gas explosion e1548871838164

Understand LEL and UEL for Flammable Gases: Values, Hazards, Measurement, and Risk Mitigation

gas explosion e1548871838164

Understand LEL and UEL for Flammable Gases: Values, Hazards, Measurement, and Risk Mitigation

The lower explosive limit (LEL) is the minimum concentration of a specific combustible gas required to fire combustion when in contact with oxygen (air). If the concentration of the gas is below the LEL value, the mix between the gas itself and the air is too weak to spark. The upper explosive limit (UEL) is the maximum level of concentration of the gas that will burn when mixed with oxygen; when the gas concentration is above the UEL value for the gas/vapor, the mix is too “fat” to ignite or explode. 

LEL AND UEL (FLAMMABLE GAS)

DEFINITION UEL/LEL

The terms LEL and UEL are critically important in various industries, including oil & gas, power generation, and construction, especially when dealing with explosive gases. They stand for “Lower Explosive Limit” and “Upper Explosive Limit,” respectively.

  • LEL (Lower Explosive Limit) is the minimum concentration of a gas or vapor in the air needed to ignite.
  • UEL (Upper Explosive Limit) is the maximum concentration where combustion can occur.
  • Below the LEL, the mixture is too lean to burn; above the UEL, it’s too rich.

Understanding these terms is essential for ensuring workplace safety, preventing accidents, and promoting an informed culture around handling flammable substances.

LEL UEL for combustible gas

The safe handling and management of flammable gases are of paramount importance across various industries.

In this comprehensive guide, we will delve deep into the critical differences between Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL). 

However, before exploring LEL and UEL in detail, it is essential to establish a foundation by defining flammability and understanding the factors that contribute to the ignition and combustion of gases.

WHAT IS FLAMMABILITY?

Flammability refers to the characteristic of a material or substance to easily catch fire and burn in the presence of an ignition source, such as a spark, flame, or heat. This property is crucial in understanding the fire risks associated with various materials, especially in industries such as construction, manufacturing, oil & gas, and power generation. Flammability is determined by several factors, including the chemical composition of the material, its physical state (gas, liquid, or solid), and the environmental conditions (e.g., temperature, pressure, presence of oxygen).

Key Concepts in Flammability

  • Ignition Point: The minimum temperature at which a material ignites and continues to burn without additional external heat. This can vary widely among different substances.
  • Flash Point: The lowest temperature at which a liquid can form an ignitable mixture in air near its surface. Liquids with lower flash points ignite more easily and are considered more flammable.
  • Flammable Range: This concept applies mainly to gases and vapors and is defined by the Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL). It describes the concentration range in air within which the substance can ignite. Outside this range, the mixture is either too lean (below LEL) or too rich (above UEL) to support combustion.
  • Combustibility: A related term that often describes the ease at which a substance burns but is usually applied to materials that catch fire and sustain combustion under specific conditions, such as wood and fabric.

Flammability Ratings and Classifications

Flammability is often classified into categories or ratings based on the material’s response to fire exposure. These classifications help in the safe handling, storage, and transportation of materials. For instance, the National Fire Protection Association (NFPA) 704 standard uses a “fire diamond” with numbers ranging from 0 to 4 to indicate the hazard level of materials, where 0 means no hazard and 4 indicates severe hazard.

Importance in Safety and Regulations

Understanding the flammability of materials is essential for safety in various settings. It guides the design of fire prevention and protection systems, the selection of materials for construction and manufacturing, and the development of emergency response plans. Regulatory standards and guidelines specify how to manage and mitigate risks associated with flammable substances, including proper labeling, storage requirements, and control measures like ventilation and fire suppression systems.

The Flammable Range (LEL/UEL %)

The range between the lower and the upper explosive limit (LEL / UEL %) is defined as the flammable range of a specific explosive and flammable gas.
Flammable range meaning (LEL)

Examples of LEL for common gases:

  • LEL for Hydrogen: 4.0
  • LEL for Methane: 5.0

The risk of explosion of combustible gases has to be managed carefully in any production site handling gases.

To fire an explosion, three conditions should occur at the same time:

  1. The presence of combustible gas, the fueling element, in a specific concentration
  2. Presence of oxygen
  3. The existence of a sparking element (that ignites the two elements)

The proportion of fuel and oxygen needed to generate an explosion depends on the type of combustible gas. Gases will ignite only when mixed with air within a specific concentration range. If the gas is mixed with oxygen with too low or too high concentrations, the gas will not ignite and explode.

The lower and the upper explosion values (LEL and UEL) define the required level of concentration by type of gas.

Explosions will occur for gas concentrations within the LEL and the UEL value, not above or below, and the maximum explosive power will be for concentration at the midpoint of the flammable range.

IMPORTANCE OF UEL & LEL IN INDUSTRY

Understanding the LEL and UEL of gases is crucial in industries where explosive gases are present. This knowledge helps in:

  • Safety: It allows for the implementation of safety measures to control the concentration of flammable gases within safe limits, significantly reducing the risk of explosions.
  • Monitoring: Gas detection systems are often set to alarm when concentrations approach the LEL to prevent reaching a potentially explosive level. Similarly, understanding the UEL can prevent the creation of too-rich mixtures that are also hazardous.
  • Process Control: In manufacturing and processing, knowing these limits ensures that reactions and processes involving flammable gases are carried out safely, maintaining concentrations within non-explosive limits.
  • Emergency Response: In the event of a leak or release of flammable gas, responders can use knowledge of LEL and UEL values to assess the explosion risk and take appropriate actions to mitigate hazards.

PRACTICAL APPLICATIONS OF LEL/UEL

To practically apply this knowledge, workplaces with hazardous gas environments often use gas detection and monitoring systems designed to measure the concentration of explosive gases in the air. These systems are calibrated to alert personnel when gas concentrations approach the LEL, allowing for timely intervention before reaching dangerous levels.

Safety practices also include proper ventilation to dilute gas concentrations, regular maintenance and inspection of equipment to prevent leaks, and training for personnel on the risks associated with explosive gases and the importance of LEL and UEL.

In summary, the concepts of LEL and UEL are fundamental in ensuring the safe handling and management of explosive gases in the oil & gas, construction, and power generation industries. By maintaining gas concentrations within safe limits, these industries can significantly reduce the risk of fire and explosion, protecting both people and assets.

LOWER EXPLOSIVE LIMIT (LEL)

The Lower Explosive Limit (LEL) of a gas or vapor refers to the lowest concentration of the substance in the air that is capable of igniting and sustaining a flame at room temperature and atmospheric pressure. Below this concentration, the gas mixture does not contain sufficient fuel to support combustion. In simple terms, if the gas concentration is below the LEL, the mixture is too “lean” to burn.

The LEL is expressed as a percentage by volume. For instance, if methane has an LEL of 5%, it means that methane can ignite only if it constitutes 5% or more of the air volume. Below this level, there isn’t enough methane in the air to start or maintain a fire.

LEL MEASURING METHODS

The measurement and constant metering of the Lower Explosive Limit (LEL) is crucial for ensuring safety in environments where flammable gases or vapors might be present. This measurement helps in preventing conditions that could lead to explosive or fire hazards.

There are several methods and technologies employed to measure the LEL of gases and vapors. The most used LEL meter is the Wheatstone bridge type, which is effective for most applications and environments.

However, the Wheatstone bridge LEL detector may not be effective for specific conditions, or gases, that require higher sensitivity sensors. The PID detectors (“Photoionization detectors”) are an option when a more accurate LEL measurement is required in hazardous environments.

PID meter LEL UEL combustion

 

Generally, if the gas concentration surpasses 20% of its Lower Explosive Limit (LEL), the environment is deemed to be moving toward unsafe conditions.

Below are some of the most commonly used devices and techniques used to monitor LEL:

Catalytic Combustion (Pellistor Sensors)

Catalytic combustion sensors, also known as pellistor sensors, are one of the oldest and most common methods for detecting flammable gases. These sensors work by oxidizing the gas on the surface of a heated catalyst, which leads to a temperature increase. The temperature change is proportional to the concentration of the gas, allowing the measurement of the LEL. Pellistor sensors are broad-spectrum detectors and can detect a wide range of flammable gases. However, they can be poisoned or inhibited by certain substances, which can limit their lifespan and effectiveness.

Infrared (IR) Absorption

Infrared absorption detectors measure flammable gases by exploiting the characteristic absorption bands of different gases in the infrared spectrum. When an IR beam passes through a gas sample, specific wavelengths are absorbed by the gas. The amount of light absorbed at these wavelengths correlates with the gas concentration. IR detectors are not susceptible to poisoning and can operate in oxygen-free environments, making them suitable for a wide range of applications. However, they may not detect some gases that do not absorb IR radiation well.

Electrochemical Sensors

Electrochemical sensors measure the concentration of flammable gases by oxidizing or reducing the gas at an electrode and measuring the resulting current. The current produced is proportional to the concentration of the target gas. These sensors are highly selective and sensitive to specific gases, which makes them useful in environments where accurate detection of a particular gas is required. However, their performance can be affected by environmental conditions such as temperature and humidity.

Semiconductor Gas Sensors

Semiconductor gas sensors detect gases through changes in the electrical resistance of a semiconductor material when exposed to a gas. The presence of the gas affects the resistance of the sensor’s material, and this change in resistance can be used to determine the gas concentration. These sensors are sensitive and can detect low levels of gases, but they may require calibration to distinguish between different types of gases and are susceptible to interference from changes in temperature and humidity.

Photoionization Detectors (PID)

Photoionization detectors use high-energy photons to ionize molecules of the gas being detected. The current generated by the ionization process is measured, and this is directly proportional to the concentration of the gas. PIDs are particularly sensitive to volatile organic compounds (VOCs) and other toxic gases. They are useful in detecting low concentrations, often below the LEL, but their effectiveness can vary based on the ionization potential of the gas.

Ultrasonic Gas Leak Detection

This method detects the acoustic signature of a gas leak rather than measuring the gas concentration directly. It is particularly useful in outdoor or ventilated areas where gas clouds might not reach detectors before dissipating. While not a direct LEL measurement method, it complements other technologies by providing early leak detection.

Selection Considerations

Choosing the appropriate LEL measurement method depends on various factors, including the specific gases present, environmental conditions, the presence of potentially interfering substances, and the required sensitivity and accuracy. Safety engineers and professionals consider these factors, along with practical considerations such as maintenance needs and cost, to select the most appropriate detection technology for their specific application.

FACTORS THAT INFLUENCE LEL

The Lower Explosive Limit (LEL) is a critical safety parameter in many industries, indicating the lowest concentration of flammable gas or vapor in air that can ignite. While the LEL values are often considered fixed for a given substance under standard conditions, several environmental and contextual factors can influence the effective LEL in a specific situation. Understanding these factors is essential for accurately assessing the risk of explosion and implementing appropriate safety measures. Here are key factors that can influence the LEL of flammable substances:

Temperature

Higher temperatures can lower the LEL of a gas or vapor. As temperature increases, substances become more volatile, increasing the concentration of flammable vapors in the air and, therefore, the potential for ignition at lower concentrations than at standard conditions.

Pressure

Changes in pressure can also affect the LEL. Higher pressures generally increase the density of gases, which could lead to a lower LEL since a smaller volume of gas would be required to reach the flammable limit. Conversely, lower pressures can lead to higher LEL values.

Oxygen Concentration

The concentration of oxygen in the environment significantly affects the LEL. In atmospheres with enriched oxygen levels, the LEL decreases because the enhanced oxygen availability facilitates combustion at lower concentrations of the flammable substance. In oxygen-deficient environments, the LEL value increases, as there is insufficient oxygen to support combustion at lower concentrations.

Humidity

The presence of water vapor can influence the LEL of certain gases and vapors. High humidity levels can dilute flammable gases, potentially raising the LEL. However, the specific effect can vary widely depending on the physical and chemical properties of the gas or vapor in question.

Presence of Other Substances

The presence of other flammable or inert gases can affect the LEL of a gas mixture. Inert gases can dilute a flammable gas mixture, increasing its LEL, while the presence of other flammable gases can create synergistic effects that may lower the overall LEL of the mixture.

Physical Space and Ventilation

The configuration of the physical space and the effectiveness of ventilation can influence the distribution and concentration of flammable gases or vapors, indirectly affecting the risk associated with the LEL. Poorly ventilated or confined spaces are more likely to contain gas concentrations near the LEL, increasing the risk of ignition.

Measurement Method and Accuracy

The method used to measure the LEL can influence the perceived risk level. Different detection technologies may have varying sensitivities and specificities to certain gases or environmental conditions, which can lead to differences in the measured LEL values. Calibration, maintenance of the detection equipment, and the presence of substances that may interfere with the detection method can also impact the accuracy of LEL measurements.

Conclusion

The LEL is a fundamental concept in fire and explosion safety, but it’s important to recognize that the effective LEL in a particular situation can be influenced by a range of environmental and contextual factors. Safety protocols must consider these factors to ensure that risk assessments are accurate and that safety measures are appropriate to prevent explosive incidents. Regular monitoring of the environment, using appropriate detection methods, and adjusting safety practices based on changing conditions are crucial steps in managing the risks associated with flammable gases and vapors.

 
 

UPPER EXPLOSIVE LEVEL (UEL)

The Upper Explosive Limit (UEL), on the other hand, is the highest concentration of a gas or vapor in air that can ignite. Above this level, the mixture is too “rich” to sustain combustion. This is because the oxygen content is too low to allow the gas mixture to burn. Just like the LEL, the UEL is also expressed as a percentage by volume.

For the same example, if methane’s UEL is 15%, this indicates that methane concentrations above 15% are too fuel-rich and lack the necessary oxygen ratio for combustion to occur.

UEL MEASURING METHODS

The Upper Explosive Limit (UEL) denotes the highest concentration of flammable gas or vapor in the air that can propagate flame. Beyond this concentration, the mixture becomes too “rich” to burn because there’s insufficient oxygen. Just like the Lower Explosive Limit (LEL), accurately measuring the UEL is vital for safety in industries dealing with flammable substances. Here we delve into various methods utilized to measure the UEL of gases and vapors, highlighting their operating principles and applications.

Catalytic Heat of Combustion Sensors

Catalytic sensors, similar to those used for LEL measurements, can also detect the UEL of gases by measuring the heat of combustion. However, for UEL applications, these sensors must be calibrated and possibly designed differently to accurately measure higher concentrations of gases. They work by oxidizing the gas on a catalyst’s surface, causing a temperature change proportional to the gas concentration, up to the UEL, beyond which the sensor readings stabilize or decline due to the lack of oxygen for combustion.

Infrared (IR) Absorption Spectroscopy

IR absorption spectroscopy can be employed for UEL measurement by detecting specific wavelengths absorbed by the gas. These systems need to be calibrated for the high end of the gas concentration range. They work well for gases that have strong infrared absorption characteristics but might not be suitable for all types of gases, especially if the gas does not absorb infrared light efficiently at higher concentrations.

Gas Chromatography

Gas chromatography is a more sophisticated technique used to measure the concentration of gases, including the UEL. It separates the components of a gas mixture and quantifies them individually. While not typically used for real-time safety monitoring due to its complexity and the time required for analysis, it can provide precise measurements of gas concentrations for laboratory analysis or validation of safety parameters.

Thermal Conductivity Sensors

Thermal conductivity sensors measure the thermal conductivity of a gas mixture, which changes with concentration. Since the thermal conductivity of a gas mixture varies significantly across different concentrations, these sensors can be calibrated to detect the UEL by identifying the point at which thermal conductivity begins to decrease as the concentration exceeds the UEL, indicating the mixture is too rich for combustion.

Electrochemical Sensors

Electrochemical sensors, which operate by measuring a current resulting from a chemical reaction between the target gas and an electrode, can be adapted for UEL measurements. They must be specifically designed for the gas of interest and calibrated for higher concentration ranges. Their effectiveness depends on the specific reaction and the design of the sensor cell.

Paramagnetic Sensors for Oxygen Depletion

While not directly measuring the concentration of the flammable gas, paramagnetic sensors can detect the depletion of oxygen in the air, which indirectly indicates when a gas concentration approaches the UEL. As the gas concentration increases, the available oxygen decreases, which these sensors can accurately measure. This method is particularly useful in enclosed spaces where oxygen levels are a critical safety concern.

Conclusion

The choice of method for measuring the UEL of gases and vapors depends on several factors, including the specific gas or vapor, the required accuracy and sensitivity, environmental conditions, and the application’s safety requirements. Technologies that provide real-time monitoring are preferred in operational settings for immediate hazard detection and response. However, more complex analytical techniques might be used for research, development, and validation of safety parameters. Regular calibration and maintenance of the detection systems are crucial to ensure their reliability and accuracy in measuring the UEL to prevent explosive and fire hazards.

FACTORS THAT INFLUENCE UEL

The Upper Explosive Limit (UEL) of a gas or vapor represents the highest concentration in the air above which the mixture becomes too “rich” to ignite and sustain a flame. This is a critical safety parameter in various industries, as maintaining gas concentrations below the UEL is crucial for preventing fire and explosion risks. While UEL values for various substances are determined under standard conditions, several factors can influence these limits in practical scenarios:

Temperature

  • Effect: Increasing temperature can increase the UEL because higher temperatures tend to enhance the vapor pressure of liquids, leading to higher concentrations of vapors in the air. Additionally, higher temperatures can make some reactions more likely to occur, affecting the combustion dynamics.
  • Application: In industrial settings where temperatures vary significantly from standard conditions, adjustments may be necessary to account for the influence on UEL values.

Pressure

  • Effect: Changes in atmospheric pressure can alter the UEL. Higher pressures can increase gas density and the number of molecules in a given volume, potentially affecting the concentration at which a gas mixture becomes too rich to burn.
  • Application: Industries operating under varied pressure conditions, such as underground mines or pressurized vessels, need to consider these effects on UEL values.

Oxygen Concentration

  • Effect: The concentration of oxygen in the environment has a direct impact on the UEL. In enriched oxygen atmospheres, the UEL may increase because the additional oxygen can support the combustion of richer mixtures. Conversely, in oxygen-depleted environments, the UEL may decrease.
  • Application: This is particularly relevant in confined spaces or controlled environments where oxygen levels might be intentionally or unintentionally altered.

Humidity

  • Effect: Water vapor in the air can affect the UEL of some gases and vapors. High humidity levels can lead to higher UEL values, as water vapor can dilute the gas mixture and absorb heat, affecting the combustion process.
  • Application: Consideration of humidity levels is important in environments with significant moisture variations, such as outdoor operations or processes involving steam.

Mixture with Other Gases

  • Effect: The presence of other flammable or inert gases can influence the UEL. Flammable gases may lower the overall UEL of a mixture, while inert gases can raise the UEL by diluting the mixture and inhibiting combustion.
  • Application: In industrial processes involving complex mixtures of gases, understanding the combined effect on UEL is crucial for safety.

Altitude

  • Effect: At higher altitudes, the reduced atmospheric pressure can affect gas concentrations and combustion processes, potentially altering UEL values.
  • Application: Operations at high altitudes, such as mountainous mining operations or high-altitude facilities, must take into account these variations.

Chemical Composition and Impurities

  • Effect: The purity of the gas or vapor and the presence of impurities can affect its combustibility and thus the UEL. Impurities may either raise or lower the UEL, depending on their nature and the combustion characteristics.
  • Application: In chemical processing and manufacturing, the quality and purity of materials should be monitored to ensure safety parameters remain valid.

Conclusion

Understanding the factors that influence the UEL of gases and vapors is essential for accurately assessing explosion risks and implementing effective safety measures. These factors highlight the importance of not solely relying on standard UEL values but also considering environmental and operational conditions that could alter these limits. By doing so, industries can better safeguard against the risks associated with flammable gases and vapors, ensuring a safer working environment.

 

DIFFERENCES BETWEEN LEL AND UEL

The concepts of Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL) are fundamental in understanding the safety parameters for handling flammable gases and vapors. These limits define the concentration range within which a flammable substance in the air can ignite and sustain a combustion reaction.

Here’s a detailed look at the differences between LEL and UEL, highlighting their significance in safety management:

DEFINITION AND CONCENTRATION

  • LEL refers to the lowest concentration of a gas or vapor in air that is capable of igniting and sustaining a flame. Below this concentration, the mixture is too lean to burn because there isn’t enough fuel to support the combustion process.
  • UEL, on the other hand, is the highest concentration of a gas or vapor in air that can ignite. Above this level, the mixture is too rich to sustain combustion, as there is not enough oxygen to support the reaction.

SAFETY IMPLICATIONS

  • Below LEL: Concentrations below the LEL are considered safe in terms of fire or explosion risk because the fuel-air mixture is too lean to ignite.
  • Between LEL and UEL: This range is the explosive or flammable range. Within these limits, the fuel-air mixture can ignite and potentially cause an explosion or fire if an ignition source is present.
  • Above UEL: Concentrations above the UEL are considered safer than those within the range, as the mixture is too rich to ignite. However, dilution of the gas or vapor to levels within the flammable range can occur, presenting a hazard if not properly managed.

DEPENDENCY ON ENVIRONMENTAL CONDITIONS

Both LEL and UEL can be influenced by environmental factors such as temperature, pressure, and the presence of other gases. However, how these factors affect LEL and UEL can be different. For example, increasing temperature generally lowers the LEL but raises the UEL because it increases the volatility of liquids, resulting in higher vapor concentrations at the same liquid temperature.

MEASUREMENT AND DETECTION

  • LEL Detectors: Devices designed to detect and warn about concentrations approaching the LEL are common in industrial and laboratory settings. These are critical for early warning systems to prevent reaching explosive concentrations.
  • UEL Measurement: While less common than LEL detectors, monitoring for UEL levels can also be important, especially in processes where high concentrations of flammable gases or vapors could be present.

SAFETY PRACTICES

  • For LEL Management: Ventilation, gas monitoring, and elimination of ignition sources are key strategies to keep gas concentrations below the LEL.
  • For UEL Management: Although managing concentrations to prevent reaching the UEL is also important, practices often focus on ensuring adequate oxygen levels and preventing conditions that could lead to concentration stratification or layering, which might bring parts of a gas cloud into the explosive range.

 

LEL UEL CHART BY GAS TYPE

Below is a table showcasing the LEL and UEL values for some major flammable gases, presented as percentages by volume in air. These values are crucial for understanding the explosive potential of these gases and ensuring safe handling in various environments.

Flammable GasLEL (%)UEL (%)
Hydrogen4.075.0
Methane (Natural Gas)5.015.0
Propane2.19.5
Butane1.88.4
Ethylene2.736.0
Acetylene2.5100.0
Ammonia15.028.0
Carbon Monoxide12.574.0
Hydrogen Sulfide4.346.0
Gasoline Vapor1.47.6
Ethanol (Alcohol)3.319.0
Methanol6.036.0
Isopropyl Alcohol2.012.0
Ethylene Oxide3.0100.0
Propylene Oxide2.037.0
Benzene1.28.0
Toluene1.17.1
Hexane1.27.5
Pentane1.47.8
Styrene0.96.8

These values are generalized and can vary slightly under different conditions of temperature and pressure. They serve as critical references for ensuring safety measures are in place to prevent the risk of fire or explosion when working with these gases.

 

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About the Author

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Projectmaterials Team

Blog.projectmaterials.com is an online resource dedicated to providing in-depth information, analysis, and educational content related to the fields of project materials management, engineering, and procurement, particularly within the oil & gas, construction, shipbuilding, energy, and renewable energy sectors. It aims to serve professionals and enthusiasts in these industries by offering valuable insights into materials, equipment, and techniques used in various projects, focusing on the selection, application, and maintenance of these resources. Key features of the blog include: * Educational Articles: Comprehensive posts that cover topics ranging from the technical aspects of piping products (pipes, valves, fittings, flanges, gaskets, bolts, instrumentation) to structural steel and process equipment (including oil extraction systems, drilling rigs, wellheads, pumps, compressors, and separation systems). * Industry Insights: Updates on the latest trends, technologies, and regulatory changes affecting the industries covered. * Guides and How-Tos: Practical advice on selecting the right materials and equipment for specific applications, as well as tips on installation, maintenance, and troubleshooting. * Safety and Standards: Information on safety equipment for production sites, risk mitigation procedures, and an overview of relevant industry standards and regulatory frameworks. The website is designed to support the professional development of engineers, procurement specialists, project managers, and other stakeholders involved in project plant businesses, by disseminating critical know-how and best practices. Whether readers are new to the field or seasoned professionals, blog.projectmaterials.com offers resources to enhance their understanding and performance in managing project materials effectively.

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10 Responses

  1. Hi every body,
    My question is that if our concern is fire and we are within the LEL i.e. out of flammable range, then why do we worry to measure the %LEL if it is 5% LEL or 10% LEL ?
    As long as we are below LEL we are safe in terms of fire hazard.

    My second question, please reply,
    If within LEL there is no risk of fire, then why do we call this device combustible detector since there is no risk of combustion ?

  2. I find it interesting that operators may use LEL detectors to monitor the gas concentration in closed environments. I think that it would be crucial to purchase these gas detection products from a trustworthy provider. Doing so could ensure that they will work properly and provide accurate results.

  3. For methane LEL 5% UEL 15% range for ignition, how much percentage of air needed within these range in order to ignite?
    What is the minimum/maximum percentage of air that combustion is impossible?

    1. Dear Jonathan, thanks for your question. I have checked with our team, and unfortunately, we do not have an answer;(
      Shall we add a forum to our site, in your opinion, so questions like yours may find an answer within the community?

      Best, Projectmaterials

    2. Hi Jonathan,

      Essentially LEL = 5 volume % and UEL = 15 volume %
      This means a part of a volume (shape/room) has to be filled to reach this level.

      So if a room is filled with 5% methane and 95% air you have reached LEL and the mixture is explosive.
      If a room is filled with 15% methane and 85% air the mixture is to rich to explode and you have reached UEL.

      If you’re using a LEL detector it will display % LEL.
      If it displays 50% LEL you will have half of the LEL so this equals 2,5 vol% and the mixture is too lean to be explosive.
      Most LEL detectors will sound a alarm at 10% LEL, so you’re really on the safe side.

      Hope this explains it.

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