Before we get into any discussions on the techniques and equipment used in BASE jumping, we need to make something very clear: BASE jumping is extremely dangerous. There is no margin for error. A slight mistake, or a little bad luck, and death is the result. BASE jumpers generally have about 100 regular skydiving jumps under their belt before they ever attempt a BASE jump, and they usually have an experienced BASE jumper who mentors them on the skills necessary to jump safely. No one should attempt BASE jumping without a lot of thought, training, experience and a good life insurance policy.
BASE jumping is essentially a variation on skydiving. For a good explanation of skydiving and the equipment used, check out How Skydiving Works. BASE jumpers use modern ram-air parachutes (the jumpers injured on El Capitan in 1966 were using older round parachutes, which contributed to their problems). Ram-air chutes are rectangular to give the jumper greater control over direction and speed once it has been deployed. There are some key differences between skydiving gear and BASE jumping gear, however, so BASE jumpers need special equipment and techniques. A parachute made especially for BASE jumping costs between $1,200 and $1,500.
BASE jumpers have to overcome two major obstacles: low altitude and the proximity of the BASE object. Skydivers typically open their chutes at around 2,000 feet. This gives them time to deploy the parachutes gradually (reducing line tangles and a sudden jerk on the diver) using a device called a slider [ref]. It also gives them a little breathing room. If there is a problem with the main parachute, they can still deploy their back-up chute.
But many BASE jumps start out well below 2,000 feet. While jump sites such as El Capitan and Angel Falls in Venezuela are around 3,000 feet, they are the exception. Skyscrapers and antenna towers are usually 1,000 to 1,500 feet tall. As a result, jumpers have to deploy their parachutes quickly.
A few alterations in basic skydiving equipment help to accomplish this. For example, some BASE jumpers use a larger pilot chute. This is the small parachute that drags open the main chute. Larger pilot chutes catch more air, create more drag and open main chutes more quickly. They are also helpful because low altitude jumps force jumpers to open their chutes at a lower velocity -- they haven't been falling long enough to achieve a freefalling human's terminal velocity (around 120 mph). Lower speeds mean reduced air pressure in the chute, so a larger chute is more effective. Because many BASE jumps are so low that only about five seconds of freefall are possible before impact, some BASE jumpers don't bother packing back-up chutes. If the main chute fails to deploy, or deploys incorrectly, there isn't the time to cut away a malfunctioning chute and deploy the back-up.