For stability during transport the rule for liquids is either the tank be filled above 80% or below 20%. The most dangerous surge of liquid affecting the stability of vehicles on road is when liquid level is between 40 to 60%.

How much above 80% is allowed?

IMDG Code states ” Portable tanks shall not be offered for transport with a degree of filling, for liquids having a viscosity less than 2,680 mm2/s at 20°C or at the maximum temperature of the substance during transport in the case of a heated substance, of more than 20% but less than 80% unless the shells of portable tanks are divided, by partitions or surge plates, into sections of not more than 7,500 L capacity.”

Tank provisions TP1 & TP2 of IMDG Code sets forth maximum degree of filling (in %) for general use & maximum degree of filling (in %) for liquids of class 6.1 and class 8, in packing groups I and II, and liquids with an absolute vapour pressure of more than 175 kPa (1.75 bar) at 65°C, or for liquids identified as marine pollutants respectively.

IMDG Code 4.2.1.9.2 : The maximum degree of filling (in %) for general use is determined by the formula: Degree of filling =

IMDG CODE 4.2.1.9.3: The maximum degree of filling (in %) for liquids of class 6.1 and class 8, in packing groups I and II, and liquids with an absolute vapour pressure of more than 175 kPa (1.75 bar) at 65°C, or for liquids identified as marine pollutants is determined by the formula: Degree of filling =

IMDG CODE 4.2.1.9.4: In these formulae, α is the mean coefficient of cubical expansion of the liquid between the mean temperature of the liquid during filling (tf) and the maximum mean bulk temperature during transport (tr) (both in °C). For liquids transported under ambient conditions, α could be calculated by the below formula. in which d15 and d50 are the densities of the liquid at 15°C and 50°C, respectively.

Below calculators may be used for deciding maximum degree of filling