According to the OSHA lockout/tagout standard (1910.147)

This unguarded shaft is…   

The inner ear responds differently to various frequencies (some frequencies sound louder and some quieter).

Noise is unwanted sound that can be irritating and damaging.

The difference between a JHA and a JSA is that a JHA is for high hazard industries and a JSA is for “safer” industries. 

Decibel = 20 * log (P / P0). The P0 term in this formula refers to:

A company does not have to perform a hazard assessment, like a JSA/JHA, to determine which PPE is required for a given job/task if they simply require all employees to use PPE at all times as a condition of employment.

Confined space entry begins when an employee fully enters the confined space.

In regard to exposure of blades, when the blades of a fan are less than seven feet above the ground the blades shall be guarded.

Affected employees are trained to perform lockout/tagout.