as yet not published, Army QRAs for the stockpile and transporting them to the disposal facility, were third-generation facilities for chemical demilitarization have included in the Army’s 1996 risk assessment. Although the extended the methodology for assessing the effects of light- study addressed only worker risks associated with accidents ning, tornados, fires, events of special interest at each site, involving release of agent, processing and handling workers and human actions (and errors), and for understanding can be directly affected by the blast of an explosion, for ex- worker risk. The analysis for lightning draws on recent ad- ample, or by dispersal of agent from an accident, and both of vances in tracking the position and strength of lightning these effects were included. (Industrial-type risks, e.g., be- strikes throughout the United States and new data that cor- ing crushed by a lift-truck, were not considered.) The QRA rects long-held assumptions about the distribution of light- results indicated a 1 in 7 probability of a worker fatality in ning. New technology for understanding the behavior of the total disposal-related worker population in the 7.1 years lightning within igloos has also been important. The analy- of disposal processing. Figure E-5 shows the contributors to sis of risk from fire has shifted from the use of a physics the average risk of fatality for disposal-related workers. model and nuclear power plant fire data to a more data-driven The 1996 QRA indicates that risks to disposal workers analysis, with more applicable data from chemical process from agent-related accidents are substantially higher than the plants having a significant impact on the results. After the Seismic events 36% MPF explosions 6% Handling 6% Other causes 8% Maintenance 44% FIGURE E-5 Contributors to the average risk of fatality for disposal-related workers at DCD and TOCDF. SOURCE: Adapted from U.S. Army (1996a).
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102 EVALUATION OF CHEMICAL EVENTS AT ARMY CHEMICAL AGENT DISPOSAL FACILITIES events of September 11, 2001, the Army decided to recon- ample, workers directly involved in an accident were as- sider the publication of site-specific QRAs for the third-gen- sumed to be killed, either from exposure to agent or from an eration incinerator-based chemical demilitarization facilities. explosion. However, the committee ascertained that these QRAs con- As attention in the chemical demilitarization program firm the dominance of the risk of continued storage of aging has shifted to include worker risk, more significant model- chemical weapons. ing of human action has been performed. None of these Improvements in the analysis of worker risk have re- improved analyses have yet been published. A variety of sulted from an increased focus on worker activities and the human reliability analysis methods have been used (Gertman adoption of more general methods for analyzing the effects and Blackman, 1994). For ongoing work, new approaches of human error. For a number of reasons discussed in the that account for details of context and human cognitive func- NRC report Risk Assessment and Management at Deseret tion are being adapted (Hollnagel, 1998; USNRC, 2000). Chemical Depot and the Tooele Chemical Agent Disposal With more careful and complete analysis, new scenarios es- Facility (NRC, 1997), very little modeling of human perfor- pecially important to worker risk are being developed. mance was done in the 1996 QRA for TOCDF.2 For ex- 2 Reporting the health effects for workers who are not directly involved, but who work in adjacent areas, would have been deceptive for several reasons: • The TOCDF dispersion model may not properly capture the close- in dose. • Projected latent effects from everyday activities (e.g., mainte- nance) are much greater than the latent effects from an agent acci- dent and were not modeled in the QRA. • The calculated latent risk to workers is very small compared with the acute risk. • Worker risk from continued storage would have required assess- ing limited worker populations and restricted activity schedules that no longer existed at DCD. • The primary goal of the QRA was to calculate the public risk from accidents in the operation of the TOCDF.