In construction when concrete is placed the free fall distance should not exceed what?

Usually they limit the free-fall distance to 3 to 5 ft (0.9 to 1.5 m), but occa- sionally the limit is as little as 2 ft (0.6 m). Neither ACI 301- 99, “Specifications for Structural Concrete,” nor ACI 318-02, “Building Code Requirements for Structural Concrete,” limit the maximum distance concrete can free fall.  

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