Whenever the heroes move onto a trap template or a square adjacent to the template the trap is triggered. All models, friendly or enemy, that are on or adjacent to the trap template are affected.
If a trap requires an offense roll to resolve its effects it will have an STR attribute that affected models must make a defense roll against. All traps have a Defense attribute. In order to disarm a trap a model must use the Disarm Trap basic action, and exceed the trap’s defense.