Indiscriminate short-ranged weapons such as flame throwers affect a broad, cone-shaped area represented by a template. Instead of rolling to hit place the template so its narrow end is touching the base of the firing model and the rest covers the maximum number of models in the target unit.
Models fully or partially under the template are hit automatically. As template weapons bathe the area in burning fuel, acidic spray, etc., all cover is ignored when resolving hits. As for blast weapons, casualties inflicted by flame weapons must be taken from amongst the models actually covered by the template.
Diagram: Flame Weapons — a teardrop-shaped flame template is placed with its narrow end touching the firing model's base. Every model fully or partially covered by the template is hit ("Hit"), including one behind a pile of rocks, since flame weapons ignore intervening cover.