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Emission Measurement Center

Method 9 - Visual Opacity

Text of Test Method 9 - Visual Opacity PDF file
Visible Emissions Field Manual PDF file
Visible Emissions Evaluation Procedures Course PDF file
Collaborative Study PDF file
Optical Properties and Visual Effects of Smoke Stack Plumes PDF file
Section 3.12 of the QA Handbook, Volume III PDF file
VE Certification Program Evaluation Form PDF file
Self-Audit Guide for VE Certification Programs PDF file
QA Guideline for VE Training PDF file
Smoke Generator Troubleshooting PDF file
Guidelines for Evaluation of VE PDF file
Guidelines for QA Program for VE PDF file
VE Program Operations Manual PDF file
Instructions for VE Observation Form PDF file


When performing a Method 9 observation, what is the correct procedure for calculating an opacity average if one or more 15–second readings are missed (plume rolling, plume obscured by fugitive emissions, distraction, etc.)?

If, for any reason, a 15-second reading is not made, a dash should be placed on the data sheet for that 15-second interval, and an explanation should be provided in the comments section of the data sheet. Running averages can include a time-lapse break in the opacity readings when caused by an event that would make taking a valid reading difficult or impossible (for example, plume obscured by fugitive emissions, plume rolling, or an improper background). Running averages should not include a time-lapse break when a valid reading could have been made, but was not (e.g., because the observer had eye strain or was distracted). In calculating running averages, you must still use 24 consecutive readings which are then summed and the total divided by 24 to yield the opacity average. For a more detailed description of the procedure, see Sections 6.1 and 4.3.2, I and J of the QA Handbook here.

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