Typically, odors are a nuisance (smell bad) but the chemical compounds are present at concentrations well below hazardous levels but not always. H2S can exist in sewers well above the IDLH value of 100 ppm LOCALIZED odor control uses several smaller odor control systems located near each odor source. Sizes and technology may vary from one location to another, CENTRALIZED odor control uses ductwork to convey odors from odor sources to common central odor control system.

Activated Carbon Odour Control System	Biological System Sulphus