Run-up distance

Operating Temperature and Pressure Arresters are certified subject to maximum operating temperatures and absolute pressures normally seen at the arrester location. Arrester placement in relation to heat sources, such as incinerators, must be selected so that the allowable temperature is not exceeded, with due consideration for the detonation potential as run-up distance is increased. 

In certain exceptional cases, a specially designed deflagration arrester may be mounted in-line without regard to run-up distance. This can be done only where the system is known to be incapable of detonation. An example is the decomposition flames of ethylene, which are briefly discussed under Special Arrester Types and Alternatives. ... 

An in-line detonation flame arrester must be used whenever there is a possibility of a detonation occurring. This is always a strong possibility in vent manifold (vapor collection) systems, where long pipe runs provide sufficient run-up distances for a deflagration-to-detonation transition to occur. Figure 3-3 shows the installation of in-line arresters of the detonation type in a vent manifold system. 

It may be necessaiy to position flame arresters away from heat sources that could cause the allowable operating temperature of the arrester to be exceeded. Positioning must be made with due consideration of DDT constraints. See Table 5-4, which shows the relationship of run-up distance to... 

In Cases I and II, depending on the run-up distance and gas velocity, there is a greater possibility of DDT than in Case III since the ignition source is further away from the flame arrester. 

Overdriven Detonation The unstahle condition that exists during a defla-gration-to-detonation transition (DDT) before a state of stable detonation is reached. Transition occurs over the length of a few pipe diameters and propagation velocities of up to 2000 m/s have been measured for hydrocarbons in air. This is greater than the speed of sound as measured at the flame front. Overdriven detonations are typically accompanied by side-on pressure ratios (at the pipe wall) in the range 50-100. A severe test for detonation flame arresters is to adjust the run-up distance so the DDT occurs at the flame arrester, subjecting the device to the overdriven detonation impulse. 

Several studies have shown that the shock sensitivity of granular expls depends on expl particle size. The consensus is that the threshold shock pressure to initiate detonation in a given expl is less for large particles than for small particles. However, the converse is true when one considers run-up distances (or run-up times) to detonation. Thus at some pressure above the threshold for both large and small particles, run-up to detonation is smaller for small particle charges than for large particle charges... 

Algebraic expressions for run-up distances, Xj, and times to detonation, tj, for the shock initiation of high density PETN pressings, taken... 

There are some experimental data available on the effects of tube diameter, initial pressure, and temperature on the run-up distance to detonation for smooth... 

In some studies, an increase in the run-up distance with tube diameter was reported, but this may be owing to the hidden influence of such factor as tube roughness. The ratio of the run-up distance to the tube diameter Xoot/D was found to be in the range of 15 0. 

In oil and gas facilities, these effects can be generally related to flame velocity, where this velocity is below 100 m/s (300 ft./s), damage is considered unlikely (Note This is generally within the limits of confinement normally found in offshore facilities). The size of a vapor cloud or plume in which such velocities can occur has been experimentally investigated at the Christian Michelsen Institute (CMI, Norway). The experiments demonstrated that flames need a "run-up" distance of approximately 5.5 meters (18 ft.) to reach damaging speeds. Therefore vapor clouds with dimensions less than this may not cause substantial damage. This is a much over-simplification of the factors and variables involved, but does assume the WCCE of congestion, confinement and gas concentrations. 

For the initial PA-DBX 1 sample, only 4 of 10 detonators met the specifications of dent depth greater than 0.01 . Other detonators would initiate but would not go high order (e.g. the RDX output charge did not appear to detonate). This could be attributed to a density problem or a run up distance issue. 

Packing density (for solid expls) 2) Expl column diameter or confinement 3) Chemical nature 4) Particle size 5) Binder content (in the 5 to 20% range obviously a 20+% binder content can exert a very strong effect and could cause failure) 6) Strength of initiation (primarily in liq expls, where weak initiation can produce a quasi-stable low velocity detonation in solid expls the strength of the initiator may affect run-up distance to stable detonation or even fail to initiate stable detonation)... 

C. Run-up to Detonation We have already had occasion to employ time-to-detonation or run-up distance to detonation (also called initiation distance) in some of our discussions. Now we will briefly describe how... 

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