4 The record articles

Representing MSS Emissions in the Emissions Inventory

Posted: March 19th, 2019

Authors: Rachel H. 

A good portion of the Texas refineries are taking a deep breath as the Refinery Sector Rule (RSR) compliance date is behind us, but the work isn’t over yet. The end of January means the environmental reporting season is upon us, but there’s no need to worry. The ALL4 team is on top of everything new in the world of Annual Emissions Inventories (AEI) in Texas. The Texas Commission on Environmental Quality (TCEQ) held an Emissions Inventory Workshop on January 24, 2019, where permit writers and technical experts described updates to AEI and discussed pitfalls as well. A particular topic that has caused confusion among the audience is the concept of representing Maintenance/Startup/Shutdown (MSS) emissions in the AEI.  Read on for some further details and explanations.

Just as the TCEQ staff begins their presentations with necessary definitions, the same strategy is being done here. Taking time to define the terminology that isn’t always intuitive can offer clarity around a confusing situation.

Understanding Key Definitions

The TCEQ has offered many resources that define the following terms.

  • MSS Emissions
  • Scheduled Maintenance/Startup/Shutdown (SMSS) Emissions
  • Emissions Event (EE)

The definitions can offer a comprehensive understanding of the terms, but I have included brief descriptions and an example to guide you through.

MSS emissions are abnormal emissions that are expected and defined in the permit. SMSS emissions are not defined in the permit, yet are known in advance, allowing TCEQ to be notified beforehand. EEs are not permitted and not known in advance. These are the unexpected upsets at a facility.

Let’s go through this with some scenarios…

Imagine you work in a chemical plant. A planned annual turnaround that has been worked into your permit falls under the MSS emissions category. Different activities such as increased flaring, vessel cleaning, or maintenance procedures will be taking place resulting in non-routine emissions. These are all planned for and happen periodically.

Now consider the turnaround has been completed and normal operations have resumed-a normal day at the plant. An operator walks into your office and says that the distillation column outside is running fine, but the walls are thinning too fast. No excess emissions are happening at this point, but you now realize that you need a new column. However, the next turnaround is in two years. You will have to shutdown the unit in the current year, but the excess emissions from a shutdown and cleanup are not written into your plan or your permit. This is a SMSS event. You have the time to alert TCEQ because nothing is urgent (for now), but this is still outside of your permitted emissions. This is not routine, but you do have time to discuss this with TCEQ.

Consider a final scenario, perhaps a few weeks later, a pinhole leak bursts from that same column that resulted in emissions greater than permit limits. This would be considered an unexpected EE.

Representing MSS Emissions in the Emissions Inventory

Now that the terms are clear, it’s important to understand how these different situations should be represented within the AEI. Our focus will be representing MSS emissions.

TCEQ has developed a hierarchy for representing MSS emissions in the AEI because there is a preferred way of including this information. Disclaimer to those attempting this for the first time: TCEQ suggests gathering your data, building a plan, and calling them to propose it before taking next steps.

The hierarchy for inputting MSS emissions data is as follows:

1. No Structure Change- Enter all the emissions as if they occurred from the one emissions point. There should be no structural addition (e.g., no changes to emissions sources, points, abatement devices, or emissions data) to the AEI. The emission point should contain both normal operational emissions and MSS emissions.

2. New MSS Emission Point Number (EPN)- Under the same Facility Identification Number (FIN) there would be two different  EPNs: one for regular emissions and another for MSS emissions.

3. New MSS Group FIN and EPN- This option would allow a new FIN that was broad and contains the MSS emissions of multiple pieces of equipment grouped together. In the example of a group of tanks, report regular emissions as their normal FIN and EPN. Then create a FIN and EPN called “Tanks 1-10 MSS” and report all their MSS emissions in that line.

4. Site Wide MSS Path- This is similar to the above example except there are no groups. There would be a “Site Emissions MSS” path that contained all the MSS emissions lumped together.

5. New Path with New FIN- This is not preferred. It involves a new FIN and path for each piece of equipment that is labeled “MSS.” It creates a lot of duplicates in the system and therefore should be a last resort.

These are the options that TCEQ laid out at the workshop. We recommend that you give TCEQ a call before embarking on a large emissions inventory and/or revisions. If none of this is your cup of tea, feel free to connect with me about this topic or a wide range of others.  I can be reached at rhenn@all4inc.com or 281-201-1244 .


    Sign up to receive 4 THE RECORD articles here. You'll get timely articles on current environmental, health, and safety regulatory topics as well as updates on webinars and training events.
    First Name: *
    Last Name: *
    Location: *
    Email: *