So a level 30 Dragon warrior with 10 levels in dragon warrior can have quite a foul breath :Level 1: Dragon Disciple, Resistance to Energy 5
Level 2: Dragon Breath 1/day
Level 3: Immune to Fear
Level 4: Elemental weapon +1, Dragon Breath 2/day
Level 5: Resistance to Energy 10,
Level 6: Dragon Breath 3/day
Level 7: Resistance to Energy 15
Level 8: Blind-Fight, Dragon Breath 4/day
Level 9: Elemental weapon +1d4
Level 10: Resistance to Energy 20, Dragon Breath 5/day
Dragon Breath: A dragon warrior can use a breath weapon once per day as a standard action. The type of breath weapon depends on the chosen dragon type. The breath weapon deals 2d12 points of damage per class level + 1d3 points per hd in a 30' cone. The Reflex save DC for the breath weapon is 15 + the dragon warrior's class level + the dragon warrior's Con modifier. This can be used once per day at 2nd level and gains another use every second level.
20d12 + 30d3 ~ 20*7 +30*2 = 200 damage AoE on average, with a DC of 25 + CON mod
Max 350 damage, reflex for half !
Maybe some foul-breathed Barbarians, Dwarven defenders and Breach Gnomes will show up their dragonblood ?

That's a lvl 20 PC, and those poor beasts failed their reflex save.