Issue 5.2 | August 2001 | Information in this issue may be out of date.
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Feedback Prodders: A Training Tool to Improve Deminer Safety

by Russell Gasser, Joseph Rowntree Quaker Fellow

Improved feedback prodders inform deminers of the amount of force exerted and alert them when the prodder’s angle approached or exceeds the 30 degree limit.


Prodding on AP mines too hard is a major cause of demining accidents in some countries, especially where the soil is hard. Field measurements of the force used by deminers showed they (1) repeatedly used more force than is required to activate some mines and (2) consistently underestimated the force they were using by large amounts, often thinking they were using about half the actual force.

Computer data-logging of force used during prodding in Afghanistan.

Field testing of prototype "feedback prodders," which warn the user of excess force being applied, gave good results. After only a few minutes, deminers were able to excavate targets with lower peak force than before. A slight change to the prodding action could at times reduce the peak forces applied to the prodder. Even if deminers need to press hard to do their work in some soils, safety could probably be improved if deminers were more aware of the amount of force they were using and they understood the importance of prodding techniques in reducing peak force. An improved feedback prodder is proposed as a training tool.

A feedback prodder, which gives a deminer information about the forces and angle of the prodder during demining, can result in a deminer gaining appreciation for the "feel" of a particular force and ultimately reduce demining accidents. In volume, production of this tool can cost as little as $30. (U.S.). Funding is now needed to refine the prototypes and produce them.

Measuring Prodding/Excavating Force

The force used by a number of deminers on active duty with Afghanistan’s Monitoring, Education and Training Agency (META) and Mine Clearance Planning Agency (MCPA) in Afghanistan was measured.1 A specially built prodder handle with three-axis strain gauges connected to a computerized data-logging system recorded all prodding actions for periods up to five minutes as deminers excavated an imagined target. 

Prodding with force-measuring prodder linked by a cable to a computer data logger (buzzing prodder on right).

Prodding/excavation was conducted in areas declared safe after survey by dogs or manual clearance in a region noted for hard soils. Deminers were asked to prod/excavate carefully as if approaching a suspected mine. One of the most common mines in the area was the PMN, which typically requires between 5 kgf and 8 kgf to detonate. Results are shown in the graph below. About two-thirds of all the prodding actions used a force of over 5 kgf (11 lbf). The highest recorded forces were about 14 kgf (31 lbf). Asking questions through an interpreter revealed that the deminers consistently underestimated the force they were using by large amounts. In general, the deminers found it hard to believe how much force they were using and repeatedly questioned the calibration of the test equipment.

One deminer in particular used lower peak forces than anyone else (including his supervisors). His technique was to push steadily and not thrust or stab at the rocky soil. These results show that simply modifying the prodding technique could lead to a reduced peak force and improved safety. Even though deminers were at times unable to feel any difference in the force they applied, the measured peak force could vary considerably with this manner of prodding and excavating. There is a clear need for a training tool that makes good working practices clear to deminers as they start training.

Testing First-Generation Feedback Prodders

The same deminers were later asked to test an early prototype of a feedback prodder that sounded a small buzzer in the handle when a preset force was exceeded. Initially, all the deminers found it difficult to work when the buzzer was triggered continually, but after only a few minutes of practice, they were able to modify their prodding action to noticeably reduce the number of warnings. Further testing of the prototype in Nicaragua also led to the same results. Initially, deminers could not believe how hard they were pushing. After only a few minutes of practice, they were able to modify their work habits. 

In both countries, deminers were enthusiastic about the feedback prodder and suggested modifications and improvements to the prototype. 

An early prototype of the buzzing prodder.
Computer logging force used during excavation.

These results suggest that simple feedback prodders could contribute to deminer safety by promoting good working practices and a better understanding of prodding force.

During training, deminers need to learn what a reasonably safe prodding force feels like and how to excavate targets with the least force necessary to get the job done. However, instructors cannot immediately see the exact amount of force being used at a particular moment by a trainee. With existing tools, learning what a particular force feels like while prodding is not based on objective criteria. Deminers are also taught to keep the prodder at a low angle to avoid the pressure-plate of a mine that is right side up. While concentrating on carefully excavating in stony soil, it is easy to momentarily move the prodder to a more upright position without noticing.

The feedback prodder is a simple training tool designed to help deminers learn these safety-related practices quickly and easily. When using in live areas, one should carefully consider the value of the warnings as opposed to the distraction they cause and other important criteria for the safety of hand tools in the event of an accidental detonation.2

Next-Generation Force/Angle Prodders

The next generation of prodder design incorporates much more sophisticated feedback than the "sudden onset" buzzer of the earlier model. In order to learn quickly, deminers need to know approximately how much force they are using and not just when they are pushing too hard. Consistent steady use of a "safe" force appears to give the best results. Unlike the earlier prodder design, which only indicated the force used, the new design has a second sensor to measure the angle of the prodder and provides warnings as the limit of 30 degrees from the horizontal is approached and exceeded. The worst combination of excess force together with too steep an angle provokes a more urgent alarm.

By using feedback prodders, trainee deminers can self-monitor themselves as they practice without having to wait for comments from an instructor. The ability to objectively assess this aspect of deminer competence by measuring how far and how often the safe working limits are exceeded could be included in the prodder design at little or no extra cost. Automatically identifying a deminer who is having a bad day or who is at risk due to illness could also be included in a feedback prodder. By using microelectronics, it would even be possible to include full data-logging for the whole day’s activities if required, though this would increase the cost of the tool.

Other features of the latest design include a commonly available battery size, low power consumption and self-monitoring with a low-battery warning. Any type of prodder blade can be attached to the handle according to the specific needs of a demining organization. The feedback prodders will not be expensive: a target cost of $30 (U.S.) per prodder has been set, though it will take large volume production to achieve this. Funding is currently required to take the prototype to production. Please contact the author if you are interested in financing this work, or if you would be interested in participating in field trials of prototype feedback prodders.


The author would like to thank the CDW and CMAC (Cambodia), DTU (University of Warwick), DTW (UK), EPSRC and M. Laing Foundation (UK), MAPA Islamabad), MCPA and META (Afghanistan) and the Nicaraguan Army Engineers for their assistance with and/or funding for this work.

1. Gasser, R. "Technology for Humanitarian Landmine Clearance," PhD Thesis, University of Warwick, 2000.

2. Smith, A. "The Facts on Protection Needs in Humanitarian Demining," Journal of Mine Action, v1, Issue 4.2, pp30—36, Summer 2000.

*All photos and graph courtesy of the author.

Contact Information

Russell Gasser
Joseph Rowntree Quaker Fellow
Bristol, UK
Tel: +44 (0) 117 377 9939