Andy Smith
MIne-action specialist

 

Magnets and safety


The use of hand-held magnets to reduce fragmentation during metal-detector search has been fairly common over the past fifteen years. Attaching large magnets (and sometimes electro-magnets) to machines has also become increasingly common. Magnets only attract ferrous materials so do not remove all scrap-metal from the ground surface, but most fragments have a ferrous content, so magnets can help to remove most harmless metal that is at or near the ground surface.

Typical minefield scrap metal

The only non-ferrous metal in this collection of scrap from a minefield is the ring-pull.

It is desirable to reduce harmless metal content because its presence slows metal-detector based search down quite dramatically. It has been widely accepted that if there are more than six fragments per square metre, it will be quicker to excavate the entire ground surface than to investigate each detector reading separately. The results of the comparative trials I conducted for GICHD in Mozambique in 2004 show that this is not true, but that the presence of those fragments made it take three times as long to clear the area as it did when fragmentation was light. It took even longer to safely excavate the entire area to the required depth. See the conclusions of the Comparative Trials of manual demining methods.

This shows a typical CMAC deminer's toolkit, complete with large speaker magnet.

Hand-held magnets have not been as widely used as might be expected because most fragments are embedded in the surface or just below the ground surface and conventional magnets do not attract them well. Magnets scavenged from loudspeakers (from radios, televisions, etc) are not very powerful and are frequently held in the hand and rubbed on the ground surface. There have been no recorded accidents doing this, but it does put the hand unacceptably close to any unintended initiation. The use of magnets became more widespread when people became aware of the increased strength of neodymium magnets. Very small neodymium magnets can attract heavy fragments (up to several kg in weight) and attract fragments that may be just under the ground surface.

The main safety issues with magnets are the fear that strong magnets will pick up active devices or fuzes, and the fear that they may activate "magnetic-influence" fuze mechanisms.

To counter fear of attracting intact devices, the user should always be looking at both the magnet and the ground where it is being used. If a small fuze system is attracted, it could be initiated by the movement. To reduce any associated risk, the magnets should be kept as far as possible from the user's hand and this may be achieved by attaching them, to a long-handled tool of some kind. This may be a rake...

...a "wand"...

Neodymium magnets on polycarbonate sticks...

....or attached to a long trowel.

In most demining scenarios, the risk of initiating a "magnetic-influence" fuze mechanism is rather low because these fuzes are battery operated and so have a limited operational life. However, if the risk assessment in an area indicates the presence of active magnetic-influence fuzes, neodymium magnets attached to hand-held tools should not normally be used.

See also: Magnet on blast resistant trowel and Magnets for fragment reduction. For safety, see also the entry on the Type 72b mine.