Your safety culture is down and no-one is correcting this. A collective agreement has been built that (these) procedures need not be followed and it has become "not done" to address this.
What are you correcting?
When it comes to the safety culture, the most important thing to address is this: "In what way do people get pulled into not following the rules, and what keeps them there?". How does the "Code of Silence" work. Very often, this is how a negative culture builds:
Somebody does something, like not following a rule or procedure, and rather than correcting his or her behaviour to rectify this, he or she exerts pressure on people to do the same. It might be that the person not following the rules is a seasoned hand, and rather than admitting his mistake he uses his authority to let people know that "people with experience can do this". If the other person buys into this, and says nothing, essentially a "secret agreement" is made to work this way. After a while, if enough people are into this game, the peer pressure will automatically draw other people in this game as well, and it becomes normal behaviour - a culture.
How are you correcting?
Importantly, check the behaviour of the manager of this team. Apparently he or she was not able to keep the team together on a positive safety culture track.
The most important thing is however that you start addressing the basics of the team behaviour ("Are we here to help each other excel?" and "How have we been working lately that is not in line with how we want to work?") and to bring the team back to the shared ambition and task of the whole team (in HRO's this is often related to caring for the lives of people).