I have been asked whether it is safest to wear a chin-strap with a visor or helmet during demining.
Q: Why do the IMAS not require a helmet or visor to be fixed to the head with a chin-strap. Was this forgotten or perhaps presumed?
A: The omission was deliberate because there is no evidence that holding the visor on the head with a chin strap is any advantage: indeed, the evidence implies that it is a disadvantage.
Anything worn on the head should be stable enough not to fall off during normal activities but demining is not like a combat situation where a soldier may have to run, make rapid sideways movements, etc. Generally, visors are held in place with adjustable head-bands.
When a blast occurs, the evidence shows that it is generally in front of the deminer and on/in the ground. The expansion of the blast gases is volumetric but the earth and stones ejected by the blast have mass and each fragments moves in (more-or-less) one direction. All the evidence from tests and accidents is that at 60cm or more, the fragments are moving in advance of the expanding blast-front. These particles are what blind deminers. At 60cm or more from an AP blast mine, the blast-front itself is no longer moving at severely damaging speed. It strikes the deminer low down momentarily before hitting him higher up and, if he is kneeling, may lift him to his feet. But the blast-front strikes his upper body and head after any associated fragments have already struck. As the blast-front passes the deminer's head, it frequently removes the visor (more than 200 recorded accidents). As long as the visor was worn in a down position, the face of the visor is marked by fragments and the deminer's face is not - even though the visor is removed by the blast front passing. In dry conditions, the low-pressure behind the expanding blast front draws in a cloud of dust and deminers sometimes get dust in their face and eyes, but because this was not moving at speed, it is usually easily washed out.
If the visor were held firmly in place, the shock wave transfer to the wearer's head and neck could be severe - and must be if the deminer were lying down with his head close to the seat of initiation. This is why lying down is not generally recommended by those who understand the risks. In one Afghanistan accident, a kneeling deminer initiated a PMN while wearing a lightweight helmet and visor with a chin-strap. His nose was severely damaged when the chin-strap slipped and ripped his nose as the visor flew away. In another accident with a kneeling deminer and a PMN, the helmet clip (metal) broke and tore deeply into the deminer's throat as the helmet and visor were blown off. So a visor or helmet/visor combination with a chin-strap can increase the risk of injury in an AP mine blast. This is not surprising. A general rule for avoiding damage or injury is to allow the blast front to pass unimpeded whenever possible. The blast gases will expand despite any attempt to block them, so let them do so.
The only argument in favour of a chin-strap that makes sense, is that it may prevent a visor falling off during normal use. The AVS design of head-frame offered by the makers of the most commonly used visor increases stability and comfort with a second velcro strap across the back of the head. Wearing this, I find that I can bend double without the visor falling off or wobbling. The addition of a chin-strap would increase discomfort and, I believe, would make injury MORE likely in the event of my detonating a mine.
So, those who insist on deminers wearing visors with a chin-strap are ignoring the evidence and may be increasing the risk of injury.
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