Approved uses shall conduct loading and unloading operations; the opening, closing or other handling of boxes, crates, containers, building materials, liquids, garbage cans, refuse or similar objects or the pneumatic or pumped loading or unloading of bulk materials in liquid, gaseous, powder or pellet form or the compacting of refuse by persons engaged in the business of scavenging or garbage collection, whether private or municipal, out of doors only between the hours of 6:30 a.m. and 8:30 p.m., Monday through Friday, and 8:00 a.m. and 5:00 p.m. on Saturday. Exempt from this limitation is the operation of snow blowers, snow throwers and snow plows when operated with a muffler for the purpose of snow removal.