It is always a good idea to wear PPE even when engineering controls are in place just to be a little bit safer. 

Full compliance with OSHA noise standards will completely eliminate hearing loss in the workplace.

While physical and atmospheric hazards are considered for the determination of whether or not a space is a permit-required confined space, configuration hazards such as sloping walls, were left out of the confined space standard due to pressure from the agriculture industry which felt that this would place an undue economic burden on the industry.

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.