This paper presents measurements of combus- tion species of low pressure laminar premixed flat meth- ane-oxygen flames inhibited by trifluoromethane (CF3H) using synchrotron radiation-molecular beam mass spec- trometry (SR-MBMS). Fire suppression chemistry of CF3H is investigated by selective detection of combustion radicals and intermediates. Results show that SR-MBMS offers a powerful tool for studying fire suppression chemistry of ha- lon replacements, which may extensively detect combustion species in the inhibited flames, especially radicals and inter- mediates. The suppressant CF3H is completely consumed in the preheat zone of premixed flames and produces fluori- nated radicals such as CF3 and CF2. CF3 is the main radical participating in flame inhibition cycles in the reactive zone. Unlike HBr, HF produced by CF3H is very stable and will not act as a radical scavenger because the bond energy of H-F is much higher than that of H-Br, which is responsible for less effectiveness than conventional bromine-based sup- pressants. This paper presents measurements of combus- tion species of low pressure laminar premixed flat meth ane-oxygen flames inhibited by trifluoromethane (CF3H) using synchrotron radiation-molecular beam mass spectrometry (SR-MBMS). Fire suppression chemistry of CF3H is by selective detection of combustion radicals and intermediates. Results show that SR-MBMS offers a powerful tool for studying fire suppression chemistry of han lon replacements, which may extensively detect combustion species in the inhibited flames, especially radicals and inter-mediates. The suppressant CF3H is completely consumed in the preheat zone of premixed flames and produces fluori- nated radicals such as CF3 and CF2. CF3 is the main radical participation in flame inhibition cycles in the reactive zone. Unlike HBr, HF produced by CF3H is very stable and will not act as a radical scavenger because the bond energy of HF is much higher than that of H-Br, which is responsible for less effective tha n conventional bromine-based sup- pressants.