A fire involving burns occurred during piperazine crystal pulling-out work in the centrifugal separation process after synthesis of piperazine. Air flowed in because an operator failed to close the exhaust valve and the cover of the handhole. Then, a combustible gas-air mixture (ranges of flammability 1-7%) of xylene was formed. Although two polyethylene bags were put between the crystal and crystal receiving drum for insulation, measures were not taken to remove static electricity. A fire was caused by electric discharge of static electricity in the separation process.