An air conditioning assembly for an environmental chamber includes an air handling unit for supplying air to the environmental chamber. A plurality of ducts in fluid communication with the air handing unit and in fluid communication with the environmental chamber are configured to draw air from one side of the environmental chamber through at least one outlet vent, and to blow air into an opposite side of the environmental chamber through at least one equal but opposite inlet vent. At least one air conditioning means in fluid communication with the at least one air handling unit is configured to condition the air flow passing through the air handling unit. The at least one air conditioning means includes an altitude simulator for changing the oxygen content of the air flow. In use, the air conditioning assembly is configured to create substantially laminar air flow throughout the environmental chamber.

A duct detector may include a detection chamber and a control circuitry stacked vertically on top of the detection chamber. A sealing gasket may seal a contact between a substrate of the control circuitry (e.g., the seal may be at the bottom surface of a printed circuit board containing the control circuitry) and the detection chamber such that particles analyzed the detection chamber may not damage the control circuitry. Therefore, by providing a sealed barrier between the control circuitry and the detection chamber, the sealing gasket allows for stacking the control circuitry and the detection chamber. As the seal does not create a barrier (the barrier is for the detection chamber) for a repair personnel to access the control circuitry, repairs to the duct detectors may be easier because the seal may not have to be broken and resealed during the repair process.