addressing uncertainty in oil and natural gas industry greenhouse

associated with them are assigned by expert judgment to be 0% in the third column. The reader should note
that if these counts of equipment had been produced in a different way, for example if they were taken from
an industry average of equipment counts at this general type of facility, uncertainty then would have to be a
real value, not zero. In that case, confidence bounds might be provided with the industry average, or may
have to be assigned again by expert judgment.
Well-known Activity Factors
Counts of other devices on site, even if produced by company personnel, may not be perfectly known. It is
possible to know the exact number of amine units with perfect certainty, but not to know some less
significant equipment components. In this hypothetical case, counts were taken from the exact facility, such
as counts of pressure relief valves (PRVs), pneumatic devices, and chemical injection pumps. However,
some small uncertainty was assigned to these counts by expert judgment since the counts are not perfectly
known. In this hypothetical case, uncertainties between 1% and 5% were assigned to the counts of PRVs,
pneumatic devices, and chemical injection pumps. For unit capacities, the fifth column in Table 5-1, these
capacities are well known, and expert judgment assigned them to be ±5%. In this hypothetical example,
“days of operation” are supplied by company experts. In this example, these estimates were not based on
measured operating hours but were estimated based on operator logs. An uncertainty of 2% was assigned
by expert judgment.
Approximated Activity Factors
For other sources, such as counts of valves, seals, flanges for fugitive emissions, there may be larger
uncertainties associated with the activity factor counts. This is true even if the count were produced for the
exact facility. The uncertainty is determined using expert judgment based on the quality of the component
inventory and the length of time since the last inventory of fugitive emission sources, since changes to the
facility and therefore component counts are possible. In this hypothetical example, the counts were not
taken for this exact facility, but were applied from average component count information from industrywide
counts of fugitive components from this general type of facility. Therefore expert judgment assigned a
much wider uncertainty to each count of ±75%. In cases where exact component counts were taken for this
facility, the uncertainty percentage would be much lower. Table 5-2 shows the activity factor counts for
fugitive components (reprinted directly from the API Compendium), and the assigned uncertainties.
Measured Activity Factors
In this hypothetical example, some of the activity factors were flow rate information measured by on-site
totalizing meters that record data. These flow rate measurements were assigned a ±15% uncertainty by
Pilot Version, September 2009 5-6