543.12  ADDITIONAL STANDARDS.
   If the sound radiated from any source is not smooth and continuous and is not radiated between the hours of 8:00 p.m. and 6:00 a.m., one or more of the corrections in the table below shall be added or deducted from each of the decibel levels above.
 
Type of Operation or Character of Sound
Correction in Decibels
Sound source operates only for an hour  once a day during 8 a.m. to 6 p.m.
Add 5 dB(A)*
Sound source operates only for 30 minutes or less once a day during 10 a.m. to 4 p.m.
Add 10 dB(A)*
Sound of impulsive character (hammering, etc.)
Deduct 5 dB(A)
Sound of periodic character (hum, screech, etc.)
Deduct 5 dB(A)
*  Apply one of these corrections only.
(1964 Code Sec. 99.12)