According to the Environmental Protection Agency - EPA - the Day-Night Sound Levels - Ldn - and the Equivalent Sound Level - Leq - should not exceed certain limits to protect public health and welfare.
Outdoor activity interference and annoyance Leq(24) < 55 dBA Outdoor areas where people spend limited time such as school yards playgrounds, etc.
Indoor activity interference and annoyance Leq(24) < 45 dBA Indoor areas with human activities such as schools, etc.
Outdoor yearly Ldn levels protect public health and welfare if they do not exceed 55 dB in sensitive areas as residences, schools, hospitals, etc.
Inside buildings yearly Ldn levels protect public health and welfare if they do not exceed 45 dB.
Note! To protect against hearing damage, one's 24-hour noise exposure at the ear should not exceed 70 dB.