The concept of ring main also applies to
demolitions. Or at least in
military demolitions, which is the context in which I learned about it.
The ring main is also known as the '
trunk line', and the attached
explosive charges are connected via what are called '
branch lines'. The thing is, most military explosives aren't sensitive. They have to be pretty stable so you can trasnport them without them going off. So they have to be sensitized by being linked somehow to sensitive explosives, mostly
blasting caps. Blasting caps have to be taken pretty well care of, isolated from each other, and transported separately from explosives.
Both the trunk lines and branch lines are made out of
detonation cord, or det cord. Det cord is just an explosive in cord form, with a layer of insulation. The difference between det cord and
time fuse is that the whole cord will detonate pretty much instantaneously.
To set off the blasting cap, you need an
ignition assembly. These are either electric or non-electric.
A typical electric ignition assembly connects a
clacker, like the ones in
movies that kind of look like staplers and they hit three times, often attached to
claymore mines, to the blasting cap via some kind of electrical wire. The clacker simply turns the clacking motion into an electrical signal that sets off the blasting cap. Our
XO explained to us that clackers suck because they're not that reliable and they make a lot of noise. Really, you can just as easily use pretty much any size
battery, as long as the wire is good, because the blasting caps are pretty sensitive, both to concussion and to electrical signal.
A typical non-electric ignition assembly connects the blasting cap to some time fuse. Time fuse works pretty much how you'd imagine. You light it, it burns along its length at a more or less constant rate and when it reaches the end, it sets off the blasting cap. The longer the time fuse, obviously, the more time you have to get the hell away from your explosive.
Once you have an ignition assembly, you attach it somewhere onto the trunk line, and this sensitizes the whole thing, because the blasting cap will set off the det cord, which will set off the explosives.
The reason it's a good idea to use a ring main is for
redundancy. If the the det cord somehow gets cut somewhere along the trunk line, the explosion will still traverse the entire trunkline from the opposite direction, and detonate all the explosive charges.