I am working on a Fire Station Project.  We are going for the EQ Credit: Enhanced Indoor Air Quality Strategies Option 1.  We are mechanically ventilated in both the Fire Station living spaces and the apparatus bay.  For the apparatus bay it is a heated and ventilated space only.  We are meeting the IMC code ventilation requirements for a garage with roof mounted exhaust fans and wall louvers. We have a minimum exhaust rate operating 24/7 with infiltration accounting for the make-up air.   We have a separate purge fan, gas detection  system, and wall louvers that will operate if there is an alarm from the gas detection system.  My question is in regard to the filtration requirement on this credit.  Are we required to filter the make-up air coming into the space through the wall louvers when the system is in purge mode?  I have a second question regarding Option 2.  The fire station has no densely occupied spaces.  Is there any type of exception allowing us to install CO2 detection in the main living areas to obtain this credit – despite not being densely occupied?