Burning people in armour

In my DF campaign the fireball spells, fire elementals and other supernatural sources of fire are normal. Now the wizard of my group is throwing 2d and 4d fireball and soon he will be able to throw 3d and 6d without problem.



By "Making Things Burn" B433 and "Catching fire" B434 I understand that after one single shot of 10 points or damage or more, a person in armor will catch fire completely (and partially after 3 points of damage).



Question 1: 10 points of damage before DR or after DR? (My guess is before DR)



10 points is not a very high threshold in DF! I would expect most of the enemies will be catching fire soon!



Question 2: The skin, scales, fur, etc... of the mosters would catch fire with the same threshold?



Let's suppose a human target with armor DR 4 has catched fire completely. Each round he will receive 1d-1 and -3DX until the fire is extinguish (B434)



Question 3: I suppose I should subtract target DR. Or maybe should I subtract half the DR? (as a "Big source of damage", I don't remember the page in the rules...)



I suppose also that, after subtracting the DR, if the damage is 0 or less then there is not a penalty against DX, isn't it?



It seems a little counter-intuitive to me that, if you are engulfed by flames because your armor has catched fire, that this armor protects you against the damage! I suppose the flames will to "go under" the very armor as it is being burnt. Am I supposing wrong?



Ok. Let's suppose the armor do protects you although it is burning.



Question 4. When it has burnt enough to stop protecting you? Maybe after 10 seconds (as in "Making things burn" B433) should I roll 3d against 16? Or never?



Thanks in advance!

Burning people in armour