Air

“Smoke School” Prepares Air Quality Inspectors to Read Visible Emissions

By Kirsten Delamarter

Every six months, Division for Air Quality (DAQ) inspectors calibrate what may seem like an unexpected instrument: their eyes.

On a sunny September morning, a group of inspectors gathered in a large parking lot, clipboards in hand, observing the emissions from a smoke-generating machine. From under a tent, the smoke school instructor turned a knob to adjust the opacity of smoke before sending a plume into the air.

With the proper training, DAQ inspectors can determine whether too much of a harmful contaminant is being released into the surrounding air by observing a plume of smoke billowing from a smoke stack. To receive that training, they attend “Smoke School.”

“Alright guys, go ahead and look up here at 50 — 50 percent opacity,” the instructor called through the PA system. “It’s half smoke, half light.”

The U.S. Environmental Protection Agency has conducted extensive field studies on the accuracy and reliability of this technique, called Method 9, and found that it is a reliable way to “read” smoke and other visible emissions, as long as the eye is properly trained.  The method allows for easy and cost effective monitoring of emissions without the need for expensive electronic devices to be installed in multiple stacks.  

Every spring and fall, DAQ inspectors attend smoke school to become re-certified in Method 9 as required by the U.S. EPA. DAQ personnel gathered in Louisville for the 2-day training.

“If you don’t use it, you lose it,” said Frankfort DAQ Field Office Supervisor Natasha Parker, who has been attending smoke school for the past 12 years. “… It’s just keeping up with our (eye) calibration, even though our instruments are biological.”

Becoming a certified smoke reader

The key to “reading smoke” is not actually looking at the smoke itself but rather looking through it.

Reading a plume is an assessment of its opacity, or the amount of light passing through it, Parker said. Generally speaking, the thicker the smoke — or the higher the opacity — the more pollution that is being omitted. Facilities that release regulated pollutants are required by the Clean Air Act to have an operating permit, which among other things places limits on the opacity of smoke or certain other visible emissions. 

To ensure that a facility is complying with the opacity limits in its operating permit, a Method 9 certified inspector will stand in front of the smoke stack and observe the smoke and objects that may be behind it.

“If you have an object behind it, you’re trying to look through the smoke and see how much of the object behind it you can see,” Parker explained. “If it’s 50 percent opacity, you should be able to see 50 percent of the object — maybe it’s not real clear, but you can still kind of see it. If it’s 100 percent opacity, you shouldn’t be able to see anything behind (the smoke) at all.”

Eastern Technical Associates use a smoke generating machine to train public regulators and members of private industry to “read” the opacity of a smoke plume. Photo by Kirsten Delamarter.

The Louisville training was conducted by Raleigh, North Carolina-based company Eastern Technical Associates (ETA). Each year, ETA certifies roughly 10,000 “smoke readers” across the U.S., as well as in Puerto Rico and Jamaica, ETA field instructor Kevin Bumpass said.

The first day of Smoke School consisted of a classroom session, attended by all first-time smoke readers as well as some DAQ veterans as a refresher. There, participants learned about the history and mechanics of Method 9. 

The next day, participants gathered outdoors at E.P. Tom Sawyer State Park to put into practice the lessons learned in the classroom. ETA demonstrated different opacities of smoke using a traveling smoke generator, which vaporizes diesel to create white smoke and inefficiently combusts an industrial paint thinner to generate black smoke. Factors such as weather condition, sun angle and cloud cover can affect the opacity readings, which is why Method 9 specifies that the observer must stand with their back to the sun, a certain distance away from the smoke stack. 

After several practice runs, ETA conducted the actual certification test. An instructor released a plume of smoke from the generator, and participants examined it. The participants marked on their test sheet what they observed the opacity to be in percent of opacity. Students then look away until the tester is ready for the next reading. 

During an actual Method 9 inspection, they have  to rest their eyes for 15 seconds between readings.

 “If we just stare at it the whole time, you get eye fatigue,” Parker said. “That can mess you up and make you think you’re seeing something you’re not really seeing.”

In order to pass the test, participants must correctly identify the opacity of 25 black smoke plumes and 25 white smoke plumes within 15 percent opacity of each plume and without the overall average error exceeding 7.5 percent opacity in each category.

The pass rate is roughly 90 percent, and if a participant doesn’t pass, he or she is not allowed to perform Method 9 inspections until they can re-test. It can be a stressful and challenging test, which is why DAQ staff celebrates one another’s Smoke School victories, Parker said.

“We’re like a big family,” she said. “Every time we pass, we’re like, ‘woohoo!’ and we try to cheer each other on.”

Socially distanced inspections

Air quality inspectors use Method 9 because it is the method required by the EPA, but it has proven to be particularly useful during the coronavirus outbreak. 

Smoke school instructors lead a Method 9 training in Louisville. Photo by Kirsten Delamarter.

Because Method 9 testing takes place outdoors and does not require face-to-face interaction with other people, it allowed the division to continue its inspections, even when many facilities were closed to visitors due to COVID-19. Smoke-reading enabled inspectors to confirm whether facilities were complying with the opacity standards outlined by their permits, Parker said.

In the field, if inspectors find that a facility is not in compliance, it must take corrective action and could face a penalty.

Parker said the inspections ultimately exist to minimize air pollution, which affects public health and overall quality of life.

“Most of the facilities are 100 percent on board with us — They say ‘We want to comply. We don’t want to pollute,’” she said. “They live in the world too. Everyone breathes the same air.”


The Division for Air Quality (DAQ) with the Energy and Environment Cabinet works to protect human health and the environment by achieving and maintaining acceptable air quality through operation of a comprehensive air monitoring network, creation of effective partnerships with air pollution sources and the public, timely dissemination of accurate and useful information, the judicious use of program resources and maintenance of a reasonable and effective compliance assurance program. Learn more about DAQ here.

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