At the high temperatures found in the modified Claus reaction furnace, the thermal decomposition and oxidation of H2S yields large quantities of desirable products, gaseous hydrogen (H-2) and sulfur (S2). However, as the temperature of the gas stream is lowered in the waste heat boiler (WHB) located downstream of the furnace, the reverse reaction occurs leading to reassociation of H2 and S2 molecules. To examine the reaction quenching capabilities of the WHB, a rigorous computer model was developed incorporating recently published intrinsic kinetic data. A sensitivity study performed with the model demonstrated that WHBs have a wide range of operation with gas mass flux in the tubes from 4 to 24 kg/(m2.s). Most important, the model showed that it was possible to operate WHBs such that quench times could be decreased to 40 ms, which is a reduction by 60 % compared to a base case scenario. Furthermore, hydrogen production could be increased by over 20% simply by reconfiguring the WHB tubes.