Detonating cord

From Wikipedia, the free encyclopedia

Detonating cord, also called detonation cord, detacord, det. cord, detcord, primer cord, primacord or cordtex, is a thin, flexible tube with an explosive core. It is a high-speed fuse which explodes, rather than burns, and is suitable for detonating high explosives, usually pentaerythritol tetranitrate (PETN, Pentrite). The velocity of detonation is sufficient to use it for synchronising multiple charges to detonate almost simultaneously even if the charges are placed at different distances from the point of initiation. It is used to reliably and inexpensively chain together multiple explosive charges. Typical uses include mining, drilling, and demolitions.

"Cordtex" is one of many tradenames which has slipped into being used as a generic.

As a transmission medium, it can act as a downline between the initiator (trigger) and the blast area, and as a trunkline connecting several different explosive charges. As a timing mechanism, detonation cord detonates at a very reliable rate (about 7000 - 8000 m/s), enabling engineers to control the pattern in which charges are detonated. This is particularly useful for demolitions, when structural elements need to be destroyed in a specific order to control the collapse of a building.

While it looks like nylon cord, the core is a compressed powdered explosive, usually PETN (Pentrite), and it is initiated by the use of a blasting cap. Detonation cord will initiate most commercial high explosives (dynamite, gelignite, sensitised gels, etc.) but will not initiate less sensitive blasting agents like ANFO on its own. 25 to 50 grain/foot (5.3 to 10.6 g/m) det cord has approximately the same initiation power as a blasting cap, but along its entire length. A small charge of PETN, TNT, or other explosive explosive booster is required to bridge between the cord and a charge of insensitive blasting agent like ANFO or most water gels. The Finnish army colloquialism is anopin pyykkinaru (mother-in-law's clothesline) as it resembles ordinary clothesline.

[edit] Rating

Detonating cord is rated in explosive mass per unit length. This is expressed in grains per foot in the United States, or in grams per metre elsewhere. A "grams per metre" rating will be roughly one fifth the "grains per foot" rating. For example, "50 grain det. cord" refers to detonating cord which has 50 grains of explosive (about 1/70th of a stick of dynamite) per foot of length — or approximately 10 g/m. This is a typical "default" rating for connecting charges for blasting; lighter detonating cords may be used for "low noise blasting" and movie special effects, while heavier cords are used where the cord is employed to have some direct explosive effect. Precision rock carving work, for example http://www.crazyhorse.org/carving/inside/index.shtml may use 50 to 250 grain/foot (10 to 50 g/m) detonating cord.

[edit] Direct employment

Low-yield detonating cord can be used as a precision cutting charge to remove cables, pipes, wiring, fiber optics, and other utility bundles by placing one or more complete wraps around the target. Higher-yield detonating cord can be used to cut down small trees, although the process is very uneconomical compared to using bulk explosive, or even a chainsaw. High-yield detonating cord placed by divers has been used to remove old dock pilings and other underwater obstructions. Creating a slipknot from detonating cord yields a field improvised device that can be quickly employed to cut a locked doorknob off a door. Anything much more substantial than these uses requires the use of additional explosives.

[edit] Unconventional use

Detonating cord has also been used for these purposes:-

• Constructing boobytraps
• Felling trees by coiling several rounds of detonating cord around them
• In ambush zones to eliminate enemy taking cover in roadside ditches, bushes, etc.
• In canopy fracturing systems in high performance aircraft
• To clear brush to effectively stop the progression of forest fires.
• Recent patents indicate the use of detonating cord in the process of deslagging coal fired power plants.
• For environmental purposes to remove nonindigenous species of fish from bodies of water; it kills all the fish, and the lake is then restocked.
• Det cord is commonly used to increase the production of water and petroleum wells.
• Expanding tubing in nuclear reactors
• Clearing landmines
• Sculpting large monuments such as Crazy Horse in South Dakota
• Separating sections of rockets, etc.