Static and Dynamic Drops

A dropped object is any object that falls from its previous position under its own weight. The distinction between two categories matters because they require different controls.

Dynamic dropped objects

An object dislodged by an applied force — a person, equipment contact, a lifting operation, vibration or wind. These occur during activity, so there is usually somebody who knows the work is happening and an exclusion zone can be in place.

Static dropped objects

An object that falls of its own accord because the thing holding it failed: corroded fixings, failed welds, fatigued brackets, vibration-loosened bolts, degraded lashings, or ice. These are far more dangerous, because they fall without warning at a time nobody chose, into areas that are occupied precisely because no work is happening there.

Static drops are controlled only by survey, inspection and securing — an exclusion zone cannot be in place for an event that has no schedule.

The energy involved

Falling objects gain energy rapidly with height. A small hand tool dropped from a modest height carries enough energy to cause a fatal head injury, and objects of a few kilograms from moderate heights are routinely fatal. Hard hats protect against a limited range of small, low-energy impacts and provide no meaningful protection against a heavier object from height — which is why the control must be preventing the fall and excluding people from beneath.

Wind, deflection off structure and bouncing mean the landing point is unpredictable. An exclusion zone must be sized generously, not to the vertical drop line.