In a refinery, a fire develops at an exchanger on a stationary atmospheric distillation unit. A seal leak is observed on the grille of a raw / residue exchanger during a diesel flush after passing through the exchanger (temperature: 290 ° C.). After isolation of the residual side exchanger and opening of the raw side by-pass, the crude inputs and outputs are isolated. The diesel flushing loop for diluting the residue is carried out. Shortly thereafter a black smoke appears at the joint of the exchanger; Corresponding to inflammation. The fire is fueled by the diesel loop. After examination, the heat exchanger gasket is tightened irregularly and insufficiently. The tightening procedure is revised and the diesel flow rate reduced to 20 t / h. The fire causes the installations to stop temporarily.