Gravity.....
Gravity..... This is why i'm very wary of cranes and the ever present danger of objects falling from booms........ Took my helmet off to wipe my face and a bracket bolt from a light scored a direct hit....... If it moves it wears, and if it wears it has a lifespan before it obeys gravity..... Regular checks of moving components on the boom with special care to be taken that all fasteners, ie, fixing bolts are double nutted and locked so as to prevent such an incident occuring again .........Ouch....