Applied Electrical Safety for High Voltage DC Systems

The HVDC systems used in a variety of emerging applications are not as well understood.

• By David Paoletta
• Mar 14, 2025

Alternating current (AC) electrical power has been used in industrial facilities and in people’s homes since 1882. Over the years, we have come to recognize the hazards associated with AC, and safety professionals have implemented 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 applications 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 electric shocks and flash burns. Higher voltage Lithium-ion battery power systems also pose additional handling, storage, and emergency response challenges that are unique to their technology.

A recent OSHA and NIOSH data analysis by Johns Hopkins University revealed that arc flash incidents included 1291 investigation reports for the period from the early 1980s to 2022. These reports cover 1823 injuries and 277 fatalities. While only one direct DC incident 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 conditions and 30 volts under wet conditions. However, newer HVDC applications can be many times higher than those safe ranges. (See “Typical High Voltage DC Levels by Applications”)

Sectors employing workers interacting with newer and more dangerous HVDC systems are often 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 predominantly focused on AC systems and older lead-acid battery technology.

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. Isolation and surge protection measures are critical as well as consumer notices and inspections.
• 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.
• Power Grid Maintenance = up to 500,000 volts: HVDC power transmission grids of up to 500 kV have been deployed in the US and require advanced fault detection and insulation monitoring systems. Workers must follow stringent procedures for de-energizing lines during maintenance.
• Microgrids = 380 volts or more: Solar and wind-powered microgrids involve HVDC components that pose grounding and surge risks. Regular inspections of grounding systems are essential.
• Robotics and Manufacturing = Up to 1,000 volts: High voltage DC motors and drives in manufacturing require insulated barriers and emergency shutoff mechanisms. Training on handling electrical faults is crucial.
• Data Centers = 380 volts: HVDC data center power networks are being deployed to improve reliability and efficiency, but are prone to overheating and fire hazards. Specialized fire suppression systems and thermal monitoring can mitigate risks.
• Aviation = 270 to 540 V DC: “More” or “All” electrified aircraft use electric systems to replace some or all of their conventional mechanical, hydraulic, and pneumatic systems. The goal of electrifying aircraft is to reduce pollution, increase fuel efficiency, and make flights more affordable. Onboard HVDC power supplies can be prone to overheating and fire hazards. Specialized fire suppression systems and thermal monitoring can mitigate risks.
• Autonomous Off-Road Vehicles and Equipment = 400 VDC or more. Farm tractors, construction equipment and other non-connected vehicles and equipment are now often controlled remotely, but must still be serviced, charged and monitored in person which can cause operating electrical exposures, particularly in wet conditions.

Identification of Potentially Hazardous Conditions

High Voltage DC (HVDC) systems differ significantly from traditional AC systems in terms of operational characteristics and associated hazards. Understanding these differences is crucial for protecting workers and mitigating risks.

High voltage DC systems lack the natural zero crossing found in AC waveforms, making arc extinguishment more difficult. This increases the risk of sustained arcs, which can lead to severe injuries. These systems also operate at constant voltage levels, posing higher risks of prolonged electric shocks when contact is made.

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 temperatures exacerbate these risks by accelerating insulation degradation and increasing the likelihood of partial discharge.

Lithium-ion batteries, a common component of HVDC systems, introduce unique hazards. Thermal runaway, a condition where the battery's internal temperature increases uncontrollably, can result in fires or explosions. Proper storage, such as maintaining batteries at appropriate temperatures and away from flammable materials, is critical.

Examples of Resulting Problems and Exposures

Workers exposed to HVDC systems face risks of severe injuries, including burns, electric shocks, and long-term health consequences. Arc-flash incidents in HVDC systems can produce higher intensity discharges than AC systems due to the constant voltage, leading to catastrophic injuries and equipment damage.

Data from the Electrical Safety Foundation International reveals that nearly 79% of electrical fatalities occur near or in contact with energized conductors. Industrial environments, such as electric vehicle manufacturing and grid maintenance, are particularly high-risk due to frequent exposure to HVDC equipment.

Recent incidents at electric vehicle charging stations illustrate the dangers. Failures in isolation or grounding systems can lead to severe arc-flashes, causing burns and equipment destruction. These examples highlight the need for robust safety protocols and training tailored to HVDC systems.

Preventative Steps and Precautions

Implementing safety measures tailored to HVDC systems is essential for minimizing risks.

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 applications, including NFPA 70E compliance.
2. Engineering Controls: Barriers, insulation, and interlock systems can prevent accidental contact with energized parts.
3. Battery Storage and Handling: Lithium-ion batteries should be stored in temperature-controlled environments and regularly inspected for signs of damage such as loss of electrolyte.
4. Maintenance Protocols: Isolation and lockout/tagout procedures must be rigorously applied to prevent accidental energization. HVDC-specific modifications, such as double-pole isolators, are recommended.
5. Emergency Preparedness: Workers must be trained in first aid and emergency response for electrical injuries and battery-related incidents, such as thermal runaway.

Evaluating and Measuring Processes and Training Outcomes

To ensure the effectiveness of safety protocols and training, organizations must establish robust evaluation mechanisms.

1. Metrics for Training Effectiveness: Assess workers' knowledge through pre- and post-training evaluations. Monitor incident rates to gauge training impact.
2. Safety Audits: Conduct regular inspections of HVDC systems and associated safety measures. Audits should include checks for compliance with appropriate ANSI/ASSP standards (i.e. ANSI/ASSP A10.10, ANSI/ASSP Z15 or ANSI/ASSP B11) and ISO 45001 requirements.
3. Compliance Indicators: Evaluate adherence to lockout/tagout procedures, PPE use, and proper handling of higher voltage batteries. Non-compliance should trigger immediate corrective actions.
4. Innovative Training Tools: Simulations and VR tools can enhance understanding of HVDC hazards by providing realistic, hands-on learning experiences.
5. Worker Feedback: Encourage workers to share observations and suggestions for improving safety practices. Feedback can identify gaps in procedures and foster a culture of continuous improvement.

Given the increasing prevalence of high voltage DC technologies, it is crucial for industry professionals to receive appropriate training and be equipped to understand and mitigate shock and arc-flash hazards from increasing HFDC adoption. Implementing safety measures becomes paramount even when not directly handling high voltage lithium-ion batteries or working on HFDC systems, but also when these systems are being constructed, transported or serviced. Additionally, workers and first responders must be familiar with emergency response actions to be taken in the event of a battery thermal runaway, fire, arc-flashes or shocks which can be caused by direct contact, accidents or improper usage.

This article originally appeared in the February/March 2025 issue of Occupational Health & Safety.