Retired scientist of the Indian Space Research Organisation (ISRO), D. Anandan, said that the selection of high bed semi-trailers for Liquefied Petroleum Gas (LPG) transportation in India is the main cause of all LPG tanker lorry accidents. He made the point while addressing a press conference here on Monday about a study report prepared by him in the wake of the December 31 LPG tanker accident at Puthentheruvu near Karunagapally.
Dr. Anandan, a former Associate Project Director of Geosynchronus Satellite Launch Vessel and Group Director of the ISRO’s Liquid Propulsion Systems Centre, said that while LPG transportation through rail and transportation of other liquids such as petrol, diesel, water and milk have no problem, only semi-trailers transporting LPG meet with such accidents.
This is because tankers transporting the other liquids are largely platform trailers that are designed with rectangular stability area. On the other hand, semi-trailers designed with a triangular stability area, have no front axle and a large portion of its weight is supported by the prime mover to which it is connected with a goose pin.
Several factors affect the stability of the semi trailers and they include insufficient stability area of the semi-trailer, the position of centre of gravity, liquid sloshing force and speed. When a semi-trailer’s centre of gravity goes out of stability line, the trailer becomes unstable and will start to tilt.
Liquid sloshing is one of the main factors that make the centre of gravity go out of stability line. The upward and downward lateral motion of the liquid in a particular frequency is sloshing, Dr. Anandan explained. In an LPG container which has no compartments, the liquid is free to move.
Any small reduction in speed forces the liquid to move forward with force proportional to the rate of speed reduction. This in turn makes the centre of gravity move too much forward reducing the lateral stability of the semi-trailer and when the centre of gravity goes out of stability area, the trailer over turns.
Therefore the option should be for either platform trailers or even low bed semi-trailers. In spite of their triangular stability area, low bed semi-trailers are being extensively used in Europe and the United States and their performance is reported to be moderately good, Dr. Anandan said. Also vital is the condition of roads, he added.
