Being able to accurately size deflagration vents is critical to safe, efficient operation of combustible dust handling equipment. NFPA 68 provides simple calculation methods for sizing deflagration vents for combustible dust deflagrations. These calculation methods have two limitations, they apply only to a limited set of operating parameters and they provide for conservative vent sizes. The simple calculation methods are limited to specific operating parameters of vessel geometry, initial pressure, maximum pressure, deflagration index and set pressure. Many combustible dust unit operations fall outside the narrow limitations of the NFPA vent sizing calculations. The NFPA 68 calculation methods for low L/D are limited. Operation outside these limits requires a performance-based design or a full-scale test. The calculations understandably err on the conservative side, sometimes making the installation of such oversized vents impossible. In this paper, an alternative approach is presented, applying the fundamental parameter of laminar flame speed.
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