PG&E would not be able to harvest a tax windfall from state authorities by taking a tax deduction for a record-setting $1.6 billion penalty because it caused a fatal explosion in San Bruno, under legislation introduced Friday by two Bay Area state lawmakers. In April, the state Public Utilities Commission imposed a $1.6 billion penalty to punish PG&E for its role in the explosion of natural gas, which killed eight and wrecked a quiet San Bruno neighborhood.