NFPA 921 Chapter 21 has almost nothing to do with explosives. Diffuse fuels are generally not considered explosives under the definitions of the IME (Institute of Makers of Explosives), not just the NFPA.

Detonation is universally defined as a reaction which takes place and propagates within the explosive medium at a speed greater than the speed of sound. The speed of sound (in air at sea level) is approximately 1116 ft/sec.

The maximum flame speeds of optimum mixtures of methane or gasoline vapors are approximately 13.1 ft/sec. respectively. [Harris]

Under normally encountered circumstances neither natural gas nor gasoline vapors can reach definitive detonation reaction speeds, though under very specialized conditions of turbulence within the confining vessel can cause transition to detonation. [Zalosh]

The terms High and low order explosion damage have been widely used in the explosion investigation lexicon for more than fifty years.

Here are some additional quotes from NFPA 921, which appear to apply to your opinions:

“14.5 Specialized Personnel and Technical Consultants.
14.5.1 General. During the planning of a fire investigation, specialized personnel may be needed to provide technical assistance. There are many different facets to fire investigation. If unfamiliar with a particular aspect, the investigator should never hesitate to call in another fire investigative expert who has more knowledge or experience in a particular aspect of the investigation. For example, there are some experts who specialize in explosions.

“14.5.1.1 Sources for these specialized personnel/experts include colleges or universities, government agencies (federal, state, and local), societies or trade groups, consulting firms, and others. … Subsections 14.5.2 through 14.5.10 list examples of professional or specific engineering and scientific disciplines, along with areas where these personnel may help the fire investigator. This section is not intended to list all sources for these specialized personnel and technical consultants.

“14.5.1.2 It should be kept in mind that fire investigation is a specialized field. Those individuals not specifically trained and experienced in the discipline of fire investigation and analysis, even though they may be expert in related fields, may not be well qualified to render opinions regarding fire origin and cause. In order to offer origin and cause opinions, additional training or experience is generally necessary.

“14.5.1.3 The descriptions in 14.5.2 through 14.5.10 are general and do not imply that the presence or absence of a referenced area of training affects the qualifications of a particular specialist.

“14.5.5 Chemical Engineer/Chemist.
14.5.5.1 A chemical engineer has education in chemical processes, fluid dynamics, and heat transfer. When a fire involves chemicals, a chemical process, or a chemical plant, the chemical engineer may help the investigator identify and analyze possible failure modes.

“14.5.5.2 A chemist has extensive education in the identification and analysis of chemicals and may be used by the investigator in identifying a particular substance found at a fire scene. The chemist may be able to test a substance to determine its chemical and physical reaction to heat. When there are concerns about toxicity or the human reaction to chemicals or chemical decomposition products, a chemist, biochemist, or microbiologist should be consulted by the investigator.”

Pat Kennedy, CFEI, CFPS, MIFireE
Fire and Explosion Analyst
Sarasota, Florida
[www.kennedy-fire.com]