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There are isolated examples of BASE jumps dating from the early 1900s. Frederick Law jumped from the Statue of Liberty in 1912; Michael Pelky and Brian Schubert jumped the cliff " El Capitan" in Yosemite Valley in 1966; and in 1976, Rick Sylvester jumped Canada's Mt Asgard for the opening sequence of the James Bond movie " The Spy Who Loved Me", giving the wider world its first look at BASE jumping. However, these and other sporadic incidents were one-off experiments, not the systematic pursuit of a new form of parachuting. The acronym "BASE" was coined by film-maker Carl Boenish , who in 1978 filmed the first jumps from El Capitan to be made using ram-air parachutes and freefall tracking technique, which effectively defines modern BASE jumping. These jumps were repeated, not as a publicity exercise or as a movie stunt, but as a true recreational activity. It was this which popularised BASE jumping more widely among parachutists. Boenish continued to publish films and informational magazines on BASE jumping until his 1984 death on a cliff jump in Norway. By this time, the concept had spread among skydivers worldwide, with hundreds of participants making fixed-object jumps.
BASE jumping grew out of skydiving (recreational parachuting from aircraft). There are three main technical differences between the two. Firstly, BASE jumps are generally made from much lower altitudes than skydives. Secondly, a BASE jump takes place in close proximity to the cliff or tower which provided the jump platform. Thirdly, the BASE jumper generally has a lower airspeed than a skydiver throughout the jump, because a BASE jump starts with zero airspeed, and (due to the limited altitude) a BASE jumper very seldom approaches the terminal velocity (airspeed) of a skydiver. All three factors have significant implications.
Firstly, the BASE parachute system has to be made to open very quickly at low airspeeds. Skydiving parachutes are reefed to slow down the opening and reduce opening shock forces. Secondly, the cliff or tower presents a risk to the BASE jumper if, for example, the parachute opens facing backwards. An off-heading opening is not considered a problem in skydiving, but has caused fatal impact injuries in BASE jumping. However, it is the low altitude which usually presents the greatest risk.
An experienced skydiver is recommended to deploy their parachute no lower than 2,000 feet (610 m). At that time, if they have already been in freefall for at least 1,000 feet (305 m), the jumper is traveling 120 miles per hour (54 m/s), and is 11 seconds from the ground. Most BASE jumps are made from less than 1,000 feet (305 m). For example, a BASE jump from a 500 foot (152 m) object is about 6 seconds from the ground if the jumper remains in freefall. On such a jump, the parachute must open at about half the airspeed of the skydiver, and more quickly (ie. in a shorter distance fallen). Standard skydiving parachute systems are not designed for this situation. Many BASE jumpers use specially designed harnesses and parachute containers, with extra large pilot chutes, and jump with only one parachute - since, with a total freefall time of 6 seconds, there would be no time to use a reserve 'chute. In these systems, the actual parachute canopy is generally a mass-produced skydiving canopy with little or no modification, but the rest of the system is designed for BASE use. Standard skydiving equipment can only be used on relatively high BASE jumps. If modified, by removing the bag and slider, stowing the lines in a tail pocket, and fitting a large pilot chute, standard skydiving gear can be used for lower BASE jumps, but is then prone to kinds of malfunction which are rare in normal skydiving (such as "line-overs" and broken lines).
The vast majority of people who try BASE jumping are those that have already learned to skydive. It is important to know how to safely fly and land a parachute, and this is best learned on airplane skydives, from higher deployment altitudes, over large fields that provide room for error in learning how to land. Most BASE jumping venues have very small areas in which to land. A beginner skydiver, after parachute deployment, may have 3 minutes or more of a parachute ride to the ground. A BASE jump from 500 feet (152 m) will have a parachute ride of about 10 to 15 seconds.
One way to make a parachute open very quickly is to use a static line or direct bag. These devices form an attachment between the parachute and the jump platform, which stretches out the parachute and suspension lines as the jumper falls, before separating and allowing the parachute to inflate. This method enables the very lowest jumps (below 200ft) to be made, although most BASE jumpers are more motivated to make higher jumps involving free fall.
In parachuting, height is safety, and by making lower altitude jumps, BASE jumpers give up the safety margins built into skydiving (such as the option of using a reserve parachute if there are problems deploying the main chute). The lower airspeed of a BASE jump is also a risk factor. Skydivers use the air flow to stabilise their position, allowing the parachute to deploy cleanly. BASE jumpers, falling at lower speeds, have less aerodynamic control, and may tumble. The attitude of the body at the moment of jumping determines the stability of flight in the first few seconds, before sufficient airspeed has built up to enable aerodynamic stability. On low BASE jumps, parachute deployment takes place during this early phase of flight, so if a poor "exit" leads into a tumble, the jumper may not be able to correct this before the opening. If the parachute is deployed while the jumper is tumbling, there is a high risk of entanglement or malfunction. Beginner BASE jumpers often make the error of rotating forwards by jumping with a swimming-pool type of diving motion, leading to an involuntary forward loop. Better technique is to exit without any rotational motion.
On higher BASE jumps, those which allow a free fall of five seconds or more, it may be necessary to use freefall tracking technique to move away from the jump object (especially on cliff jumps). Jump platforms providing an overhang, such as arch bridges or naturally overhung cliffs, are more forgiving in this respect and so are more suitable for beginner BASE jumpers.
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