https://www.d20srd.org/srd/variant/adventuring/injury.htmInjury
The d20 game’s hit point system is an easy and effective way of measuring character health—but it’s somewhat abstract.
This variant eliminates hit points, and simply determines whether characters are hurt or killed every time they’re hit in combat.
Determining Injuries
When using the injury variant, characters no longer have hit points. Instead, a character’s injuries accumulate until he becomes disabled or dying (or staggered or unconscious, if he has taken nonlethal damage).
When a character or creature takes damage, divide the damage dealt by the attack by 5 (rounding up). The result is the damage value of the attack. For example, if you are hit by an attack that deals 12 points of damage, the attack has a damage value of 3 (12 divided by 5, rounded up).
To determine if you are injured, make a Fortitude save to resist injury. The DC is 15 + the damage value.
If you succeed on the save, you suffer no ill effect from the attack.
If you fail the save by less than 10, you have taken a hit. (If the attack dealt nonlethal damage, the hit is a nonlethal hit.) Each hit you take imposes a cumulative -1 modifier on future Fortitude saves to resist injury.
If you fail the save by 10 or more, you are disabled. (If the attack dealt nonlethal damage, you are staggered.)
Automatic Success and Failure
A natural 20 on a Fortitude save to resist injury is treated as an automatic success, just as normal. A natural 1 is always treated as if the save failed by 10 or more.
