Fenceline monitoring at industrial sites: continuous monitoring and emission detection

Fenceline monitoringAtmospheric conditions are essential to prevent damage to human health and to reduce the causes of increased mortality or serious effects of exposure to po...
Read more in industrial facilities makes it possible to continuously measure pollutants at the industrial perimeter, including volatile organic compounds (VOCs), methane (CH₄)Methane, known chemically as CH₄, is a gas that is harmful to the atmosphere and to living beings because it has a high heat-trapping capacity. For this ...
Read more, hydrogen sulphide (H₂S)Hydrogen sulphide (H2S), also known as hydrosulphuric acid or sewer gas, is a gas unmistakable due to its characteristic rotten egg smell, noticeable even ...
Read more, sulphur dioxide (SO₂)Sulphur dioxide (SO2) is a colourless gas with a pungent odour that causes an irritating sensation similar to shortness of breath. Its origin is anthropoge...
Read more and particulate matter (PM)Atmospheric particulate matter are microscopic elements suspended in the air, consisting of solid and liquid substances. They have a wide range of sizes an...
Read more, among others, detecting real emissions in real time. Thanks to Kunak fenceline monitoring sensors and IoT networks, industries can ensure control of industrial emissions, comply with European and North American regulations (EPA, IED), prevent incidents, optimise operations and protect the health of nearby communities through a reliable, continuous and traceable perimeter safety monitoring system.

This is why, since 2018, the US EPA has required all refineries in the country to deploy continuous monitoring systems at the industrial fenceline to measure concentrations of air pollutantsAir pollution caused by atmospheric contaminants is one of the most critical and complex environmental problems we face today, both because of its global r...
Read more as hazardous to nearby communities as benzene (a highly toxic VOC) along the full length of their fenceline. The rule (under 40 CFR § 63.658 approved in 2015) is unambiguous: if the annual average benzene concentration at the perimeter exceeds 9 μg/m³, the facility must activate a root cause analysis protocol and apply corrective actions.

The logic is the same on the other side of the border. In Canada, under Ontario provincial regulations, Imperial Oil’s Sarnia refineries are demonstrating the value of fenceline monitoring following the implementation of an extensive LDAR programme (Leak Detection and Repair) with which they have reduced benzene emissions by 88% .

These are not isolated cases. In Saudi Arabia, one of the largest petrochemical complexes in the world has deployed four real-time analysers distributed around its perimeter, each covering ten sampling points, to ensure regulatory compliance and immediate detection of any VOC leak.

In Europe, the revision of the Industrial Emissions Directive (IED 2024/1785) is redefining environmental control requirements for thousands of industrial facilities, with new obligations that will push many industrial plants to move from point-in-time measurement to continuous monitoring at the industrial perimeter. The regulatory, technological and social context is converging on one conclusion: measuring at the stack is no longer enough.

This article analyses in detail what a perimeter emissions monitoring network is, which pollutants it measures, how it is designed and integrated into cloud platforms, and how it turns industrial environmental compliance into a real operational advantage. It also addresses the role of near-reference sensors for industrial emissions control, the logic of industrial emissions reporting and traceability, and the technical criteria that differentiate an effective perimeter network from a sensor installation with no strategy. Because fenceline monitoring in refineries and chemical plants, as well as in any facility with an environmental impact on its surroundings, does not start with the sensor. It starts with understanding exactly which problem needs to be solved.

Perimeter monitoring transforms the relationship between the facility and its social environment.

What fenceline monitoring in industrial facilities is

Fenceline monitoring in industrial facilities is a continuous measurement system for air qualityAir quality refers to the state of the air we breathe and its composition in terms of pollutants present in the atmosphere. It is considered good when poll...
Read more deployed at the physical boundary between an industrial facility and its surroundings. It does not measure inside the plant or at the stacks, it measures at the boundary, where emissions stop being an internal issue and become a real impact on the people, ecosystems and communities around the facility.

The industrial perimeter is not just a line on a drawing. It is the threshold where production activity meets the outside world. And, paradoxically, it is the historically least instrumented point in industrial environmental control. A refinery can have dozens of internal analysers and comply with all stack emission limit values, while at the same time generating concentrations of VOCs, CH₄, H₂S or PM at its perimeter that exceed health protection thresholds without anyone recording them. The perimeter emissions monitoring network resolves exactly that gap.

The global fenceline monitoring systems market was valued at USD 1.8 billion in 2025 and is projected to reach USD 3.2 billion by 2034, with annual growth of 7.2%.

Fenceline monitoring vs point-in-time monitoring

Point-in-time sampling (measurement at a specific moment, at a specific point) has long been the standard practice in many facilities. It is useful for audits and regulatory checks, but it has a structural limitation because it only captures what is happening at that moment and in that place. Emission episodes, however, are discontinuous, variable and dependent on weather conditions. For example, point-in-time sampling carried out on a day of low activity or with favourable wind can produce results that are completely different from what occurs during a process start-up, an operational failure or a high-temperature episode.

Continuous community monitoring networks captured more PM elevation episodes than conventional regulatory monitors, demonstrating that point-in-time sampling systematically underestimates pollution events. Wong, M. et al. (2018).

Continuous monitoring at the industrial perimeter operates with a radically different logic:

• Total time coverage: sensors record data without interruption, 24 hours a day, 365 days a year, without depending on scheduled visits.
• Distributed spatial coverage: an IoT network for emissions monitoring places stations at multiple points around the perimeter, eliminating the blind spots that point-in-time sampling cannot cover.
• Real-time correlation: data are cross-referenced with meteorological variables (wind direction and speed, temperature, humidity) to identify not only what is emitted, but also where it comes from and where it moves.
• Automatic traceability: each data point is recorded with a verifiable timestamp, building an audited history that point-in-time sampling can never match.

Environmental safety and community protection

The real detection of emissions at the industrial perimeter has a dimension that goes beyond regulatory compliance: the protection of people who live and work close to the facility. Pollutants such as benzene, hydrogen sulphide or fine particulate matter PM_2.5 have no impact threshold below which risk is zero. Chronic exposure to low concentrations over time has effects on the respiratory, cardiovascular and oncological health of exposed populations.

An effective perimeter safety monitoring system acts at three simultaneous levels:

• Early detection and warning: it identifies threshold exceedances in real time and activates protocols before the episode escalates.
• Evidence for incident management: in the event of a complaint or environmental investigation, continuous perimeter data are the only objective evidence of what happened, when it happened and at what concentration.
• Transparency with the community: publishing fenceline monitoring data transforms the relationship between industry and neighbours, replacing mistrust with verifiable evidence.

There is no one-size-fits-all configuration for designing a perimeter monitoring network.

Pollutants and critical sources

Not all industrial pollutants behave in the same way, and their presence at the facility perimeter does not pose the same level of risk. Knowing which are the most relevant, where they originate and why they escape conventional control is the first step in designing a perimeter emissions monitoring network that genuinely works.

Volatile organic compounds (VOCs)

VOCs are the group of pollutants most closely associated with fenceline monitoring in refineries and chemical plants. They evaporate at room temperature, disperse easily and many of them (benzene, toluene, xylene, styrene) are toxic or directly carcinogenic under prolonged exposure.

Their most problematic characteristic from a control perspective is that a significant proportion of VOC emissions in industrial environments does not come from controlled sources such as stacks or flares, but from fugitive emissions, including leaks in flanges, valves, compressors, storage tanks and wastewater treatment systems. These emissions are diffuse, intermittent and practically invisible to point-of-emission control. Only the detection of leaks and emissions at the industrial perimeter through distributed sensors makes it possible to identify them, quantify them and correlate them with their origin.

Methane (CH₄) and greenhouse gases

Methane is the pollutant that best illustrates the convergence between industrial environmental compliance and climate objectives. With a global warming potential 80 times higher than CO₂ over a 20-year horizon, CH₄ has moved from being a secondary issue to occupying the centre of the regulatory agenda, especially after the approval of the European Methane Regulation (EU) 2024/1787, which requires companies in the fossil fuel sector to measure, report and reduce their emissions in a verifiable way.

In industrial facilities and power plants, methane escapes mainly through the same mechanisms as VOCs, such as defective seals, relief valves, scheduled venting and leaks in the internal distribution network. Continuous monitoring at the industrial perimeter with sensors calibrated for CH₄, such as Kunak’s, makes it possible to detect these events as they happen, before they accumulate in the annual emissions inventory as an abstract figure. It is the difference between managing methane and merely accounting for it.

Hydrogen sulphide (H₂S) and sulphur dioxide (SO₂)

H₂S and SO₂ are the most characteristic pollutants in perimeter gas monitoring for refineries, petrochemical plants and crude oil treatment facilities. H₂S is generated in desulphurisation processes, sour water treatment and sulphur recovery units; SO₂ appears mainly in the combustion of high-sulphur fuels and in industrial flares.

Both compounds present a dual risk profile, as they are toxic at relatively low concentrations (H₂S has an odour threshold of barely 0.5 ppb, but becomes lethal above 100 ppm) and have direct regulatory implications under the European Industrial Emissions Directive (IED) and the WHO guideline values. A fenceline monitoring network for NO_x, PM and VOCs that does not include H₂S and SO₂ in refining and petrochemical environments is incomplete by definition. The real detection of these gases at the industrial perimeter protects nearby communities and, at the same time, warns of internal operational deviations before they develop into major incidents.

After reducing fugitive emissions from an industrial complex, the benzene concentration at the perimeter fell by 85% and lifetime cancer risk (LCR) dropped by one order of magnitude, reaching acceptable levels according to the WHO. Colman, J.E. et al. (2014).

Perimeter monitoring makes the detection of leaks and emissions around industrial sites a continuous and verifiable process.

Benefits of fenceline monitoring

Implementing a perimeter emissions monitoring network is not only a compliance decision. It is a management decision that makes it possible to move from reacting to incidents to anticipating them, from declaring environmental performance to proving it, and from seeing emissions as an unavoidable cost to treating them as an optimisable variable.

The most immediate advantage of continuous monitoring at the industrial perimeter is the ability to detect fugitive emissions as they happen, not days later when they appear in an audit report. Occasional events, such as an H₂S leak in a desulphurisation unit, an abnormal increase in VOCs at the perimeter during a process start-up or a rise in CH₄ correlated with a relief valve, are some of the events that a well-configured fenceline monitoring system can identify, geolocate and alert on in real time.

This capacity for detecting leaks and emissions at the industrial perimeter has a direct impact on operational safety. If episodes are not detected in time, they do not disappear. They accumulate, worsen and eventually lead to incidents with environmental, regulatory and reputational consequences that are far more costly than investment in the detection system.

Industrial environmental compliance, under the IED and EPA regulations, is no longer based exclusively on point-in-time measurements and periodic declarations. Regulators require continuous, verifiable and traceable data. Perimeter data are the evidence that is hardest to challenge. They have a timestamp, are georeferenced and are generated autonomously, without human intervention in the recording process.

The industrial emissions reporting and traceability generated by a perimeter network properly integrated with cloud platforms makes it possible to:

• Respond to regulatory requests with data that are already structured and auditable.
• Demonstrate continuous improvement trends with verifiable historical series.
• Prove that perimeter limit values are respected both under normal conditions and during start-ups, shutdowns and extraordinary events.

Likewise, every VOC or CH₄ leak that escapes the industrial perimeter is both an environmental impact and a loss of product. In a refinery or petrochemical plant, the compounds emitted fugitively are exactly the same compounds that constitute the raw material or final product of the process. The real detection of emissions at the industrial perimeter not only identifies where the environmental problem lies, but also shows where the economic loss is occurring.

Facilities that have implemented near-reference monitoring systems for industrial emissions control combined with LDAR programmes report notable reductions in product losses, fewer unplanned shutdowns and maintenance management that is more predictive and less reactive. In many cases, the operating cost of the monitoring system is recovered with the first leak identified and corrected before it develops into a major incident.

The communities that live close to industrial facilities have a relationship with those industries that has historically been shaped by information asymmetry, because the plant knows what it emits, but residents do not. This asymmetry generates mistrust, conflict and, in many cases, social opposition that makes it harder to operate and expand facilities that could be perfectly compatible with their surroundings if the data were accessible.

By contrast, a perimeter safety monitoring system that publishes its data in real time transforms that relationship. Not because the data are always perfect, but because their continuous availability demonstrates that the facility has nothing to hide. Industrial sustainability is not declared, it is demonstrated with evidence; and that evidence is stronger when it is generated automatically, every day, at the facility perimeter.

Perimeter monitoring measures, in real time, the concentrations of pollutants released into the atmosphere from an industrial facility.

Implementation of fenceline monitoring networks

Deploying an IoT network for emissions monitoring at the perimeter of an industrial facility is not a matter of installing sensors and waiting for data. It is an environmental engineering exercise that begins long before the first monitoring network station is installed. It is based on analysis of the facility, its emitting processes, its geometry and its relationship with its surroundings. A poorly designed network generates data that are not useful for decision-making. A well-designed network turns the perimeter into the most valuable environmental control system in the plant.

Kunak fenceline monitoring sensor networks are conceived according to the following logic:

• Near-reference devices with IoT connectivity
• Autonomous operation (with optional solar power for remote points).
• Continuous data transmission to a cloud platform for analysis, visualisation and reporting.
• Modular design that allows the network to scale without major additional infrastructure, adapting both to compact perimeters and to the complex geometries of large petrochemical complexes and refineries.

A fenceline monitoring study with heavy metals showed that EPA regulatory models underestimate actual concentrations in fenceline communities, and that fine particulate matter (PM), which penetrates deeper into the lungs, is the main exposure vector. Tehrani, M. et al. (2023).

Designing the perimeter sensor network

There is no universal configuration for designing a perimeter monitoring network. The design of an effective fenceline monitoring network for NO_x, PM, VOCs and other pollutants requires a prior analysis that considers at least four variables:

• Prevailing wind rose: stations must be concentrated in the directions from which the wind transports emissions towards sensitive receptors (urban areas, residential zones, protected natural areas, etc.). A sensor placed against the prevailing wind captures far less useful information than one located in the direction of greatest dispersion.
• Geometry and internal sources: not all points around the perimeter have the same probability of recording relevant emissions. Areas close to storage tanks, process units with known fugitive emissions or loading and unloading points require a higher density of stations.
• External receptors: the location of homes, schools or healthcare facilities in the surroundings affects both network density and the alert thresholds that must be configured.
• Environmental background stations: at least one measurement point must be located outside the plant’s direct influence to characterise background air quality. Without that reference data point, it is impossible to distinguish the facility’s contribution from background pollution.

A typical configuration in medium-sized facilities for fenceline monitoring combines between four and eight distributed perimeter stations, one or two background stations and, optionally, stations located next to the highest-risk sources within the monitored site. The IoT connectivity of each station ensures that all data flow in real time to the central platform, where they are processed, contextualised and ultimately converted into actionable information.

The Kunak Cloud platform dashboard showing multi-point perimeter monitoring deployed at an industrial site.

Integration with LDAR programmes and leak control

Fenceline monitoring in industrial facilities reaches its full potential when it is integrated with the LDAR programmes that refineries, petrochemical plants and gas operators are already required to maintain under current regulations. Both systems are complementary by design. While LDAR identifies and repairs leaks component by component through periodic inspections with portable detectors, the perimeter monitoring network verifies in real time whether these actions are having the expected effect on concentrations at the facility perimeter.

Operational integration works in two directions.

• When leak and emission detection through plant fenceline monitoring records an anomaly (for example, a sustained increase in VOCs in a specific sector of the perimeter, correlated with a specific wind direction), that signal can trigger a focused LDAR inspection in the corresponding internal area, instead of waiting for the next scheduled audit.
• Conversely, when an LDAR programme identifies and repairs a significant leak, subsequent perimeter data confirm whether the repair has been effective or whether the emission persists.

This feedback turns the real-time industrial emissions control system into more than a surveillance system. It becomes a continuous improvement tool with independent verification capability. And that verification capability is precisely what regulators and communities close to facilities are beginning to demand as the minimum standard for industrial environmental transparency.

An LDAR programme in five industrial plants found that fugitive VOC emissions exceeded the EPA’s carcinogenic risk thresholds for on-site workers, and that the average reduction after repairs was 20.5%, with flanges as the most repairable component (–47.5 kg/year per flange). Zhao, F. et al. (2023).

Detecting leaks and emissions around industrial sites through perimeter monitoring makes it possible to identify product losses before they lead to incidents.

Best practices in industrial emissions monitoring

A fenceline monitoring system in industrial facilities is only as reliable as the processes that support it. Technology is necessary, but not sufficient without rigorous calibration, operational integration and a defined reporting strategy. A perimeter sensor network that does not have these characteristics becomes infrastructure that generates data without generating value.

The credibility of any perimeter emissions monitoring network depends on the quality of the data at source. Near-reference sensors for industrial emissions control require periodic calibration protocols (against certified reference gases) and cross-verification with reference instruments to ensure that readings remain within the uncertainty margins accepted by international standards (EPA, CEN/TS 17660, WHO).

Best practices in this area include:

• Field calibration: at a frequency defined according to the pollutant and the site’s environmental conditions.
• Drift control: periodic verification that the sensor does not progressively move away from the reference value between calibrations.
• Documented preventive maintenance: systematic recording of each intervention, with full traceability to support regulatory audits.
• Redundancy at critical points: duplicating stations in the highest-risk areas guarantees data continuity in the event of occasional sensor failure.

Without these protocols, perimeter data lose their status as audited evidence and become a non-verifiable estimate. In the context of industrial environmental compliance, that difference is decisive.

Continuous monitoring at the industrial perimeter does not replace environmental audits or LDAR programmes, it strengthens them. The most effective practice is to build a closed loop in which each tool feeds the others:

1. The perimeter network detects an anomaly in the concentration of a pollutant, for example VOCs or CH₄, in a specific sector.
2. That signal triggers a focused LDAR inspection in the corresponding internal area.
3. The inspection identifies the leaking component and repairs it.
4. Subsequent perimeter data confirm whether the concentration has returned to normal levels.

This cycle turns the detection of leaks and emissions at the industrial perimeter into a continuous and verifiable process, far superior to the traditional logic of scheduled audits with dates known in advance. Periodic environmental audits retain their value as independent verification of the system, but they cease to be the only control mechanism. The real-time industrial emissions control system acts as a permanent auditor that does not stop on public holidays or night shifts.

The final link in an effective fenceline monitoring strategy is data communication. Industrial emissions reporting and traceability has two audiences with different needs that must be addressed simultaneously:

• Regulators and auditors: they need structured, validated and exportable data in formats compatible with official reporting systems. The integration of perimeter monitoring systems with cloud platforms makes it possible to generate these reports automatically, with calibration and validation metadata incorporated.
• Communities and citizens: they need accessible, understandable and real-time data. A public dashboard with simple visual indicators (air quality traffic lights, episode histories, comparisons with WHO guideline values) transforms the relationship between the facility and its social environment. This is not corporate communication, it is giving access to the same evidence that the plant has, without filters or intermediaries.

A perimeter monitoring system in industrial facilities is only as reliable as the processes that underpin it.

Frequently asked questions about fenceline monitoring

What is fenceline monitoring in industrial facilities?

It is the deployment of a continuous network of sensors for fenceline monitoring at the physical boundary of an industrial facility to measure in real time the concentrations of pollutants that leave the site. Unlike stack control, it measures the real impact on the surrounding environment (immission), not only at the emission point.

Which gases and particles are monitored at industrial perimeters?

The most common pollutants in fenceline monitoring are volatile organic compounds (VOCs) such as benzene, toluene and xylene; methane (CH₄); hydrogen sulphide (H₂S); sulphur dioxide (SO₂); nitrogen oxides (NO_x); and particulate matter PM_2.5 and PM₁₀. The selection depends on the specific operational and production processes that take place in each industrial facility.

How does fenceline monitoring help meet environmental regulations?

It generates continuous, traceable and auditable data that demonstrate industrial environmental compliance with regulations such as the European IED (2024/1785) or the US EPA’s 40 CFR § 63.658. Automated industrial emissions reporting and traceability eliminates dependence on point-in-time sampling and builds an environmental file that is verifiable in real time.

What operational benefits does it bring to industry?

The detection of leaks and emissions at the industrial perimeter makes it possible to identify product losses before they lead to incidents, optimise LDAR programmes with focused inspections and reduce unplanned shutdowns. Every leak detected in time is both an avoided environmental impact and an avoided economic loss.

Is it possible to share the data with the community?

Yes. The integration of perimeter monitoring systems with cloud platforms allows data to be published in real time through dashboards accessible to citizens. Reference facilities in North America and Europe already do this, turning environmental transparency into an asset for trust and industrial reputation.

Continuous monitoring around industrial sites does not replace environmental audits or LDAR programmes; rather, it enhances them.

Conclusion: the perimeter is the new standard

For a long time, industrial environmental control has been based on an inside-out logic: measure at the source, report to the regulator, archive the data. It is a model that complied with the rule, but did not answer the question that really matters: what happens to the air breathed by the people who live on the other side of the fence?

Perimeter monitoring in industrial facilities reverses that logic. It places measurement where the impact becomes real, turns the perimeter into the facility’s most valuable control point and transforms emissions data into a continuous management tool. Operational safety, industrial environmental compliance and production efficiency stop being objectives in tension and become consequences of the same well-implemented system. The goal is to detect earlier, act faster and demonstrate with evidence what until now was only declared.

In refineries and chemical plants, where fugitive VOC, H₂S and CH₄ emissions simultaneously represent an environmental risk and a loss of product, the perimeter emissions monitoring network is already a first-level operational tool. In power plants, continuous monitoring at the industrial perimeter for NO_x, SO₂ and PM particulate matter is the only way to verify that the facility’s real performance is aligned with its climate and regulatory commitments. In the chemical industry, fenceline monitoring of gases and VOCs closes the only blind spot that internal control systems cannot cover by definition, namely what happens at the boundary with the outside.

Kunak fenceline monitoring sensors are designed to operate in these industrial environments with the accuracy, ruggedness and traceability required by both regulators and communities. Near-reference technology, native IoT connectivity, integration with cloud platforms and validation under EPA, WHO and CEN/TS 17660 standards. These are the tools that allow the perimeter to stop being the most opaque point in industrial environmental control and become its strongest evidence.

References

• Lerner, J.E., Kohajda, T., Aguilar, M.E., Massolo, L.A., Sánchez, E.Y., Porta, A.A., Opitz, P., Wichmann, G., Herbarth, O., Mueller, A. Improvement of health risk factors after reduction of VOC concentrations in industrial and urban areas. Environ Sci Pollut Res Int. 2014;21(16):9676-88. https://pubmed.ncbi.nlm.nih.gov/24788932/
• Zhao, F., Peng, Y., Huang, L., Li, Z., Tu, W., Wu, B. Fugitive emissions of volatile organic compounds from the pharmaceutical industry in China based on leak detection and repair monitoring, atmospheric prediction, and health risk assessment. J Environ Sci Health A Tox Hazard Subst Environ Eng. 2023;58(7):647-660. https://pubmed.ncbi.nlm.nih.gov/37102223/
• Wong, M., Bejarano, E., Carvlin, G., Fellows, K., King, G. et al.  Combining Community Engagement and Scientific Approaches in Next-Generation Monitor Siting: The Case of the Imperial County Community Air Network. International Journal of Environmental Research and Public Health; Basel Vol. 15, no. 3, (Mar 2018): 523. https://www.proquest.com/docview/2108406265?sourcetype=Scholarly%20Journals
• Tehrani, M., Fortner, E.,Robinson, E., Chiger, A., Sheu,R.,Werden, B., Gigot, G., Yacovitch, T., Van Bramer, S., Burke, T., Koehler, K.,Nachman, K., Rule, A., DeCarlo, P. Characterizing metals in particulate pollution in communities at the fenceline of heavy industry: combining mobile monitoring and size-resolved filter measurements. Environ. Sci.: Processes Impacts, 2023, 25, 1491. https://pubs.rsc.org/en/content/articlepdf/2023/em/d3em00142c
• EPA, Fenceline air monitoring guidelines (2022). https://www.epa.gov/system/files/documents/2022-10/AAMG%20Monitoring%20Conference_Fenceline_Ned%20Shappley.pdf
• (2025). Enforcement alert: benzene fenceline monitoring at petroleum refineries. https://www.epa.gov/enforcement/enforcement-alert-benzene-fenceline-monitoring-petroleum-refineries
• European Commission. (2024). Revised Industrial Emissions Directive (IED 2.0), Directive (EU) 2024/1785. European Commission Environment. https://environment.ec.europa.eu/news/revised-industrial-emissions-directive-comes-effect-2024-08-02_en