All mines and ERW are subject to atrophy. The fuze systems may corrode, chemicals decay or the explosive may dry out and fall apart. The changes may be accelerated by climate, human interaction or random events such as bushfire.
The effects of decay may be positive. The firing train may be broken so that the device is no longer capable of exploding. Mechanical parts of the firing train may have become incapable of movement. Chemical parts may have changed their properties and become "inert".
The effects may also be negative. The firing train may have become unstable so that the device can be initiated with far less force, or force applied in a different way than its designer intended.
Sometimes the effect is positive, but with a negative spin-off. This might occur when the firing train is no longer capable of functioning as deisgned, but the detonator and high explosive are accessible and may be attractive to children or for misuse.
Changes may also be temporary. Some detonators may not function when wet, but may function again if allowed to dry out.
If it can be reliably inferred that devices at a worksite are incapable of detonation, this has significant consequences for the choice of procedures, tools and safety distances that are appropriate to use when clearing the devices. It may also affect the prioritisation of work in one area over another.
A study covering how mines age that identifies types of mine and ERW that reliably cease to function after a period of time in a given context is required. The same study should identify mines and ERW that frequently become more sensitive and unredictable over a period of time.
I first raised the need for this study more than ten years ago and the idea was rejected because "the context is so varied that the conditions surrounding the device could not be predicted: also, different batches of a particular mine might use different materials and so have different aging characteristics". These comments are true, but do not remove the need for a study in which as many of the relevant variables as possible are recorded. The chemicals in some detonators and boosters atrophy quickly, and without a functional initiation system the mine is relatively harmless. Other mines and fuzes are manufactured using plastics that UV degrade, so when exposed to prolonged sunlight the device may become more or less sensitive. When making a risk assessment in any context the condition of the anticipated devices can be very important to know, and can influence the way that the area is processed. For example, it is reported that the Portuguese
M969 mines found extensively on the border of Mozambique / Tanzania reliably decays such that the small initiators required to set off the detonator are "empty". These mines have been in place for more than thirty years and it seems that the chemical content of the initiators has decayed. If this report is reliable, it may be appropriate to process areas with these mines using ground-engaging machines. No mines will be initiated, but if the machine can reliably break up the mine case and so separate the small detonator from the high explosive, that might be thought to reduce risk to an acceptable level (depending on intended land use - but the border will remain a border). Cost savings and the advantages of deploying deminers in areas that present a greater risk to civilians have to be taken into account.
Apparently a study was funded by the U.S. and conducted, but I have not had access to any useful results. I hope that it draws from field experience and avoids overlaying safety factors that prevent the conclusions having practical applications in the HMA world. If it did reach any genuinely useful conclusions, I think I would have heard of the results.
In the meantime, a few examples of mine atrophy are given under "Assessing the threat " under Resurvey.