Helicopters covered in foam
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US Black Hawk helicopters in fire-drill foam accident

27 August 2014 Last updated at 12:36 BST

A number of Black Hawk helicopters were left covered in foam after a fire drill went wrong at a US military base in Oklahoma.

The fire alarm system in an aircraft hangar was being tested when fire suppression equipment was triggered - filling the structure with foam and almost burying the nearby helicopters.

No injuries have been reported.

Andrew Humphrey reports.