Parents of a Black Country sailor who died in an explosion on board a submarine said they hoped valuable lessons could be learned after a report concluded the Ministry of Defence was “complacent” about safety improvements.

The investigation followed a blast on HMS Tireless in March last year which killed Leading Operator Mechanic Paul McCann, 32, of Halesowen. Operator Maintainer Anthony Huntrod, 20, of Sunderland, also died and a third crew member was injured.

It happened when a self-contained oxygen generator (SCOG) – used to provide oxygen in an emergency – exploded while the submarine was under the ice off Alaska. Results of the investigation found the MoD to be “complacent” about improvements in safety over introducing SCOGs.

It also said the MoD’s analysis of the risks of an explosion was “flawed”.Speaking from Spain, Mr McCann’s father Brian, 66, said today: “There have been major flaws all of the way along. As a family we are very disappointed that these systems were not in place. The incident should never have happened.”

The report also highlighted “shortcomings” in the way the MoD handled and managed SCOGs and said logistics processes were “neither consistently applied nor comprehensively followed”.

A Board of Inquiry report into the accident published in June concluded that the blast was caused by a faulty SCOG during a routine drill.

It identified the most likely cause as “significant internal contamination of the SCOG canister with oil, possibly exacerbated by cracking within the canister”.

Armed forces minister Bob Ainsworth said that the subsequent investigation found the MoD had mistakenly believed that the new unit delivered a “substantial improvement” in safety.

It also wrongly thought that a cap and seal in the new design would prevent against any contamination.

He said: “The investigation has, however, made it clear that this belief, and therefore the resultant understanding of any risk of explosion, was flawed and that we were complacent about the improvement in safety the new SCOGs delivered.”

The investigation has made 14 recommendations for improvements across the logistics process including in handling, storage and tracking of SCOGs.