The animals systematically evaluate filters in a caged set-up, and will indicate the occurrence of explosives.

The animals are trained to walk lanes on the suspected field and search for the exact position of buried mines.

Residual Explosive Scent Tracing (REST) is a technology for the reduction of large suspected areas to the real mine contaminated areas. Currently, this technology is mainly applied for the clearance of roads.

Residual Explosive Scent Tracing (REST) is a technology for the reduction of large suspected areas to the real mine contaminated areas. Currently, this technology is mainly applied for the clearance of roads.

In this system, vapour filters are being sucked from above the suspected mine areas. In this process, the explosive vapours will adhere to the filters. The animals then systematically evaluate these filters in a caged set-up, and will indicate the occurrence of explosives.

Once a filter is evaluated as being positive, the area where it was taken will be considered highly suspected and a subsequent mine clearance will be carried out.

Though this system is not widely in use yet, it has a very high potential in efficiency and cost saving. APOPO, in co-operation with GICHD and other organizations, is therefore putting a lot of effort to further develop and document this technology.

Special low-density mine fields have been established for the research on REST. These are boxes of 40 * 40 meter, which are in turn sub-divided in 5*5 meter boxes. This allows systematic research on the detectability of the vapour plume, in relation to the climatic and environmental conditions, as well as the mine types. The results of this research could provide the data for the implementation of REST for open field area reduction. (see testing facilities )

Furthermore, APOPO is also testing a series of filter types, in order to reduce the costs of the training process and improve the efficiency of REST. In cooperation with JENEL TVD, APOPO has developed an explosive vapor preconcentrator which is analyzed by Gas Chromatography. This produces quantitative data to be compared with the animal's response on the REST filters

In analogy to free roaming dogs, rats conditioned on TNT are trained to walk lanes on the suspected field and search for the exact position of buried mines.

Different training devices and training methods have been tried out.

The result is a system with search bar or string, which allows the animal to move systematically over the field. (photo search bar, photo string). The animals walk on a leash, which is attached to a glider on a 6m long bar that can be progressively forwarded into the suspected area. After experimenting with different widths, the width of lanes a rat has to explore was set at 0.5m.

When a rat reaches the end of the box, the search bar is shifted forward, in order to scan the next lane. Rats are introduced in the corner of a 5mx20m box and have to process the whole box (100sqm) meaning that it has to cover forty lanes. On average it takes the rats about 28 min to complete a box.

Two people are present while the rat is working. Both persons take position at opposite sides of the search bar, in the safe lane. The trainer is observing the behavior of the rat and rewards the animal when it indicates a buried mine. Rats indicate positions of mines by scratching or biting the surface at the spot where it sniffs the explosive device. To reward it, the trainer clicks and the animal moves to the trainer, gets a reward after which it starts searching the next lane. The second person, the observer, takes notes on the behavior and performance of the rat while working. Apart from the indicated spots, where the rat got rewarded, 12 different specific behavior patterns are recorded.

After the rat has been fully trained on the training fields in Tanzania, a series of blind tests is carried out during a period of 6 weeks. If the animal meets the performance requirements during these tests, it can be selected for de-mining operations abroad. As with dogs, the rats are re-calibrated on the specific mines found in the demining operations, before being deployed.

This system has been successfully being tested on a real minefield in Mozambique in co-operation with MgM. Other trials are underway with NPA. The field experience will direct further improvements of the technology.