The hours of reliability show the number of hours per year that the control device is expected to operate. The number of hours was determined by an internal TCEQ Tier I review of semiconductor permits issued since 1994, except for oxidation which is based on vendor information. NSR recognizes the special need for the semiconductor industry to operate continuously and the need for scheduled maintenance. Therefore, manufacturing operations are assumed to continue during scheduled maintenance of the control device as long as the impacts are acceptable and the downtime is limited.
It is also assumed that the industry will continue to procure add-on control equipment with high values of expected mean-time-between-failures (MTBF.) This does not preclude the installation of backup equipment or extra control capacity (typical for scrubbers), nor does it relieve the facility from taking necessary measures if the failure of add-on control equipment will result in unacceptable impacts.
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