Security officers cleared the building at 9 a.m. (0700 GMT) following the anonymous call which said the device would explode at 9.20 a.m.. The all-clear was given 15 minutes later.

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The delivery device had to explode the air inside its breathing chamber at supersonic speeds to form an aerosol cloud of insulin.

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He agreed that the device did not explode owing to a defect in the timing unit and an error in the mix of paraffin and diesel fuel contained in the cylinders.

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The police said the fuse on the device had been lit, but had burnt itself out and did not explode.

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