Lessons Learned Events at SLAC Mike Woods, SLAC National Accelerator Laboratory
SLAC Lessons Learned Compilation Definition of a Lessons Learned Event event or observation that identifies a best practice, improvement opportunity or the lack of a required safety barrier. This can be related to any of the following safety configuration engineering controls administrative procedures laser eyewear requirement posted signs and labels how training is done Lessons learned are routinely compiled from SLAC s laser operations and communicated to SLAC laser personnel. Each event report includes fields for event description, cause, corrective actions and lessons learned.
SLAC Lessons Learned Compilation
SLAC Lessons Learned Compilation The compilation has 28 events in last 4 years of laser operation, including: 3 ORPS-reportable incidents: - eye exposure injury (2009, reported on at LSOW-2010) - Class 1 laser not enclosed (2011) - laser operator enters NHZ without protective eyewear (2012) required laser safety barrier compromised (13 events) safety configuration control issues (3 events) engineering configuration design issues (7 events) malfunctions in the engineered laser safety system (9 events) - safety shutter (2) - unlocked door (2) - electronic warning sign (2) - safety cabling (2) - programming error (1) administrative procedure mis-steps (9 events) electrical safety issues (3 events) laser eyewear issues (4 events) best practices identified (5 events)
LL Example: Shutter Failure 5
LL Example: Stray Beam Not Blocked 6
LL Example: Safety System Programming Error 7
LL Example: Exposed Electrical Hazards in some flashlamp-pumped lasers SLAC has add to add protective barriers on some flashlamp-pumped lasers (shown in photo with associated warning labels) some commercial lasers have exposed HV hazards when covers are removed for service/maintenance (ex. cavity optics tuning or aligning injection seeder) + need to address CoHE and evaluate need for LOTO when changing flashlamps 8
LL Example: Entry Door Closer needed for Hutches that are often uncontrolled areas 9
2011 Class 1 Enclosure Incident Laser source inside enclosure Shutter enclosure with safety shutter removed and 2 covers removed Laser beam path (shown in red) if temporary beam block removed Incident Description: Laser operator noticed red laser beam on shirt sleeve while locating a new laser optic in stretcher enclosure downbeam of the shutter enclosure, during Class 1 operation mode when laser beams are required to be fully enclosed No PPE laser eyewear was being worn, since not required for Class 1
2011 Class 1 Enclosure Incident Incident Details Day prior to incident, safety shutter removed to accommodate a new optic being installed (Faraday isolator to prevent back reflections into oscillator). Laser system then operated in Class 4 maintenance mode (PPE required) but safety shutter functionality not restored. At end of day, laser system is put to Class 1 mode, but without the required safety shutter and 2 covers Following morning, laser operator enters to work in Class 1 (PPE not required) when event occurs. Root Causes Lessons Learned: 1. Inadequate Work Planning and Control to assess potential hazards associated with moving a safety shutter and to determine if supervisor approval was needed. 2. Inadequate configuration control for laser safety devices. 3. Priority given to laser optics work rather than to restoring functionality of a laser safety device. 4. Failure to verify laser safety enclosures to ensure that a zero energy condition exists to allow Class 1 operation mode with no laser eyewear required.
For Laser Lab 2011 Class 1 Enclosure Incident: Corrective Actions OJT and SOP updates to address configuration control and verification procedures when setting Laser Off and Class 1 modes Relocated safety shutter and implemented smaller enclosure for safety shutter Laser safety device label over securing bolts for safety shutter Posted procedure for setting Class 1 mode at point-of-use at control panel For Laser Safety Program/Other laser labs Safety configuration control requirements: - OJT syllabus and SOP must include these (ex. moving a safety shutter) Class 1 Operation: - Unattended Class 1 should not be permitted if removable enclosures are not interlocked or secured with administrative locks - In uncontrolled areas, removable Class 1 enclosures must have non-defeatable interlocks (exception may sometimes be approved for administrative control lock) - Class 1 conditions must be verified when setting Class 1 mode and when entering or exiting the lab in this mode Lessons Learned document on this incident distributed to SLAC personnel and DOE laser safety group
2012 Incident Laser Operator forgets to put on Eyewear PPE when entering NHZ Computer Station Nominal Hazard Zone Computer Station Location Worker realizes not wearing protective Laser Eyewear Laser Curtain Shared Optics System Outer Entry Door PPE Storage (Eyewear) Key Controlled Access Laser Entry Vestibule Work Area 0utside NHZ (No PPE Required) Key Controlled Access Coherent Laser System Chiller NHZ (PPE Required) Thales Laser System Inner Entry Door Operator realizes mistake after ~5 minutes, when notices light at an uncovered enclosure when returning to a computer work station outside the NHZ
2012 Incident Exposure to Diffuse Scattered Laser Light determined that no credible exposure risk to primary or stray beam, and that exposure to diffuse radiation was below MPE Beam paths at unenclosed UV tripler Color-coded beam paths added to photo. Camera has much better sensitivity to 760nm than eye. Laser worker would likely have perceived a low level of diffuse scattered 380nm radiation rather than 760nm radiation.
2012 incident: Causes, Corrective Actions, Lessons Learned Contributing Causes Human error forgetting to put on eyewear Lab configuration: lack of robust warning barrier indicating eyewear required at curtain entry to NHZ Laser operator worked in this lab infrequently Added sign-barrier above that you bump into as entering NHZ through laser curtain maze Corrective Actions Sign-barrier added at NHZ entry Root cause analysis investigation (just completed) Incident communicated to all SLAC laser personnel Lessons Learned Mistakes occur. Need fault-tolerant systems so single mistake won t lead to an exposure Laser personnel need awareness of diffuse exposure hazards and importance of eyewear protection for this Best Practice: lab has very good barriers, enclosures so no credible exposure risk to primary/stray beam Extent of Condition: this is only SLAC lab with a work area inside an LCA that is outside the NHZ, but expect similar configurations in future NHZ entryway requirements for these
Lessons Learned Events: Summary Comments Important to identify and communicate lessons learned! Lessons learned and near misses are precursors to injury accidents understanding these and implementing corrective actions can help prevent an injury Identify best practices as well as needed corrective actions Encourage reporting regular communication of lessons learned can foster this