Gravitational Energy Blocking
Gravitational energy blocking is the practice of physically restraining or securing equipment so it cannot move, drop, or fall under gravity while workers are exposed to the hazard. In Canadian safety practice, WorkSafeBC treats gravity as a form of hazardous energy and describes blocking/restraint devices such as blocks, pins, bars, chains, and cribbing used to control gravitational potential energy.
In a manufacturing or shop-floor setting, gravitational energy blocking involves using a mechanical restraint or blocking method before a worker enters a danger zone, works under suspended or elevated parts, or services components that could descend if a support fails. Examples include blocking a raised press ram, securing an overhead door, cribbing elevated machinery, or using positional blocking on gates/valves where gravity holds the device in position. Before maintenance or cleaning, workers isolate the energy source and install a physical restraint so a suspended or elevated component cannot descend if the primary support, actuator, or control fails. Blocking devices may include steel blocks, pins, bars, chains, or cribbing, and must be selected to resist the credible load for the application. For some systems, positional blocking is acceptable when the device is designed to hold a component in an open, closed, or intermediate position; in certain cases, gravity itself can serve as positional blocking if the configuration is appropriate.
Is gravitational energy 'stored energy' or 'hazardous energy'?
In hazardous-energy control practice, it is both a form of potential energy and a hazardous energy source when it can release in a way that harms workers.
What is the engineering basis for blocking?
The block must resist the maximum credible force acting on the apparatus in its secured position; BC Hydro distinguishes full-force blocking from positional blocking, with full-force blocking designed to withstand actuator force plus other forces.
When is gravity alone considered acceptable blocking?
BC Hydro states that for certain large gates and valves, if the physical configuration is appropriate, gravity can fulfill positional blocking requirements.
How does this relate to lockout/tagout?
Gravity-related hazards are not eliminated by electrical or mechanical lockout alone; the system must also be blocked or restrained so suspended or elevated components cannot move unexpectedly.
What is the operational test of adequacy?
The practical test is whether the worker is protected from inadvertent movement, descent, or release of the component under all credible conditions of failure or disturbance.