Section 239(1)(b) in The West Bengal Motor Vehicles Rules, 1989
(b)if the height of the sides of the body or of the sills of the windows, as the case may be, above the highest part of any seat is less than 46 centimetres, provision shall be made by means of guard rails or otherwise. to prevent the arms of seated passengers being thrust through and being injured by passing vehicle, or the extent to which the side windows or venetians can be lowered in such a manner that when lowered their top-edge is not less than 46 centimetres above the highest part of any seat;