The selection of the odorant to be injected is an important aspect of total system implementation. Selecting the specific odorant to be injected involves knowledge of the chemical composition of the gas, the physical and chemical characteristics of available odorants, the physical layout of the pipeline system and local storage tank, ambient conditions, the desired odorant level, and the current recognition of smell that the local population has. Sometimes changing odorant may create problems in that the smell may be slightly different than what the population is used to. Always consult the chemical manufacturer when selecting or changing the chemical odorant is contemplated.
Odorants that are commonly used today are typically a blend made of the following components;
- Tertiary Butyl Mercaptan or (TBM)
- Isopropyl Mercaptan or (IPM)
- Normal Propyl Mercaptan or (NPM)
- Secondary Butyl Mercaptan or (SBM)
- Dimethyl Sulfide (DMS)
- Methyl Ethyl Sulfide (MES)
- Tetrahydrothiophene (THT)
Note that THT is sometimes used by itself as an odorant.
Each of these components has characteristics which when used as a component of an odorant blend in a specific percentage make it suitable for specific applications.
For example, a typical odorant blend that is comprised of 75-80% TBM and 20-25% DMS is very suitable for an injection-type system because of the characteristics of the components. The characteristics to consider when selecting an odorant or odorant blend includes;
- Vapor pressure
- Gassy odor
- Soil penetrability
- Resistance to oxidation
Each manufacturer of chemical odorant has rigid specifications for the chemicals they produce. Consultation with the manufacturer is highly recommended in order to attain the correct chemical for each application.
Critically important to the odorant system is the local delivery of odorant. This is another area that chemical manufacturers take great care in addressing. It is important that no odorant be released as well as limit fugitive odor emissions during the filling process. The odorant manufacturer typically has systems onboard the chemical truck to allow for the safe delivery of the chemical. For smaller injection applications, odorant can be delivered in transportable containers from which the odorant can be transferred or in some cases the chemical can be injected directly from these containers.