© 2002 by Richard Smith
None of the falling rules that I've seen I've liked. This is my attempt to build some rules that are fairly realistic but simple.
Take the distance to be fallen in meters and divide by 3 discarding fractions. Multiply this number by 1 die - 1 damage. That is the basic amount of damage done from a fall.
The first 2 hits of falling damage are treated as subdual hits. These sorts of hits will cause bruises, sprains, and may knock you unconscious, but you can not die from them.
Any sort of armor (not shields) will protect for 2 hits. No other forms of armor will help including magic. (Magic armor works by making the 'skin' tougher. But when your internal organs & bones are moving thru each other, a tougher surface does not help.)
Exception: Better armor does protect from the doubling or tripling from spikes or the *1.5 times damage from landing on rough uneven ground.
Broken bones are very common from falls of 8 meters or greater. For falls of greater than 12 meters, serious injuries are common and may give 1 or more bleeding criticals. (A bleeding critical will make you take 1 point of bleeding damage per minute.)
If you are prepared to fall and carefully drop you may subtract 2 meters from the distance fallen. Whereas if you are unprepared or tossed down head first the GM may add a couple of meters to your fall.
If you have Acrobatics or Judo talent (or any talent that teaches you how to break your fall) you may reduce the distance fallen by 2 meters.
Large creatures do not take falls well. Multiply the damage done (before taking off any for armor) by the size of the creature, in hexes, plus one.
These rules work well up to heights of 15 meters. If the fall is higher than that the GM should feel free to dish out extra damage, broken bones & internal bleeding, broken backs, crushed skulls, etc.
Assuming that the force of gravity accelerates you at 10 meters per second squared, you will fall 5 meters in the first second of free fall. You are traveling at 10 meters per second at the end of this time so let us say your energy you have on impact is X. When you fall for 2 seconds you travel 20 meters your speed is 20 meters per turn and so your energy on impact is 4X. (The energy goes up with a square function.) When you fall for 3 seconds you travel 45 meters and your speed on impact is 30 meters per second so your energy on impact is 9X. If you fall 4 seconds the distance you fall is 80 meters and the energy on impact is 16X.
d = 1/2 a * t * t (assume a is 10.0 m/s/s )
v = a * t
E = 1/2 m * v * v (we assume mass is a constant.)
The damage done will be proportional to the energy at impact.
The problem is that normally in a game the GM knows how far the person has fallen, but there is no simple relationship between distance fallen and speed. For now let us work with seconds of time spent falling and see where that gets us.
A 5 meter fall does a very variable amount of damage. Many people have fallen that distance and walked away from it with no damage (a roofer fell off my house for that distance and there was no visible effect). However it is easily possible to break a bone (or your neck) from a fall of that distance. As a first guess, let us say a fall of 5 meters does 2d-2 damage (average 5 points). I think this is too high given the average person has 10 ST.
(Note that in GURPS 1d-1 damage is done per yard fallen. I consider this too dangerous.)
Using this base distance and the fact that energy is squared as velocity is doubled and let us see what damages we get for longer falls.
These damages are suitably lethal for long falls.
A fall of 0.5 seconds (1.25 meters) should do the square root of 2d-2. The square root of 5 is 2.2 so this could be simulated not too badly by 1d-1 (2.5 damage instead of 2.2). However most people would rather fall 1.25 meters than get stabbed by a dagger. This makes me think that the 2d-2 damage is too much for our base damage of 2d-2 for 5 meters.
Let us say that the damage from falling 5 meters is 2d-4. This would mean the most that you could take from falling off a roof would be 8 points (say a badly broken leg). If you are a wimp (and unlucky), you could be killed by such a fall. The average damage would be 2 * 1d-2.
1d-2 averages to: (4 + 3 + 2 + 1 + 0 + 0) / 6 = 1.667
In other words 2d-4 = 3.33 damage on average.
The square root of 3.33 damage is 1.825 damage which is not too badly simulated by 1d-2 (1.667 damage on average). An average human is not going to be killed by a 1.25 meter fall but the maximum damage (4 points) seems a bit much. One third of the time an average human would take 1/3 of a mortal wound by a 1.25 meter fall?
I think what is going on here is that humans have built in armor for falls of a meter or two.
My friend Steve points out that you should not underestimate falls of 4 feet. In Judo he dropped people from that height and it takes a lot out of you, especially if you land wrong. Despite this point, I still think that 1/6 th of the time taking 4 points and 1/6th of the time you take 3 points of real (not subdual) damage is too deadly.
If we assume 2d-4 for 5 meters what do we get:
These average damages seem too modest. In particular a 20 meter fall should smear most people. But using this system, while the average damage will kill a typical person, with a slightly below damage roll they might walk away from the fall. A 20 meter fall becomes quite survivable if we allow even a few points of TFT armor to protect them.
Not good.
While 2d-4 does OK damage for short falls, it does not do enough for long falls. I think we should use the 2d-2 damage as our base amount, but give people some built in armor against falling. With short falls the falling armor can stop most of the hits, but it is overwhelmed for longer falls.
Now the next problem is how to handle the non-linear relationship between distance fallen and damage. We only need to handle up to 20 meters or so because after that falls just become death drops.
Falling damage = 1d-1 for 2 meter fall, + 1d-1 for each extra 3 meters.
Where does this get us assuming humans have 2 points of falling armor? (Armor included below:)
Remember that if a 5 meter fall does 2d-2 damage we get 20 points of damage from the energy of a 20 meter fall. Using the system above we would get about 18 points of damage before the 2 falling armor kicks in. This is close enough for a fantasy game.
Now the surface you land on is important. I think I will use the system above and allow some modifiers depending on if the surface is soft or hard, and how prepared the person is for the fall.
There are many people who have survived falls of 15 meters. But typically what happens is that their legs turn to jelly (which will require amputation). Falls of 8 meters or more should have a very good chance of breaking bones / crippling limbs / paralyzation. Or the GM could hand out internal damage that causes bleeding for 1 point of damage per minute or so. Season the details to GM taste.
I think the guidelines above are realistic. But my actual rules will be a bit less deadly and simpler; this is a frpg after all.