Referring to the clause stated in TBDY 2018 188.8.131.52, the environmental exposure class will be specified on the drawing sheets, you can select the "Environmental exposure class" from the drop-down list on the Analysis Settings/Other tab to be shown on the drawing letterheads .
Open the Analysis Settings dialog.
Click on the other tab.
Choose from the list of environmental exposure classes.
The selection you made on the letterheads will appear when you draw.