Q859. Are visual inspections still required for thief hatches if a visual inspection is unsafe to perform due to the contents of the storage tank?

A859. There are multiple methods for determining whether a storage tank thief hatch is open in 40 CFR 98.233(j)(7). 40 CFR 98.233(j)(7) first specifies that if an applicable operating thief hatch sensor is present and operating on the tank, sensor data must be used to inform the periods of time that a thief hatch is open. 40 CFR 98.233(j)(7) then specifies that if a thief hatch sensor is not operating but an applicable operating tank pressure sensor is present and operating on a controlled atmospheric pressure storage tank, reporters must use data obtained from the pressure sensor to determine periods when the thief hatch is open. Finally, under 40 CFR 98.233(j)(7) reporters must only perform a visual inspection of each thief hatch on a controlled atmospheric storage tank if neither an applicable thief hatch sensor nor an applicable tank pressure sensor is operating on that controlled atmospheric storage tank, including during periods of time when the sensors are malfunctioning, for longer than 30 days. In such circumstances, reporters must perform a visual inspection of each thief hatch on a controlled atmospheric pressure storage tank in accordance with 40 CFR 98.233 (j)(7)(i)-(iii).

Subpart W also provides procedures for estimating missing data. Under the provisions of 40 CFR 98.235, except as specified in 40 CFR 98.233, whenever a value of a parameter is unavailable for a GHG emission calculation required by subpart W (including, but not limited to, if a measuring device malfunctions during unit operation or activity data are not collected), reporters must follow the procedures specified in that provision as applicable, including 40 CFR 98.235(g) which applies for activity data not addressed in another paragraph of 40 CFR 98.235. Where applicable, 40 CFR 98.235(g) requires that for each missing value of any activity data, reporters must substitute data value(s) using the best available estimate(s) of the parameter(s), based on all applicable and available process or other data (including, but not limited to, processing rates, operating hours). Thus if a controlled atmospheric storage tank does not have an applicable operating thief hatch sensor or an applicable operating controlled atmospheric tank pressure sensor, including during periods of time when the sensors are malfunctioning, for longer than 30 days, and a visual inspection cannot be performed safely, reporters would use the missing data provisions of 40 CFR 98.235, particularly 40 CFR 98.235(g), and meet the requirements of that provision. In such circumstances, reporters also must provide the information required in 40 CFR 98.236(bb), including the procedures used to determine whether the thief hatch was open and the duration that it was open. Reporters must also keep the records required by 40 CFR 98.3(g)(4) and 98.237(f), which in such circumstances would include a record explaining why the visual inspection was unsafe to perform, resulting in the need to use missing data procedures.