The Oddity's page

As a quick option on how to rule it you could compare his running speed to the speed of a fall and use this as a guideline for the damage he takes.

As to RAW there is no damage: If I jump off a cliff and declare to bullrush someone on the ground do I take damage? I should not as I am not falling I am willingly bullrushing someone.

I could even say that I think I had seen indication that there is someone invisible down there and try to bullrush him.

** spoiler omitted **
If you find something wrong in this estimate (wasn't a real calculation with all that rounding and guessing) let me know.
Would perhaps have been easier to do just in feet but I'm used to using meters for calculation.

Your math is incorrect. The formula for determining the final velocity is:

v = square root of (2 * acceleration * distance)

Plugging in the numbers, for a 10 foot fall (1d6 damage), you hit the ground at 17mph, which equates to pretty close to 150'/round:

((17mph * 5280 feet per mile)/3600 seconds per hour)*6 seconds per round

Compare this to the Feather Fall spell which describes falling 60'/round as equivalent to dropping a few feet and does no damage.

So, unless the character was running at 150'/round I'd probably just have them be stunned, maybe take some minor damage depending on how fast they were going.

Also, I am having a hard time imagining a character running head-first into what they think is an open hallway. Headlong maybe, but not head-first.

That's the size of a typical pre-schooler. Most preschoolers have trouble carrying a gallon of milk, because it's too heavy for them.

This is a bit of an exaggeration, I feel. My son could deadlift a gallon of milk one handed when he was 15 months old. Admittedly he is a bit of a beast. Broke my nose with a sippy cup when he was 9 months old. I was so proud!

2) Falling damage should go up geometricly. A 10 foot drop does 1D6 damage. A 20 foot drop does 1D6 * 1D6 or 1-36 damage in excessive realism.

Actually, this is incorrect. Sure, gravity is constantly accelerating you as you fall, but as you gain velocity it takes you less time to travel through each 10' increment so for each 10' you fall you have less time to accelerate before hitting the next 10' increment. (Wow that sounds confusing)

In any case, the formula for calculating your velocity after falling a given distance is:

v = square root of (2 * acceleration * distance)

(assuming 0 initial velocity and ignoring wind resistance)
If we punch in 32 feet per second squared for gravity (messy imperial units, I know) and adjust to mph, we can arrive at the following approximate velocities for distance fallen:

10' 17mph
20' 24mph
30' 30mph
40' 35mph
50' 39mph
60' 42mph
70' 46mph
80' 49mph
90' 52mph
100' 55mph
110' 57mph
120' 60mph
130' 62mph
140' 65mph
150' 67mph
160' 69mph
170' 71mph
180' 73mph
190' 75mph
200' 77mph

So, if we consider that fall damage is a factor of how fast you are going when you hit the ground, 1d6 per 10' is actually too much damage. If each 17mph increment represents 1d6 damage, then you shouldn't take 2d6 until 40', 3d6 until 90', 4d6 until 150' or 160', and you never reach 5d6 (85mph).

My god the things I do to avoid watching recorded CW shows with my wife!