When doing an LCA that models processes like forestry, quarrying, mining, that rely on the use of heavy machinery, such as excavators, crushers, conveyors, dump trucks, it is necessary to account for the emissions associated with the production of that machinery/equipment that is deemed to be consumed in the process.
In order to work that out, you need to know the machinery unit numbers (how many of each are used), their service life, and their weights in some instances. The unit amount will be divided by the service life to get the amount consumed during each year. Then that amount needs to be allocated by the production volume (mass), i.e. how much product is the machine used to produce per year.
As some ecoinvent data points are based on specific unit sizes, which are stated in the description if applicable, the actual unit weight needs to be divided by the ecoinvent assumption to get the actual consumption. The value from that calculation will be the multiplication factor used to change the actual unit amount consumed to take into account the ecoinvent assumption weight difference.
For example, if we take a dump truck and use the data point Lorry production, 40 metric ton (Reference product: lorry, 40 metric ton ), and there are two dump trucks in use on site with a service life of 10 years each. We first divide 2 units by 10 years to get 0.2 units/year. If we say we produce 10 000 tonnes of product per year, then we divide 0.2 by 10 000 to give us 0.00002 units/tonne. If our dump truck weighs 50 metric tons, then 50 divided by 40 gives us a factor of 1.25 which we multiply by 0.00002 to get 0.000025 units/tonne.
The default weights found in the ecoinvent resources can be used if they represent a close enough approximation of the actual used vehicle/machine.
If the chosen ecoinvent data point is in units (rather than in kg), the transportation impacts need to be accounted for separately under Additional transport. The weight for transported mass is the quantity given in A3 multiplied by the weight of vehicle. Taking our example above, we have 0,000025 of Lorry production, and the lorry weighs 50 t, then the transported mass is 0,000025 * 50 000 = 1.25 kg.
Please note that only machinery directly involved in the manufacturing needs to be accounted for and usually it would not apply to simple factory-produced products, which can have the capital goods excluded.