Idk about the perfect solution. But if you don’t catch fire some damage should be right and when you catch fire normally those additional damage will stop + some system of stamina drain by fire could be added so we don’t see people running in 20m of flame and when you run out of a puddle of fire at least you stop 3 second to recharge the stamina.
Btw, i don’t have sprint or vitality perk on those soldier.
Could damage a bit running through the flames, a bit like with barbed wires 
Yeah a small damage united with stamina drain so basically if you start running in pool of fire(like the 3° clip) you burn in the middle of it and if you run in a puddle(1° clip) just some minor damage and 3 sec to kinda recharge the stamina much or less
If was thinking to a visual effect too something like suppression in Hell let Loose but maybe will be kinda to much lol
DF really has made most forms of fire just mediocre
Fire hurts.
Fire should damage those who walk on it by default.
The way fire hazards work in-game, unless you are “on fire”, you take no damage at all. With the nerf to incendiary weapons, soldiers have a short period before they are considered “on fire”, but the said period is long enough for you to literally sprint through a patch of flames.