Box 1.

Difference between attributional and consequential LCA.

Attributional impact is given by:

WALCA = WO + (WS.TS)/TO

where WALCA is total attributional impact measured in Watts, WO is Watts consumed when operating, WS is Watts consumed in standby, TS is total standby time and TO is total operational time.

In an example where the operational power consumption of a scanner is 500W per hour, standby power is 100W per hour, and the scanner is only operational for 2 h per day, with it being in standby the rest of the time, the attributional impact per hour of operation is:

1,600 W = 500 + (100×22)/2

In a consequential analysis, the proportion of standby energy is not included, as the scanner is sitting in standby regardless of whether it is used or not. The consequence of using the scanner, therefore, is only the difference between standby and operational power, and hence the consequential impact per hour of operation is 400W (500W – 100W).