The OGI Camera vs. the Method 21 Device
April 22, 2023
Which Is Better: The OGI Camera or the Method 21 Device?
Maybe you’ve heard or said something along these lines: “Well, that’s a real fancy camera, but you can’t measure a leak with that!” Sound familiar?
In a previous blog post, we addressed some of the regulatory fears and financial concerns that cause hesitation in adopting Alternative Work Practice (AWP). Here, we’re going to compare the technologies of AWP and Method 21: The Optical Gas Imaging (OGI) camera and the handheld gas detector.
Rate measurement
First up, let’s talk about quantitative leak rates. Naysayers of AWP point out that OGI cameras can’t provide a quantitative leak rate. Well, they’re right. But neither can Method 21 devices.
What a Method 21 device does is give a concentration reading of parts per million (ppm) at a single point. Per Method 21 regulation, that reading is then used in an emission factor correlation equation from the EPA to calculate a leak rate. In other words, it doesn’t give you a flow rate.
On the other hand, what an OGI camera provides is a quantitative estimate of how big a leak is. And this estimation is more than 1000x accurate than Method 21 ppm readings over the full range of leak rates. We’ve got the data to prove it, too.
In the following table, you’ll see a range of ppm readings and emission rates determined using the EPA correlation equation. In the fourth column, you’ll see the actual emission rates for each ppm reading.
**Table taken from screenshot at 18:34 of webinar video**
These readings are based on thousands of emission leaks in which we took a ppm reading but then subsequently measured the same leaks with a hi-flow sampler. As you can see, the correlation factors are fairly accurate when measuring leaks between 500 to 100,000 ppm. But when leaks reach a certain size, the correlation estimates start to diverge significantly.
The difference between a small leak and a large leak is vast when you’re measuring leak rates. But if you’re using emission factors and ppm readings, the difference between a small leak and a large leak isn’t that big. It’s quite a small range. The correlation factors simply don’t work for large leaks. Speaking of leak size, that brings us to our next measure of comparison.
Detection based on leak size
“Hey, we find more leaks with Method 21 because the camera can’t see 500 ppm leaks.”
Fair enough. A Method 21 device will find the smaller leaks that an OGI camera can’t see. But those small leaks make up a very minute portion of the total emissions from a facility. The reality is that the larger leaks make up the bulk of the volume. That means finding the largest leaks and repairing them faster make a much larger impact than finding the small leaks.
Think of a Method 21 device and an OGI camera as tools used to find needles in a haystack. Using Method 21, you’re forced to pick up and feel each individual piece of straw to make sure it’s not a needle. With OGI, you simply look at the haystack to see exactly how many needles there are and where they’re hiding. An OGI camera works a lot like a magnet, pulling the needles out of the hay so you don’t have to search each individual piece of straw.
And while some of the needles are microscopic, other needles can be the size of a car. You obviously want to get the biggest needles out of the haystack first since they’re the most dangerous. An OGI camera makes it easy to see which needles are the largest. Meanwhile, a Method 21 device treats all needles the same, so you may end up finding a microscopic needle but not that sedan-sized one right beside it.
A real-life comparison of OGI and Method 21 technologies
A Montrose client operating an LNG Liquefaction and Export Terminal contracted us for an AWP monitoring program. Their facility contained over 130,000 components. Our annual Method 21 survey schedule of the facility overlapped with our implementation of OGI inspections. This gave us the opportunity to see how the two methods stacked up in a real-world scenario. The findings are in the table below:
**Table taken from screenshot at 22:00 of webinar video**
While the Method 21 device found more of the leaks (60%), the actual sizes of those leaks were smaller than the ones found using an OGI camera. The OGI-detected leaks made up 90% of the total emission volumes. If we apply how much faster these leaks were found, this equates to 99.92% emission reduction versus the Method 21 program.
This table doesn’t consider detection date and repair date impacts, which are significant. Even though you may miss small leaks during an OGI survey, they account for a small part of the facility’s leak profile. Going after those big leaks and repairing them faster will make the most significant impact. To do so, operators must shift their mindset to prioritize leak rates over leak count.
Another example of good measure
In another facility, a connector leak was found using an OGI camera on January 14th, 2019. The leak is what we would consider to be medium sized, which is about a leak rate of 100,000 ppm or .32 cfm.
**Table taken from screenshot at 24:23 of webinar video**
If we take that medium-sized leak of about 100,000 ppm and assume it had existed for roughly 14 days (given that the OGI inspection was done on January 14th), then approximately 6,451 cubic feet of gas was emitted before the leak was found.
Now imagine if we had been maintaining Method 21 program instead of AWP. This facility would only conduct annual inspections of connector components, per state and federal requirements. So, it’s very likely that the connector leak could go undetected for 365 days. Here’s a quick breakdown of how the emission volumes would increase had the leak been detected via Method 21 at any point during that time:
Possible times of detection using Method 21
If AWP wasn’t in place and Method 21 had been the only survey method used, the facility could have experienced an increase of 2 to 25x emissions.
Pound for pound, OGI cameras are the super technology for leak detection
The volume of medium-to-large leaks found sooner with AWP significantly outweighs the volume from smaller leaks that may be below an OGI camera’s detection limit (up to 10,000x greater). You can learn more about AWP here. Or, if you’re ready to take the next step in implementing AWP as part of your LDAR program, get in touch.
