Expert insight: test method basics for oxidizer permit requirements

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Courtesy of Catalytic Products International (CPI)

Whenever a new oxidizer is installed to control Volatile Organic Compound (VOC) emissions, the question often comes up: What test method should I use to demonstrate that the device meets permit requirements?
 
Most states allow you the choice of three EPA Test Methods: 18, 25 and 25A. Of these, use of Method 25A is usually the most desirable, for a few reasons. One, Method 25A provides real time results, so you will have certainty that the control device is operating properly while the test company is on site. Second, Method 25A is far less interference prone than Method 25 and generally less expensive than both Method 25 and Method 18.
 
Method 25A uses a device called a Flame Ionization Analyzer that detects hydrocarbon compounds. It reports the concentration of all hydrocarbons as a single reading. That is, Method 25A is not designed to distinguish individual compounds.
 
It is important to note that, per EPA guidance, Method 25A can only be used if the total VOC concentration in the outlet of the control device is less than 50 parts per million (as carbon). However, methane and ethane do not count as VOCs, so provisions should be made to measure methane and ethane in the event that it is necessary to subtract those two compounds to get under the 50 ppm line.
 
Finally, the presence of high concentrations of certain chlorinated or oxygenated hydrocarbons can interfere with the accuracy of Method 25A results. Examples of such compounds include chemicals like methyl chloride, acetic acid and methanol. If your exhaust stream contains significant amounts of such compounds, modifications to Method 25A or the use of another test method may be indicated.

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