Green Car Safety

Green Car Safety

In a car, power sources like electricity and natural gas seem threatening, but once you look into it, you'll find these alternatives might be different from gasoline, but they're not necessarily more dangerous.

Crash Tests

More than safety features, crash tests are the best way to gauge how well a particular model might protect you and your family in a collision. Thankfully, hybrids are well represented in these tests. Our preferred crash-testing agency, the Insurance Institute for Highway Safety, has tested two of the three dedicated hybrid models, the Honda Insight and Toyota Prius. As of this writing, the small Honda CR-Z hasn't been tested. The agency says the market's remaining hybrids, which are versions of gas-only models, are covered by the same tests.

"As long as the weight of the hybrid is not significantly greater, and the automaker made no structural modifications to the front of the vehicle to accommodate the hybrid system, then there should be no difference in frontal or side crash-test performance," IIHS spokesman Russ Rader said.

One exception to this guideline involves the agency's roof-strength tests. This IIHS rating is based on the tested roof's ability to withstand the vehicle's own weight. The roofs are all the same, but the additional hybrid hardware and batteries can add enough weight to the car to change the rating. For example, the Ford Escape is rated Marginal, but the Escape Hybrid is rated Poor. A relatively new rating, roof strength has revealed weaknesses that the automakers haven't had the opportunity to address. The results are particularly disappointing among SUVs, some of which otherwise score well. Some cars are borderline enough that weight differences — be they from hybrid technology or four-wheel drive — can be the difference between one rating and another for the same model.

High Voltage

The two newest and most recognized high-voltage cars, the Chevrolet Volt and Nissan Leaf, will be tested by IIHS, but they haven't been as of this writing. While the battery packs used by these and future plug-in cars are larger than hybrids have had, the voltage levels are in the same ballpark. As such, the clean safety record of hybrids over the past decade should help allay concerns about the plug-in models as well.

In all plug-ins and full hybrids, the battery pack is designed to withstand the harsh mobile environment, which includes vibration, jolts and temperature extremes. The packs are also protected from crashes by the vehicle's structure, and they contain dozens — even hundreds — of separate cells. Even in the case of a severe breach, individual cells might be damaged, but the pack itself isn't full of acid that would all spill out. As mentioned, the hybrid battery packs have performed well throughout their history.

To prevent shocks, the packs typically are equipped with voltage-leak sensors and inertial cutoffs that disconnect the battery from the rest of the car if something goes wrong. An airbag deployment, for example, usually isolates the battery immediately.

The majority of post-collision car fires are caused not by fuel but by electrical short-circuits from pinched 12-volt cables, and this is why first responders' first step after a crash is to pop the hood and disconnect the 12-volt battery. Normal cars don't have the safety provisions found on high-voltage cars. Just to be sure, though, rescue workers have insisted that makers of cars like the Leaf and Volt provide a master cutoff switch just for them. In the Leaf, it's under an access panel in the floor, accessible from the backseat. In the Volt, a 12-volt cable in the side of the cargo area, when cut, disconnects both the 12-volt battery and the high-voltage battery pack remotely, allowing workers to disable both power sources at the same time.

How will first responders know where to look? Manufacturers work with firefighter associations to educate rescuers about their products, how to disable them and where to cut when an extraction is necessary, providing resources like this one from GM. Such efforts are more extensive than you might think, because even regular cars are filled with explosive devices like airbags and seatbelt pretensioners. Cutting into a car in the wrong place can be very dangerous for rescuer and victim alike. Chevrolet and Nissan are engaged in Volt and Leaf training programs with first responder organizations nationwide, starting in their initial launch markets.

Natural Gas, Hydrogen and Biofuels

On some level, all alternative energy sources sound scary, mainly because we've come to take gasoline for granted. Gasoline is very dangerous because it's volatile and highly combustible. If gasoline ignites, it will keep on burning and there's a risk of explosion, though vehicle fuel tanks are designed to withstand tremendous trauma.

In comparison, natural gas is lighter than air and dissipates readily. (Propane is heavier than air, but there are no retail propane-powered vehicles.) Though it exists only in large-scale test fleets, including Honda's FCX Clarity and Chevrolet's fuel-cell Equinox, hydrogen is lighter still. Though these gases are certainly dangerous, there's no reason to think they're more dangerous than gasoline. They're simply different.

Like liquid fuel tanks, the tanks that hold these gases are designed to withstand impacts and high heat levels, and they are equipped with safety valves to prevent unintended leaks in the instance of trauma. Currently, there's only one natural-gas-powered car on the mass market, the Honda Civic GX, and it's offered in only a handful of states.

It's a similar story for biofuels such as ethanol and biodiesel. E85, which comprises 85 percent ethanol and 15 percent gasoline, shares almost identical systems in a car. From the safety standpoint, they're roughly the same.

The properties of regular petroleum diesel fuel make it less combustible than gasoline, which is one of the reasons it can be used in confined spaces, even inside buildings. Biodiesel is a similar story, and in its pure form, B100 (100 percent biodiesel) is theoretically nontoxic. In practice, though, B100 is rare. Most biodiesel comes mixed with petroleum diesel, such as in B20. Note that biodiesel isn't vegetable oil, though it can be derived from cooking oil and the like. Biodiesel can be used in any diesel engine. Vegetable oil requires engine modifications. Theoretically, vegetable oil is also nontoxic, though consuming it wouldn't be a good idea, especially if it's been used to fry food.

Alternative fuels and propulsion systems present engineers with a new set of challenges, but none have proved more dangerous than the conventional fuels we've come to take for granted.

© 11/3/2010