Environmental Impact on the Functionality of Landmines: Does Aging Matter?

by Martin Jebens [ The Danish Coastal Authorities ]

Mines buried in Skallingen, Denmark, during World War II have since shown varying reactions to their environments in beach, dune and marsh areas. This article explains the results of several tests that may assist in the development of a more efficient, cost-effective demining plan in these areas. It also posits that a similar analysis of mines and soils in other old minefields could result in more flexibility with clearance, leading to greater efficiency.

Figure 1: Orthophoto of Skallingen peninsula and the outline of the WWII minefields prior to the mine clearance in 2006–2008. Currently the southern part remains to be cleared, which will commence in 2010.
Figure 1: Orthophoto of Skallingen peninsula and the outline of the WWII minefields prior to the mine clearance in 2006–2008. Currently the southern part remains to be cleared, which will commence in 2010.
Photo courtesy of Danish Coastal Authority

During 1944 and 1945, German forces placed 72,000 anti-personnel and anti-tank mines at Skallingen on the Danish coast. This dynamic coastal area’s migrating dunes would quickly hide these mines, making post-war mine clearance difficult and causing some of the mines to be missed. The mines had also been randomly positioned, which added to the challenge of detecting and removing them. In 1999 the Danish military concluded that 5% of the remaining 10,000 mines were fully functional and could resurface because of ongoing erosion. At the same time, the Danish government ratified the Ottawa Convention, which led to clearance of the area commencing. The clearance is being conducted by the Danish Coastal Authorities, together with different contractors, and is scheduled to reach completion in 2011/2012.

Figure 2: Aerial photo of clearance work on the beach during the second clearance phase. The dunes and marsh are seen behind the beach.
Figure 2: Aerial photo of clearance work on the beach during the second clearance phase. The dunes and marsh are seen behind the beach.
Photo courtesy of Luftfoto Syd

The clearance of the first two areas and the preliminary survey of the last area have resulted in an increased knowledge regarding the condition of old mines and the effect different coastal environments—beach, dune and marsh—have on mines.

This paper will show that the mines buried during WWII that have been in contact with salt water cannot work as intended and have been nonfunctional for a considerable amount of time. This inoperability is due to the alteration of explosives in the detonators from their interaction with salt water and the degradation and corrosion of fuzes. Even in areas where the mines have not been in contact with salt water, dust and rain water have changed the ability of the detonators and fuzes to work. This relatively inexpensive analysis has resulted in the use of different mine-clearance techniques in different geomorphologic terrain types at Skallingen, each targeting the specific threat. With the changed risk assessment, the remaining clearance on this site will be conducted more efficiently, faster and with a lower cost in certain areas. A similar analysis of mines and soil composition in other mined areas could result in a more flexible approach to the clearance work, thereby avoiding an unnecessary, expensive, high-risk mine-clearance operation.

Figure 3: Aerial photo of Skallingen showing beach, dune and marsh areas.
Figure 3: Aerial photo of Skallingen showing beach, dune and marsh areas.
Photo courtesy of Lurtfoto Syd

Geography and Soil Composition

Skallingen is situated on the Danish west coast bordering the North Sea (see Figure 1). The shoreline is oriented northwest–southeast and is freely exposed to the predominant westerly and southwesterly onshore winds from the North Sea. The storm frequency is especially high in the wintertime, resulting in storm surges that attain elevations of up to 4.4 m above the Danish Vertical Reference.1 The area is further influenced by tidewater, with a mean tidal range of 1.5 m.2

The marsh (see Figures 2 and 3) is a frequently flooded marine wetland that has well-defined vegetation because of the high salt content and low topography. It is influenced on a daily basis by tidewater, which results in waterlogged soils and standing water. The yearly sedimentation rate is low and only 2–3 mm of silt and clay minerals are deposited together with organic material. Since 1944, therefore, the total sediment accumulation has been 20 cm. Marsh sediments often have a low pH (acidity), which could influence the state of landmines; the pH of the subsoil in the marsh has been analyzed and is noted in Table 1.2

Table 1: The table shows pH values from soil sediments in the marsh as well as the average pH values from Danish salt water and rain water. Most soil samples are slightly acidic, except from samples 2 and 4.
(Click image to enlarge)
Table 1: The table shows pH values from soil sediments in the marsh as well as the average pH values from Danish salt water and rain water. Most soil samples are slightly acidic, except from samples 2 and 4.

The beach zone is a deposit of unconsolidated, sand-rich sediment that is easily influenced by wind processes, as well as hydrodynamic processes (see Figures 2 and 3) Therefore, the beach surface is often uneven with series of low, broad, sandy bars separated by linear depressions. Finally, the area is subject to erosion, which results in changing coastlines and topography. The beach surface can change considerably on a daily basis, especially in the wintertime. On the beach, mines have been found down to 1.3 m below the surface.

The dunes are an accumulation of sand built by wind processes (see Figures 2 and 3). Because they are entirely composed of unconsolidated sand sediment, dunes tend to be fragile, mobile and susceptible to erosion. Colonizing plants act to stabilize the dunes by capturing migrating sediments. Mines have been found between 10 cm and 12 m below the present surface of the dunes. Dunes are regarded as the most protective environment for landmines since they are not affected by salt water like the marsh, nor the wave action on the beach.

Explosives and Metallic Composition of Detonators and Mines

During 2007 and 2008, continuous investigations and analyses were made of explosives and mines in order to review the risk assessment. The results and conclusions of this work have shown that the three geomorphologic areas described above have different impacts on the state of landmines. This fact is reflected in the degradation state of both explosives and metals. In the following sections, special attention is given to the type of detonator and the ZZ42 fuze, which is present in all AP mines (stock mines and wooden-case mines) in the area.

Explosives and metallic composition of detonators and percussion caps. The Netherlands Organisation for Applied Scientific Research (TNO) performed the chemical analysis of explosives using x-ray diffraction (XRD).3,4 The composition of explosives was analyzed using a Philips PW3020 Diffractometer with a 40-kV tension and 50-mA current. An accurate quantitative analysis of a number of primer mixtures is not yet available. However, XRD offers the best method to perform qualitative and semi-quantitative analyses.

Table 2: Overview of the chemical composition of explosives and alteration products in the detonators compared to environment.
(Click image to enlarge)
Table 2: Overview of the chemical composition of explosives and alteration products in the detonators compared to environment.

The composition of metals and explosives was tested in 33 detonators (see Table 2 and Figure 4) and nine percussion caps. All detonators were made of alumina. Primary explosives in the detonators were identified as lead azide and tetryl. In most cases the explosives had been altered to different non-explosive products (lead carbonate hydrate and lead oxide) and a few detonators were found empty.3,4

Figure 4: Cross section of detonator with dimensions of 4.5 x 0.7 cm. In many detonators the primary explosives have been partly dissolved and altered to different degradation products
Figure 4: Cross section of detonator with dimensions of 4.5 x 0.7 cm. In many detonators the primary explosives have been partly dissolved and altered to different degradation products
(see Table 2 on page 76).
Graphic courtesy of Danish Coastal Authority
Table 3: Composition of five ZZ42 fuzes. One can see that the spring and the nut differ in composition, which will change the geophysical signature. Only inside one fuze was oxidation identified: Fe, Zn, Cr (chromium) and Cu.
(Click image to enlarge)
Table 3: Composition of five ZZ42 fuzes. One can see that the spring and the nut differ in composition, which will change the geophysical signature. Only inside one fuze was oxidation identified: Fe, Zn, Cr (chromium) and Cu.

The percussion caps were all corroded and corrosion products such as ZnO (zinc oxide) were found around the caps. Four percussion caps showed inside traces of Cu (copper), Pb (lead), Zn (zinc) and Fe (iron). Three caps were found empty, which reflect dissolution of explosives by percolating fluids. Finally, two caps showed a confined primer degradation product. Traces of mercury fulminate could not be detected in any of these caps.

The main explosives in the mines have not been analyzed. However, from German WWII documents and visual identification, the explosives in the AP mines have been identified as TNT.

Metallic composition of fuzes and stock mines. The analyses of the metal composition and degradation stage were initially done as a project to improve detection capability. In addition, this work also had some significance identifying the effect different environments had on fuzes and mines. The chemical analysis was made using a JEOL JXA-8900 SuperProbe (E-SEM, electronic microprobe) at Aalborg Portland, Research and Development Centre. Operating conditions for spot analyses were 15 kV and 20 nA; spot sizes were 10 μm.

ZZ42 fuze. The ZZ42 fuze is a mechanical fuze produced by Germany during WWII (see Figures 5 and 6). It was the standard fuze in a number of German mines like schutz mines and stock mines, and also frequently used in the S-mines. The ZZ42 fuze has been found in large numbers at Skallingen.

Figure 5 (at left): Schematic illustration of the ZZ42 fuze. The dimension is approximately 1.2 x 8.5 cm. Notice the position of the plug, which is composed of a mixture of sand grains, oil and rust.
Figure 5: Schematic illustration of the ZZ42 fuze. The dimension is approximately 1.2 x 8.5 cm. Notice the position of the plug, which is composed of a mixture of sand grains, oil and rust.
Graphic courtesy of Danish Coastal Authority

Visually, the ZZ42 fuzes appeared to be in different disintegration stages (see Figure 6). In general, the bakelite surrounding the metal parts had been preserved well in all areas. Further, the springs and firing pins, which often were soaked in oil, functioned well. However, the fuzes were normally corroded at the top of the firing pin, preventing them from moving freely. The bakelite had not completely sealed off the vital parts inside the fuzes. Therefore, in the majority of ZZ42 fuzes, the oil, sand and rust had mixed to a hard plug just between the hammer and the percussion cap. This obstruction dramatically lowered the ability of the hammer to ignite the percussion cap, whereby the ZZ42 fuze could become harmless (see Figure 5).

All fuzes that underwent the chemical tests had been found in the dunes, which offer the best protection from salt water. This occurrence is reflected by the fact that only one sample had started to oxidize (see Figure 7). The protective environment had not completely prevented water from penetrating the metals, however.

Stock mines. The stock mines were made of concrete with a large number of encapsulated metal fragments, (as seen in Figure 8). In all stock mines found, the mine body was generally robust and the green paint often well-preserved (see Figure 9). Most stock mines had been found as an empty concrete and iron casing (see Figure 8). When found with explosives, the explosives were identified as TNT. The fuze and detonator used on the stock mines were the ZZ42 fuze and the detonator described earlier. In most stock mines, the metal fragments in contact with free air had started to corrode because of oxidation and the repeating cycle between wet and dry conditions.

Figure 6 Example of ZZ42 fuze with detonator found at Skallingen.
Figure 6: Example of ZZ42 fuze with detonator found at Skallingen.
Photo courtesy of Danish Coastal Authority

The chemical composition of metal fragments in nine stock mines from the marsh showed a large compositional variation—not only in metal parts, which had been in contact with free air, but also in parts that had been sealed by concrete. It was possible to identify unaltered and altered areas in all metal fragments when they were cut through, even in parts that appeared unaltered on the outside. The unaltered areas were generally made of iron. The altered areas were a mixture of C (carbon), N (nitrogen), Na (sodium), Cl (chlorine), Si (silica) and Al (aluminum) (see Figure 10). This element signature is likely to reflect the steel production and a decomposition signature reflecting the local environment.

The C content can be explained by steel manufacturing where it was added to Fe but also by the large chemical release of C when organic material decomposed. Decomposition of organic material also releases N. The release of C and N is an ongoing process in marsh areas.2 The content of Na and Cl is best explained by the presence of salt water, which is supported by the findings of salt crystals inside the Fe metal fragments (see Figure 11). Finally, clay minerals, which make up the majority of marsh soils, are rich in Si and Al.

The corrosion of metal leads to fracturing whereby water can enter along cracks. Therefore, it is likely that fluids, in this case salt water, dissolved C and N as well as clay minerals (Si and Al) and penetrated into the metal along small fractures. Inside the metal, the elements had precipitated from the fluid. This variation in composition changes the geophysical signature.

Figure 7: Backscatter picture of hammer from sample 3 in Table 3. Black spots are oxidized areas.
Figure 7: Backscatter picture of hammer from sample 3 in Table 3. Black spots are oxidized areas.
Photo courtesy of the Danish Coastal Authority

Wooden-case and Teller Mines

A number of wooden-case mines (AP and AT) and Teller-42 mines (AT) were found in the area. The wood surrounding the wooden-case mines had, in most cases, dissolved irrespective of terrain type. The remaining parts that indicated the former presence of wooden-case mines were blocks of TNT with the attached ZZ42 fuze and detonator described earlier. In a few cases the wooden-case mines were complete, but only when found in sand sediment. Therefore, most complete mines have been found inside the dunes.

At the time of writing, all Teller mines had been found in the dunes at a depth between 2 and 3 m, except for one that was found near the surface in the marsh. In all cases, the metal covering the explosives was corroded but intact.

Functionality of Landmines

When establishing the functionality of landmines, the most important issue is the resistance of the detonating mechanism to decomposition. Hence, if the fuze and detonator do not work, the mine will not work.

Figure 8: Cross section of a stock mine. Even though many iron parts appear to be in a good condition, most are partly corroded.
Figure 8: Cross section of a stock mine. Even though many iron parts appear to be in a good condition, most are partly corroded.
Photo courtesy of Danish Coastal Authority

The chemical analysis of the detonators showed that the degradation of explosives in general is in an advanced state. A number were either empty or contained byproducts from the altered explosives, most likely due to the percolating water that was observed inside metals from stock mines. To further establish their functionality, 12 detonators were put through a detonation test (see Table 4). The functionality test of the detonators was performed at TNO by placing a squib in the open side of the detonators, causing the functional detonators to ignite from the generated flame.

The test showed that 50% of the detonators found in the dunes were functional when tested, while all detonators from the marsh tested negative. Due to these results, the marsh detonators were then given an impact-sensitivity test, conducted with a Federal Institute for Materials Research and Testing (BAM) Fallhammer apparatus. The BAM equipment performed the test on the primer of those detonators that showed any presence of intact primary explosives (lead azide) determined by X-ray diffraction. The test was made by TNO using a 1-kg drop weight at 50 cm (5 Nm) and 5-kg drop weight at 20 cm (10 Nm). In this case, three of four worked when exposed to 5 Nm and the last worked at 10 Nm.

It was evident from the chemical analysis of explosives that the percussion caps were in an advanced degradation stage and therefore unlikely to work. Further, several field tests failed to ignite the percussion cap.

Figure 9: Example of a stock mine detected and found in the dunes 1.3 m below the present surface. The mine is complete and is still attached to the stick.
Figure 9: Example of a stock mine detected and found in the dunes 1.3 m below the present surface. The mine is complete and is still attached to the stick.
Photo courtesy of Danish Coastal Authority

Finally, the fact that the ZZ42 fuze had been altered and was in most cases not functional was true in all areas, even though the metallic composition had shown that it was less common for the mines in the dunes to be nonfunctional. This discovery is in accordance with the data obtained by TNO, which reinforces the findings that dunes tend to preserve landmines better than marshes, seeing as the detonators have been known to work and ignite the main explosive in the dune areas even after 60 years.3

From the above, it is evident that the detonators and ZZ42 fuzes decompose and become inactive in contact with water, wet soils and dust and that no detonators and ZZ42 fuzes have worked as intended when found in the marsh. Further, lead azide, which is used in detonators, will dissolve and react with salt in the ocean water, creating different non-explosive alteration products.3,4 In this case, the lead azide is likely to be completely altered or dissolved after three years of contact with salt water.3,4 Therefore it is unlikely that stock mines and wooden case mines will work when found in the marsh. Additionally, the wood surrounding wooden case mines has in most cases decayed. Inside the dunes, stock mines and wooden case mines could work (see Table 5).

Using this information, coupled with the fact that the area is a natural heritage area that will not be exposed to construction work in the future, has lead to the conclusion that AP mines with ZZ42 fuzes and detonators do not need to be removed from the marsh. This conclusion means the detection work can be reduced significantly in the overall area. AP mines will be removed from the dunes since the dunes offer the most protective environment and erosion can make them resurface and move them out on the beach.

Table 5: The functionality of fuses, detonators, percussion caps and mines found in different coastal environments on Skallingen.
(Click image to enlarge)
Table 5: The functionality of fuses, detonators, percussion caps and mines found in different coastal environments on Skallingen. + indicate ability to work and ÷ cannot work as intended. Most fuzes are observed having a plug between the hammer and percussion cap except for a number in the dunes.
* 1The majority of percussion caps do not work regardless of environment. Though, it is likely that a number could work inside the protective dune environment.
**2,3 If the fuze, percussion cap and detonator is functional the stock mine and wooden case mine is likely to work.

On the beach, AP mines will only be a threat if they have recently moved there, as the detonators will become inactive when exposed to salt water.3 Furthermore, the hydrodynamic forces are very strong, especially during stormy conditions, so wooden case mines and stock mines will break apart and the mines will be carried into the ocean. Not all AP mines on the beach can be detected at the investigated depth of 1.3 m, but because the mines become inactive after three years or eroded into the ocean in less than one year, they are not a lasting danger. The Teller-42 mine does not have a ZZ42 fuze attached and the T-Mi.Zdr.42 fuze used is encapsulated by a pressure plate, which protects it from free air, soil and water. Field tests of the Teller mines found in the dunes have revealed that the mechanics of the fuzes are likely to work, as well as percussion caps, detonators and the main explosive charge. The Teller mines shall therefore be considered fully active and the Teller-42 mine will be removed from all areas (see Table 5).

Over time, the functionality of landmines seems to depend on the environment they are placed in and the composition materials.5 In Skallingen the influence of salt water (which changes the chemistry of lead azide) and the continuing exposure to the cycle of wet and dry conditions have led to inactive fuzes and detonators in the marsh area. The pH in this case did not have any influence on the decomposition, but it could affect the decomposition in other soils. Landmines found buried in the dunes are in better condition because of the lower influence from water. Still, a number of fuzes and detonators are inactive in the dunes because of dust that has entered the mechanical parts and rain water, which has led to corrosion and the slow dissolution of explosives inside percussion caps. On the beach there might be a small risk that the mines will work if they have recently been eroded from the dunes. Once on the beach, however, they will quickly decompose or break apart because of wave action and water. Even though not all mines have been tested for functionality, the clearance work thus far has shown that less than 5% of the mines are fully functional.

Figure 10: Spectrum of the alteration area shown in Figure 11 below. The area has a more complex chemistry than the surroundings, which is mainly made of Fe.
(Click image to enlarge)
Figure 10: Spectrum of the alteration area shown in Figure 11 below. The area has a more complex chemistry than the surroundings, which is mainly made of Fe.
Image courtesy of Danish Coastal Authority

There is no way to definitively tell when the mines became inoperative, but the inside alteration of metal parts and the degree of corrosion of mines and fuzes from the marsh would indicate that they have been inoperative for a considerable amount of time.

Use in Other Minefields

The main aim of this work has been to analyze the state and composition of old metal and wooden-case mines. Many mines are made of plastic, however, with a limited amount of metal. Still, the last 20 years have shown that the life span of plastic in nature is not infinite. An increasing number of phthalates are being detected in waterways and rivers, reflecting the decomposition of plastic. Also, museums have difficulties preserving plastic items, which become sticky and fragile.6 Further, recent scientific developments have revealed that plastic in the ocean decomposes as it is exposed to rain, sun and other environmental conditions, and that polystyrene begins to decompose within one year.7 Therefore, it is likely that plastic mines, as well as concrete, metal and wooden case mines, will slowly become fragile and crack, which could open an entryway for water and dissolve the explosives. The decomposition of plastic will, like other materials, depend on the chemical composition and amount of water in the soil and the climate.

Figure 11: Backscatter picture of metal part from stock mine showing a circular alteration zone with a number of salt crystals.
Figure 11: Backscatter picture of metal part from stock mine showing a circular alteration zone with a number of salt crystals.
Photo courtesy of Danish Coastal Authority

The above review supports an approach in which a flexible response to different minefields, targeting the specific threat of a given minefield, will be preferable instead of using a standard response. However, it requires a thorough Technical Survey that will provide the planners of the demining activities with crucial information to make area reduction and clearance possible.8

The inexpensive testing of explosives, landmine condition and soil chemistry described here will reveal the functionality of mines. The consequence of this experience could result in a cheap, low-risk mine-clearance operation and prevent an expensive, high-risk mine-clearance operation. Therefore, it is interesting and valuable for the mine-action community to look further at the deactivation of landmines by passive decomposition.


Biography

JebensMartin Jebens is currently Geographic Information Systems Manager at the Danish Coastal Authorities’ demining project at Skallingen, where his work includes coastal morphology, detection techniques, topographical models and functionality of landmines. He has a Master of Science in geology from the University of Copenhagen with background as an exploration geologist, focusing on diamond, nickel and gold deposits in Scandinavia and Greenland. He previously worked at the Geological Survey of Denmark and Greenland, and also at a Danish exploration company.

Endnotes

  1. The Danish Vertical Reference (DVR90) is a height reference system for maps that relates to the measurement of the mean sea level, calculated by the Danish Meteorological Institute, over the course of 100 years in 10 Danish ports. DVR90 is positioned 4.6 cm below the local mean sea level observed and recorded in 1990. From http://www.esbjerghavn.dk/website/sider/dvr90.htm, accessed 29 April 2010.
  2. Aagaard, T., Nielsen, N. and Nielsen, J. (1995): “Skallingen – Origin and Evolution of a Barrier Spit.” Meddelelser fra Skalling-Laboratoriet, XXXV. Geographical Institute, Copenhagen.
  3. Aalbregt, M., Duvalois, W. and van Ham, N. H. A. (2008): Risk of old detonators. TNO report. TNO-DV 2008 C135. p. 25.
  4. Duvalois, W., van Ham, N. H. A. and Aalbregt, M. (2009): Risk of old detonators. TNO report. TNO-DV-2009 C018. p. 41.
  5. King, Colin. “As Mines Grow Old.” Journal of Mine Action, Issue 11.2 (Spring 2008: 4–5).
    http://www.jmu.edu/cisr/journal/11.2/editorials/king/king.shtml. Accessed 5 April 2010.
  6. Shashoua, Y. (2009): “Plastik – nutidens drøm, fremtidens mareridt?” [Plastic–Today’s Dream, Tomorrow’s Nightmare?] The Danish National Museum review paper. http://www.nationalmuseet.dk/graphics/Klub/FebruarYS.pdf. Accessed 9 April 2010.
  7. “Plastics In Oceans Decompose, Release Hazardous Chemicals, Surprising New Study Says.” ScienceDaily. 20 August 2009. http://www.sciencedaily.com/releases/2009/08/090819234651.htm. Accessed 5 April 2010.
  8. Van der Merwe, J. J. “Application of the Technical Survey in the Demining Process.” Journal of Mine Action, Issue 6.1. (Winter 2002: 72–77). http://www.jmu.edu/cisr/journal/6.1/notes/vandermerwe/vandermerwe.htmAccessed 5 April 2010.

Contact Information

Martin Jebens
GIS-Manager
Mine Clearance Skallingen
The Danish Coastal Authority
Højbovej 1, Postbox 100
Tel: +45 402 729 14
E-mail: mje@kyst.dk, Martin.Jebens@yahoo.dk
Web site: http://www.kyst.dk