During routine maintenance on a Slingsby TA9 seven function manipulator jaw assembly, while removing the finger retaining bolts, a bolt with 80% of the thread exposed as it was being removed was explosively ejected. Fortunately, the bolt narrowly missed the technician’s face.
The ROV vehicle had been working in a water depth of 110 metres for the previous 10 months. It was not known if the finger retaining bolts had been removed during that period. The vehicle had recently completed a series of long duration dives. It is thought that there may have been a gas build up caused by interaction between the metals concerned.
There are many bolts fitted to blind holes on various ROVs and sub assemblies; therefore as a general precaution care should be taken when disassembling all equipment that has been subjected to prolonged water pressure, or where bolts are fitted in blind holes where gassing could have taken place.
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