Tripwires and accidents
Two questions about tripwires. Andy, from your database is it reasonable to say that tripwire-operated fragmentation mines are the greatest danger to deminers? And more generally, when tripwires are laid, what kind of tension is there typically in the wire? Is it possible to generalise, and if so, can you give maximum and minimum values?
Question 1) "Is it reasonable to say that tripwire-operated fragmentation mines are the greatest danger to deminers?"
I hate to sound like a politician, but the answer is that "it all depends". Here is a general answer using the data in the database (DDAS).
In terms of numbers of accidents, "No, it is not reasonable". Most accidents occur with pressure activated AP blast mines (which are by far the most commonly found items in global terms, except when working in arms dumps). Tripwires are generally used with fragmentation mines or booby traps/IEDs.
In terms of numbers of severe injuries, "No, it is not reasonable". The preponderance of AP blast mine accidents means that even though few of them result in severe injury, enough do to outnumber the severe injuries from fragmentation mines.
In terms of deaths caused by a particular type of mine, "Er, sort of Yes, it may sometimes be reasonable to say that tripwire-operated fragmentation mines are the greatest danger to deminers". Most mine accidents do not result in death, but some types of fragmentation mine (especially bounding fragmentation mines) cause injuries that are commonly fatal. However, in some countries functional fragmentation mines are absent or rare, and in some where tripwire operated fragmentation mines are a risk, the greatest risk of death appears to be presented by ordnance other than mines....
So an unconditional statement that "tripwire-operated fragmentation mines are the greatest danger to deminers" would usually be false.
I can say that.... "As a crude ratio of fatality against numbers of a mine-type found, the mine-type most likely to cause deminer fatality is a functional tripwire operated fragmentation mine". I think that is an uncontroversial statement... but the precise wording is important.
It may be relevant to add that accidental initiation by pulling the tripwire is not common in HD (it may be with civilians). Initiation during disarming or demolition, or initiation by striking the fuze directly (PROM-1 in particular) are more common than most would expect. When a deminer is killed after striking the fuze, it is often not possible to know with any certainty whether he pulled the wire or hit the fuze with a tool (usually a vegetation cutter or detector search-head). If any wire is found, it tends to be presumed that he pulled the wire, but in most cases the mine has bounded very close to the victim and so he could have struck the fuze.
Question 2: "When tripwires are laid, what kind of tension is there typically in the wire?"
ANDY SMITH ANSWERS:
This answer draws more on personal experience than on evidence in the database.
You have to distinguish between mine types, elapsed time and the climate/context of placement. And since most minefields are old by the time they are cleared in Humanitarian Demining, I am not sure that tripwire "tension when originally placed" is often an appropriate concern. Regardless of how they were originally placed, all wires I have seen have been slack, but most have also been broken (by corrosion, fire or by being pulled without an initiation). Plastic coated wires in a European climate are often the exception.
Also, you really should distinguish between fuzes. For example, the POMZ and the OZM range usually have MUV type pin-pull fuzes. The pin is exposed and corrosion is common. I have had to soak fuze bodies in penetrating oil and really work hard with pliers to get a corroded pin out. In those cases, the tripwire would probably have snapped or the mine been uprooted without pulling the pin. But in a few, the pin has been hanging out and the sprung initiator poised on almost nothing. The PROMs and the V69/J69 have tilt fuzes - a pulled wire tilts the fuze head. This allows multiple wires to be attached to the same fuze, but by definition radial wires have to allow movement so cannot be taut. A single wire can be taut, but.... the person placing the mine is not into taking unnecessary risk so is unlikely to go for maximum tension. Where there is undergrowth, once a foot picks up a wire it hardly matters that the victim has moved a footstep before it is taut. The undergrowth catches on your feet anyway, so the victim will not feel a slack wire. On open ground, tripwires have to be less slack.... In ambush or IED situations or when wires are placed for night-only protection (so can be reliably placed where visible in daylight) different scenarios apply. Mines that deploy their own tripwires (such as the M74 or the BLU 92B Gator) seem to use a rather sensitive breakwire at the end of the tripwire so that the tension required to "pull" it is probably very low.
The answer is never as simple as we would like and in my opinion, in an old tripwire minefield, there is no predictable tension that could always be reliably considered safe or unsafe.
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