Hybrid cars have become a popular alternative to traditional gasoline-only forms of transportation. These automobiles combine an internal combustion engine with a battery pack and electric motor. These additional components allow the vehicle to travel longer distances on less fuel and emit fewer emissions.
The battery pack consists of many small, low-voltage batteries called cells stacked on top of each other to create one larger high-voltage (HV) stick [source: Honda]. These sticks are then connected to form one high-voltage battery module. Most hybrids use a nickel-metal hydride (NiMH) battery pack that can both give and receive power; it gives power to the electric motor and receives power from the generator when recharging. On an eco-friendly note, these batteries can be recycled -- although car manufacturers are working on developing even greener batteries to use in their hybrids.
The amount of voltage in these cars, however small, has raised some concerns about driver and passenger safety. Specifically, what happens to that voltage in an accident? How safe is it for emergency personnel to extract an occupant or work with a hybrid at the scene of an accident? What happens when a hybrid gets submerged in water? We'll find out, starting on the next page.
Containing Hybrid Voltage
We mentioned on the last page that voltage in hybrid vehicles can vary in range, but keep in mind that hybrids produce more than enough electricity to kill. According to the Centers for Disease Control, a 7.5 watt, 120-volt lamp draws enough current to cause electrocution [source: Casini]. The two most prolific hybrid manufacturers on the market, Toyota and Honda, each have battery packs with around 100 to 200 volts. In the case of the 2010 Toyota Prius, however, the voltage sent to the electric motor can be boosted up to 600 volts through a voltage converter [source: Webster]. Since the battery packs used by most hybrids produce around 100 to 300 volts of electricity, they are deemed "high-voltage" and must be labeled as such on the parts of the vehicle through which this voltage flows.
To contain the voltage, the battery used to run the electric motor is placed in a metal box that's insulated from the rest of the car's body and labeled with "high-voltage" signs. This battery box is placed behind the rear passenger seats, where it's not likely to be damaged in a car accident [source: Honda]. According to both Honda and Toyota's emergency response guides published for Emergency Medical Technicians (EMTs) and first responders, penetration of the plastic casing around the metal box and the box itself is highly unlikely, even in a severe collision.
In addition to the battery box, high-voltage cables run from the battery to the motor and are insulated with heavy-duty orange plastic casings. Both the metal box and these high-voltage cables are insulated from the vehicle's chassis, and manufacturers insist there's no risk of electrocution by touching the chassis [source: Honda and Toyota].
Although the voltage is contained, it doesn't mean that all risks are removed. Go on to the next page to find out what happens to a hybrid's voltage when it's submerged, on fire, or in an accident.
Hybrid Voltage Safety
A traffic accident is the most common situation an EMT will encounter with a hybrid, so let's take a look at some of the steps to ensure that electricity is shut off to the vehicle.
According to Honda and Toyota's emergency response guides, electrocution is unlikely for two reasons: Contact with the battery and other electrical components can only occur if the box is damaged, exposing the contents, or if it's incorrectly accessed. In addition, high voltage cables are clearly marked so people can avoid them easily.
One of the easiest ways to ensure that voltage is not flowing through the cables is to simply turn the ignition off [source: Honda]. Each hybrid manufacturer has a different system for shutting off the vehicle. It's important to note that even when the engine is not running, the vehicle's electrical system may still be switched on.
When the ignition switch is turned off, the electrical current is shut off and cannot flow into the high-voltage cables, although the electricity may still be running through some cables on certain hybrids for several minutes after the ignition is shut off [source: Toyota].
When dealing with a submerged hybrid or a hybrid that's on fire, response to the situation depends on the type of vehicle involved. For instance, if a Honda hybrid is submerged, Honda recommends pulling the "vehicle from water, then follow recommended procedures for preventing high-voltage current flow" [source: Honda]. In other words, get the car out of the water and turn the ignition off. On the other hand, Toyota recommends disabling the high-voltage battery pack, Supplemental Restraint System (SRS) airbags and fuel pump first, then removing the vehicle from the water [source: Toyota].
To find out more information about EMFs and how hybrid voltage works, go on to the next page.
The Hybrid X concept car from Toyota sparked interest in another Prius-like model. Learn how the Hybrid X evolved and what Toyota's plans are for it.
Related HowStuffWorks Articles
- Casini, Virgil. "Worker Deaths by Electrocution." National Institute for Occupational Safety and Health. 1998. (April 17, 2009)http://www.cdc.gov/niosh/docs/98-131/overview.html
- Honda. "Honda 2005 Emergency Response Guide." 2004. (April 8, 2009) https://techinfo.honda.com/rjanisis/pubs/CI/AXX28935.pdf
- International Commission on Non-Ionizing Radiation Protection. (April 10, 2009). http://www.icnirp.de/index.html
- Motavalli, Jim. "Fear, but Few Facts, on Hybrid Risk." The New York Times. April 27, 2008. (April 8, 2009) http://www.nytimes.com/2008/04/27/automobiles/27EMF.html)
- Pines, Sara. Email Correspondence. Honda Public Relations. American Honda Motor Co., Inc. (April 9, 2009)
- Toyota. "Toyota Prius 2nd Generation Emergency Response Guide." Jan. 1, 2004. (April 8, 2009). http://www.safetycenter.navy.mil/osh/firedata/Toyota_ER_Guides/Prius_2G_ ERG.pdf
- Webster, Larry. "2010 Toyota Prius Hybrid Electric Car Technology Exposed." March 2, 2009. (April 18, 2009)http://www.popularmechanics.com/blogs/automotive_news/4306961.html