Mass balance chain of custody
Mass balance chain of custody is a model for tracking a specified material characteristic through a defined system where eligible and ineligible inputs may be mixed. Records reconcile quantities and allocate the characteristic to outputs under stated rules and periods, without claiming that the same physical molecules are present in each attributed product.
In simple terms
Within Chain of custody, the model sets the participating organizations or sites, eligible inputs, accounting boundary, balancing period, conversion factors, losses, inventory rules, allocation method, output claims, and verification. Mass balance accounting assigns qualifying characteristics only within the quantity supported by eligible input after the applicable calculations. Physical mixing is allowed, so an attributed output is not proof that it contains a proportional set of the original eligible molecules. Standards and certification schemes can implement mass balance differently; claims cannot be transferred between them merely because both use the same model name.
Why it matters
Mass balance can preserve a controlled sustainability claim where industrial processes or supply networks make physical segregation impractical. It can support demand for preferred inputs while maintaining quantitative limits. Poorly defined boundaries, unjustified conversion factors, long balancing periods, multiple allocation of the same input, or vague product wording can instead enable double counting and misleading claims.
Example
A processor mixes verified recycled and virgin feedstocks in shared equipment. During the approved balancing period, it records input quantities, process losses, inventories, and outputs, then assigns the recycled attribute to no more output than the scheme permits. Customer documentation states a mass-balance-attributed claim rather than asserting that the particular item contains those same recycled molecules.
How it differs
Chain of custody
Chain of custody is the broader control of a claim through transfers and transformations; mass balance is one chain-of-custody model that permits controlled mixing and accounting-based allocation.
Mass balance accounting
Mass balance accounting is the quantitative reconciliation and allocation technique; mass balance chain of custody is the wider custody model governing participants, boundaries, controls, records, verification, and claims that use that accounting.