Fire resistance : how much?

[Porphyre]

The potion of Fire Resistance, it is said "gives a +2 for saving throws against Fire Balls and Dragon Fire,
 and it takes -1 away from damage caused by these and from Balrog immolation."

I was wondering what the "-1" do damage was: minus 1 hit point (which isn't a verey good protection) or minus 1 hit dice (but that may cause problem with the dragon breath)?

[makofan]

-1 per dice (i.e a 7-die dragon breath would subtract 7 points; a 6 dice fireball would subtract 6 points)

[Porphyre]

You're probably right. Thanks!