mine ventilation
... that the cost of operating mine ventilation fans can account for one-third of the entire electrical power cost for a typical underground mine?
... that the cost of operating <b id="mwAuQ"><a href="./Underground_mine_ventilation" id="mwAuU" rel="mw:WikiLink" title="Underground mine ventilation">mine ventilation</a></b> fans can account for one-third of the entire electrical power cost for a typical <a class="mw-redirect" href="./Underground_mining" id="mwAuY" rel="mw:WikiLink" title="Underground mining">underground mine</a>?