High-Voltage Hazards and De-Energization Procedures
EV high-voltage systems operate at 400–800V DC with available fault current capable of causing lethal electrocution, severe burns, and arc blast. The orange cables and orange-colored components throughout the vehicle identify the high-voltage circuit. First responder safety protocols begin with scene assessment: approach the vehicle from the side (not from the front or rear, which may be closer to high-voltage battery pack sections), maintain awareness of potential high-voltage cable paths. Battery pack locations vary by manufacturer: floor-mounted skateboard platforms (Tesla, most modern EVs — full vehicle floor), T-shaped packs in the center tunnel and floor (Chevrolet Bolt early design), and rear-mounted packs. Manufacturer Emergency Response Guides (ERGs), available on the NFPA and OEM websites, provide vehicle-specific pack locations, manual service disconnect locations, and recommended cut zone restrictions. The manual service disconnect (MSD) or high-voltage interlock is the primary de-energization method. It is typically accessed from the vehicle interior (under the rear seat, in the trunk, or behind a labeled panel) or the engine bay (some manufacturers) and manually disconnects the high-voltage battery circuit. After pulling the MSD, wait a minimum of 5–10 minutes before touching any high-voltage component — capacitors in the inverter store significant energy at full system voltage and require time to discharge through internal bleeder resistors. Dielectric gloves rated for the vehicle's system voltage (Category II, rated 17,000V for a 1,000V max use environment) are required PPE for any contact with high-voltage components. If the MSD cannot be accessed, the 12V accessory battery (separate from the HV pack) can be disconnected to prevent the HV contactors from closing — though this does not discharge the existing HV system if already energized.