Detonation limits

TABLE 11-27 Flammability and Detonability Limits of Hydrogen and Methane Gas... 

Gordon, W.E., Detonation Limits in Condensed Explosives, in Fourth Symposium (International) on Detonation, ACR-126 (edited by Jacobs, S.J.), Office of Naval Research, Washington, DC, 1966, pp. 179-197. 

Despite the nnmber of existing stndies on detonation over the past decades, it is nnfortnnate that, apart from the most common hydrocarbon fnels and hydrogen, the ability to predict detonation limits is still virtnally nonexistent. Nettleton (1987) does present some eqnations for estimating... 

Detonation Limits (Vol %) for Confined and Unconfined Explosions and Flammability Limits (Vol %) in Oxygen and Air... 

Fuel Confined detonation limit, O2 Confined detonation limit, air Unconfined detonation limit, O2 Unconfined detonation limit, air Flammability limit, air Flammability limit, O2 ... 

Experimental data are available for detonation limits for a limited number of fuel-air and fuel-oxygen mixtures at atmospheric pressure in both confined and nnconfined situations. These are presented in Table 4-4 (Nettleton 1987). 

Relatively little information is available on the influence of initial pressure and initial temperature on detonation limits, in confined situations. The general effect of an increase in inidal pressure is to widen the detonations limits, and the same applies to an increase in the initial temperature. The widening is more marked for die upper limit. 

For a more detailed discussion of detonations and detonation limits, the books by Netdeton (1987), Glassman (1996), and Lewis and von Elbe (1987) are recommended. 

Detonations can only take place within the detonable limits, which fall inside the flammable limits. Mixture composition may vary widely in some systems, and this can further depend on the number of connections feeding a manifolded header. There are few cases where it can be assumed that a nondetonating flammable mixture will be produced hence, most in-line flame arrester applications involve the use of detonation flame arresters. 

Detonable Limits The minimnm and maximnm concentrations of a com-bnstible material, in a homogeneons mixtnre with a gaseons oxidizer, that will propagate a detonation. 

A fuel-air mixture is detonable only if its composition is between the detonabil-ity limits. The detonation limits for fuel-air mixtures are substantially narrower than their range of flammability (Benedick et al. 1970). However, the question of whether a nonhomogeneous mixture can sustain a detonation wave is more relevant to the vapor cloud detonation problem because, as described in Section 3.1, the composition of a vapor cloud dispersing in the atmosphere is, in general, far from homogeneous. 

If environmental and atmospheric conditions are such that vapor cloud dispersion can be expected to be very slow, the possibility of unconfined vapor cloud detonation should be considered if, in addition, a long ignition delay is likely. In that case, the full quantity of fuel mixed within detonable limits should be assumed for a fuel-air charge whose initial strength is maximum 10. 

Benedick, W. B., J. D. Kennedy, and B. Morosin. 1970. Detonation limits of unconfined hydrocarbon-air mixtures. Combust, and Flame. 15 83-84. 

Lu, Vyn, Sandus and Slagg (Ref 17) conducted ignition delay time and initiation studies on solid fuel powder-air mixts in an attempt to determine the feasibility of solid-air detonations. The materials investigated included Al, Mg, Mg-Al alloy, C and PETN. Ignition delay time was used as a method of screening the candidate fuels for further work in initiation studies which determined detonation wave speed, detonation pressure, detonation limits, initiation requirements, and the effect of particle size and confinement. The testing showed the importance of large surface area per unit mass, since the most... 

R. BCnystautas, C. Guirao, J.H.S. Lee, and A. Sulmistras, Measurements of cell size in hydrocarbon-air mixtures and prediction of critical tube diameter, critical initiation energy and detonability limits, AIAA Prog. Astronautics Aeronautics, 94, 23-37,1984. 

A warning was given that the 5 molar solution in ether used as a solvent for Diels-Alder reactions would lead to explosions [1], Such a reaction of dimethyl acetylenedicarboxylate and cyclooctatetraene in this solvent exploded very violently on heating. The cyclooctatetraene was blamed, with no supporting evidence [2], It would appear desirable to find the detonability limits of the mixture with ether before any attempt is made to scale up. A safe alternative to lithium perchlorate/ether as a solvent for Diels-Alder reactions is proposed [3],... 

A plant explosion involved a mixture of nitrobenzene, nitric acid and a substantial quantity of water. Detonation occurred with a speed and power comparable to TNT. This was unexpected in view of the presence of water in the mixture [1]. The later reference deals with a detailed practical and theoretical study of this system and determination of the detonability limits and shock-sensitivity. The limits of detonability coincided with the limits of miscibility over a wide portion of the ternary composition diagram. In absence of water, very high sensitivity (similar to that of glyceryl nitrate) occurred between 50 and 80% nitric acid, the stoicheiometric proportion being 73% [2],... 

Detonation limit diagrams for hydrogen peroxide, water, acetone systms are given [11],... 

Homogeneous mixtures of concentrated peroxide with alcohols or other peroxide-miscible organic liquids are capable of detonation by shock or heat [1]. Furfuryl alcohol ignites in contact with 85% peroxide within 1 s [2], Detonability limits of mixtures with 2-propanol have been measured. Approximately stoichiometric combinations of 50% hydrogen peroxide and the alcohol could be made to detonate, as could a wider range of mixtures with higher test peroxide [3],... 

The maximum and minimum concentrations of a gas, vapor, mist, spray, or dust in the air or other gaseous oxidant for a stable detonation to occur are the so-called upper and lower detonation limits. These limits depend on the size and geometry of the surroundings as well as other factors. Therefore, detonation limits found in the literature should be used with caution. Detonation limits are sometimes confused with deflagration limits and the term explosive limits is then used inconsiderately [40]. 

Detonation limits for any fuel-oxidizer mixture depend on the nature and degree of confinement among other factors [42]. 

Flammability and detonability limits. The broader flammability and detonability limits of hydrogen coupled with its rapid burning velocity renders hydrogen a greater explosive threat than methane or gasoline. 

---