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Car in the Water
Published on Jan 01, 2009Email To Friend    Print Version

By Slim Ray,  link to original article CFS Press

That Sunday evening of October 4th, seven to ten inches of rain in a few hours had forced the creek out of its banks and over the bridge on which Hudson’s and several other cars were then crossing. Hudson, whose body was found the next day, was unfortunately not alone. Two other cars besides his were washed off the bridge, taking six other people to their deaths with them. By the time the night was over, a total of twelve people had drowned in the Kansas City area, ten of them either in their cars or trying to escape from them. A number of other drivers narrowly escaped.

While these incidents in Kansas City made up one of the worst swiftwater disasters in recent years, they were far from unique. Cars, either swept off a flooded street or running off an embankment into the water, are the most common type of swiftwater emergency in the U.S. In this article we’ll cover the causes of and responses to the first type of accident and leave cars in deeper water for later.

Roughly 75% of the cars are swept away at night or during periods of poor visibility, in part because judging the speed and depth of muddy water at night is extremely difficult. Many swiftwater rescues start this way—a driver, not wanting to take a lengthy detour, ignores a barricade and tries to cross a flooded street. The water is flowing swiftly across the pavement, but it doesn’t look that deep. The car enters the water, which quickly reaches the doors. Just when it seems to be coming back up out of the water, the engine suddenly speeds up and the steering wheel goes slack. As the driver watches helplessly the car begins heading toward the nearby creek, which is flooding out of its banks.

Behavior of cars in swiftwater
What does it take to float a car? A rough rule of thumb is that each foot of water pushes against the broad side of a typical car with about 500 lbf (227 kgf) of force and displaces about 1,500 lbs (680 kg). Thus, two feet (less than a meter) of water will float most cars. However, a car can be washed away in less, depending on variables such as the speed of the current, the design of the car, whether the car is sideways or end-on to the current, and the type of bottom. For example, where the current is swift, the bottom hard and smooth, and the car’s body low to the ground, as little as one foot (30 cm) of water with a speed of 6 mph (10 km/hr) or 10 feet per second (3 m/sec) will move most cars. On the other hand, if the car is heavy and has plenty of ground clearance, the bottom is sand or gravel, and the current slow, it may take deeper water to move the car.

The type of river bottom has a lot to do with a partially-submerged car’s behavior in the water. If the bottom is slick with no obstructions (e.g., pavement or concrete), the car is very likely to continue to slide or roll, especially if it is broadside to the current. This can be very dangerous to both the occupants and rescuers, since a sudden weight shift to the downstream side can cause the car to roll. Those inside the car should practice the reverse high side, that is, keeping their weight on the upstream side of the car to keep it from rolling. If the bottom is soft, however (e.g., sand or gravel), the water will quickly excavate the soil under the tires so that the car’s chassis rests on the riverbed. This results in a more stable situation in which the car is much less likely to roll. If the bottom is really soft (e.g. mud) the car often ends up buried engine-end first in the mud with the other end out of the water. Once the car stops moving, it then acts like any other river obstacle, except that is much more likely to move unexpectedly.

Rescue considerations
The rescuer’s first thoughts should be to stabilize the vehicle so that it does not either roll or float downstream, and to get PFDs to the passengers. If the situation is marginal, the weight shift as the passengers are being rescued may cause the car to move. To prevent this, rescuers should attach stabilizing ropes to the car. If possible, these ropes should go to both banks. Rescuers should also routinely dispatch a tow truck (or two) to any incident involving a car in the water.

Once the car is stabilized, the rescue can begin. Rescuers should follow the same Reach-Throw-Row-Go sequence as with any other swiftwater rescue, and attempt to minimize the exposure of their personnel. Sometimes the car can be reached by fire ladders or with an aerial ladder, allowing the victims to climb to safety or be picked off. If the rescuers need to approach the car directly, whether by wading, swimming, or boat, they should do so from downstream, using the eddy that the car creates. Rescuers should, however, exercise caution until the car is stabilized, especially on hard bottoms, since the car may slide or roll over downstream at any time. In most cases, however, the roll will be a slow one, giving an alert rescuer time to escape.

If the victims end up on top of the car, they can be treated like any other stranded victims, although with the understanding that their car may not be a very stable refuge. In other cases, rescuers may have to break the car windows to get to them. While there are a number of exciting videos showing victims being plucked from the tops of cars with helicopters, this should, as always, be considered a high-risk option.

It is worth practicing and preplanning this type of rescue, since it is one that rescuers may be called upon to do at any time with scant notice.

Slim Ray is an internationally-recognized authority on flood, swiftwater and whitewater safety and rescue, including course development and instruction with Rescue 3 International, Canyonlands Field Institute, and the Nantahala Outdoor Center. For more articles and books written by Slim Ray, see link to  http://www.cfspress.com. This article originally appeared in Fire & Rescue Magazine (UK).


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