40 CFR §63.7120

1. (a)You must monitor and collect data according to this section.
2. (b)Except for monitor malfunctions, associated repairs, required quality assurance or control activities (including, as applicable, calibration checks and required zero adjustments), and except for PSH operations subject to monthly VE testing, you must monitor continuously (or collect data at all required intervals) at all times that the emission unit is operating.
3. (c)Data recorded during the conditions described in paragraphs (c)(1) and (2) of this section may not be used either in data averages or calculations of emission or operating limits; or in fulfilling a minimum data availability requirement. You must use all the data collected during all other periods in assessing the operation of the control device and associated control system.
   1. (1)Monitoring system breakdowns, repairs, preventive maintenance, calibration checks, and zero (low-level) and high-level adjustments;
   2. (2)Periods of non-operation of the process unit (or portion thereof), resulting in cessation of the emissions to which the monitoring applies; and