I looked into this.
Forges go obsolete with Metal Casting i don't see how the tech Fire Brigades would make them obsolete. Maybe i missed something?
Edit:
Did you mean you can't build forges after Fire Brigades that could be possible because of the Bonus Prereqs you need one of those.
Code:
<BonusType>BONUS_CHARCOAL</BonusType>
<BonusType>BONUS_COAL</BonusType>
<BonusType>BONUS_INGOT_COPPER</BonusType>
<BonusType>BONUS_INGOT_TIN</BonusType>
<BonusType>BONUS_INGOT_IRON</BonusType>
<BonusType>BONUS_INGOT_LEAD</BonusType>
<BonusType>BONUS_INGOT_SILVER</BonusType>
<BonusType>BONUS_INGOT_GOLD</BonusType>
<BonusType>BONUS_INGOT_PLATINUM</BonusType>
<BonusType>BONUS_INGOT_BRASS</BonusType>
<BonusType>BONUS_INGOT_ELECTRUM</BonusType>
<BonusType>BONUS_INGOT_TITANIUM</BonusType>
<BonusType>BONUS_STEEL</BonusType>
<BonusType>BONUS_ALUMINUM</BonusType>