Photo by Dušan Cvetanović on pexels

If we are planning to ship liquid dangerous goods or liquid marine pollutants in portable tanks, we will reach the tank provisions TP1 or TP2, key rules in the IMDG Code (sections 4.2.1.9.2 and 4.2.1.9.3), for calculating the “degree of filling”, which tells us how full we can safely load our tank without things going wrong.

Degree of filling means the ratio, expressed in %, of the volume of liquid or solid introduced at 15°C into the means of containment and the volume of the means of containment ready for use. – IMDG Code Chapter 1.2

These formulas, TP1 & TP2 in sections 4.2.1.9.2 and 4.2.1.9.3, are all about accounting for coefficient of thermal expansion (α), based on our liquid’s densities at 15°C and 50° C to calculate the max fill percentage. For most stuff, it’s something like 97% adjusted for expansion, and 95% for higher hazardous goods and marine pollutants.

Why is this important?

Expansion of the liquid if they heat up during transport, and overfilling could increase the pressure inside the tank barrel, risking leaks, bursts, or worse. Nobody wants a pressurized surprise on the high seas or even on the road!

Then there is the mandatory requirement of IMDG 4.2.1.9.6.1 (for road transport see ADR 2025 4.2.1.9), which throws in a requirement for bigger tanks over 7,500 liters.
If our liquid cargo’s viscosity is less than 2,680 mm²/s at 20°C (example runny stuff like fuels), we can’t ship with a fill level between 20% and 80% unless the tank is divided into smaller compartments or fitted with surge plates.

This is to avoid “sloshing” or surge of liquid inside the tank that could slam hydraulic forces against the tank walls, causing potentially dangerous situation during transport.

To calculate degree of filling enter density at 15 Deg, 50 Deg C & volume of the tank in the below calculator

Calculate Degree of Filling

What about non dangerous liquids in portable tanks?

IMDG Code is for safe transport of dangerous goods and marine pollutants by sea, but we must not forget these degree of filling guidelines while shipping non-dangerous and/or non marine pollutants liquids in portable tanks. Thermal expansion and surge risks do not discriminate whether the cargo is harmless apple juice or plain water, over or under filling can still lead to pressure build-up, spills, or instability during transit. Sticking to similar principles keeps our cargo and everyone around it safe, no matter what is inside.

To highlight the importance of adhering to degree of filling we can look at IMO’s CSS Code (Code of Safe Practice for Cargo Stowage and Securing), which states: “Portable tanks should not be offered for shipment in an ullage condition liable to produce an unacceptable hydraulic force due to surge within the tank.”
Ullage is that empty headspace, and too much of it in a partially filled tank can turn our cargo into a wave pool on wheels on road or at sea.

These rules, of degree of filling, keep everything safe, stable, and spill free.

Remember, in shipping prevention beats cleanup and emergency response every time!