Sandians experienced 8 shock events involving capacitors in the past two years, approximately half of all electrical shock events. Capacitors are energy storage devices that must be positively discharged before they are safe to handle. Removing external power from circuits containing capacitors may not remove the stored energy from a capacitor. An energy level of 10 joules is a shock hazard and lower levels can cause a startle reaction that could lead to other injuries. Capacitors the size of a 'D' flashlight battery can attain 10 joules of energy and should be considered hazardous. The actual energy can be calculated from:

Energy (joules) = 1/2 CV² ; Where C = capacitance in farads, and V = voltage in volts.

Required Safety Practices for working with capacitors are contained in the Electrical Safety Manual, MN471004, Section 4.6. Requirements from that section must be included in operating procedures for personnel who work with capacitors. These workers must understand how to apply these requirements. A review of these required ES&H safety practices has identified the need for additional requirements which are included below. Below is only a summary of the requirements in Section 4.6 and is not inclusive.

Required Safety Practices

(for capacitors storing 10 joules of energy or more and recommended for all other capacitor operations)

• Barriers must be established to keep out unqualified workers.
  
  
• Qualified workers must be trained in the proper handling, storage, and hazards recognition of capacitors.
  
  
• Procedures must be established for bypassing and restoring safety interlocks, including a log of events.
  
  
• Use automatic shorting devices that operate when equipment is de-energized (including interlock operation).
  
  
• Visually verify that the automatic shorting devices have functioned properly (including wiring integrity).
  
  
• Inspect shorting and grounding devices for general condition and connection integrity before each use.
  
  
• Use proper PPE when applying shorting and grounding devices (hand, eye, face, and body protection).
  
  
• Use approved shorting sticks to assure that the capacitor has been de-energized.
  
  
• Short and ground the capacitor before servicing. Maintain the short and ground while servicing.
  
  
• Remove all shorts and grounds before re-energizing.

Additions to Requirements

Where the operation of automatic shorting devices cannot be visually verified, a voltage measurement must be taken to verify de-energization before shorting and grounding. During development or diagnostic work when the automatic shorting devices are not active, a current limiting grounding device with an impedance capable of limiting the current to 500 amps or less may be used to verify de-energization.

Worker training must include the worker demonstrating how to safely discharge the capacitor for servicing. New designs must incorporate safety features for maintenance and troubleshooting personnel.

Recommendations

• A mini-checklist at the work area will help the worker remember the steps to de-energize.
  
• Permanent meters or indicators across capacitor circuits will indicate a hazardous situation.
  
• Management walkthroughs and self assessments should identify capacitor hazards.
  

Until operating procedures are changed, this Bulletin may be attached to existing procedures.