Maintaining Opacity Systems for Compliance


Maintaining Opacity Systems for Compliance

Ongoing requirements of a Continuous Opacity Monitoring System (COMS)

Having a certified Continuous Opacity Monitoring System (COMS) carries requirements for testing and maintenance in order to keep that monitor operational and demonstrate continued compliance.  There are four major areas to address:

  1. Quarterly Preventative Maintenance
  2. Quarterly Filter Audits
  3. Annual Clear Stack (or Off-stack) Audits
  4. A QA/QC Manual

continuous opacity monitor

Quarterly Preventative Maintenance

Every opacity unit needs attention on a regular basis:

  • Typically, a blower system is included to keep the ports clean and with that is a requirement to change the blower filter(s).
  • The lenses and mirrors need to be cleaned as dirt build-up will create a false reading.  The type of cleaning cloth is important - never use a shop rag, even a clean one, as they are often lightly oiled.
  • The alignment needs to be checked and the unit re-aligned if necessary.

continuous opacity monitor

Quarterly Filter Audits and Annual Clear Stack

  • Quarterly - EPA regulations require quarterly opacity filter audits.  Each quarter the opacity unit is challenged with three (most States require three, some States require 4) filters of varying opacity values (zero, low, mid & high).  Each filter is run five times and the values recorded.  The readings are checked to make sure they are within a required percentage of the filter value.  A complete report is assembled and kept at the plant in the event of a compliance audit.
  • Annually - Once a year the opacity unit is taken off the stack for a complete filter audit.  This is called a Clear-Stack Audit (or sometimes an Off-Stack Audit).  This must be done with the opacity unit attached to it's final recording device.  This can be done outside or indoors, as long as the test stands can be separated far enough to match the stack flange-to-flange distance.  Again, the final report should be kept on file in the event of a compliance audit by a regulatory agency.

QA/QC Manual

The EPA regulations require Opacity users to have a Quality Assurance/Quality Control Manual to detail the steps that are taken to maintain their compliance monitor.  This is a "plant-specific" manual that includes an organization chart and a complete list of daily, monthly, and annual QA/QC activities. 

Typically compiled by the equipment supplier this manual details the instrument completely from measurement technology to operation description, to formulas and calculations used in determining opacity values.  It's an extensive document that sets out how the Continuous Opacity Monitoring System (COMS) will be proven reliable and in compliance throughout its lifespan.

Happy to help.

Monitoring Solutions is your full-service provider of opacity systems and ongoing maintenance and compliance testing.  Give us a call at 908-500-4010 or email us at and we will assist you any way that we can.

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