Combustible gases are present in many industrial environments, from oil refineries and chemical plants to wastewater facilities and confined spaces. Among the most critical safety considerations in these settings is the potential for explosions caused by gas accumulation.
Understanding the concept of Lower Explosive Limit (LEL) is a key step in preventing hazardous incidents.
LEL, or Lower Explosive Limit, refers to the lowest concentration of a combustible gas in air that can ignite. Below this point, the gas is too lean to burn. Once it reaches or exceeds the LEL, any ignition source—such as a spark—can trigger an explosion.
LEL values differ by gas type. For instance, methane ignites at about 5% volume in air, while propane ignites at around 2.1%. Other flammable gases like butane, hydrogen sulphide (H₂S), and carbon monoxide (CO) also have specific LEL thresholds.
Understanding lel gas meaning also involves the role of oxygen. Combustion won’t occur without enough oxygen, though typical ambient air usually contains enough for ignition once the LEL is reached.
Some gases, like propane and butane, are heavier than air and settle in low-lying areas, increasing the risk in confined or poorly ventilated spaces. This makes early detection and continuous monitoring a key part of safety protocols.
Monitoring LEL levels on gas monitors is a critical safeguard in environments where combustible gases may be present. These monitors measure gas concentration as a percentage of the LEL. For example, a 50% reading means the atmosphere has reached half the concentration needed for ignition.
The purpose isn’t to wait until the LEL is reached—it’s to take action well before. Alarms are typically set to trigger at 10–20% LEL, giving teams time to respond by increasing ventilation, shutting down systems, or evacuating the area.
LEL gas monitors come in both portable and fixed formats, providing flexibility for different work environments.
Monitoring is especially important in confined spaces like tanks, tunnels, or sewers, where gases can accumulate rapidly. A small leak in these areas can quickly create a dangerous atmosphere with little warning.
To be effective, monitoring equipment must be properly calibrated and maintained. Faulty sensors or neglected calibration can result in missed alarms or false positives—either of which can compromise safety.
Many industries work with or generate combustible gases capable of reaching LEL thresholds. One of the most common is methane, found in natural gas, landfill emissions, and wastewater treatment.
Propane and butane, used as fuels in heating and industrial equipment, are heavier than air and prone to pooling in low areas—especially dangerous in enclosed spaces.
Hydrogen sulphide (H₂S), common in oil, gas, and sewage operations, is both toxic and flammable. Carbon monoxide (CO), often produced by incomplete combustion, can also contribute to explosive mixtures under the right conditions.
Leaks from storage tanks, piping, or equipment can release these gases. Even routine tasks—like purging or venting—can introduce flammable concentrations without proper controls. That’s why monitoring and prevention are necessary wherever these gases are handled or generated.
The main hazard of reaching the LEL is the risk of fire or explosion. When a combustible gas mixes with air and finds an ignition source—such as a spark or static discharge—the result can be immediate and severe.
These risks are higher in confined or poorly ventilated spaces, where even small leaks can create explosive atmospheres quickly.
Some gases also pose direct health risks below their LEL. Hydrogen sulphide (H₂S) and carbon monoxide (CO), for example, are toxic and can harm the nervous or respiratory systems at low concentrations.
A thorough risk assessment should identify potential leak points, ignition sources, and exposure risks. PPE, such as respiratory protection, and ventilation systems are critical controls to reduce these dangers.
Detecting combustible gases before they reach hazardous levels is a cornerstone of safety in industrial environments. Whether used in confined spaces, open work zones, or near potential leak sources, reliable gas detection systems are essential for identifying dangerous concentrations and triggering timely responses.
LEL detection typically relies on one of three main sensor technologies: catalytic bead, infrared (IR), and MPS (Molecular Property Spectrometer).
Catalytic bead sensors detect combustible gases through a heated element that causes oxidation when gas is present. This reaction produces a measurable change in resistance, which is used to determine gas concentration.
Infrared sensors measure how gas absorbs specific wavelengths of light. These sensors tend to be more stable over time and less affected by humidity or poisoning, making them a strong choice for fixed installations.
MPS LEL sensors represent a newer, advanced option. They can detect over a dozen different flammable gases simultaneously—including hydrogen—and report individual concentrations. They are immune to poisoning, drift, and environmental interference, require no calibration or maintenance during their lifetime, and feature a built-in self-test to maintain accuracy and safety. They also consume little power and deliver fast, precise readings across the full 0–100% LEL range. Although their initial cost is higher and they may require specialised training for integration, they are ideal for sites handling multiple flammable gases.
Gas detectors are available in two main formats:
● Portable monitors are ideal for mobile personnel, confined space entry, or temporary work in high-risk areas. Many models, including those equipped with MPS sensors, allow workers to carry them on their person, receiving real-time alerts to changing gas levels. A trusted option in this category is the MultiRAE, a multi-gas monitor suitable for a variety of environments.
● Fixed detection systems are installed in permanent locations, such as machinery rooms, storage areas, or production lines. Some systems can be specified with MPS sensor technology for continuous multi-gas detection. They offer constant coverage and are often connected to control panels, ventilation systems, and emergency alarms. The Sensepoint XRL is one such detector, offering Bluetooth-enabled calibration and flexible installation options.
MPS Sensor Advantages:
○ They can detect over a dozen different flammable gases simultaneously, including hydrogen, methane, propane, and butane, and can report the individual concentration of each gas.
○ MPS sensors are immune to poisoning, drift, decay, and interference from environmental factors like humidity, fog, dust, and ambient light.
○ They do not require calibration or maintenance throughout their lifetime.
○ These sensors have a built-in self-test function that continuously ensures accuracy and safety.
MPS Sensor Drawbacks:
○ Their initial cost is generally higher than traditional sensors.
○ The complex technology may require specialized training for proper integration and use.
○ For niche applications where only one or two gases need to be monitored, MPS sensors might be more versatile than necessar
To remain accurate, all gas detection equipment must be properly maintained and tested. For catalytic bead and IR systems, regular bump tests and calibration checks help verify sensor performance. MPS sensors do not require calibration but still benefit from functional checks as part of routine safety inspections.
For a complete range of detection solutions, including devices with catalytic bead, IR, or MPS sensors, OBW Technologies offers both portable gas detectors and fixed gas detection systems, each selected for performance, durability, and ease of use.
Working with flammable gases requires compliance with national and industry regulations. In Europe, ATEX and IECEx certifications ensure that equipment used in explosive atmospheres meets safety standards. Employers must also follow national guidelines, such as those from the Health and Safety Authority (Ireland) and the Health and Safety Executive (UK).
Employers are also required to assess explosion risks, define hazardous zones, and implement controls. This includes regular inspections, sensor calibration, and employee training.
Non-compliance can lead to fines, shutdowns, or liability in the event of an incident. Using certified equipment and documented procedures helps maintain both safety and legal standing.
Even with the best monitoring systems in place, leaks can still happen. That’s why every facility handling combustible gases should have clear, actionable contingency plans to respond to LEL incidents quickly and effectively.
An effective plan begins with emergency response protocols that define exactly what to do when gas levels rise above safe thresholds. This often includes automatic shutdown of equipment, activation of ventilation systems, and triggering of visual and audible alarms.
Evacuation procedures should be well-established and regularly practised. Staff must know exit routes, muster points, and their role during a gas leak scenario. The speed and coordination of this response can make all the difference in preventing harm.
Prevention also plays a large role. This includes:
● Routine inspection of valves, hoses, storage tanks, and gas lines
● Maintenance schedules that address wear and corrosion
● Continuous training to reinforce safe handling practices
Hazard mitigation strategies may also involve gas suppression systems, containment barriers, and the use of intrinsically safe equipment that won’t trigger ignition.
It’s good practice to keep documentation of all safety drills, equipment maintenance, and sensor calibrations. In the event of an incident, these records show that reasonable precautions were taken.
Having a plan is one thing—making sure it’s practical, known, and regularly reviewed is another. That’s where many organisations fall short. A contingency strategy is only effective if it’s implemented consistently across teams and work sites.
Minimising the risk of gas-related incidents begins long before a leak occurs. It starts with how gases are stored, transferred, and monitored in day-to-day operations. Adopting safe handling practices reduces the chance of reaching hazardous concentrations and creates a culture of responsibility across the workplace.
Here are key principles to follow:
● Start with the right equipment
Use gas detectors and monitoring tools that are certified for hazardous environments. Instruments like the MultiRAE and Sensepoint XRL are built to handle tough conditions while delivering accurate, dependable readings.
● Inspect equipment regularly
Visual checks of gas cylinders, valves, hoses, and connections should be part of daily routines. Any signs of corrosion, wear, or loose fittings need to be addressed immediately.
● Schedule routine maintenance
Beyond daily inspections, equipment—especially gas monitors—should follow a strict maintenance and calibration schedule. Bump tests and full calibration verify that sensors are responding accurately.
● Provide adequate ventilation
Whether natural or mechanical, airflow prevents gases from building up. Ventilation is especially important in confined spaces or underground environments.
● Limit ignition sources
Implement controls to eliminate sparks or flames in hazardous zones. Use only intrinsically safe tools and ensure electrical systems are compliant with ATEX or IECEx standards.
● Train personnel
Workers should be briefed on handling procedures, emergency protocols, and how to use detection equipment. Safety doesn’t rely on one department—it’s shared across every role on-site.
By embedding these practices into daily operations, teams can create a safer environment without slowing productivity or adding unnecessary complexity.
Having the right equipment is only part of the equation. To build a truly safe workplace, employees need to understand the risks, recognise warning signs, and respond appropriately. That’s where training and awareness programmes come in.
These programmes should cover the basics of LEL gas meaning, how detection systems work, and what different alarm levels indicate. It’s not enough for just supervisors or safety officers to be trained—everyone who enters a hazardous area should be briefed.
Effective programmes typically include:
● Induction training for new hires working near combustible gases
● Regular refreshers to reinforce key concepts and updates in safety procedures
● Emergency drills that simulate real gas leak scenarios
● Hands-on training in the use of portable monitors and PPE
● Certification schemes, where appropriate, to validate skills and understanding
Training also plays a critical role in developing a risk-aware culture. When workers understand why certain procedures exist—such as why a tank must be purged before entry or why a bump test is done daily—they’re more likely to follow protocols consistently.
Operational teams benefit from tools such as checklists, instructional signage, and quick-reference guides near work areas. These keep safety front of mind, especially during high-risk tasks like confined space entry, maintenance, or start-up operations.
Ultimately, safety is not just a policy—it’s a behaviour reinforced by clear training, open communication, and shared responsibility.
Have programmes that include induction and refreshers, along with hands‑on emergency drills. OBW’s article on Gas Shutdown Maintenance highlights how teams should be trained to interpret alerts, position monitors effectively, respond to alarms, and perform self‑checks.
LEL values apply to combustible gases—those that can ignite when mixed with air. Common examples include:
● Methane (natural gas)
● Propane and butane (used in heating and industrial applications)
● Hydrogen sulphide (H₂S) (present in oil, gas, and wastewater sectors)
● Carbon monoxide (CO) (a by-product of incomplete combustion)
● Various flammable gas mixtures found in manufacturing and chemical processing
Each gas has a specific LEL percentage by volume in air, below which it cannot ignite.
LEL values for gases are determined through laboratory testing and published by regulatory bodies. In the field, gas detectors calculate current gas levels as a percentage of the LEL. For example, a reading of 25% means the gas concentration is one-quarter of what would be required for ignition.
Gas detection systems use sensors to continuously measure these levels, and regular calibration ensures accuracy.
Prevention relies on a combination of:
● Continuous monitoring using portable or fixed gas detectors
● Leak prevention through equipment checks and maintenance
● Adequate ventilation to disperse gases
● Safe storage and handling procedures
● Alarm systems to prompt early intervention
Implementing these controls helps keep concentrations well below dangerous thresholds.
No—not all gas monitors are equipped with LEL sensors. Some are designed to detect specific toxic gases (like H₂S or CO) only. Always check the sensor configuration to confirm that LEL detection is included before use in flammable environments.
Calibration schedules vary by environment and device, but a good rule of thumb is to perform full calibration every 6 months, along with daily bump tests. Harsh or high-risk environments may require more frequent checks.
For more information on gas detection systems or to speak with a safety specialist, visit OBW Technologies or contact us directly.
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