FM Approvals is an organization, which performs third party testing and certification. Their main focus is property loss prevention and fire and wind (storm) are two main causes of property losses. As a leader in this market, there advice is requested by many insurances and having a an FM Approved certificate is definitely a reason to get a cheaper insurance.
A flat roof is always a major risk for major losses due to storm (wind) and fire risks during maintenance. For that reason, FM developed a standard to describe the testing of a steel deck roof for fire and wind risks. Contrary to ASTM and EN, this well written standard is free of charge and the responsible author can be contacted directly for discussion.
The standard describes the fire and wind testing and put some limiting values. Large monolithic GLAPOR cellular glass boards with an adapted adhesive could become a good candidate for this certificate. They have a large strength in tension (monolithic) to resist windload and are non-combustible. The adhesive can be improved with fire retardants and fasteners can be avoided. However, a wind load up to 300 km/h is simulated to get the highest approval.