Evaluated Effectiveness of Varying Gas Leak Detectors for Methane Leaks on Northeastern University Campus**
By Joe Platte, Nirali Thakor, Kai Gravel-Pucillo, and Katie Neinast_
Gas leaks pose a great threat to society causing pollution and potentially combustible gases to be undetectable by the naked eye. As a result, methane, the primary constituent of natural gas, can be hazardous and lethal if ignited. This research primarily focuses on the usage of three different sensors: the Bascom-Turner Gas Sentry detector, the Yeezou portable gas leak detector and the Perfect Prime sensor. These were used at two different locations on Northeastern's Boston campus; Chicken Lou's and Ruggles Street. The data was then visualized through graphs comparing the concentration levels to the approximate distance from the point of highest concentration to determine the center of the leak. Maps were also digitally created to represent the data points and make an analysis of the sensors possible. The analysis provided in this research can be used as a resource to identify future gas leaks and determine which sensors allow for more reliable and affordable data collection.
Gas leaks represent a virtually invisible risk to society. Apart from a few indicators (road markings, holes drilled by gas-providing companies, localized dead plants, the smell of gas) of which most citizens are not made to be aware, these polluting and potentially combustible gases are not visible to the naked eye and, for the most part, go largely unnoticed by the greater population. As a result, the invisibility of a gas leak can pose a major risk to society resulting in spontaneous combustibility if ignited, and leading to detrimental fires and explosions. Methane, which is the primary constituent of natural gas, is a "potent greenhouse gas whose global warming potential is 34 to 86 times greater than carbon dioxide" (Hendrick 2016, p. 710). It is also considered as a simple asphyxiant which means that it can displace oxygen from the air. If the leak is in a small-enclosed space, the resulting lack of oxygen may result in "hypoxia, headaches, decreased vision, fatigue, shortness of breath and loss of consciousness" (British Columbia Drug BCDPIC).
Gas leaks can be broken down into three different categories. A Grade 1 leak represents an existing or probable hazard to people and requires immediate repair or continuous action until the conditions are no longer hazardous. This would be a reading that is greater than 80% of the Lower Explosive Limit (LEL). A grade 2 gas leak is "a leak that is recognized as being not hazardous at the time of detection but justifies scheduled repair based on the potential for creating a future hazard." (Washington State Legislature) LEL is a measure of flammability and the percentage value means the "lowest concentration of a gas or vapor in air capable of producing a flash of fire in the presence of an ignition source". The LEL of methane is 5% (NIOSH), so a grade 2 gas leak has a LEL of 20% to 80%.
Not only do gas leaks waste energy and money, they also contribute to greenhouse gas pollution in a significant way, with methane alone accounting for a total of "10% of all U.S. greenhouse gas (GHG) emissions" (Hendrick, 2016, p. 7). Researching and examining gas leaks remains a salient issue, especially considering the consistency of most of the leaks which can often be a result of how long they frequently go unrepaired. Part of the reason gas leaks go neglected for such lengths of time is due to the energy and resources required to dig up and rebuild the roads that sit on top of the gas pipes requiring repair. As one of the nation's oldest major cities, surrounded by countless universities, Boston's aging natural gas pipes are prone to corrosion and leaks. In response, this project aims to examine data collected on gas leaks at Northeastern's campus, primarily at 50 Forsyth Street (the address of restaurant Chicken Lou's) and 480 Ruggles St utilizing three different methane sensors. Our primary objectives include researching the following questions: First, can we detect a grade 2 leaks using three available gas sensors? Second, how can we identify the physical signals that might help us to better discover gas leaks? And finally, are there any measures we can take to better inform campus members and students about any identifiable leaks on campus, that might prove applicable to the greater community?
Methods and Materials**
To collect data on the gas leaks, three different sensors were used at both the Ruggles St. and the Chicken Lou's sites which were each reported to have had grade 2 leaks within the last several years according to the HEET gas leak map. The first of the sensors was a professional-grade, portable Bascom-Turner Gas-Sentry detector at a price point of around $1000. The second sensor used was the Yeezou portable gas leak detector which sold on Amazon for $30. The last sensor used was the Perfect Prime portable gas leak detector which sold on Amazon for $22.
For the Bascom-Turner sensor, a straw-like probe projecting from the monitor measures the percentage of gas in the area of detection. The Yeezou sensor presents the concentration of gas in terms of a scale from 1-6 with 6 being the most concentrated, and it has a sensitivity dial that can be adjusted. When using the Yeezou, the sensitivity dial was turned all the way up until a leak was detected, then the dial was turned down to the lowest setting that still detected the leak to get a more accurate reading of the scale at which the leak read. The Perfect Prime sensor requires a 200 second warm up period and presents gas concentrations in ppm, lighting up green, orange, or red according to the severity of the concentration of the leak with red being the most concentrated.
At each of the sites, gas leaks were identified by the yellow painted markings on the road from National Grid on or around small holes drilled into the ground. To collect data, each of the sensors was inserted into the holes to get as precise a reading as possible. The weather, date, time, weather conditions, date of gas leak report, National Grid gas leak grade classification, and gas leak read were recorded for each sensor at each location. In addition, the total distance of the spread of the holes at each site was recorded so that the distance from the hole with the highest concentration could be determined.
This data was visualized through graphs comparing concentration levels to the distances from the point of highest concentration in order to potentially determine the approximate center of the leak. The averages of the % gas between points was used as the response variable to show the changes in concentration between readings. Maps of the sites were digitally recreated to organize the data points.
Table 1: Feature Comparison of Sensors
Site Classification Information
Table 2: Site Information and Classifications
Site 1: Ruggles Street
Figure 1: Ruggles Street Gas Leak Map (not to scale)
Table 3: Ruggles Street Gas Leak Data
Table 4: Distances from highest reading and average % gas between points
Figure 2: Scatter Plot of Distance from Highest Reading Vs. Average % Gas for the Ruggles Leak
Site 2: Chicken Lou's
Figure 3: Chicken Lou's Gas Leak Map (not to scale)
Table 5: Chicken Lou's Gas Leak Data
Table 6: Distances from highest reading and average % gas between points
Figure 3: Scatter Plot of Distance from Highest Reading Vs. Average % Gas for the Chicken Lou's Leak
As depicted in Table 1, the Bascom-Turner sensor was the most expensive at about $1000 USD, yet featured the widest array of measurement forms including LEL, percent gas, and ppm. The Yeezou and Perfect Prime sensors were significantly less expensive (at about $30 and $22 USD, respectively), yet featured fewer forms of measurement: The Yeezou sensor was only able to convey the absence or presence of a gas leak, while the Perfect Prime sensor was limited to ppm.
Site Classification Information
Both sites were classified by National Grid as a grade 2 gas leak (Table 2). The Ruggles Street leak was reported in May of 2015, about 4.5 years before our examination of the site, while the Chicken Lou's leak was reported in April of 2018, a little over 1.5 years prior to our site analysis (Table 2). The data collection was conducted between 11:30 AM and 12:30 PM on November 25th of 2019, and the weather was around 52 degrees with a moderate breeze and no precipitation (Table 2).
Sites 1 and 2: Ruggles Street and Chicken Lou's
Figures 1 and 3 depict maps of the examined locations (not to scale), reduced to sites of data measurements and relevant landmarks. Each location where data was collected is labeled with a location number (1-12 for Ruggles Street and 1-5 for Chicken Lou's) that corresponds to the data presented in the respective table (Tables 3 and 5).
Tables 3 and 5 outline the measurements found using the various sensors at each location, as well as the timestamp of when the measurements were taken. "ND" stands for "No Data," which was applied when the sensor was unable to provide an accurate or consistent reading, or otherwise malfunctioned. We were only able to obtain one consistent reading at the Ruggles Street site (location 1) and one consistent reading at the Chicken Lou's site (location 2) using the Perfect Prime sensor. The Yeezou sensor is intended to measure the presence or absence of a gas leak and not provide a specific measurement; therefore a value of 0 for this sensor indicates an absence of a gas leak while a value of 1 or higher indicates the detection of a gas leak. At Ruggles Street location 3, three measurements were taken at different times across a span of roughly five minutes with varying magnitudes represented, demonstrating that the quantity of gas leaking from each location is likely to fluctuate over time (Table 3).
Conclusion and Limitations**
While the Bascom-Turner Gas-Sentry detector was clearly the most detailed and accurate gas leak detector, its use in citizen science would be quite limited due to its price point. Based on the data collected, the Yeezou sensor is the most recommendable gas leak detector for use in citizen science. While this sensor is limited to indication of presence or absence of a gas leak, it is easy to use and shows clear, accurate results on top of being affordable.
The data from the Perfect Prime sensor was virtually unusable. One of the sensors would shut off immediately after sensing a leak, making it impossible to take a reading, while another of the sensors consistently displayed very high readings regardless of proximity to the source of the leak, making the accuracy of the readings invalid. While this sensor was the most affordable, it was clearly the least effective device available for citizen science use. Based on the inability to collect accurate data with this sensor, it cannot be recommended as a sufficient tool for gas leak detection since its value seems to be limited to only accurately detecting a binary reading of either presence or absence of a leak at an incredibly short range. Even then, one of the Perfect Prime sensors always displayed the presence of a leak whether or not it was near one.
Overall, the Yeezou sensor is an affordable tool for detecting the presence or absence of a natural gas leak, making it well-equipped for everyday use. An individual would benefit from purchasing a Yeezou sensor to identify the locations of local gas leaks, while a community organization may see it fit to purchase the more expensive Bascom-Turner sensor to revisit these locations and gather specific data on the quantity of gas being omitted from these leaks.
Our data demonstrates that the Yeezou sensor will sufficiently identify the location of gas leaks, while the Bascom-Turner sensor can be used to get a better sense of gas quantity and the epicenter of the leak.
Comparing our two graphs reveals a normal distribution of the data from the Ruggles street leak (Figure 2), indicating that the epicenter of the gas leak was approximately between points 9 and 10, while the gas leak in front of Chicken Lou's maintained a fairly constant level of gas emission across the length of the leak site. Nine days after our survey, National Grid returned to the site of the gas leak by Chicken Lou's and reevaluated the leak, determining it to have escalated to a Grade 1 leak, at which point they drilled into the road to repair the leak. This would explain the near-constant level of gas leaking across the 35ft radius of the measured site, as the gas was likely escaping the gas pipe faster than it could exit from beneath the road, causing even diffusion of the gas beneath the street and thus resulting in the change in classification from a Grade 2 to a Grade 1 leak.
It may be feasible in the future to utilize other technological resources in order to identify gas leaks and to see if we could further assess the size of the leaks. These sensors were able to detect the leaks and quantify them at a relatively affordable price (except for Bascom- Turner sensor), however, it may be beneficial to utilize other forms of technologies such as drones and program them to locate a gas leak more precisely. Furthermore, it may be feasible to see if we can develop a phone app that would alert students at Northeastern when they are approaching a gas leak. It can also be beneficial to post the data online or to make the leak visually apparent to the public by posting information about the leak at the site so that when people walk by they can learn about these invisible risks.
- HEET Gas Leak Map: https://www.google.com/maps/d/u/0/viewer?mid=1UYDq5GYgwqDi-VbcGsiTFmlebgk&ll=42.32341330869828%2C-71.11165624636845&z=11
- Perfect Prime Sensor Website: https://perfectprime.com/products/ga0080
- Yeezou Sensor Website: https://yeezou.com/product/gas321/
- Gas Sentry Sensor Website: https://www.bascomturner.com/store/index.php?main_page=product_info&products_id=446
- https://www.sciencedirect.com/science/article/pii/S0269749116300938- Hendrick reading
- Health Effects: http://www.dpic.org/faq/natural-gas
- Grade 2 leak: https://apps.leg.wa.gov/wac/default.aspx?cite=480-93-18601
- Leak description: https://www.cdc.gov/niosh/docs/2014-100/pdfs/2014-100.pdf