Abstract: At 2:30 a.m. on March 13, 1996, Employees #1 and #2 were preparing to remove a blind from the discharge line of pump #5G8A in hydrogen fluoride alkylation unit #5. Employee #1 went to the operations office and was told that the blind was ready to be pulled. Employee #2 gathered the proper tools and checked the vacuum gauge to confirm that the line had 20 inches of vacuum. Neither the maintenance supervisor nor the operations foreman initiated a fresh air permit check, which would have indicated if type B protection would be necessary. Instead, they believed that type C protection would be adequate since they had used it on previous occasions for this job. Employee #1 used a wrench to remove seven of the eight bolts holding the blind without any leakage. When he removed the last bolt, hydrogen fluoride mist struck him in the face. Employee #2 was standing by with the water hose and was also hit in the face by hydrogen fluoride. Both employees suffered chemical burns and Employee #1 was hospitalized. The bleeder line from this pump had become plugged and had never been repaired. This meant that the upper side of the pump was still under pressure and the vacuum was only being drawn from the lower side of the pump. Employees #1 and #2 were unaware of this condition.