BASE jumping is the sport of using a parachute to jump from fixed objects. "BASE" is an acronym that stands for the four categories of objects from which one can jump; (B)uilding, (A)ntenna, (S)pan (the word used for a bridge), and (E)arth (the word used for a cliff).
BASE jumps are generally from much lower height than a traditional airplane parachute jump, although there are notable exceptions. In the United States, an "advanced" skydiver (over 100 airplane skydives) is recommended, on an airplane jump, to deploy the main parachute no lower than 2,000 feet. At that time, if the airplane jumper had already been in freefall for at least 1,000 feet, the jumper is traveling 120 miles per hour, and is 11 seconds from the ground. Some BASE jumps, very high cliffs, can be from heights of over 5,000 feet, though these are rare. Most BASE jumps are made from less than 1,000 feet. A BASE jump from a 500 foot object is about 6 seconds from the ground.
At these lower heights, it is not recommended to use airplane skydiving equipment for deceleration since the BASE jumper will be deploying the parachute at a much slower airspeed and much closer to the ground, a situation for which airplane skydiving parachutes are not designed. Many BASE jumpers use specially designed harnesses and parachute containers, and jump with only one parachute. On the face of it that may seem absurd, but the quantity of data that exists for this system to be utilized effectively are why the most experienced in the sport choose this method.
In the United States, skydiving from an airplane involves regulations set by the FAA, notably the requirement of an airplane jumper to carry two parachutes. Since BASE jumping does not involve an airplane, the FAA has no jurisdiction.
The vast majority of people who will try BASE jumping are those that have already learned to skydive. It is important to know how to safely fly 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 the canopy with great precision. Most BASE jumping venues have very small areas in which to safely 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 will have a parachute ride of about 10 to 15 seconds.
The legal issues that a BASE jumper must consider are the permissions to utilize the object that is being jumped, and the permissions to utilize the area used for landing. The general reluctance of the owners of jumpable objects to allow their object to be used as a platform leads many BASE jumpers to attempt to jump from them covertly. Notable exceptions are a bridge in Idaho, and, once a year, on the third Saturday in October ('Bridge Day') when jumping is legal from the New River Gorge Bridge in Fayetteville, West Virginia. The bridge deck is 876 feet above the river. A rock dropped from the deck will hit the water in 8.8 seconds. This annual event attracts about 350 BASE jumpers, and nearly 200,000 spectators. If the conditions are good, in the 6 hours that it is legal, there may be over 800 jumps at Bridge Day. For many skydivers who would like to try BASE jumping, this will be the only fixed object from which they ever jump.
It is not known how many people have tried at least one BASE jump, however, when a jumper completes a jump from each of the four categories of objects, they may choose to apply for a "BASE number". These are awarded sequentially. In 1981, Phil Smith of Houston, Texas, was awarded BASE-1. Currently over 700 BASE numbers have been awarded.