"I don't think anyone in the industry, including ourselves, were fully aware of the potential of dust as a hazard, " Mr. Mechler said.

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The inhalation of these fine dust particles represents a health hazard that was known to the military as long ago as 1974.

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With each explosion, the tunnels, some centuries old, some less than a metre high, fill with thick clouds of dust one more hazard to add to the effects of consuming coca leaves, fiery local alcohol and rough cigarettes, and the risk of poisoning from handling mercury.

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Aviation officials feared the dust could stop jet engines - an unacceptable hazard - and Ms McDonagh was among the thousands left stranded.

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The view from the hazard-avoidance camera with and without the clear dust cover.

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