Page 39 - OHS, February/March 2025

E L E C T R I C A L S A F E T Y
Applied Electrical Safety for High Voltage DC Systems
Applied Electrical Safety for High Voltage DC Systems
Th e HVDC systems used in a variety of emerging applications are not as well understood.
Th e HVDC systems used in a variety of emerging applications are not as well understood.
BY DAVID PAOLETTA, MS, CSP, CUSP, CESCP
BY DAVID PAOLETTA, MS, CSP, CUSP, CESCP
in industrial facilities and in people’s homes since 1882.
Alternating current (AC) electrical power has been used
Over the years, we have come to recognize the hazards
associated with AC, and safety professionals have imple-
mented regulations and procedures for managing their risks.
However, the hazards of what might be termed higher voltage
direct current (HVDC) systems, from a variety of emerging ap-
plications ranging from electric vehicle charging stations and auto
repair to high voltage data centers, are not as well understood.
As HVDC systems become more common and more powerful,
they bring some of the same safety concerns as AC power like elec-
tric shocks and fl ash burns. Higher voltage Lithium-ion battery
power systems also pose additional handling, storage, and emer-
gency response challenges that are unique to their technology.
A recent OSHA and NIOSH data analysis by Johns Hopkins Uni-
versity1 revealed that arc fl ash2 incidents included 1291 investigation
reports for the period from the early 1980s to 2022. Th ese reports
cover 1823 injuries and 277 fatalities. While only one direct DC in-
cident was listed, the bulk of the accidents appear to be in situations
where applications are likely employing DC lower voltage ranges
such as welding, or telecommunications transmission. “Safe” DC
voltage ranges are considered to be less than 60 volts under dry con-
ditions and 30 volts under wet conditions.3 However, newer HVDC
applications can be many times higher than those safe ranges. (See
enclosed table: “Typical High Voltage DC Levels by Applications”)
Sectors employing workers interacting with newer and more
dangerous HVDC systems are oft en unsure of how to manage the
unique risks presented by the technology. Alongside this is a lack
of guidance on how to protect workers exposed to DC hazards, as
most regulatory standards and references have been predominant-
ly focused on AC systems and older lead-acid battery technology.
Identifi cation of Potentially Hazardous Conditions
HVDC systems diff er signifi cantly from traditional AC systems in
terms of operational characteristics and associated hazards. Un-
derstanding these diff erences is crucial for protecting workers.
High voltage DC systems lack the natural zero crossing found
in AC waveforms, making arc extinguishment more diffi cult. Th is
increases the risk of sustained arcs, which can lead to severe inju-
ries. Th ese systems also operate at constant voltage levels, posing
higher risks of prolonged electric shocks when contact is made.4
Key indicators of HVDC carrying wire/cable insulation failure,
such as discoloration, cracking, or heat marks, should be closely
monitored. Environmental conditions like humidity and high tem-
peratures exacerbate these risks by accelerating insulation degra-
dation and increasing the likelihood of partial discharge.5
Lithium-ion batteries, a common component of HVDC sys-
tems, introduce unique hazards. Th ermal runaway, a condition
where the battery’s internal temperature increases uncontrollably,
can result in fi res or explosions. Proper storage, such as maintain-
ing batteries at appropriate temperatures and away from fl amma-
ble materials, is critical.6
www.ohsonline.com Examples of Resulting Problems and Exposures
Workers exposed to HVDC systems face risks of severe injuries,
including burns, electric shocks, and long-term health conse-
quences. Arc-fl ash incidents in HVDC systems can produce higher
intensity discharges than AC systems due to the constant voltage,
leading to catastrophic injuries and equipment damage.7
Data from the Electrical Safety Foundation International re-
veals that nearly 79 percent of electrical fatalities occur near or in
contact with energized conductors.8 Industrial environments, such
as electric vehicle manufacturing and grid maintenance, are par-
ticularly high-risk due to frequent exposure to HVDC equipment.
Recent incidents at electric vehicle charging stations illustrate
the dangers.9 Failures in isolation or grounding systems can lead
to severe arc-fl ashes. Th ese examples highlight the need for robust
HVDC safety protocols and training.
Preventative Steps and Precautions
Implementing safety measures for HVDC systems is essential:
1. Personal Protective Equipment (PPE): Workers should use
arc-rated clothing, electrically insulated gloves, and non-sparking
tools. PPE should meet the highest standards for HVDC applica-
tions, including NFPA 70E compliance.
2. Engineering Controls: Barriers, insulation, and interlock
systems can prevent accidental contact with energized parts.
TYPICAL HIGH VOLTAGE DC LEVELS BY APPLICATIONS
Electric Vehicle Charging Stations = Up to 500 volts: HVDC systems are
integral to electric vehicle fast-charging stations. Unique hazards include
high power levels and frequent power surges. tinyurl.com/4yk7etmd
Electric Vehicle Repair = Up to 800 volts: Technicians must de-
energize HVDC systems and use insulated tools. Workshops should
have proper ventilation and safety signage. tinyurl.com/3dyrjjvr
Power Grid Maintenance = up to 500,000 volts: HVDC power transmis-
sion grids of up to 500 kV have been deployed in the US and require ad-
vanced fault detection and insulation monitoring. tinyurl.com/3aacd8m7
Microgrids = 380 volts or more: Solar and wind-powered microgrids
involve HVDC components that pose grounding and surge risks. Regu-
lar inspections of grounding systems are key. tinyurl.com/47axn3sf
Robotics and Manufacturing = Up to 1,000 volts: High voltage DC
motors and drives in manufacturing require insulated barriers and emer-
gency shutoff mechanisms. Training is crucial.tinyurl.com/3ftkymr4
Data Centers = 380 volts: HVDC data center power networks are
being deployed to improve reliability and effi ciency, but are prone to
overheating and fi re hazards. tinyurl.com/58zuywd6
Aviation = 270 to 540 V DC: To cut costs and pollution, more aircraft
use electric systems employing HVDC power supplies to replace me-
chanical, hydraulic, and pneumatic systems. tinyurl.com/y9w8sx96
Autonomous Off-Road Vehicles and Equipment = 400 VDC or more.
Farm and construction tractors and other vehicles are often controlled
remotely, but must be serviced and charged. tinyurl.com/eybaphbt
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