Q: What kind of hydraulic fluid does the Jaws of Life use? A: Oil is the most commonly used incompressible fluid for hydraulic machines. However, the Jaws of Life equipment uses a phosphate-ester fluid, which is fire resistant and electrically non-conductive.

Driving down the interstate, you reach down to grab the road map from the passenger-side floorboard. In an instant, you inadvertently swerve onto the shoulder of the road, and your car flips as you attempt to regain control. When your car comes to rest, you've got a broken leg, your car is upside down and you're pinned underneath the dashboard. In this type of situation, rescue workers will use a set of tools commonly called the "Jaws of Life" to cut away the car and get you out.

The Jaws of Life is actually a brand of tools that is trademarked by the Hurst Jaws of Life company, but the name is often used when talking about other brands of rescue systems. The term "Jaws of Life" refers to several types of piston-rod hydraulic tools known as cutters, spreaders and rams, which are used to pry open vehicles involved in accidents when a victim may be trapped.

To extricate accident victims, firefighters may make a relief
cut to open up the vehicle's roof. See more Jaws of Life images.

During emergencies, when a few wasted seconds can cost lives, the Jaws of Life are brought in to remove victims from the crashed vehicle. These devices are also used to extricate victims from collapsed concrete and steel structures after earthquakes. In this article, you will learn how these simple hydraulic systems work, the purpose of each device and how they're powered.

Simple Hydraulics
If you've read How Hydraulic Machines Work, you know that hydraulic equipment is based on a simple concept -- the transmission of forces from point to point through a fluid. Most hydraulic machines use some sort of incompressible fluid, which is a fluid that is at its maximum density.

Oil is the most commonly used incompressible fluid for hydraulic machines. However, the Jaws of Life equipment uses a phosphate-ester fluid, which is fire resistant and electrically non-conductive. At a crash scene, this type of synthetic fluid is favored over conventional oil.

In a simple hydraulic system, when a piston pushes down on the oil, the oil transmits all of the original force to another piston, which is driven up.

The Jaws of Life equipment is some of the most unsophisticated hydraulic machinery, because there are very few parts involved in making the devices work. In the cutter and spreader, a portable engine pumps pressurized hydraulic fluid into the piston cylinder through one of two hose ports. A typical Jaws of Life machine uses about 1 quart of hydraulic fluid. An operator-controlled valve switch controls which port the fluid enters through. If it enters one port, the fluid forces the rod up and opens the arms of the spreader or blades of the cutter. The operator can then toggle the switch and cause the rod to retract, closing the arms or blades.

A portable gasoline power unit sends pressurized hydraulic fluid to the equipment.

In the next two sections, we will take a closer look at the types of equipment that are generally referred to as the "Jaws of Life."