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Electrical Risk Assessment

Risk Assessment

Risk assessment for electrical research operations at Virginia Tech is based upon the Department of Energy's Handbook 1092-2013 and NFPA 70E-2021 (for traditional electrical hazards). There are hazard classification charts to cover 60 Hz, DC, capacitors, batteries, sub-RF, and RF power sources. It is possible that a system has more than one energy source. Hazard classification charts are available in the DOE handbook and are provided during Environmental Health and Safety Electrical Safety for Research training. Charts and tables for more traditional electrical work are available in Environmental Health & Safety's Electrical Qualified Person training. Depending on the nature of the research project, both trainings may be beneficial.

Students, in conjunction with their professor and/or Lab Manager, should determine the hazard class for each power source present in the research apparatus. The hazard class will then be used to determine appropriate guidance for the mode of operations being performed at any given time.

Refer to the various thresholds listed in this section. If the thresholds are crossed, appropriate hazard controls and/or personal protective equipment will be necessary as defined per the hazard class.

Threshold Requirements

If an electrical shock or arc flash threshold is exceeded (by the design of the system/equipment/components) or crossed by personnel in proximity to exposed, energized electrical component, hazard controls must be implemented to eliminate or reduce exposure to an acceptable level. Where the risk cannot be eliminated or reduced to an acceptable level, electrical personal protective equipment must be selected for the voltage and incident energy expected and worn by qualified personnel who are working within the approach boundaries.

Electrical Shock Thresholds

In research and development, conditions and controls found in a typical electrical system may be temporarily removed or not within the scope of the project. For example, covers and barriers may be removed from energized systems exposing personnel to a shock hazard. Electrical shock can be fatal. The following thresholds for defining shock hazards are to be observed in research and development applications.

  • AC (60 Hz): greater than 50 volts and greater than 5 mA
  • DC (all): greater than 100 volts and greater than 40 mA
  • Capacitors (all): greater than 100 volts and greater than 1 J, or greater than 400 volts and greater than 0.25 J
  • Batteries (all): greater than 100 volts
  • Sub-RF (1 Hz - 3 kHz): greater than 50 volts and greater than 5 mA
  • RF (3 kHz - 100 MHz): a function of frequency

Arc-flash Thresholds

Arc flash burns may be caused by electric arcs, and are similar to any other heat burn; however, arc-blast hazards (at much greater energy potential resulting in serious injury or death) may be present during research and development applications. Arc-blasts occur rapidly and can result in significant injury or death, as well as equipment destruction. The following arc-flash thresholds are to be observed in research and development applications.

  • AC (60 Hz): 
    • Less than 240 volts and the transformer supplying the circuit is rated greater than 125 kVA
    • Less than 240 volts and the transformer supplying the circuit is supplied by more than one transformer
    • Greater than 240 volts
  • DC (all): greater than 100 volts and greater than 500 amps
  • Capacitors (all): greater than 100 volts and greater than 10 kJ
  • Batteries (all): greater than 100 volts and greater than 500 amps
  • Sub-RF (1 Hz - 3 kHz): greater than 250 volts and greater than 500 amps
  • RF: N/A

Approach Boundaries

When these approach boundaries to exposed, energized electrical components are crossed, hazard controls appropriate for the risk category must be implemented. Risk categories are determined via tables and charts provided in DOE-HDBK-1092-2013, Appendix D. This information is covered during training. Risk categories include: "no hazard, "little to no hazard," "injury or death could occur by close proximity or contact," "injury or death could occur by proximity or contact," or a "high level of risk where significant engineering and administrative controls are necessary to manage the hazard."