Attachment X

Pneumatic Devices

Jim Bolander

Southwestern Energy
Peer-review of “Report for Oil and Natural Gas Sector Pneumatic Devices”, April 2014,

U.S. EPA Office of Air Quality Planning and Standards (OAQPS)

By Jim Bolander, P.E., Senior Vice President, Southwestern Energy (SWN)

I. General comments: 

The Report for Oil and Natural Gas Sector Pneumatic Devices report (“White Paper”) is 

a compendium of prior measurements and analysis of methane emissions and control 

technologies related to gas driven pneumatic devices in the natural gas sector. The 

stated purpose of the white paper is to provide a “summary of the EPA’s understanding of 

emissions from natural gas-driven pneumatic controllers and pumps in the oil and natural gas 

sector, the mitigation techniques available to reduce these emissions, the efficacy of these 

techniques and prevalence of these techniques in the field.” In general, the summary 

developed in the White Paper is an accurate summary of the data contained in the 

reference source but it is our recommendation that EPA fully consider the 

characterization and limitations in these reports that lead up to the summary results

that are reported. These comments reflect Southwestern Energy’s (SWN) collective 

thoughts on these sources with respect to emissions and mitigation opportunities. We 

will not attempt to reiterate the summaries characterized in the White Paper. In 

addition to the reference sources that EPA employs in the document, there are other 

technical documents that we recommend the EPA consider in improving its 

understanding of the emissions profile and techniques from pneumatic devices.

SWN believes that it is important to separate out actual measurement studies from 

literature surveys and desktop analysis to understand the characterization and efficacy 

of pneumatic devices in operations. We recommend that EPA consider actual 

measured data, especially the more recent measurements, to develop characterization 

of emission factors and policy options. There is an important new study underway led 

by Dr. David Allen with University of Texas to further evaluate and characterize 

methane emissions from pneumatic devices at upstream natural gas facilities (Phase II 

UT study). This Phase II UT study is expected to be published in a peer-reviewed 

journal by mid-summer 2014. We strongly urge the EPA to fully analyze this new 

Allen et al. paper in developing its policy recommendations.

The emissions estimation methods employed by the EPA and others rely on the 

emission factor and activity data. While there have been studies, including the ones 

referenced in this White Paper, that have measured or analyzed the emission factors, 

there has been very limited effort to address the equally important second part of the 

emissions equation- i.e. the activity data- how many pneumatic devices and pumps are 

operational in the industry? The activity data generation for EPA’s national emissions 
inventory is an estimation which relies on seminal 1996 GRI/EPA report1 for the 

activity data to essentially scale up the data in subsequent reports. A total of 22 sites 

were used in the 1996 GRI/EPA report to establish a count of pneumatic devices for 

production sites and to determine the fraction of intermittent versus continuous bleed 

devices at each site. To this day, the EPA relies on the data collected at these 22 sites as 

the core basis for the activity data related to pneumatic devices.

We highly recommend that EPA revisit the activity data related to pneumatic devices 

in the natural gas industry and embark on a more comprehensive program 

employing both reports submitted by companies under the Subpart W2 reporting 

program and field results to develop the appropriate activity data.

The EPA estimated in the 2012 National Emissions Inventory (NEI) that emissions from 

pneumatic devices in the production sector were approximately 334.4 giga grams (Gg) 

for the year3. This net estimate for pneumatic devices is derived by subtracting the 

imputed reductions from EPA Gas STAR program of 873.1 Gg4 from the potential 

emissions of 1207.5 Gg5. The concern with this technique is that the methane reductions 

from the EPA Gas STAR program for 2012 do not match the reductions incorporated 

into the NEI. We understand the two different goals of the Gas STAR and NEI, but as 

long as EPA continues to rely on Gas STAR reductions in the NEI, it should make all 

attempts to ensure the data reported and extrapolated is reasonable. The EPA Gas 

STAR reductions for 2012 are provided in Figure 1 showing the EPA estimate of about 

5.4 bcf of methane reductions or roughly 103 Gg6 from pneumatic devices. As 

explained by the EPA7, the main reason for this difference is because the EPA Gas STAR 

assumes a sunsetting period after 10 years of replacement of a technology (e.g. 

replacement of “high bleeds” with “low-bleed” pneumatic devices) but the NEI 

assumes “perpetual credit” for such a replacement. 

We have evaluated EPA’s indicated credits and have not been able to reconcile or 

reproduce the 873.1 Gg of methane emissions credited as part of the EPA Gas STAR 

reductions in the 2012 inventory. 

 1 Gas Research Institute (GRI)/U.S. Environmental Protection Agency. 1996c. Research and Development, 

Methane Emissions from the Natural Gas Industry, Volume 12: Pneumatic Devices. June 1996. (EPA-600/R-96-

080l). This report estimated 249,111± 48% pneumatic controllers in operations in 1992 based on the sum 

of the regional values of the ratio of number of devices per gas well and the number of devices per 

marketed gas production.

2 40 CFR Part 98, Subpart W

3 ANNEX 3 Methodological Descriptions for Additional Source or Sink Categories Table A-141: Net 

emissions for select sources

4 Table A-135: CH4 Reductions Derived from the Natural Gas STAR Program

5 Id, Table A-137: National CH4 Potential Emission Estimates from the Natural Gas Production Stage, and 

Reductions from the Natural Gas STAR Program and Regulations

6 Conversion factor: One scf of methane contains 19.2 g methane

7 Personal correspondence with US EPA
Figure 1: 2012 EPA Gas STAR Reductions from the Production Sector.

Using the 2012 activity data of 447,379 pneumatic devices and employing conservative 

assumptions that the mix of “intermittent” and “continuous” bleed devices are similar 

to the 65%:35% ratio identified in the 1995 GRI/EPA report and assuming all 

continuous bleeds (regardless whether they are high or low bleed devices) are reduced 

to a rate of 6 scfh, we estimate the total methane reductions would be about 560 Gg. 

This theoretical exercise demonstrates that EPA’s methods for estimating methane

emissions in the NEI are not reasonable. Therefore, SWN recommends that the EPA 

conduct a comprehensive evaluation of the best available data to generate more 

accurate activity data for pneumatic devices to inform its policy decisions.

Pneumatic devices are classified as an “unsteady source of emissions8” and annual 

emissions were computed in the 1996 GRI/EPA report based on assessing emissions 

per event. As noted in the 1996 GRI/EPA report, “[f]ive sources of information were 

used to determine the methane emissions from pneumatic devices used in the 

production segment”. These included measurements from 19 snap-acting and 16 

throttling controllers from “oil battery” facilities in Canada9

 8 ESTIMATE OF METHANE EMISSIONS FROM THE U.S. NATURAL GAS INDUSTRY David A. 

Kirchgessner, Robert A. Lott, R. Michael Cowgill, Matthew R. Harrison, Theresa M. Shires, Chemosphere, 

Vol. 35, No.6, pp. 1365-1390, 1997 Published by Elsevier Science Ltd

, field measurements from 

Chevron and Tenneco which employed measurements using a flow meter and 

emissions were “extrapolated” to a daily rate. The device count fraction from the 22 

9 A Detailed Inventory of CH4 and VOC Emissions form Upstream Oil and Gas Operations in Alberta, D. 

J. Picard, B.D. Ross, and D.W.H.Koon, Clearstone Engineering Ltd, March 1992 for Canadian Petroleum 

Association
sites (65% “non continuous bleed” and 35% “continuous bleed”) was used to scale the 

associated emission factors from the sources above to generate “one emission factor for 

a “generic” pneumatic device10. The extrapolation of short term measurements to daily 

or annual estimates must be carefully analyzed in these studies, especially related to 

intermittent devices. These issues are further highlighted in the next section.

II. Methane Measurements

a. Characterization of methane emissions from Pneumatic devices

The white paper focuses on characterization of pneumatic devices by their emissions 

profile. As definitions are critical for policy and regulatory decisions, we would 

recommend the EPA to carefully consider the pneumatic characterizations in the 1996 

GRI/EPA report11. 

In addition, we emphasize the importance of time series classification. In general, 

intermittent bleed devices have a clear actuation pattern and returns to zero between 

actuations (i.e. stationary bleed rate equals 0). Continuous bleeds on the other hand 

have a non-zero bleed rate. We believe that classification of continuous bleed devices 

into high-bleed (>6 scfh12) and low-bleed (<6 scfh) are arbitrary and insufficient for 

policy development. Instead, EPA should review emission profiles and understand 

their characteristics before developing appropriate policies. The actuation frequency 

and the vent rate per actuation are important considerations in assessing the emissions 

characteristics of pneumatic devices. Pneumatic controllers have an actuating bleed 

rate (when the actuator is depressured) and a stationary bleed rate, which can be zero 

for “snap-acting” or intermittent devices. Various parameters can impact these bleed 

rates including device maintenance, supply gas pressure, actuating chamber size and 

type of manufacturer/design (as noted in the Prasino Study13).

It should be noted that there are no continuous emissions monitoring systems 

employed in any of the studies to measure methane emissions from pneumatic devices. 

Instead, measurement studies relied on measurement of the supply gas entering the 

pneumatic device using a flow meter or measurement of the gas actuated from 

controller using a Hi Flow sampler. The EPA should analyze all measurement studies, 

including the 1996 GRI/EPA study to assess whether the sample size and distribution is 

representative of current day operations; whether the measurements had adequate 

sampling time to capture representative actuations; whether measurements covered all 

 10 Id. at Table 4-6, Methane Emission Factor for Average Device = 345 ± 40% scfd/device,

11 Table 3-1

12 6 scfh is roughly equal to 1 ton per year of methane.

13 The Prasino Group. 2013. Determining Bleed Rates for Pneumatic Devices in British Columbia; Final Report. 

Prepared for the Science and Community Environmental Knowledge Fund. December 18, 2013. Available 

at http://www.env.gov.bc.ca/cas/mitigation/ggrcta/reportingregulation/pdf/Prasino_Pneumatic_GHG_EF_Final_Report.pdf.
pneumatic devices or a sub-set (e.g. pneumatic devices that were leaking as identified 

by an infra-red camera or a random sample or just pneumatic devices over a certain 

bleed rates) and how the study author handled the devices that did not leak or were

below the detection level of the instrument during the limited duration of the sampling. 

While most measurement studies measure emissions per actuation for a set sampling 

period, care should be taken in extrapolating a short duration sample (say 15 minute) 

to an hourly or daily rate and EPA should carefully review the sampling data to 

assess how the author handled the scale-up and associated uncertainty. The actuation 

frequency over the time period of interest (hourly or daily or annual) should be well 

understood and characterized. This can vary from one facility to the other and depends 

on the process being controlled. Simplistic extrapolation of short-term measurements to 

an average hourly or daily or even annual methane rate quite often leads to incorrect 

results.

In addition, regional differences and type of application are other important 

characteristics that define the total annual emissions. As noted in the Allen et al14 Phase 

I UT Study, there were significant variations among regions, with the pneumatic 

devices in the Rocky Mountain regions exhibiting lower emission than devices in the 

Gulf Coast. In addition, the type of application of the controller may play an important 

role in total emissions and should be considered in all policy decisions. There are two 

main applications of these devices: a) control valves to regulate flow and b) isolation 

valves to isolate equipment and pipelines. As controllers, they are used in numerous 

devices such as separators, process heaters, compressors, dehydrators, flares etc. 

Isolation valves that are typically found at compressor and storage stations are used to 

isolate the facility in case of an emergency or if there are repairs or maintenance work to 

be carried out. Such type of pneumatics, including controllers employed in gas 

production sites on emergency devices actuate infrequently or in case of emergencies, 

but do emit large volumes when actuated and there is a potential that when averaged 

over an hour, these devices may emit greater than 6 scfh. 

b. “Fat-tails”: small number of sources are responsible for majority of the 

emissions

Recent studies from Allen et al. and from the Prasino Group have clearly indicated that 

a small fraction of the pneumatic controllers are responsible for a large portion of the 

emissions.

Figure 2 provides the average emission rates from 305 devices measured as part of the 

Allen et al. Phase I study. In this study, a total of 25% (or 77 devices) had methane 

emissions greater than the study reported average of 0.175 scfm and about 40% of the 

 14 Allen, David, T., et al. 2013. Measurements of methane emissions at natural gas production sites in the United 

States. Proceedings of the National Academy of Sciences (PNAS). October 29, 2013. 

(http://www.pnas.org/content/early/2013/09/10/1304880110.full.pdf+html).
devices emitted over 6 scfh. As noted in Figure 3, 80% of the emissions were from 27% 

of the devices. The Prasino study reviewed 581 controllers and 184 pumps. Similarly 

the Prasino Study which 44% of devices with emissions greater than 6 scf/h accounted 

for 91% of emissions. In addition to results from “top-down” studies15

Hence, it is amply clear from actual measurement studies that a small fraction of the 

pneumatic devices or even facilities are responsible for a large portion of the emissions. 

Therefore, it is important to understand the regional differences, actuation 

characteristics from the recent and upcoming methane studies. These studies will 

provide significant understanding of emissions profile from gas driven pneumatic 

devices.

, indicate the 

same “fat-tail” or super-emitter phenomenon, though at a source level. 

From a policy stand-point, a “one-size” approach to replacing such devices will not be 

appropriate. For example, a policy that requires replacement of such intermittent, 

infrequent controllers/valves with low-bleed continuous devices emitting less than 6 

scfh, even if operationally possible yields a negative environmental outcome since the 

annual emissions from the controllers on emergency devices or isolation valves may be 

much smaller than the low bleed continuous device. Hence, EPA should avoid 

adopting any “one-size” policy with respect to mitigation technologies.

I. Other comments

a. Did this paper appropriately characterize the different studies and data 

sources that quantify emissions from pneumatic controllers and 

pneumatic pumps in the oil and gas sector? 

We believe the paper appropriately characterizes the different studies and data sources. 

It is more important for EPA to fully understand the basis and inferences that can be 

drawn by the study findings. Just relying on the “central estimates” reported in the 

studies without fully understanding the basis for the estimates or control technologies 

reported may hinder the policy responses.

Figure 2: Pneumatic Measurements from Allen et al., 2013

 15 See D. Caulton, et al., Toward a better understanding and quantification of methane emissions from 

shale gas development, April 14, 2014, doi: 10.1073/pnas. 1316546111, PNAS (April 14, 2014); A.R. 

Brandt, et al., Methane Leaks from North American Natural Gas Systems, Science, Vo. 343 (Feb. 14, 2014); 

G. Petron, et al., A new look at methane and non-methane hydrocarbon emissions from oil and natural 

gas operations in the Colorado Denver-Julesburg Basin, Journal of Geophysical Research: Atmospheres, 

doi: 10.1002/2013JD021272.
Figure 3: Pneumatic Devices Emissions Profile (Allen et al., 2013)

a. Please discuss explanations for the wide range of emission rates that have 

been observed in direct measurement studies of pneumatic controller 

emissions (e.g., Allen et al., 2013 and Prasino 2013). Are these differences 

driven purely by the design of the monitored controllers or are there 

operational characteristics, such as supply pressure, that play a crucial 

role in determining emissions? 

Avg, 0.175 scfm

0.000

0.500

1.000

1.500

2.000

2.500

0 50 100 150 200 250 300 350

Measured Methane Emissions (scfm)

No of Devices

Methane Emissions 

Measured

Average Methane Rate
This question has been addressed in the previous sections of this report. Yes, direct 

measurement studies are clearly indicating a “fat-tail” issue. In addition, there are 

regional variations and variations depending on the type of service. The actuation 

frequency, the volume per actuation, controller design, supply pressure, maintenance 

practices are important parameters in determining the emissions. 

b. Did this paper capture the full range of technologies available to reduce 

emissions from pneumatic controllers and pneumatic pumps oil and gas 

facilities? 

We emphasize that control technologies outlined in this report while theoretically 

correct does not address the key findings from the various direct measurement studies 

and therefore we disagree with the summaries outlined below:

“Low bleed gas-driven controllers can replace high bleed gas-driven controllers 

in many, but not all, applications.”

“Where a reliable source of electrical power is available, instrument air systems 

can replace natural gas-driven pneumatic controllers, and result in no methane 

or VOC emissions.”

“Zero bleed, mechanical, and solar-powered controllers can replace continuous 

bleed controllers in certain applications, but are not broadly applicable to all 

segments of the oil and natural gas industry.”

First, these conclusions are rather simple and do not account for the fact that a vast

majority of the pneumatic devices simply do not have “leakage” issue. There are “fattails” and appropriate smart policies have to be developed to address these issues. In 

actual operations, pneumatic controllers are called in response to demands that are not 

easily predictable in many cases. Hence, two similar controllers (same model and 

manufacturer) can have a totally different emissions profile depending on the location 

and operational characteristics of the process it supports. As noted in the Simpson 

paper, intermittent devices typically offer the lowest emissions in most applications 

since there is no bleed between actuations, each application must be analyzed 

independently to consider local operational and safety considerations. Hence, a 

mandate to replace high bleeds with low or zero bleed via regulations or mandate 

replacement of intermittent devices with low or zero bleeds, may result in waste of 

capital and resources.

4. Please comment on the pros and cons of the different emission reduction 

technologies. Please discuss efficacy, cost and feasibility for both new and existing 

pneumatics. 
See response to previous question.

9. Are there ongoing or planned studies that will substantially improve the current 

understanding of VOC and methane emissions from pneumatic controllers and 

pneumatic pumps and available techniques for increased product recovery and 

emissions reductions? 

1) Methane Emissions from Process Equipment at Natural Gas Production Sites in 

the United States: Pneumatic Controllers, David Allen et al. ( to be published 

2014)

2) Clearinghouse of Technological Options for Reducing Anthropogenic Non-CO2 GHG 

Emissions from All Sectors, Jeff Kuo, Ph.D., P.E., Dept. of Civil and Environmental 

Engineering, California State University, Fullerton, Prepared for: State of 

California Air Resources Board Research Division. May 14, 2008