What is Velocity of Detonation (V.O.D) ?
Definition, physics, typical values and why V.O.D is the most cited performance metric of a high explosive.
Definition
The Velocity of Detonation, abbreviated V.O.D, is the speed at which the detonation wave front travels through a detonating explosive. It is a steady state property of a self sustained detonation, distinct from the burning rate of a deflagration.
For any given explosive, the V.O.D depends on the formulation, the density, the particle size, the charge diameter and the degree of confinement. Environmental factors such as ingress of water, static and dynamic pressure also influence the value reached in the field.
Units and orders of magnitude
V.O.D is expressed in meters per second, in kilometers per second or in feet per second. Industrial bulk explosives typically detonate between approximately 3,000 and 6,500 m/s.
Military high explosives such as TNT, RDX or HMX based compositions can exceed 8,000 m/s. Detonating cords sit between roughly 6,000 and 7,500 m/s depending on the core load.
Why measure V.O.D. ?
V.O.D controls how energy is released by the explosive, as a combination of shock energy and heave energy. This balance directly affects rock fragmentation, muck pile profile, throw and the cost of extraction in mining and quarrying. In manufacturing, V.O.D is a quality control indicator that ties back to formulation, sensitization and aging.
Published V.O.D values describe ideal conditions. In real blast holes, the actual V.O.D can deviate significantly because of diameter, confinement, water content, temperature or substandard initiation. The only way to verify performance is to measure V.O.D in operating conditions.
How V.O.D. is measured ?
A V.O.D recorder times the passage of the detonation wave between two or more sensing points placed along the explosive column at known distances. Dividing the distance by the time of flight returns the average V.O.D over each interval.
Two families of sensors are commonly used. Continuous resistive probes deliver a resistance versus time curve from which V.O.D is derived. Point by point fiber optic probes detect the light flash emitted by the detonation as it reaches each fiber tip, and are insensitive to electromagnetic interference.
Kontinitro instruments
Kontinitro V.O.D recorders use fiber optic point by point measurement. The Explomet 2 Series is the laboratory reference instrument, with six fiber inputs, five counters and a timing precision of 0.01 microsecond. The Explomet 3 is engineered for field deployment in quarries, mines and operational test sites, and works with the EasyProbe System and the DCS Duplex Cable System.
For very large measurement campaigns, the High Capacity Systems extend the Explomet 2 platform to 20, 24 or 30 channels.
FAQ
Common questions
What is Velocity of Detonation in simple terms?
It is how fast the detonation travels through the explosive itself, not how fast the blast moves through the rock. It is the most commonly used indicator for a high-explosive.A charge detonating at 5,000 m/s consumes one meter of explosive column in 200 microseconds.
What are typical V.O.D values?
Industrial bulk explosives sit between about 3,000 and 6,500 m/s. Military compositions can exceed 8,000 m/s, and detonating cords fall between roughly 6,000 and 7,500 m/s. The actual values always depend on density, diameter, confinement and initiation.
Why does V.O.D need to be measured?
The published V.O.D. values describe an explosive under ideal conditions. Catalog values assume ideal diameter, confinement and dryness. Water, an undersized hole or a weak initiation lower the velocity actually reached, and only a measurement in operating conditions reveals it.
What instrument measure V.O.D. ?
Dedicated VOD recorders are used. They measure the passage of the detonation wave between two or more detection points along the explosive column, then calculate the velocity. Kontinitro Explomet instruments record the light pulse emitted by the detonation via plastic optical fibers and reproduce the VOD with a timing accuracy of ±0.01 microseconds.