Q817. Do enclosed flare systems have to report emissions under 40 CFR part 98 subpart C?
A817. Yes, in most cases enclosed flare systems are required to report under subpart C.
The definition of flare in 40 CFR part 98.6 is “a combustion device, whether at ground level or elevated, that uses an open flame to burn combustible gases with combustion air provided by uncontrolled ambient air around the flame.” Per 40 CFR 98.30(b)(4), flares that meet this definition are excluded from subpart C and do not need to report emissions, unless otherwise required by provisions of another subpart under 40 CFR part 98.
An enclosed flare system does not meet the definition of flare in 40 CFR part 98.6 when (1) it has a fully enclosed flame (i.e., does not have an “open flame”), and (2) it has a means to control air flow. In general, enclosed flare systems are very similar to natural draft process heaters or boilers which are covered under subpart C because they do not actively supply air to the combustion chamber, but they can control the amount of air that enters the combustion chamber.
A shroud to prevent wind effects on the flame does not constitute a means to control air flow. Therefore, a flare with a shroud does meet the definition of flare in 40 CFR part 98.6 and is not required to report under subpart C.