JLab-TN-06-046 Safety and Health Analysis of the ... - Jefferson Lab

JLab-TN-06-046Safety and Health Analysis of the Arc Magnet Plan for the 12 GeV UpgradeProjectP. Hunt and R. MayI. Description of Baseline Approach ConditionsThe 12 GeV CEBAF Upgrade project includes modifications to the magnets in therecirculation arcs and their power supplies to keep the higher energy beam confined to theexisting beam path. In addition, a tenth arc-beam line will provide an extra pass through theNorth Linac.With respect to the recirculation arc magnets, the Baseline Approach includes extensive reuseof existing dipoles. These modified magnets will be driven with approximately double thecurrent at which they are presently used. No additional cooling is planned for the magnets;this will result in the magnets being significantly hotter than at present. The approximatepredicted conditions were as follows:Table 1, Initial Predicted ConditionsAmbient Air TempMagnet Surface Temp10 min 1 hour10 min1 hour afterDuring ops after after During ops afteraccessaccess accessaccess135 F (57 C) 135 F 135 F 135 F (57 C) 135 F 130 F (54 C)The ESH&Q staff evaluated the hazards associated with elevated magnet temperature.• No specific guidance exists in the existing JLab ESH&Q Manual on working on oraround hot surfaces.• The ESH&Q Manual Chapter 6670, Thermal Stress, gives exposure limits for workunder non-solar, heat stress conditions. These limits are based on ACGIH ThresholdLimit Values that are derived from wet bulb globe temperature (heat index)measurements. Heat index measurement takes into consideration air temperature,humidity, air movement, radiant heat from hot objects, and body cooling due to sweatevaporation. A heat index of 135 F, which can be reached in ambient temperatures ofabout 105 F - 130 F depending on humidity and other conditions, constitutes apotentially dangerous work condition.II. Initial response to elevated air temperaturesAs a result of potentially dangerous heat stress conditions, an air conditioning system with100-ton capacity was designed to cool the air in the vicinity of the recirculation arc magnets.An analysis of the added cooling results in the following predicted conditions:

Table 2, Predicted Conditions With Air CoolingAmbient Air TempMagnet Surface Temp1 hour10 min 1 hour10 min afterDuringDuring opsafterafter afteraccessopsaccessaccess access105 F (54 C) 95 F (35 C) 95 F 135 F 135 F 130 FAs can be seen, the added cooling produces substantially cooler ambient air temperatureshortly after beam shutdown. The air conditioning system was then added to the 12 GeVUpgrade Project scope and incorporated into the Baseline Approach.For the analysis presented in the remainder of this document, the conditions a worker mightencounter with the Baseline Approach are those represented in Table 2 above.III. Hazard criteria for exposure to hot surfacesAs mentioned above, the ESH&Q Manual Chapter 6670, Thermal Stress, gives exposurelimits for work under non-solar, heat stress conditions. In addition, OSHA provides guidancein Publication 3154 for working elevated air temperature. Because the manual contains labrequirements on heat stress consistent with OSHA guidance, no additional information on thishazard (beyond that associated with actual workplace measurements) is discussed in thisdocument. There are, however, no federal statues that apply directly to workplace hazardsassociated with hot surfaces.OSHA provides general requirements in 29 CFR 1910 Section 5(a)(1), General Duty Clause,which states that an employer must “furnish to each of his employees employment and a placeof employment which are free from recognized hazards…”An August, 19, 1998 OSHA Interpretation indicates that, “Workers must be protected fromhazards of heated (hot) surfaces.”A. Information exists on health effects from contact exposure to industrial surfaces suchas those furnished by Eastman Kodak in Table 3 below.Table 3, Industrial Surface Temperature EffectsMaterialContact ThresholdsPain, 1 sec Burn, 1 sec Burn 4 secMetals 113F (45C) 149F (65C) 140F (60C)Glass 131F 185FWood 167F 239-284F*B. State law exists on the subject with respect to certain conditions. For example, theCalifornia Code of Regulations Subchapter 7, Group 2, Article 7 says, “Pipes or otherexposed surfaces having external surface temperature sufficient to burn human skin onmomentary contact and located within 7 feet measured vertically from the floor orworking level or within 15 inches measured horizontally from stairways, ramps, orfixed ladders shall be covered with a thermal insulating material or otherwise guarded

against contact.” This reference is important in that it identifies administrative controlrequirements and barriers to mitigate burn hazards.C. The American Society for Testing Materials (ASTM), which produces nationalconsensus standard, published C 1055-92, "Standard Guide for Heated SystemConditions that Produce Contact Burn Injuries". This guide provides a means bywhich an engineer can analyze conditions and determine the acceptable surfacetemperature of an existing system where skin contact with a heated surface can occur.Together the above references provide a method to evaluate hazards from hot surfaces andprovide guidance on what constitutes acceptable hazard mitigation. The resultant protocol isoutlined in the following section of this document.IV. Hazard Analysis BasisASTM C 1055-92 defines the following analysis process:A. Establish an acceptable injury level: In our case, avoidance of first degree burns(reversible epidermal injury)B. Establish contact exposure time: For industrial processes, 5 seconds.C. Determine the maximum operating temperature (consistent with C 680 method)D. Use the contact time and maximum operating temperature with Figure 1 belowIf the maximum operating temperature falls below the selected injury threshold in Fig. 1, thenno further analysis is required. If the maximum operating temperature is above the injurythreshold, further analysis is required in the form of additional calculations or directmeasurements.Access to the accelerator tunnel is controlled by the Operations Staff. Personnel cannot enterthe tunnel without the Operations crew and the individuals who intend to enter the tunnel witha specified set of steps that are monitored and controlled. A minimum time an individual canenter the tunnel after the magnets are turned off is cannot occur until several minutes after deenergizingthe magnets. This can be set at 10 minutes.

Using the data provided by the 12 GeV engineers, the maximum magnet surface temperaturefor an arc magnet is 135 F 10 minutes after they are de-energized. Using 5 seconds as amaximum contact time for inadvertent contact, the associated point on Fig. 1 fallsapproximately on or about the Threshold B curve. Based on this information, no additionalanalysis is planned and a redesign of the arc magnet cooling is not warranted. However,heated surfaces and elevated air temperature remain workplace hazards and a strategy isneeded to address them.V. Strategy and Hazard MitigationsThere are generally two conditions under which accelerator tunnel access is made:A. Long-delay access with pre-scheduled maintenance workB. Unscheduled access with short delay between de-energizing the magnets andpersonnel in the tunnelDepending on the quantity of work and the long-term accelerator operations schedule, ascheduled access requires pre-work planning including an associated task hazard analysis. Inaddition, a scheduled access is often preceded by a several shifts (to several days) to allow forradioactive decay. According to information from the Engineering Department, within about16 hours, magnet surface temperature will return to ambient temperature (inlet magnet watercooling temperature) in the region of the recirculation arcs: about 95 F. Task hazard analysescan be augmented to identify any new conditions but, for the most part, heat stress and(thermally) hot magnet surfaces will require no special precautions over those normallyassociated with accelerator tunnel access. Therefore, the remainder of this section is focusedon unscheduled (and thus short delay after magnet de-energizing) accelerator tunnel access inthe vicinity of the recirculation arcs and the associated hazards: contact burn and heat stress.These conditions discussed above are represented in Table 4, below:Table 4, Hazard Mitigations(for various work situations and exposure types)Delay priorto accessExposuretypeInadvertentRequired bytasking(beyond thatneeded forInadvertent)Short delay• OSP• Training• Posted “safe zone”• Flashing signs• OSP• Training• Guarding/shielding• Measure heatindex• Spot cooling• PPE• Work/rest regimenLongdelayNA(Nohazard)NA(Nohazard)

Potential frequency of exposure:An analysis of accelerator operations logs for unscheduled accelerator tunnel access producedthe following information:There have been 18 recent unscheduled access events in approximately 18 months thatresulted in 2 events that brought workers to the vicinity of the recirculation arc magnets.At approximately 1 event per year, exposure to this hazard is infrequent.In addition, the accelerator has a Personnel Safety System (PSS) designed to precludetunnel access during operations. The PSS also limits personnel access during other nonoperationalconditions such as those associated with unscheduled access events. Theopportunity for worker exposure and the exposed worker population is small.This evaluation notwithstanding, more frequent accesses will no doubt be needed during 12GeV commissioning. It is still not unreasonable to assume that there is infrequent need foraccess to the vicinity of the recirculation arc magnets and inadvertent exposure to the hazardsin these areas is inconsequential.Even though inadvertent exposure to contact burn and heat stress is minimal, work may berequired that results in worker exposure to these hazards for short durations. Contact burnavoidance will be accomplished several ways:a) Thermometry installed on reference magnet surfaces will illuminate signs at theentrances to recirculation arcs and warn of surface temperatures >135 Fb) Signs will be posted on magnet metal surfaces that are likely to exceed 113 F and131 F for other non-metal magnet related materials if applicablec) Floor markings that will be used to designate “Keep Out” zones when the warningsigns are illuminatedd) Data from reference magnet thermometry will be available in the Machine ControlRoom for review by staff prior to accesse) IR scans be used to determine magnet surface temperature in the immediatevicinity of work. PPE and guarding requirements will be determined at specificwork locationsHeat stress exposure controls will be accomplished several ways depending on the specificwork situations:a) Monitoring of heat stress conditions will be accomplished by permanentinstallation of WBGT thermometry will be installed at reference locations in therecirculation arcs. Illuminated warning signs at the entrances to the recirculationarcs will be powered if the heat stress index reaches a predetermined value; datawill be available in the Machine Control Roomb) Spot cooling will be used to moderate air temperature at work locations as neededc) Floor markings in the arc will be used to designate “Keep Out” zones when thewarning signs are illuminatedd) All potentially exposed workers will receive medical evaluation and screening andspecific training to allow them to recognize and prevent signs and symptoms ofheat stresse) Task hazard analysis for unscheduled access with short delay will include abriefing of heat stress conditions

f) Specific procedures to be followed for heat-related emergency situations includingprovisions that first aid be administered immediately to employees displayingsymptoms of heat-related illnessg) Work limitations will be based on ACGIH 2006 Threshold Limit Values forChemical Substances and Physical and Biological Exposure Indices; work will belimited by location and predefined work/rest regimes will be used as a defaultcondition until heat stress index measurements are made at the work location orheat index values at reference positions return to nominal valuesAll of the above will be captured in an OSP for scheduled, long-delay accesses and one forunscheduled, short-delay accesses.In summary, a task hazard analysis (THA) will be conducted for any unscheduled task. ThisTHA, along with data from installed equipment that measures in situ workplace conditions,will be compared to requirements in an Operational Safety Procedure (OSP). Engineeredcontrols, PPE, and work restrictions identified in the OSP will be used to safely conduct workassociated with an unscheduled access.VI.SummaryA reasoned combination of active and passive controls will be used to address the hazardspresented in the Baseline Approach. Active controls will be used to display contact burn andheat stress conditions in the recirculation arcs and administrative (passive) controls such aswork procedures, PPE, and barriers will be used when monitoring data exceeds predeterminedthresholds. The combination of these controls will mitigate the hazard such that the risk isacceptable for work by appropriately trained personnel (ESH&Q Manual 3210, Risk Code ≤2).ReferencesASTM C 1055-92, Standard Guide for Heated System Conditions that Produce Contact BurnInjuriesCalifornia Code of Regulations Subchapter 7, Group 2, Article 7Limits on Surface Temperature to Avoid Pain and Burns with Different Contact PeriodsAgainst Skin, 1983, Eastman KodakJefferson Lab ESH&Q Manual, Chapter 6670, Thermal StressVolume 04.06, 2004 C 680-04e1, Practice for Estimate of the Heat Gain or Loss and theSurface Temperatures of Insulated Flat, Cylindrical, and Spherical Systems by Use ofComputer ProgramsACGIH 2006 Threshold Limit Values for Chemical Substances and Physical and BiologicalExposure Indices