Whether or not they realize it, fans of the old Looney Tunes cartoons understand vertical velocity. How many times did Wile E. Coyote think he'd rigged the perfect rock-and-rope device to squash the Road Runner? Invariably, things went south for the poor prairie wolf, and his panicked look flashed on-screen before he vanished from sight as his own invention dragged him down.
Thanks to gravity, falling objects gain speed the longer and farther they have to fall. While this may be funny in cartoons, it's scary for those who work at heights. It's this same principle of physics that can turn a harmless torque wrench into a plummeting projectile streaking down from the sky.
Fortunately, there are several solutions designed to improve worker safety by reducing the forces required to slow that moving object back to zero.
The Tool Stops Here
If a falling object decelerates abruptly upon impact against the ground, pavement or another solid surface, that object likely will be bent or broken. If that same object strikes a person below, the impact could be fatal. There are solutions to help protect or cover people and objects below, but a better approach is to prevent that impact in the first place.
An accepted way to keep tools and other gear secure at heights is by tethering. Essentially a leash, the following have been used as tethers:
But those options can't eliminate gravity – or improve deceleration. A falling object "caught" by a tether is subject to "shock" loads instead of impact. This shock is force transmitted instantly to the whole system: the tool, its attachment point, the tether itself and the tether's anchor. Each of these components needs to be considered.
Normally, shock load is not a concern for a hardened steel tool, like a wrench or a pry bar. But a power tool or sensitive instrument is a different story. Internal components may break free or collide. Those lessons were learned by studying worker fall protection: a rigid, static lifeline might keep a body from hitting the ground, but could be the indirect cause of whiplash or severe internal injuries.
Similarly, the point of attachment – where the tether meets the tool – and the anchor point – at the other end of the tether – have to survive shock loading. If not designed for these sudden forces, both attachment points and anchors can deform, break or tear loose.
When the worker is used as the anchor, shock can be transmitted to the worker's body. In a worst-case scenario, that falling object can be the initiator that pulls the worker down with it.