Environmental issues are usually included in process design and operation. Once mass and energy balances have been completed, the life cycle inventory (LCI) can be carried out with an environmental load balance. This paper discusses a methodology for developing this balance, which can be taught at the same level of chemical engineering fundamentals at which basic mass and energy balances are dealt with. The LCIs of electricity and steam produced by a co-generation unit and conventional plants are compared to illustrate the method.