Methane, Propane & Butane (& its mixtures) are the most commonly carried hydrocarbon gas cargoes on ships. These gases are also very commonly used at homes & also sold as fuel gases. These gasses being colourless & odourless, it becomes very difficult to detect them in case of a leakage. The process of introducing a compound with a high degree of smell / odour & which does not interfere with the physical & chemical properties of the fuel gas is called odourising or most commonly also as stenching. Odourising or stenching is mostly carried out at shore terminals, but sometimes due to requirements of a specific trade this is placed as an added responsibility to the shipboard staff. Most common places where these operations are carried out on ships is Indian Sub-continent, Far East Asia, West Africa & The Caribbean Islands. It is recommended that shipboard odourisation does not take place unless there is no reasonably practical alternative. Wherever possible, the equipment should always be installed and the operation undertaken ashore in the terminal. This is because:
Organosulphur compounds are the most common odourisers used in the industry & some of them are the most odorous substances known. Two most common compounds currently in use as odorants are Mercaptans and sulphides. Some examples are as below:
Of these EM is the most suitable for the stenching of LPG and is most commonly used. It can be detected at concentrations lower than 1 ppb (parts per billion) in air. |