The Division for Investigation of Maritime Accidents/Danish Maritime Accident Investigation Board has published a report about a diving accident on 24 July 2010, where a diver was killed while working at approximately 41 meter’s water depth at a wind farm. The diver's umbilical got caught and his air hose was squeezed flat by which his air supply was blocked.
The diver had three emergency air supply options, however none of which he was able to use when in distress.
A standby diver was sent down to rescue. But it failed to help the diver early enough to restore his air supply.
A long range of conditions mentioned in this report either caused and/or contributed to the fatal accident and the failed rescue attempt.
The report can be downloaded in PDF format here.