ofxBox2d - remove bounds


i am using ofxBox2d addon for dealing with particle physics inside the window app.
I created bounds of the size of the window to prevent the particles to go off screen.
But at a moment i would like to remove these boundaries and let the particles to fall and die off screen.

How can i achieve that ?
I am using box2d->createBounds() but i can’t see a boundaries destructor…

thanks a lot.