Net Weight vs. Volume Measurements
At DGM New York we are frequently asked by freight forwarders to assist with airline rejections of shipper's dangerous goods shipments. One cause for rejection that comes up from time to time is a net weight of a dangerous goods being different that the volume of hazardous materials being declared on the dangerous goods declaration.
The thought that the weight (kg / kilograms) of product is the same as the volume (L / liters) is incorrect. Different materials whether it be liquids, gases or solids have different densities. If the contrary were correct it would mean that any all objects of the same size would also have the same weight.
An easy visual example is a balloon filled with a gas the size and shape of an elephant does not weigh the same as a real elephant of the same size and shape. They each have different densities even though their volumes are the same. For the remainder of this entry the focus will only be on liquids.
Volume; L (liters): The amount of space that a substance or object occupies, or that is enclosed within a container
Weight (Mass) kg (kilograms net): The force at which a body is attracted towards the earth and is equal to the mass multiplied by the acceleration due to gravity. For practical purposes, mass and weight are used interchangeable in the regulations.
Specific Gravity (SG): The ratio of the density of a substance to the density of a standard.
Equating the net weight (kg) to the volumetric measurement (L) of a shipment of dangerous goods would be inaccurate.
Net mass (kg) = specific gravity (SG) x volume (L)
kg = SG x L
A shipment was rejected with the following perimeters due to the net weight being different than the liters declared on the dangerous goods declaration.
UN1197, Extracts, flavouring, liquid, 3, III
1 Plastic Jerrican x 25.96 L
Material net weight: 22 kg
kg= SG x L
22 kg= SG x 25.96 L
22 kg / 25.96 L = SG
From the SDS (safety data sheet) Section 9. Physical and Chemical Properties
Specific Gravity: 0.82 - 0.86
This value range verifies our calculations.
For this example we have 5 liters of each of the following materials. We will then calculate and compare the weight of each.
Mercury SG= 13.6
Chloroform SG= 1.49
Hexene SG= 0.678
Formula kg = SG x L
Mercury Chloroform Hexene
kg = 13.6 x 5 L kg = 1.49 x 5 L kg = 0.678 x 5 L
weight = 68 kg weight = 7.45 kg weight = 3.39 kg
As we can see through the above calculations the volume (Liters) of a liquid does not directly correspond to the weight (kilograms).