Not every oil or condensate tank is regulated the same way; a tank becomes subject to specific federal control requirements only once it emits enough volatile organic compounds to cross a threshold. When it does, it becomes what the new source performance standards call a storage vessel affected facility. This guide explains how a tank's VOC potential to emit determines whether it is a regulated storage vessel affected facility, what the required control efficiency means, and how throughput and vapor-control monitoring data supports both the applicability determination and the demonstration that controls are working.
Storage Vessel Affected Facility in one line: A storage vessel affected facility is a tank that has become subject to federal new source performance standards because its potential to emit volatile organic compounds equals or exceeds a threshold of six tons per year. Once a tank crosses that VOC potential-to-emit threshold, the operator must reduce its emissions, typically by routing vapors to a control device that achieves at least ninety-five percent reduction. Whether a tank is an affected facility, and whether its controls perform, both depend on knowing its throughput and vapor-control operation.
The trigger for regulation as a storage vessel affected facility is the tank's potential to emit volatile organic compounds. When that VOC potential to emit equals or exceeds six tons per year, the tank falls within the affected facility definition and the control requirements attach; below that threshold it does not. The determination is made on a per-vessel basis using the tank's potential emissions, which depend on the volatility of the liquid it stores and how much liquid moves through it.
Throughput is central to the calculation because a tank's emissions scale with how much liquid it turns over. Flash emissions occur each time volatile liquid enters the tank and light ends break out of solution, and working losses occur as the level rises and falls, so a tank handling a high volume of volatile crude or condensate reaches the six-ton threshold far sooner than a low-throughput tank holding a stabilized, low-vapor-pressure stock. The volatility of the stored liquid, often characterized through its vapor pressure, is the other main driver.
Because the threshold is based on potential rather than a single past year, a tank's status can change as conditions change. A tank that starts below the threshold can cross it if throughput increases or if it begins receiving a more volatile stock, and a determination made once is not necessarily valid forever. This makes the applicability question an ongoing one tied to how the tank is actually being used, which is why the throughput and stock data that feed the calculation matter well beyond the initial assessment.
Once a tank is an affected facility, the operator must reduce its VOC emissions rather than let them go to atmosphere, and the standard control requirement is to achieve at least ninety-five percent reduction of the tank's emissions. In practice this means routing the tank's vapors to a control device, such as a vapor recovery unit that captures them or a combustion device such as an enclosed combustor or flare that destroys them, that is capable of removing or destroying at least ninety-five percent of the VOC that would otherwise be released.
Achieving ninety-five percent on paper is not the same as achieving it in service. The vapors have to actually reach the control device, which means the tank's connections must be closed and the routing must be intact, and the control device has to be operating properly whenever the tank is emitting. A combustor with an extinguished flame, a vapor line that is blocked or open to atmosphere, or a hatch left open all defeat the control regardless of the device's rated efficiency, so demonstrating compliance is as much about continuous proper operation as about the device's design.
This is why the control requirement comes bundled with monitoring and recordkeeping expectations. The operator has to be able to show that the control device was operating and that the vapors were routed to it during the periods the tank was in service, which turns a one-time efficiency rating into an ongoing operational demonstration. A tank that is nominally controlled but whose control device was frequently down or bypassed is not meeting the ninety-five percent requirement in any meaningful sense.
Both halves of a storage vessel affected facility's compliance story rest on data a monitoring system already handles. On the applicability side, the potential-to-emit determination depends on throughput and stock volatility, and a cloud SCADA platform such as Merobix reads tank levels and metered throughput continuously, so the volume moving through each tank is measured rather than estimated. That measured throughput, paired with the volatility of the stored liquid, is what makes an applicability determination defensible and lets an operator see when a tank's use is trending toward the threshold.
On the control side, the requirement is to show that the ninety-five percent control was actually in effect while the tank was emitting, and that demonstration is fundamentally about the status of the control device and the integrity of the routing. Monitoring the operation of the vapor recovery unit or combustor, such as whether a combustor's pilot or flame is present and whether the vapor path is intact, produces the time-stamped record that proves the control was working when it needed to be, or flags when it was not so the operator can respond.
Bringing throughput and control-device monitoring into one platform ties the whole demonstration together for each tank. The operator can show what the tank handled, that its potential to emit was accounted for, and that whenever it was in service its vapors were routed to a properly operating control device. For a company managing many tank batteries, having that applicability and control data flowing into a single system is what makes it practical to keep each affected facility both correctly classified and continuously demonstrating the reduction its status requires.
A tank becomes a storage vessel affected facility when its potential to emit volatile organic compounds equals or exceeds six tons per year. Below that VOC potential-to-emit threshold the control requirements do not attach. The determination is made per vessel using the tank's potential emissions, which depend on the volatility of the stored liquid and how much liquid moves through the tank.
It means the tank's vapors must be routed to a control device capable of removing or destroying at least ninety-five percent of the VOC that would otherwise be released, such as a vapor recovery unit or a combustion device. Achieving this in practice requires that the connections stay closed, the vapor routing stays intact, and the control device operates properly whenever the tank is emitting, not just that the device is rated for ninety-five percent.
Yes. Because the threshold is based on potential to emit, which depends on throughput and the volatility of the stored liquid, a tank that starts below the threshold can cross it if throughput increases or it begins receiving a more volatile stock. A determination made once is not necessarily valid forever, which is why the throughput and stock data behind the calculation matter on an ongoing basis.
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