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Intermittent Low/High Use Gas Criteria for Subpart I 

With SIA Comment 

The text in italics below is taken from SIA’s 4/18/12 response to EPA’s stack method summary. 

The black text is from EPA’s original summary, while the blue text is from SIA’s response. 

Low Use and/or Infrequently Used Gases During Stack Testing. EPA and SIA are still 

discussing the options for addressing low use and infrequently used gases. EPA plans to 

resolve these issues by April 19, 2012. Part of the options being considered would include the 

following: 

For EPA consideration, here is a proposed approach to intermittent low use F-gases:

Define an “intermittent low use” F-GHG as one that: 

 Was not used on the day of the stack test, but is used by the Fab 

 The estimated sum of F-GHG emissions from the gas is less than 10,000 metric ton 

CO2e per year as determined using the Tier 2a method, and 

 The projected F-GHG emissions does not constitute greater than 15 % of the total FGHG CO2e emissions from the Fab. 

If a F-GHG qualifies as an intermittent low use F-GHG, then the emissions will be estimated 

based on gas usage and updated Tier 2a emission factors (EFs) and POU abatement DREs, 

accounting for the typical (historical) downtime of those POU devices 

Define an “intermittent high use” F-GHG as one that: 

 Was not used on the day of the stack test, and which does not qualify as a low use gas. 

If the gas is an intermittent high use F-GHG and the gas was not used at the time of the stack 

testing; then the stack systems associated with the utilization of the intermittent high use gas 

would require retesting at a time when the gas is in use at a magnitude that would enable the 

determination of emission factors. 

EPA agrees with SIA’s suggestion of “intermittent low use” F-GHG. To complement this 

definition, EPA would propose to define “intermittent high use” F-GHG as the following: 

 Intermittent high use F-gas: a gas not used on the day(s) of stack testing that is either 

(1) over 10,000 metric tons CO2e per year or (2) represents greater than 15% of total FGHG emissions. 

 To determine whether a gas meets this definition, the facility should use the IPCC Tier 

2a method, accounting for abatement system use. 

 If a gas meets this definition, then a retest would be triggered. 

In addition to the definition above, EPA also notes that it anticipates reporters would use the 

following provisions for stack testing: 
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 Determine the F-GHGs expected to be consumed or emitted from the stack system 

(inputs and byproducts) based on an analysis of all F-GHGs consumed or emitted in the 

previous and current reporting years by process tools connected to the stack system. 

 When conducting stack testing, reporters would measure emissions for all F-GHGs 

expected to be emitted from or consumed by the stack system tested. 

 Reporters would schedule stack system tests for a period that is representative of 

normal operation and when all anticipated F-GHGs that will be consumed during the 

year are flowing to the process tools connected to the stack system. Comment [A1]: This language is inappropriate 

given the definitions above. The people scheduling 

the tests are not in a position to know what gases 

will be used weeks in advance – that is the reason 

that the intermittent high gas provision will require 

re-testing if a gas of high importance is missed.