Not capable of being done or accomplished; impracticable.

not capable of being carried out or put into practice; "refloating the sunken ship proved impracticable because of its fragility"; "a suggested reform that was unfeasible in the prevailing circumstances"

Not feasible.

Impossible to perform the construction work using a conventional fall protection system (i.e., guardrail system, safety net system, or personal fall arrest system) or technologically impossible to use any one of these systems to provide fall protection.