How best can a Head of Safety cope with General Manager, Project Manager and Construction who are indifferent about Safety?

The head of security can call for a meeting and present the vulnerabilities, best practices and recommendations to the relevant stake holders and circulate the documents. If they approve, it in everyone's interest. If not, the HOS would not be held liable for any future untoward incident arising out of noncompliance.  

The best method is to present the HSE KPIs of the project in a weekly meeting describing efficiency of the the controls towards increasing performance.