Do people hit by flamers have to roll Agility to resist being set on fire even if the damage isn't enough to actually penetrate their AP & TB, and do they continue to lose fatigue even if their TB is high enough to ignore the 1d10/round damage from being on fire?
The text doesn't make a clear differentiation between the strength of the attack (the damage rolled) and actuall injury (what the target suffers), and just calls both things damage.
I'm leaning toward it only setting them on fire if it penetrates AP & TB and actually does injury, as otherwise flamers are basically intant-win against low-agility enemies no matter how though they are as they'll end up drained of Fatigue and passing out in a few turns. Also, it makes no sense that the initiall hit wouldn't do anything at all and fail to get through your armour, but still set you on fire.
F.ex. the Greater Deamon (Walking Nightmare) from Edge of the Abyss has 0 chance of putting itself out (as it only has 18 Agility and it's a Hard[-20] test), so unless it can resist the attack by thoughing it out you can just shoot it once with a flamer, run away, and then it'll fall down unconscious from Fatigue 10 rounds later, and if it wakes up, it's still on fire, so it goes down again in 1 round.