Effects of Ageing on Munitions

Countless organisations are engaged in the management, clearance and disposal of explosive ordnance on a daily basis, much of which originates from the Cold War era. Most of the ammunition used during the Vietnam conflict, for example, was manufac­tured in the 1950s and 60s; some even originated from WW2 stockpiles. These munitions were built with a shelf life of a very few years; they were expected to be maintained in protective storage and designed to function on deployment, yet they have now been exposed to the outside environment for decades.

This prolonged exposure is well beyond any anticipated design consideration and, not surprisingly, abandoned and unexploded ordnance (AXO and UXO) has often deteriorated significantly.Yet very little work has been done to understand the effects of ageing, and their implications for the explosive ordnance disposal (EOD) industry.Until Fenix Insight Ltd began undertaking studies into the ageing of ordnance a few years ago, the consequences were largely unknown.

In many post-conflict situations (such as Vietnam, or England and Germany after WW2) it is completely impractical to locate and clear every item of UXO, especially those that are deep-buried. Meanwhile, vast quantities of Cold War era ordnance remain in depots around the world, with no prospect of disposal within the foreseeable future. Studying the effects of ageing is key to evaluating the hazard posed by these munitions and, importantly, understanding the future ‘residual’ risk as the ammunition continues to age.

Vast Cold War legacy ammunition stockpiles exist in many countries

Perception and evidence

In the absence of reliable data, the subject has been dominated by popular myth and speculation, with a widespread assumption that explosive ordnance becomes more dangerous as it gets older. Even experienced EOD personnel use emotive and non-technical terms such as “volatile” to describe their expectation of increased risk, yet there is little reliable evidence to support this misconcep­tion. In fact, analysis suggests that the majority of ordnance becomes safer as it ages.

Fenix, in conjunction with CISR, was funded to undertake an initial 3-year study into ageing and has continued this work for many years since. Being constantly engaged in overseas operations involving the disassembly, analysis and disposal of ordnance, Fenix is ideally placed to gather vital data.  

Much of the work on ageing has been in support of GICHD, to understand the residual risk from explosive remnants of war, primarily considering the potential for interaction between people and ordnance. Those people may be local communities farming their land, machine operators and builders involved in development projects, aid workers, or EOD operators from clearance agencies. Wherever their activities coincide with the location of abandoned or unexploded munitions, the potential for an accident to occur is likely to depend heavily on the condition of the item encountered.

Technical Investigation

All work begins with desk-top studies on the weapons concerned, and detailed risk assessments for the planned activities. In most cases, the UXO has already been recovered, or at least located by the agency undertaking the clearance, but it’s normally fully armed. AXO from stockpiles is normally unarmed, but maybe fully fuzed. Wherever possible, the intention is to conduct ‘exploitation’, meaning the complete disassembly, examination and testing of key components.

Primarily, exploitation helps to quantify the risk from the weapon, but there are often many other benefits, including identifying the causes of failure and charting changes in appearance. Other issues, such as changes to the detectability of minimum-metal mines may also be important. Following exploitation, disassembled munitions are often reconstructed to create inert training aids.

Much ammunition can be dismantled by simply reversing the assembly procedure, while plastic and thin metal casings can be cut by hand. For ordnance with thick steel casings, such as bombs and projectiles, commercial bandsaws are used to gain access to the casings. Although it defies conventional wisdom, a bandsaw is capable of cutting through casings and explosives – including live detonators – without causing initiation.

Using a commercial bandsaw to cut through a 2,000 lb Mk 84 bomb
A section through an M904 fuze in an unexploded Mk 82 bomb

Visual VISUAL examination usually gives a good indication of functionality but, wherever possible, this is backed up with practical mechanical and explosive testing. Since detonators are both critical to function and vulnerable to degradation, their testing is often a priority. In order to do this, the output from the fuzing mechanism is replicated as closely as possible, usually using the original weapon fuze, which has been cleaned, rebuilt and tested to ensure its functionality.

All explosive munitions contain multiple assem­blies and energetic materials that are critical to their function, and the majority of these are vulnerable to degradation. In most cases, the failure of any critical component will lead to the item becoming incapable of working as designed. As an analogy, there is no expectation that a 1960s car, camera or typewriter, abandoned in the open for decades, would remain operational. Similarly, it is inevitable that munitions – manu­factured from everyday materials – will also fail. Some have already done so, while many others are nearing the end of their functional life.

The inability of a system to function as designed does not necessarily make it safe; in rare instances, it may lead to the creation of a new and unintended means of initiation. Examples include the release of a mechanism by a weakened component, or a chemical interaction leading to the formation of a sensitive compound. In these exceptional cases, the alternative hazard will be temporary, but the degree and duration of the new risk may be difficult to establish.

Findings

One of the most obvious findings is that appearance often changes over time, resulting not only in discolouration, but sometimes in fundamental alteration as components are lost and surfaces corrode.  Training and awareness materials tend to show images of clean, new munitions, but the aged items encountered in the field by soldiers, aid workers or villagers may be completely unrecognisable.  Even experienced EOD personnel may struggle to recognise ordnance that no longer exhibits the distinguishing characteristics that they’d usually identify.

American M16 mines in SE Asia are hard to identify without their external identifying features. Appearance can change radically with age, yet most training and awareness material depicts ordnance ‘as new’
A section through a degraded M16 bounding mine. When used correctly, a bandsaw can cut through a detonator without setting it off

Appearance is often a good indicator of functionality; in other words, what you see is what you get. However, this is not always the case with the external appearance, which can be deceptive. A heavily degraded sacrificial casing may have protected internal assemblies, or conversely, a resilient casing may house vulnerable components. Mines illustrate this point well, with some steel-cased types remaining functional despite appearing hopelessly degraded, and fresh-looking plastic-cased types being totally non-functional.

Once the casing has been penetrated, it is often water that does the damage. Steel springs lose their ability to provide energy and move other components, while expansion due to corrosion often leads to metallic parts seizing. Water can also lead to the degradation of energetic materials, particularly the pyrotechnic compositions used to initiate detonators and squibs. It doesn’t take very much water to do damage once it gets inside, but even in very dry conditions, fine dust can also block a mechanism effectively.

Rusty shipping containers conceal SA-3 missiles in good condition. Even where the container has rusted through, the missile casing provides further protection for internal components

The dependence of complex weapons on the interaction of multiple components and assemblies can make them more vulnerable to degradation, with numerous parallel routes to failure. This is another area where the perception of risk can be very different from the reality. A simple example occurred recently in the Falkland Islands, where clearance teams simultaneously encountered two booby traps based on grenades. One, using the complex Spanish M5 grenade was considered highly dangerous, and was left well alone. The other, incorporating the familiar US M67 grenade, was considered relatively safe and was recovered. In fact, deterioration of the numerous internal components of the M5 had caused multiple points of failure, while the simple M67 remained fully functional.

Ageing of the complex M5 grenade has resulted in multiple points of failure

In minimum metal mines, corrosion can affect detectability by lowering the metallic mass below the detection threshold of the locator. In some cases, where the detectable metal is not critical to the fuze function, this can lead to the worst-case scenario of a mine that is effectively undetectable, yet remains capable of functioning. This has been observed in the Chinese Type 72, as the arming spring and striker rust away, and in the Belgian M35, which uses two spring steel wires as firing pins.

The corrosion of a wire striker in the top left M35 mine fuze takes it below the detection threshold, but the second striker is in better condition, meaning that the mine remains functional

Electrical power is another area of uncertainty during the ageing process. In weapons where stored electrical energy is needed for initiation, self-deactivation is inevitable since all batteries and capacitors will inevitably discharge, but the rate at which they do so is both variable and highly unpredictable. As with other components, this may be influenced by several factors, including design, damage sustained during deployment and various environmental elements. Military-grade batteries may last for decades, but commercial cells – often used in IEDs – tend to discharge within months.

Lithium batteries in this electronically fuzed Spanish SNA submunition remain charged, despite being more than 20 years old

High explosive fillings tend to be remarkably stable, with TNT from the First World War still functional after more than 100 years. Even the primary explosives used in detonators seems to be resilient, although their pyrotechnic initiation compositions, which are vulnerable to prolonged exposure to moisture, are frequently a cause of failure. Unfortunately, propellants are less predictable, with the phenomenon of autocatalytic initiation being well proven; large rocket motors are definitely high on the priority list within abandoned stockpiles.

The TNT-filled warheads on these old Russian 24B rockets are stable, but the rocket motors are a source of great concern

Summary

Ammunition components are made from materials with varying degrees of vulnerability to their immediate environment, and most will degrade until they can no longer perform their role. At this point, the munition can no longer function as intended, although it is possible – in rare circumstances – for a new and unintended initiation mechanism to form, albeit temporarily.

Water almost always plays the key role in degradation, with the rate of change accelerating rapidly once moisture gets inside the casing; this means, in turn, that the resilience of the casing is often critical to the longevity of ammunition. But there are countless other influences on the ageing process, including damage from vegetation growth or human and animal activity; temperature and UV exposure; and, for buried ordnance, the acidity, microbial activity and oxygen content of the soil.

The effects of ageing are also relevant for improvised explosive devices (IEDs), with strong evidence to suggest that degradation usually occurs much faster in IEDs than in conventional weapons. Many IEDs use flimsy casings, low-grade commercial batteries and water-soluble explosive mixtures, all of which are prone to rapid deterioration.

Understanding the influences on ordnance ageing – yet alone how they interact with one another – is difficult and makes it extremely difficult to accurately predict the effects and time scales. What can be said is that the process is universal and inevitable, that the visual appearance of critical components is often a good indicator of functionality, and that every data point we collect helps to build a more accurate picture.

Conclusion

In countries throughout the world, abandoned and unexploded ordnance is undergoing major changes as a result of the ageing process. These effects are critical to recognition, detection and clear­ance techniques and – most importantly – to the residual risk they pose. That means that ordnance ageing is also critical to decision-makers, such as donors and programme managers, who should be basing funding and work priorities on the evidence of risk.

Yet, despite their importance to stakeholders at every level, very little is understood about the ageing of ammunition; a situation that the EOD industry should be working hard to change.