At one of our VUV beam lines, a visiting research group needed to supply a negative electrical bias to a sample under study. With no guidance and little experience, members of the group attempted to modify the high voltage connections on a 2000-volt, 100 mA DC power supply to provide the needed bias. The modification was improperly done and resulted in a significant shock hazard on the shell of the SHV connector of the high voltage cable. The power supply did not operate properly after this modification and the users ceased their efforts, but did not restore the supply to its original configuration; thereby leaving a potentially hazardous condition for subsequent groups. The next user at the beam line also sought to use the power supply, and contacted the Local Contact (not present at the NSLS) for advice when he realized that it was not functioning properly. He was unable to determine the problem and also discontinued use of the power supply. Several days later, the local contact returned, quickly identified the problem and reported it to the NSLS. No one was injured and there was no electrical shock to personnel, but an unsafe condition was created and existed off and on for a number of days before it was identified and corrected.
Lessons Learned (pdf)