The Board's analysis objectives were twofold: (1) the Board determined the most likely accident scenario leading to separation of the rope and the subsequent fatal injury to the Buddy, a Security Police Officer; and (2) the Board analyzed management structures, policies, procedures, and common practices in effect at DOE Headquarters, SR, WSI-SRS, and WSRC.
The first objective focused on the Rappel Tower, the equipment, and the actions taken by the Rappeller, the Buddy, and other SRT personnel present during the training exercise. The second objective of the analysis was pursued to determine if there had been programmatic breakdowns that could have contributed to the fatal accident at the Rappel Tower.
The Board used several analytical tools and techniques to analyze the causes and effect of the Rappel Tower accident. Based on these analyses, the Board determined the direct, probable, and root causes of the accident. The root causes are those deficiencies that when corrected may prevent recurrence of this accident or similar accidents.
In addition, the Board developed judgments of need for correcting deficiencies that contributed to the accident. The Board used the MORT methodology to apply events and causal factors charting, analytical trees, barrier analysis, and change analysis in analyzing the accident.
The Board constructed an Events and Causal Factors Chart for use in the analysis. The Events and Causal Factors Chart is a graphic depiction of events, causal factors, and conditions leading to the accident. Contributing conditions were developed into effects such as "procedures did not exist" and "training was less than adequate." Two versions of the Board's Events and Causal Factors Chart were prepared for this report. Figure 3-1, the Summary Level of the chart, is included in this section. The complete version of the chart is available on request from EH.
The Events and Causal Factors Chart is used to determine the sequence of events leading to the accident and to show the relationship between events and associated causal factors. An Events and Causal Factor Chart, Summary Level, is shown in Figure 3-1. An Integrated Event Sequence included in Appendix O shows the interaction of those involved in the accident and provides a detailed account of the events preceding the accident. Causal factors that arose from analysis of the Events and Causal Factors Chart are as follows:
Analysis of the emergency response to the accident is focused on actions of the WSRC and WSI-SRS EMTs, and other aspects of the emergency including the SRSOC. All EMTs who responded to the accident are trained and certified to South Carolina Department of Health and Environmental Control (SCDHEC) standards. The emergency medical assistance that they provided within seconds of the accident and throughout the emergency was well handled and adequate.
Analysis of other emergency actions, including the SRSOC, gathered from interviews and the audio recordings made at the SRSOC, revealed three areas that could be improved for emergency response to future accidents.
SRS has an approved SSSP that consists of seven Master Safeguards and Security Agreements (MSSAs) and a supporting Vulnerability Assessment (VA) for each MSSA. The MSSAs are for five SRS facilities that contain Category I quantities of Special Nuclear Material (SNM) and have a containment protection strategy; one SRS facility that has a denial strategy due to the radiological threat; and one SRS activity (onsite transportation of Category I quantities of SNM) that also has a containment protection strategy. Each MSSA and VA was jointly developed by SR, the lead DOE Headquarters cognizant secretarial office at the time of the SSSP development (Defense Programs), NN, WSRC, and WSI-SRS. The protection strategy and associated risks contained in each MSSA and VA were approved by the SR Manager and the appropriate DOE Headquarters cognizant secretarial offices. All of the MSSAs were approved between March 22 and October 31, 1994. SRT rappelling is not mentioned in the protection strategy for the interdiction, interruption, neutralization, or recapture missions of the protective force.
DOE 5632.7A, "Protective Force Program," does not contain a prescriptive requirement that SRT have a rappelling capability, but rappelling can be justified by site-specific conditions. The SSSP documents the DOE-approved containment protection strategy and the associated risk acceptance for vital SRS facilities. SRT operational and tactical response plans must be integrated in the SSSP but do not identify an SRT aerial/building rappelling mission.
NN has reviewed and approved the WSI-SRS protective force training program and, during a separate audit, certified the WSI-SRS Special Response Team training program that included rappelling. Neither NN appraisal of the WSI-SRS training programs were conducted with other stakeholders (i.e., program office) participation. These assessments were performed in accordance with DOE 5630.15 that requires NN to "conduct annual reviews of safeguards and security training programs DOE-wide" and "serve as the approving authority for certifying that local safeguards and security training programs meet Departmental standards." NN has advised the Board that protective force training and qualifications criteria are established by the CTA and approved by NN in accordance with 10 CFR 1046, Appendix B to SUBPART B, B. (1)" and the NN "policy is that Departmental training criteria will be followed."
Interviews with SR and WSI-SRS management provided the following explanations why the SRT rappel mission requirement was contained in the WSI-SRS contract. The individual interviewees believe that:
The Board examined the above information and found these explanations unsupported by site-specific need as defined by the SSSP. Although some explanations had some merit based on the NN interview and DOE 5632.7A requirements, site-specific needs do not support rappelling operations at SRS, regardless of how the status of CTA lesson plans are perceived.
The need for the current SRT rappelling contractual requirement, first contained in the 1988 WSI-SRS contract, has not been reassessed by SR management despite changes to the DOE Design Basis Threat Policy, SRS mission requirements, or SSSP protection strategy.
WSI-SRS participation in competitions has been authorized by SR-OSS through a "performance direction" memorandum and not through a contract modification. The rationale for this authorization has been that WSI-SRS participation in competitions is considered by SR-OSS to be within the scope of the contract, and as a result, funding for competitions has been justified as "mission travel."
Historically, WSI-SRS has submitted competition standing to the Award Fee Board's Performance Evaluation Committee, and competitions were perceived as assessment factors. SR has allowed WSI-SRS to participate in competitions because "it is consistent with past practices, it provides a vehicle for DOE to gauge SRT training levels, it enhances SRT training, and it builds morale within the SRT." Despite the fact that there have been more than 11 rappelling accidents or incidents at SRS in the last 10 years, SR has allowed WSI-SRS to continue onsite rappelling operations and offsite rappelling competitions.
The relevance of the Buddy Rappel technique to DOE or SRT operations is obscure. Some interviewees associated the technique with rescuing injured personnel (although several other rescue rappel techniques are available) or to quickly insert an individual with mission-relevant technical skills who is unfamiliar with individual rappelling techniques. The competition team viewed the Buddy Rappel technique strictly as a method to increase their chances of winning the competition by descending two rappellers at one time to reduce the overall event completion time. As in past competitions, the WSI-SRS Team knew that specific event requirements changed from year to year and that the final event requirements would not be briefed until just prior to the event. The competition team assumed there would be a timed rappelling event at the Spartanburg competition and concluded that the Buddy Rappel might be a solution to reducing the event task time. The Buddy Rappel technique is neither covered by procedures or training lesson plans, nor approved for use by WSI-SRS.
WSI-SRS SRT management and training management were presented with several opportunities to explicitly direct the exclusion of the Buddy Rappel technique from SWAT competition training, which they did not. Interview information suggests that discussions that occurred the morning of the accident centered on the use of safety lines for the Buddy Rappel (There is a difference of opinion as to which type - top belay or sling rope - was discussed.). A top belay safety line was not used during competition training, but a sling rope (tying the Rappeller and Buddy together) was employed. During interviews, management personnel stressed that the personnel selected for the competition were the most experienced and seasoned SRT veterans on the entire WSI-SRS force, most with more than 10 years' experience as WSI-SRS SRT personnel as well as previous military experience. It was implied that this vast experience gave the competition team the authority to conduct whatever rappelling operations the team deemed safe and appropriate to facilitate winning the competition. This reliance on "experience" also was explained as the reason that the required Rappellers Safety Brief Checklist (see Appendix L) was executed from memory and was not physically present at the ATTA Rappel Tower. Broad individual experience and the competitive spirit of the members of the competition team led to the following:
The presence of a multifaceted command and control structure at the ATTA facility on the morning of the accident resulted in competition event training responsibilities being informally split among several SRT personnel. This fragmentation of command and control authority foreclosed any opportunity for a focused, carefully directed training and safety regimen overseen by a single leader. The absence of written SWAT competition training procedures incorporating lessons learned from previous SRT competitions resulted in the team relying on experience and memory to drive their training and safety practices.
The Board arrived at SRS on April 4, 1995, and took responsibility for the Rappel Tower and the equipment associated with the accident. WSI-SRS had posted a 24-hour guard at the entrance to the ATTA shortly after the accident. Because rain and wind were predicted, WSI-SRS had also erected a tent and covered the gates with clear plastic sheeting to preserve the scene of the accident, as shown in Figure 3-2.
The Board concurred with the actions taken and agreed that WSI-SRS should continue to maintain security at the Rappel Tower until it was returned to WSI-SRS for training operations.
Based on a review of meteorological conditions, the Board determined that weather was not a factor in the accident. On the day of the accident, the sky was clear, the temperature did not exceed 70 degrees Fahrenheit, and the wind was from the north at 9 miles per hour.
When the accident occurred, the elasticity of the rope caused it to recoil from the gate on top of the tower. The rope is shown in Figure 3-3 where it came to rest. The gate had been opened after the accident and before this picture was taken.
Figure 3-3. Top of Rappel Tower
A closeup view of the rope separation on top of the tower is shown in Figure 3-4. The gate lock-pin housing that was in contact with the rope at the time of the separation is shown in Figure 3-5. Rope fibers can be seen next to the edge where the rope abraded the point prior to the separation.
The impact area of the victim at the base of the tower is shown in Figure 3-6, as seen from the top of the tower. Another view of the impact area is shown from ground level in Figure 3-7. The rope used for single person rappels was still in place on the tower. Another view of the impact area and the rope in use at the time of the accident are shown in Figure 3-8. A closeup of the broken rope is shown in Figure 3-9, as it came to rest after the accident. The Board concluded its examination of the Rappel Tower and returned it to WSI-SRS for normal range operations, except for rappelling, on April 17, 1995.
A discussion of rope construction and the various types of ropes that are available for rappelling may be found in Appendix F.
The rope used in the rappel training exercise at the time of the accident was a 7/16-inch diameter nylon mountaineering operations rope, which measured 93 feet 4 inches in length. The rope was 120 feet long when purchased and had apparently been shortened by 26 feet 8 inches. The shortening had no bearing on the accident, as the Board found the length of the rope not to be a relevant factor. The rope was purchased from the Defense Industrial Supply Center under Federal Stock Number 4020-00-931-8793. This is consistent with the WSI-SRS Standard Procedure 1-5600, "Rappelling," Rev. 2, dated May 2, 1994, which defines the requirements for rappel rope.
The minimum tensile strength of the rope was stated in the rappel procedure as 3,840 pounds. This is inconsistent with the tensile strength of 4,500 pounds specified for the rope purchased under the Federal Stock Number referenced above. The origin of the 3,840-pound tensile strength was found to be taken from a Department of the Army Training Circular, C1, TC 90-6-1, dated 30 September 1976, entitled, "Military Mountaineering." This reference states: "Nylon rope is most commonly used in climbing. The rope is 1.1cm (11mm) in diameter and is issued in 36-1/2 meter lengths. The actual separating strength when dry averages 3,840 pounds (+5 percent). The separating strength is reduced by 18 percent when the rope is wet."
The rope being used for rappelling at SRS is also known as "Military Green Line" due to its color. The 7/16-inch rope that separated is normally the smallest diameter rope used for rappelling. Increasing use of 1/2-inch rope was noted in Reference 39 because of its greater tensile strength.
When a rope is used for rappelling, a working load of 7 percent or less (a safety factor of 15:1) is recommended (Reference 40). The working load is defined as the percent of the tensile strength of the rope that should be used for rappelling.
Based on the above, the maximum recommended load on the rope that was involved in the accident would have been 315 pounds (0.07 x 4,500). The actual weight of the Rappeller and the Buddy plus their gear was estimated to be 484 pounds.
Figure 3-4. Closeup of Rappel Rope
Figure 3-7. Impact Area as Seen from Ground Level
Sections of the rope involved in the accident and a new "reference" rope taken from inventory were subjected to tensile testing by WSRC to determine if the rope met the original specification tensile requirement of 4,500 pounds.
Tests were also conducted to simulate the small radius edge of the safety gate lock-pin housing that caused the rope to separate. In addition, static and dynamic analyses were conducted to determine the actual loads on the rappel rope at various positions of the Rappeller during the descent. Forces were also calculated on the Rappeller's legs that were required to maintain the combined center of mass at various distances from the tower wall.
The results of the tests and analyses are contained in WSRC Technical Report WSRC-TR-95-0194, "An Evaluation of Rappelling Rope Capacity and Loading" (Appendix J), and are summarized in the following paragraphs.
The average breaking strength of the reference rope was 5,600 pounds. The average separating strength of the rope involved in the accident was 5,370 pounds. Both ropes exceeded the tensile strength requirement of 4,500 pounds found in the rope specification.
The average breaking strength of the reference rope over a small diameter edge simulating the safety lock-pin housing was 767 pounds. The average separating strength of the rope involved in the accident subjected to the same condition was 783 pounds.
The static rope tension force present during the rappel was the combined weight of the Rappellers (484 pounds). The dynamic shock load in the accident rope due to the rope sliding from the top rail of the gate to the pin housing, a 7.25-inch vertical drop, was calculated to be between 780 pounds and 1,150 pounds, depending on the stiffness of the rope and the position of the Rappeller relative to the tower wall. Assuming an average value of 965 pounds, the dynamic load on the rope exceeded the load capacity (783 pounds) of the rope when in contact with the small radius of the lock-pin housing, resulting in the rope separation.
The results of the rappel rope testing were further confirmed when compared to the test for determining the dynamic rope strength specified by the International Union of Alpine Associations (see Reference 40). For this test, a weight of 176 pounds is tied to the end of an 11mm rope and dropped from a height of 16.4 feet over an edge with a radius of 1.0mm. The rope failure rate was observed to be 100 percent when subjected to those dynamic conditions. The rappel rope that separated and resulted in the fatality was in contact with a radius of less than 0.1mm. Therefore, the rope separation was predictable with a high degree of certainty.
The WSRC report also discusses the forces on the legs of the Rappellers at various rope angles and center of mass distances from the tower wall. Assuming a rope angle of 40 degrees from the vertical at the start of the rappel, the force on the Rappeller's legs would have been approximately 400 pounds. This explains the difficulty he experienced in trying to establish an "L" position at the top of the wall as he initiated the rappel.
Last Modified: Friday, 28-Feb-97 10:09:00