It is intuitively obvious that the most important part of jumping is immediate velocity at the moment of impact. Here is a simple graph to illustrate the basics of Newtonian physics - or how gravity can influence your activity.
The problem is that there is no publicly available simply searchable statistical data on deadliness of this method. Famous Places (like Nuselský most; see below) frequently reported in the news are usually reported for jump attempts rather than for successfully committed acts.
Nevertheless, a clue for proper impact velocity can be found in motoristic, hitchhiking or biophysical literature. From that we can learn:
- it is optimal to "straight dive" as the body is most vulnerable to overload . To exemplify the different speeds, one can perform tests. Try the diving tower at your local swimming pool. If someone is considering this method, it is very important to be sure about the technique!
- approx. 90 km/h is generally recognized by transportation authorities as standard maximum permitted speed with respect to protective technologies that used to be built into passenger cars when the standards were approved.
- according to television fiction(!) show Numb3rs, episode 205, an effective way to kill oneself is to jump from a window 25 meters above the terrain.
Based on Dominick J. Di Maio's Forensic Pathology (pp 148-150):
Soft Tissue Injuries
Not life threatening.
Fractures of the Skull
The degree of skull deformation depends on amount of hair, thickness of the scalp, configuration and thickness of the skull, elasticity of the bone at the point of impact, the shape, weight and consistency of the object impacting or impacted by the head, the velocity at which the head strikes the object.
The amount of energy required for production of a fracture depends on whether the head strikes hard or soft yielding surface. In case of hard surface (steel plate) it takes approx. 33 - 75 ft lb of energy to produce a single linear fracture. This energy is absorbed in 0.0012 s. The first 0.0006 s is used in deforming and compressing the scalp and the last 0.0006 s is used in deforming the bone. The amount of energy necessary to produce multiple linear fractures or stellate fractures is only slightly increased. In fact, that skull fractures commonly occur when individuals fall on the back of the head.
If a head strikes a deformable object, the energy is partially absorbed by the object which will tend to deform and wrap around the head. Thus, the energy is not localized in the focus reducing the possibility of the fracture. Instrument panel of a motor vehicle required kinetic energy level at impact of 268 - 581 ft lbs i.e. impact velocities 43 - 65 ft/s. In one test, a human head impacting at 577 ft lb of energy didn't fracture.
The Famous Places Of Jump Suiciders
|place||height [m]||pad to fall|
|Nuselský most (Prague, CZ)||42,5||concrete, lawn|
- Israeli Hiker Falls To Death Out Of Rescue Helicopter  - 50 meters fall may be lethal, but not immediately (note: older articles refer to 20 meters, newer correct the altitude)
- in 1977 a paratrooper survived free fall when his parachute didn't open. One of his legs had to be amputed though. The link contains an interview with the survivor. .
Many bridges have suffered from jumpers trying suicides. The incidents have been serious breaches of security, so some measures have been tried to discourage suicides by jumping. Adding barriers have been done somewhere. Part-time or even full-time closures of some bridges to pedestrians and possibly cyclists might reduce jumping, but they cannot always prevent occupants of any vehicles allowed on the bridges from getting off to jump off the bridges.