the invention relates to a fluid storage tank having an interior volume and a floor and having an internal spill containment chamber comprising a vent gas scrubbing apparatus or scrubber . the chamber may be defined by a containment wall which completely separates the chamber from the tank interior volume . the containment wall may comprise an exterior portion which extends beyond the tank wall . the scrubber is disposed within the chamber and comprises a gas inlet passing through the containment wall into the tank interior volume , a gas outlet for venting scrubbed gases , and a gas scrubbing chemical storage and circulation system .