Our previous post contained an overview of continuous emission monitoring systems, known more familiarly within the industry as CEMSs. I also mentioned that the mere mention of a CEMS can strike fear in the heart of most any facility manager, simply because there are so many problems associated with the systems.
But with a little planning, you can greatly minimize the probability of these headaches, even with a system that is in — as its name implies — continuous use. Here are some of the most common CEMS-related problems and what you can do to minimize the chances they rear their ugly heads.
Not Following the QAP (Quality Assurance Plan)
To maintain compliance, almost all regulations require a CEMS to be in “good operating condition” — which boils down to maximizing the amount of accurate data while minimizing the use of missing data procedures. To reach that goal, each CEMS should have a quality assurance plan (QAP) that outlines what is needed to ensure the system is collecting accurate data.
Problems often arise simply because folks don’t follow their QAP, including basic steps such as not performing maintenance at the manufacturer-recommended intervals.
Solution: Have a QAP in place — and stick to it. You’ll minimize not only the amount of missing data but also the amount of potential AQMD violations.
Missing Data Procedures
Missing data procedures are established methods for removing certain data and replacing it with new data when a system has malfunctioned or is unable to collect valid data. There are numerous types of missing data procedures, so to know which one you should use, refer to the rule that required the CEMS in the first place.
Missing data is the first part of your problem. But it gets worse: The problem is compounded if a system uses an incorrect missing data procedure (i.e., not the one prescribed by the rule for which the CEMS was installed), which can often result in inaccurate reported emissions.
Not too long ago, there were only a few types of data systems available, several of which have historically been found to apply missing data procedures incorrectly. The problem is further exacerbated if the missing data is noticed too far down the line, such as when someone takes a deep data dive, usually during an annual audit or inspection, which may happen years after the error occurred.
Solution: Since the use of missing data procedures almost always leads to an overestimation of the emissions from your equipment, it’s good practice to schedule regular review of the CEMS data to make sure everything’s running as smoothly as it should.
Calibration Gas Availability
As part of the EPA’s QA/QC (quality assurance/quality control) requirements, a CEMS must undergo a daily calibration. Sometimes, problems arise with these calibrations when there isn’t enough gas in the system’s bottle and there isn’t a spare bottle in inventory.
Murphy’s law requires systems to run out of gas at the most inconvenient time, such as during a weekend or holiday when no one is around to change out the bottle. The problem only worsens when you discover your vendor can’t get your custom gas blend for several weeks.
In most cases, if a CEMS cannot complete a daily calibration, the data collected that day is considered to be invalid. In order for collected data to once again be considered valid, the system must pass a successful calibration (which can take days, weeks, months or longer) and missing data procedures must be used.
Solution: Make it a part of your facility’s regular schedule to check the gas bottle on a regular basis, and to double-check before a holiday or weekend. Keep extra calibration gas on hand as a backup. As a backup to your backup, ask your gas vendor to keep an inventory of gases for you at their facility so that you can always get a bottle if you run out. If you want to be triply secure, you can even have two gas vendors, just in case one falls through.
As with any system with a lot of moving parts, things break down. With a CEMS, if one part goes, it might cause the entire system to fail — kind of like an old set of Christmas lights where a single faulty bulb could make the entire string go kaput.
For example, if the sample pump breaks, there’s no way to get the sample from the exhaust stack into the CEMS for analysis, which means the CEMS can’t do its job of collecting valid data (and you’ll have to rely on the dreaded missing data procedure mentioned above).
Solution: Keep an on-site inventory of spare parts so that repairs can be made as quickly as possible to minimize downtime. Just remember that not all parts of a CEMS can be changed out freely; in some cases, replacing a part will require a calibration, while extreme situations will require a whole new RATA (relative accuracy test audit) to re-validate the system. More info can be found in AQMD Technical Guidance Document R-002.
System Breakdowns & Malfunctions
As with any piece of machinery, a CEMS can malfunction — or even break down completely. If this happens, refer to the rule that required the CEMS to determine how to deal with the breakdown (usually by notifying the agency and reporting).
For example, in AQMD Rule 218:
The CEMS owner or operator shall notify the Executive Officer within 24 hours or the next working day, in the event of a system failure or shutdown, which exceeds 24 hours.
There may also be cases where a variance petition is needed to allow a facility to operate in compliance with a CEMS broken for more than 96 hours.
Regardless of time limits, when a CEMS breaks or malfunctions, it’s best to get the unit back online as soon as possible, so concentrate on getting the system back up and running rather than reading and interrupting rules.
Solution: Have a procedure prepared that outlines how you will respond to a CEMS breakdown, including having a draft variance prepared in case one is needed.
Did we miss a SEMS problem in the list above? Let us know in the comments, or send us a message describing your experience.