Ever since we were kids, it’s been drilled into us that water and electricity don’t mix. When we get to the fire academy we are once again reminded to never use water on energized electrical fires. It all makes perfectly good sense until you sit down and review the dozens of Emergency Response Guides (ERGs) for hybrid and electric vehicle which indicate the best way to put out an HEV or EV fire is with “copious amounts of water”. So you think to yourself….it doesn’t get more energized than a vehicle with a drive system that operates of 650v right? Well there is a perfectly logical answer to that question as it’s all about the circuit.
In our typical responses to energized electrical fires we are dealing with electrical circuits that are grounded to earth. Simply put, if you place your body in the path between the electrical source and the earth or ground you may complete the circuit, and electricity can flow through your body. Electrical circuits in HEVs and EVs are designed differently as they are isolated from the vehicle chassis with no direct connection to the earth or ground. In this case, a circuit would not be completed by a fire stream, through the firefighter, and into the ground.
You should, however, still avoid coming in direct contact with high voltage wiring during the firefighting operation as touching both sides of a high voltage conductor does present a risk of a potentially dangerous electrical shock.
Hopefully this clears up the question of why it’s “OK” to put water on an HEV/EV fire without risking an electrical current traveling up the fire stream….just remember….electrical flow is all about a having a path or circuit. If the path isn’t there, the electricity doesn’t flow.