The world isn't a pretty place. During your adventures, you may suffer any amount of hazards, like:
Falling: This deals 1 point of stun damage per meter fallen for fairly 'mild' surfaces -- water or moss, or a handy tarp, or 1 point of lethal damage if you fall on something you shouldn't, such as bare rock or a rusted-out car. For these purposes, a fall is any height greater than your (Agility + Acrobatics dice) / 2 meters.
Fire: Fire deals from d4 stun damage (a match) to 1d12 lethal damage (a blazing inferno) every round. Simlarly, cold deals from 1d4 stun damage a round (0 celsius) to 1d12 lethal damage (-100 celsius). Extremely intense heat or cold (plasma, or liquid nitrogen) deals 4d12 lethal damage.
Poison: Poison deals stun damage, as well as side effects. Each poison has an Intensity (from 1d6 to 4d12); subtract the character's Health check (i.e., roll of Health + Race). If even one point of stun damage, one level of effect is done; for every full 5 points of stun damage, another level of effect is done. Destructive poison deals 1 wound per level of effect; debilitative poison makes the character at -1 die to all actions per level of effect; paralyzing poison makes the character unable to move for 1d6 minutes per level of effect. Disease is similar, but had a different set of effects at each, and needs 1d4-3d6 days to 'incubate' between effects; the common cold just makes you lose 1d6 extra stun every 1d4 days, while pneumonia causes one wound every 1d6 days per extra level of effect.
Radiation: Get the square root of the rads per minute, and make a Health check every turn against it. For every point you lost by, lose one stun; for every five full points you lost by, lose one stun permanently. If you lose all stun, you are comatose. In addition, if you roll three ones in a roll, you get cancer, and you will die in (roll Health) months. At least you've got enough time to look pretty for your coffin.
Suffocation: You can survive (roll of Health) rounds; any race that has Swimming as a natural skill can survive (roll of Health + roll of Race) rounds. After this time, roll Health (or Health + Race for those with Swimming as a natural skill) every round; if you roll under the number of rounds you've been under, you lose as much stun as you lost by, and if you rolled all 1s, you lost a wound. If you lose a wound, you are automatically unconscious, and do not roll from then on -- you automatically lose 1 more wound every round after that as you suffer brain damage.