Hallo there,
I seem to remember that somewhere in a handbook there is a rule that helps you determine if a flame weapon did set your target on fire (I mean: it flares up and becomes a torch) but I can’t find it: can you help me locate this rule?
Thank you in advance

Don't have my book with me, but it should be split across two different sections.

First, in the equipment section, under weapon qualities, read flame. It details that if the target fails the right tests, they are "on fire".

Next, look at the damage section (should be same page with other environmental hazards (e.g. the void), and it should state how the damage for being "on fire" is dealt.

Exactly what I was looking for: thank you for your assistance!