NFPA 67-2019 Guide on Explosion Protection for Gaseous Mixtures in Pipe Systems.
3.1 General. The definitions contained in this chapter apply to the terms used in this guide. Where terms are not defined in this chapter or within another chapter, they should be defined using their ordinarily accepted meanings within the context in which they are used. Merriam-Webster’s Collegiate Dictionary, 11th edition, is the source for the ordinarily accepted meaning. 3.2 NFPA Official Definitions. 3.2.1* Approved. Acceptable to the authority having jurisdic- tion. 3.2.2* Authority Having Jurisdiction (AHJ). An organization, office, or individual responsible for enforcing the requirements of a code or standard, or for approving equipment, materials, an installation, or a procedure. 3.2.3 Guide. A document that is advisory or informative in nature and that contains only nonmandatory provisions. A guide may contain mandatory statements such as when a guide can be used, but the document as a whole is not suitable for adoption into law. ，3.2.4 Labeled. Equipment or materials to which has been attached a label, symbol, or other identifying mark of an organ- ization that is acceptable to the authority having jurisdiction and concerned with product evaluation, that maintains peri- odic inspection of production of labeled equipment or materi- als，and by whose labeling the manufacturer indicates compliance with appropriate standards or performance in a specified manner.
3.3.3 Deflagration. Propagation of a combustion zone at a velocity that is less than the speed of sound in the unreacted medium. 3.3.4 Dellagration-to-Detonation Transition (DDT). The tran- sition point to an unstable detonation. 3.3.5* Detonation. Propagation of a combustion zone at a velocity that is greater than the speed of sound in the unreac- ted medium. 3.3.6 Detonation Cell Size. (Reserved) 3.3.7 Dynamic Load Factor (DLF). The ratio of the deforma- tion in a detonation to the deformation expected for a static load based on the Chapman-Jouguet detonation pressure (see Equation 188.8.131.52). 3.3.8 Equivalence Ratio. For a particular fuel-oxidant mixture, the fuel oxidant ratio of a particular mixture divided by the fuel oxidant ratio of the stoichiometric mixture. 3.3.9* Flame Arrester. A device that prevents the transmission of a flame through a flammable gas/air mixture by quenching the flame on the surfaces of an array of small passages through which the flame must pass. [69, 2019] 3.3.10 Flame Speed (Sr). The speed of a flame front relative to a fixed reference point. 3.3.11 Flammable Limits. The minimum and maximum concentrations of a combustible material, in a homogeneous mixture with a gaseous xidizer, that will propagate a flame. 3.3.12 Flammable Mixture. A mixture of fuel, oxygen (or other oxidant), and inert gases that has a composition in the flammable range.NFPA 67 pdf download.