Four Oakland firefighters walked through the Ghost Ship warehouse two years before a fire there killed 36 people, one of them testified Tuesday. Oakland Fire Captain George Freelen said he became concerned during the informal 20-minute survey about the “high fire load” of material stocked inside the artist collective. He sent a one-page report to the department’s Fire Prevention Bureau to get clarity on what the building was supposed to be used for. Freelen said he never heard back. And he didn’t follow up.