Where the relief of excess pressure from process vessels might result in undue hazard to persons or property through excessive release of flammable or toxic materials, the Chief may require the operating pressure of process vessels to be a suitable margin below the design pressure. In determining the required margin, due consideration shall be given to the operating characteristics of the processes and of the facilities for relieving excess pressure. As an alternative thereto, the Chief may permit a system for safe disposal of materials vented from the facilities for relieving excess pressure.