This is a working Swing Bridge - that you can also blow up!
The bridge functions normally, opening and closing automatically or on demand. However, it also calculates damage when struck by bullets or other projectiles (*) and when enough damage is received, the bridge blows up!
(* Bullets/projectiles must be physical scripted objects. Particles, phantom prims, and 'combat systems' will not be registered by the bridge. Damage is calculated as a function of mass and speed -- in other words, good old fashioned kinetic energy.)
You can see a working explodable swing bridge at Waikiti, next to my main store Atashi's Art and Oddities.
Bridge is Mod/Copy (scripts are copy-only). The bridge base is 5 prims and the bridge is 47 prims. Exploded bridge bits are about 35 prims but they are temp prims.