The measurement of the temporal and spatial distribution of a suppression agent is essential for characterizing the fire extinguishment process and for certifying a fire-suppression system. A time response of 10 ms to 50 ms is required for dry-bay suppression studies and 100 ms to 200 ms for ground-vehicle crew compartment deflagration protection. The Differential Infrared Rapid Agent Concentration Sensor (DIRRACS) is being developed to provide such measurements. The first version of the instrument consisted of an infrared (IR) source, narrowband pass filter, chopper, and pyroelectric sensor. While the device was capable of providing qualitative data as fast as 30 ms, the device was affected by air flow and had low signal-to-noise ratio and a too-slow time response.