Embodiments of the invention provide a containment system having a primary air inlet and an alternate inlet. In one embodiment, a containment system includes a housing configured to retain a main filter, the housing having a primary air inlet and an access door configured to access an interior of the housing. The access door has an alternate airflow inlet. In another embodiment, an air distribution plate includes a front surface having a first edge and an opposing second edge, wherein the front surface is configured to allow air to pass therethrough. Flow resistance through the front surface is greater proximate the second edge relative the first edge. In yet another embodiment, a method for testing a filter includes closing a damper and flowing air into a containment housing through an inlet formed though an access door and across an air distribution plate to a filter, and testing the filter.