An analysis was performed to provide design guidance on the cooling of an NIST-developed in situ fire visualization device, called Burn Observation Bubble (BOB). The analysis was to address the question of how long the device can operate in a fire without being damaged by the fire. The analysis included consideration of single-pass and recirculating cooling systems. The resulting design equations depend on the fire scenario, the cooling water flow rate, and the volume ratio of the device volume to recirculating cooling water reservoir. In the limit of an infinite recirculating cooling water reservoir, the design equations reduce to those of a single-pass system. Sample calculations were given to illustrate the applicability of the equations.