Health and safety is often derided as a tiresome issue of little relevance to day-to-day workers but the oil industry is entirely different.

For the thousands of men and women who work offshore, health and safety is a matter of life and death.

So why are there still so many unanswered questions about the reliability of the helicopters used to take workers to and from the platforms?

The concern around this issue has been growing for some time. Earlier this year, a fatal accident inquiry into the Bond Super Puma crash in 2009 in which 16 men were killed concluded that maintenance was not always carried out by the book at Bond.

However, it was also decided that there would be no criminal prosecution in the case, which left families feeling that that they had been let down by the system.

Now similar concerns have been raised by a House of Commons Transport Committee over the Super Puma crash in Shetland last year in which four passengers were killed.

In its report, the committee highlighted an investigation by the Air Accidents Investigation Branch which uncovered the fact that the pre-flight safety briefing conducted before the Shetland crash did not properly explain how to use the emergency breathing equipment.

The passengers on board the Super Puma helicopter, which was operated by CHC, only discovered the problem when they tried to use the equipment.

Such a fatal failure of procedure can never be acceptable but, if workers' confidence in offshore safety is ever to recover, the reasons why such failures have been allowed to happen must be exposed. The committee of MPs heard that there was a macho culture in the industry which meant that risks were played down; just weeks before the Shetland crash, for instance, workers were reportedly told by officials of the company to put on "big boy pants" or resign.

In its response to the committee's report, the Department of Transport must explain how it will address this issue and, in particular, why the Civil Aviation Authority (CAA) did not look at the impact of commercial pressure on helicopter safety in its review of the Shetland crash.

The North Sea is a tough, competitive place to work but competition must never be allowed to come before safety.

The role of the Civil Aviation Authority itself should also be up for discussion. Does it really have the remit and powers it needs to hold the helicopter companies to account? And has its approach to the companies been far too light touch, as Frank Doran, the Labour MP for Aberdeen North, believes?

Regardless of the answers, the confidence of offshore workers in helicopter safety is at rock bottom and it is hardly surprising. There have been four accidents in five years and yet there have been no prosecutions. Clearly, lessons are still to be learned.

The Department of Transport must now demonstrate what it will do to force companies to obey the rules every minute of every day and punish those who fail to do so.