It's not terribly wise for every single member of staff you employer to have access to all the areas on your premises, especially if certain zones are dangerous. As an employer, it's your responsibility to make sure only highly trained people can gain access to those hazardous areas where they can operate according to their set of skills.
Otherwise, the temptation is for anyone to go into those spaces when they need to. Members of staff often enter areas they probably shouldn't for well-meaning reasons. If they have a task that needs completing and they don't want to disturb the technical team, they might go and do it themselves because it seems like the easier thing to do.
However, this goes against your safety procedure. Sometimes staff need protecting against themselves and against their own sense of diligence.
This is why it makes sense to make hazardous zones on your site restricted access areas. Access control is not always about deterring trespassers and keeping thieves out. Sometimes it's about looking after the members of your team and making sure the safest course of action is taken every time.