An Ergonomic Aspect of Humanitarian Demining

ERGONOMICS

Dino Busuladzic and James Trevelyan

1. Deminer's Posture

Diagram 1.

Vegetation clearance in humanitarian demining occurs in two steps. These are vegetation clearance:

1. above and to ground level, and
2. below ground level.

Diagram 1 shows a further division into three areas of reach while clearing vegetation above and to the ground level. When a person is in a standing posture, with arms in the natural position at the sides of the body, it is important to identify points at knee and hand height from ground level. With regards to these two points three areas of reach can be defined as:

a) Upper-area of reach - Area at and above the point of hand height;
b) Mid-area of reach - Area between knee and hand heights;
c) Lower-area of reach - Area between ground level and knee height.

Photo 2.

A posture, in the deminer's perception, could be characterized as the 'most comfortable' position for the required situation. Comfort is based on the individual's perception, and there are numerous factors that must be taken into consideration when observing why a specific posture is characterized by a particular deminer as 'comfortable'. For example, the cultural background of the deminer could be involved in his decision. Photos 2 shows Cambodian deminers having a lunch break by squatting. However, Bosnian deminers would rather sit while having a lunch break. The following postures are used by Cambodian deminers:

1. standing,
2. bending,
3. squatting,
4. kneeling on one knee, and
5. kneeling on both knees.

a) Upper - area of Reach

Photos 3 shows that in the removal of vegetation above ground level within the upper-area of reach the posture used is a standing one. The upper arms are close to the body, whilst the forearms are held approximately perpendicular to them.

Photo 3.

Diagram 4 .

The deminer's head is held so that his eyes look naturally forwards onto the location where a cut is performed, as shown in Diagram 4. This is important to avoid any additional stress to the eyes, but at the same time it is necessary to use the neck muscles to turn the head in the direction of the cut location.

b) Mid - area of Reach

Photo 5.

A bending posture, shown in Photos 5, is used in the removal of vegetation above ground level within the mid-area of reach, (see Diagram 1). The eyes and arms are in a position corresponding to a standing posture, giving maximum support to the primary senses of sight and touch. This posture should be avoided, if possible, because additional stress is placed on the spine and back muscles.

The mid-area of reach can be worked from the standing posture if the tool handle is long enough. With a longer handle, a deminer can work on the same or larger area with less bending. Conversely, when a handle is too long the weight of the tool increases dramatically and renders it more difficult to handle. The mid-area of reach can be worked by squatting or kneeling on one or both knees.

c) Lower - area of Reach

Photo 6.

Squatting, kneeling on one or both knees are used in the removal of vegetation above ground level, within the lower-area of reach, or for removing roots of vegetation below ground level whilst prodding, (see Diagram 1). As with other postures, the position of the deminer's head in these postures allows undisturbed sight over the working area and tool.

Conclusion

Diagram 7.

Ultimately, regardless of the body's posture, deminers always place their arms in a similar position, as shown in Diagram 7. This position is called 'the lever system of third class' .

The shortest distance of the load [L] and effort forces [E] from the instantaneous centre of rotation (or fulcrum F) are called the load arm … and effort arm …

One can conclude that to lower the effort made by a muscle it is better to keep a job close to the body, and consequently keep as short as possible the distance of the 'load arm'.

From this one can conclude that:

Cambodian deminers maintain a posture of least muscular stress for the required situation.
Arms are placed to allow the muscles to deliver their greatest force.
In all definitions so far of body and arms positions, both hands are free to deliver the required force to the handle (or handles) of the tool, ensuring absolute control.
Hands are in a position that enhances the sense of touch.
The deminer's head is in a position that allows an undisturbed view. Likewise, he has control over the distance between the top of the tool and target location, and close surroundings.
In all five described postures deminers expose a large part of their bodies to the possibility of an accidental explosion. Because of the need for freedom of body movement and comfort, special attention should be given to the design of protective clothing.
By applying ergonomic and anthropometric knowledge to the design of the shape and length of the tool handle (or handles), postural stress can be decreased.

1.1. Lying Posture

The lying posture is mandated (according to SOP's) as the safest posture. In comparison with the other five postures, while lying the deminer exposes his head and one arm to the risk of an accidental explosion. On the other hand, in squatting or standing postures exposure to this danger is much higher. Even though lying is safer, deminers in Afghanistan, Bosnian and Cambodian mostly squat or kneel.

Some contributing reasons were found through interviews with Afghanistan deminers done by Assoc. Prof. J.P. Trevelyan and HARC, and confirmed during the writer's visit to Cambodian minefields. These reasons are:

Only through an informal discussion with the deminers, was it found that they do not lie on the ground because they do not want to get dirty. To get dirty for people of high status is inappropriate, they explained. The writer got the same answer from his guide whilst visiting the Cambodian minefields. According to the guide, the Cambodian deminer is paid US $160 per month, while an average salary is about US $ 20. In Afghanistan and Cambodian cultures, a good job and reputation do not go with working in dirty clothes.
Additionally, deminers complain about being uncomfortable and disturbed by insects, grass or stones when lying on the ground. Furthermore, the area of body exposed to solar heat is greater, and is less able to be cooled by air convection and evaporation.

Photo 8.

Furthermore, in comparison with the 'lever system of third class' the fulcrum F is in the deminer's shoulder, and the load arm is equal to the length of the deminer's arm. The deminer with a tool in his hand must keep his arm stretched whilst cutting. In this paper this is called the 'stretched' position of an arm.

For the purpose of understanding better what the consequences are of holding an arm in the neutral or stretched position, a static analysis of an arm in a position between these two extreme ones is made. This analysis allows correlation between effort E of an arm in the neutral position and effort E1 of an arm in a stretched position given in following equation.

Cos = E / E1

Given that the angle is

0° < < 90°

Diagram 9.

for a stretched arm, the conclusion is that the effort needed to hold same load with a stretched arm is always greater than when the arm is in the neutral position with the upper-arm close to the body.

The deminer's head is close to the ground and lifted with eyes focused on the target location having the front view, as shown in Diagram 9. This position of the head causes additional stress to the neck muscles. Diagram 9 shows that the deminer has no clear view of the contact place between the tool and cutting location, and no visual control over the background of the cutting location.

Conclusion

The lying posture causes rapid muscular exhaustion of the arm stretched out to cut vegetation, or to prod. The deminer simultaneously feels discomfort in the neck and elbows and later has an urge for a rest.
The lying posture allows one arm to be used in the work, while the other balances the deminer's body.
The hand involved in manual demining work is unable to deliver the greatest force to the handle of a tool, because of the muscular stress produced by a lying posture.
The hand involved in manual demining work is not free to enhance touch because of the postural stress effects.
The deminer's head is in a position to give him a front view of a cut location. Therefore, the deminer tends to raise his head to get a better view over the location causing fatigue.
A deminer exposes the head, neck, one arm and hand to the possibility of an accidental explosion while in a lying posture. Because of the smaller exposure of the body, in comparison with all other postures, the lying posture is judged to be the safest.

This information was collected while visiting Cambodian minefields in Battambang province - May 1998.

Dino Busuladzic - June, 1999.