Table of Contents
ToggleThe 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: WHY ARE IMPORTANT?
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). By gaining a thorough understanding of these concepts, industries can enhance safety protocols, minimize risks, and create a secure working environment.
I. Fundamentals of Flammability:
1.1. Definition of Flammability:
Before exploring LEL and UEL, it is essential to establish a foundation by defining flammability and understanding the factors that contribute to the ignition and combustion of gases.
1.2. Significance of Flammability in Industrial Settings:
The implications of flammable gases in industrial environments necessitate a meticulous examination of their properties. This section will highlight the potential risks and consequences associated with the mishandling of flammable substances.
II. Lower Explosive Limit (LEL):
2.1. Definition and Explanation:
LEL represents the lowest concentration of a flammable gas in the air that can ignite. Understanding the concept of LEL is crucial for establishing safe working conditions and preventing explosive atmospheres.
2.2. Measurement Methods:
Various methods are employed to measure LEL, including catalytic bead sensors, infrared sensors, and flame ionization detectors. This section will explore these methods and their applicability in different industrial settings.
2.3. Factors Influencing LEL:
Several factors, such as temperature and pressure, can influence the LEL of a gas. This part of the article will provide insights into the variables that impact LEL and how they contribute to the overall flammability of a substance.
III. Upper Explosive Limit (UEL):
3.1. Definition and Explanation:
UEL represents the highest concentration of a flammable gas in the air that can ignite. This section will delve into the concept of UEL and its significance in risk assessment and safety protocols.
3.2. Measurement Methods:
Similar to LEL, UEL is measured using various techniques. This part of the guide will explore the methods employed to determine UEL, including the advantages and limitations of each.
3.3. Factors Influencing UEL:
Just as with LEL, factors like temperature and pressure play a role in determining UEL. Understanding these factors is crucial for maintaining a safe environment and preventing explosive conditions.
IV. Differences Between LEL and UEL:
4.1. Definitional Contrast:
This section will provide a clear and concise definitional contrast between LEL and UEL, emphasizing the fundamental differences in their definitions and applications.
4.2. Practical Implications:
Understanding the practical implications of LEL and UEL is vital for implementing effective safety measures. This part of the article will explore real-world scenarios where the knowledge of these limits is critical.
4.3. Importance in Risk Assessment:
Both LEL and UEL play a pivotal role in risk assessment processes. This section will discuss how industries can integrate these limits into their risk management strategies to enhance overall safety.
V. Case Studies:
5.1. Industrial Accidents:
Analyzing historical industrial accidents related to flammable gases will provide valuable insights into the consequences of neglecting LEL and UEL considerations. Case studies will highlight the importance of adhering to safety protocols.
5.2. Successful Implementation of Safety Measures:
On a positive note, case studies showcasing successful implementation of safety measures based on LEL and UEL considerations will serve as examples for other industries to follow.
VI. Best Practices for Safe Handling of Flammable Gases:
6.1. Engineering Controls:
Implementing engineering controls, such as ventilation systems and gas detection systems, is crucial for maintaining gas concentrations within safe limits. This section will discuss the role of engineering controls in mitigating risks.
6.2. Personal Protective Equipment (PPE):
Proper selection and use of personal protective equipment are essential components of ensuring worker safety. This part of the article will outline recommended PPE for working with flammable gases.
6.3. Emergency Response Planning:
Developing comprehensive emergency response plans is critical for minimizing the impact of potential incidents. This section will provide guidelines for creating effective emergency response strategies tailored to LEL and UEL considerations.
VII. Regulatory Framework:
7.1. Occupational Safety and Health Administration (OSHA) Guidelines:
This part of the guide will provide an overview of OSHA guidelines related to flammable gases, emphasizing the legal obligations of industries to adhere to safety standards.
7.2. International Standards:
Understanding international standards and harmonization efforts in the context of LEL and UEL will help industries ensure global compliance and consistency in safety practices.
Conclusion:
In conclusion, the differences between Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL) are fundamental to ensuring the safe handling of flammable gases in various industrial settings. By comprehensively understanding these concepts, industries can implement effective safety measures, minimize risks, and create a secure working environment. This guide serves as a valuable resource for professionals, safety officers, and decision-makers looking to enhance their knowledge and improve safety protocols in their respective industries.
LEL / UEL RANGE
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.
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:
- The presence of combustible gas, the fueling element, in a specific concentration
- Presence of oxygen
- The existence of a sparking element (that ignites the two elements)
The proportion of fuel and the 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.
LEL UEL CHART BY GAS TYPE
(Note: LEL / UEL values are based on room temperature and atmospheric pressure, ignition fired by a tube of 2-inch diameter.
As the temperature, the pressure and the ignition increase, the explosive limits by gas vary.
The values are determined empirically and may change depending on the source of the information). The lower and the upper explosive limits by gas are:
LEL Gas | LEL % | UEL % | |
Acetone | 2.6 | 13.0 | |
Acetylene | 2.5 | 100.0 | |
Acrylonitrile | 3.0 | 17 | |
Allene | 1.5 | 11.5 | |
Ammonia | 15.0 | 28.0 | |
Benzene | 1.3 | 7.9 | |
1,3-Butadiene | 2.0 | 12.0 | |
Butane | 1.8 | 8.4 | |
n-Butanol | 1.7 | 12.0 | |
1-Butene | 1.6 | 10.0 | |
Cis-2-Butene | 1.7 | 9.7 | |
Trans-2-Butene | 1.7 | 9.7 | |
Butyl Acetate | 1.4 | 8.0 | |
Carbon Monoxide | 12.5 | 74.0 | |
Carbonyl Sulfide | 12.0 | 29.0 | |
Chlorotrifluoroethylene | 8.4 | 38.7 | |
Cumene | 0.9 | 6.5 | |
Cyanogen | 6.6 | 32.0 | |
Cyclohexane | 1.3 | 7.8 | |
Cyclopropane | 2.4 | 10.4 | |
Deuterium | 4.9 | 75.0 | |
Diborane | 0.8 | 88.0 | |
Dichlorosilane | 4.1 | 98.8 | |
Diethylbenzene | 0.8 |
– |
|
1,1-Difluoro-1-Chloroethane | 9.0 | 14.8 | |
1,1-Difluoroethane | 5.1 | 17.1 | |
1,1-Difluoroethylene | 5.5 | 21.3 | |
Dimethylamine | 2.8 | 14.4 | |
Dimethyl Ether | 3.4 | 27.0 | |
2,2-Dimethylpropane | 1.4 | 7.5 | |
Ethane | 3.0 | 12.4 | |
Ethanol | 3.3 | 19.0 | |
Ethyl Acetate | 2.2 | 11.0 | |
Ethyl Benzene | 1.0 | 6.7 | |
Ethyl Chloride | 3.8 | 15.4 | |
Ethylene | 2.7 | 36.0 | |
Ethylene Oxide | 3.6 | 100.0 | |
Gasoline | 1.2 | 7.1 |
Gas | LEL | UEL | |
Heptane | 1.1 | 6.7 | |
Hexane | 1.2 | 7.4 | |
Hydrogen | 4.0 | 75.0 | |
Hydrogen Cyanide | 5.6 | 40.0 | |
Hydrogen Sulfide | 4.0 | 44.0 | |
Isobutane | 1.8 | 8.4 | |
Isobutylene | 1.8 | 9.6 | |
Isopropanol | 2.2 |
– |
|
Methane | 5.0 | 15.0 | |
Methanol | 6.7 | 36.0 | |
Methylacetylene | 1.7 | 11.7 | |
Methyl Bromide | 10.0 | 15.0 | |
3-Methyl-1-Butene | 1.5 | 9.1 | |
Methyl Cellosolve | 2.5 | 20.0 | |
Methyl Chloride | 7.0 | 17.4 | |
Methyl Ethyl Ketone | 1.9 | 10.0 | |
Methyl Mercaptan | 3.9 | 21.8 | |
Methyl Vinyl Ether | 2.6 | 39.0 | |
Monoethylamine | 3.5 | 14.0 | |
Monomethylamine | 4.9 | 20.7 | |
Nickel Carbonyl | 2.0 |
– |
|
Pentane | 1.4 | 7.8 | |
Picoline | 1.4 |
– |
|
Propane | 2.1 | 9.5 | |
Propylene | 2.4 | 11.0 | |
Propylene Oxide | 2.8 | 37.0 | |
Styrene | 1.1 |
– |
|
Tetrafluoroethylene | 4.0 | 43.0 | |
Tetrahydrofuran | 2.0 |
– |
|
Toluene | 1.2 | 7.1 | |
Trichloroethylene | 12.0 | 40.0 | |
Trimethylamine | 2.0 | 12.0 | |
Turpentine | 0.7 |
– |
|
Vinyl Acetate | 2.6 |
– |
|
Vinyl Bromide | 9.0 | 14.0 | |
Vinyl Chloride | 4.0 | 22.0 | |
Vinyl Fluoride | 2.6 | 21.7 | |
Xylene | 1.1 | 6.6 |
MEASURING LEL/UEL: METERS
To operate safely in hazardous environments, i.e. closed spaces with combustible gases present, the concentration of the gas should be monitored closely.
As the concentration of the gas exceeds 20% of the gas LEL, is considered unsafe.
To monitor gas concentration value in closed and hazardous environments, operators may use LEL meters (also called, LEL meters/detectors) which are designed with catalytic bead and infrared sensing elements to measure the lower explosive limit of gases.
These gas detectors give warnings to the operators whenever the combustible gas is present in the environment at levels around 10%.
LEL meters are rather sophisticated devices, that feature microprocessors based modular design with self-calibration and digital display of the information.
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 can measure the concentration of inflammable gases and other toxic gases even at very low levels (from ppb, i.e. parts per billion, up to 10k ppm, i.e. 1%).
PIDs are way more sensitive tools then common LEL meters and are generally more expensive. PIDs are suited to measure the following organic compounds:
- Alcohol
- Aromatics
- Amines & Amides
- Chlorinated hydrocarbons
- Ketones & Aldehydes
- Sulfur compounds
- Unsaturated hydrocarbons
- Saturated hydrocarbons – like butane and octane
The inorganic compounds that can be measured by photoionization detectors are:
- Ammonia
- Bromine
- Iodine
- Hydrogen sulfide
- Nitric Oxide
- Semiconductor gases
10 Responses
This is my first time visit at here and i am actually pleassant to read all at single place.
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?
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
Answer: 5-15, but…2.5 if you add a particle like coal dust
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.
86 to 96
air with oxygen concentration between 19.5% to 23.5%
As per ISGOTT Flammabillity diagram minimum percentage of air for combustion is around 12% by volume, max 20.9%
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.
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 ?