The model of the pseudo-homogeneous, one-dimensional, cooled tubular reactor is applied to two consecutive, irreversible first order reactions. A criterion is derived to obtain a desired integral yield. Based on this criterion three requirements are formulated, which enable us to choose the relevant design and operating conditions. If any of the requirements are met, the reactor is also safe with respect to runaway. In an illustration the results are applied to the production of phthalic anhydride via the oxidation of naphthalene. It is shown that the requirements formulated can be used for the design of the reactor and for its immediate adjustment to a change in operating conditions. In view of the special behaviour of consecutive reactions in a tubular reactor a fine tuning of the operating conditions remains necessary after this adjustment.