Little Pro on 2016-01-13 Explosive limits specify the concentration range of a material in air which will burn or explode in the presence of an ignition source. There are two types of explosive limits: lower explosive limit (LEL) and upper explosive limit (UEL).

1. The explosive limits are usually given as the percent by volume of the material in the air (i.e., 5%).
2. You can often find it in the section 9 of a safety data sheet (SDS).
3. Lower explosive limit (LEL) : the lowest concentration of gas or vapour which will burn or explode if ignited.
4. Upper explosive limit (UEL) : the highest concentration of gas or vapour which will burn or explode if ignited.

From the LEL to the UEL, the mixture is explosive. Below the LEL, the mixture is too lean to burn. Above the UEL, the mixture is too rich to burn. However, concentrations above the UEL are still very dangerous because, if the concentration is lowered (for example, by introducing fresh air), it will enter the explosive range.

What is a safe LEL level?

This appendix is a non-mandatory set of guidelines provided to assist employers in complying with the requirements of this subpart. This appendix neither creates additional obligations nor detracts from obligations otherwise contained in the standard.

1. It is intended to provide explanatory information and educational material to employers and employees to foster understanding of, and compliance with, the standard.
2. Sections 1915.11 through 1915.16,
3. These standards are minimum safety standards for entering and working safely in vessel tanks and compartments.

Section 1915.11(b) Definition of “Hot work.” There are several instances in which circumstances do not necessitate that grinding, drilling, abrasive blasting be regarded as hot work. Some examples are: 1. Abrasive blasting of the external surface of the vessel (the hull) for paint preparation does not necessitate pumping and cleaning the tanks of the vessel.2.

Prior to hot work on any hollow structure, the void space should be tested and appropriate precautions taken. Section 1915.11(b) Definition of “Lower explosive limit.” The terms lower flammable limit (LFL) and lower explosive limit (LEL) are used interchangeably in fire science literature. Section 1915.11(b) Definition of “Upper explosive limit.” The terms upper flammable limit (UFL) and upper explosive limit (UEL) are used interchangeably in fire science literature.

Section 1915.12(a)(3), After a tank has been properly washed and ventilated, the tank should contain 20.8 percent oxygen by volume. This is the same amount found in our normal atmosphere at sea level. However, it is possible that the oxygen content will be lower.

• When this is the case, the reasons for this deficiency should be determined and corrective action taken.
• An oxygen content of 19.5 percent can support life and is adequate for entry.
• However, any oxygen level greater than 20.8 percent by volume should alert the competent person to look for the cause of the oxygen-enriched atmosphere and correct it prior to entry.

In addition, any oxygen level lower than 19.5 percent level should also alert the competent person to look for the cause of the oxygen-deficiency and correct it prior to entry. Section 1915.12(b)(3) Flammable atmospheres, Atmospheres with a concentration of flammable vapors at or above 10 percent of the lower explosive limit (LEL) are considered hazardous when located in confined spaces.

However, atmospheres with flammable vapors below 10 percent of the LEL are not necessarily safe. Such atmospheres are too lean to burn. Nevertheless, when a space contains or produces measurable flammable vapors below the 10 percent LEL, it might indicate that flammable vapors are being released or introduced into the space and could present a hazard in time.

Therefore, the cause of the vapors should be investigated and, if possible, eliminated prior to entry. Some situations that have produced measurable concentrations of flammable vapors that could exceed 10 percent of the LEL in time are: 1. Pipelines that should have been blanked or disconnected have opened, allowing product into the space.2.

• The vessel may have shifted, allowing product not previously cleaned and removed during washing to move into other areas of the vessel.3.
• Residues may be producing the atmosphere by releasing flammable vapor.
• Section 1915.12(b)(6) Flammable atmospheres that are toxic,
• An atmosphere with a measurable concentration of a flammable substance below 10 percent of the LEL may be above the OSHA permissible exposure limit for that substance.

In that case, refer to § 1915.12(c) (2), (3), and (4). Sections 1915.13(b)(4), 1915.15(c), and 1915.15(e), The frequency with which a tank is monitored to determine if atmospheric conditions are being maintained is a function of several factors that are discussed below: 1.

Temperature, Higher temperatures will cause a combustible or flammable liquid to vaporize at a faster rate than lower temperatures. This is important since hotter days may cause tank residues to produce more vapors and that may result in the vapors exceeding 10 percent of the LEL or an overexposure to toxic contaminants.2.

Work in the tank, Any activity in the tank could change the atmospheric conditions in that tank. Oxygen from a leaking oxyfuel hose or torch could result in an oxygen-enriched atmosphere that would more easily propagate a flame. Some welding operations use inert gas, and leaks can result in an oxygen-deficient atmosphere.

Manual tank cleaning with high pressure spray devices can stir up residues and result in exposures to toxic contaminants. Simple cleaning or mucking out, where employees walk through and shovel residues and sludge, can create a change in atmospheric conditions.3. Period of time elapsed, If a period of time has elapsed since a Marine Chemist or Coast Guard authorized person has certified a tank as safe, the atmospheric condition should be rechecked by the competent person prior to entry and starting work.4.

Unattended tanks or spaces, When a tank or space has been tested and declared safe, then subsequently left unattended for a period of time, it should be retested prior to entry and starting work. For example, when barges are left unattended at night, unidentified products from another barge are sometimes dumped into their empty tanks.

1. Since this would result in a changed atmosphere, the tanks should be retested prior to entry and starting work.5.
2. Work break,
3. When workers take a break or leave at the end of the shift, equipment sometimes is inadvertently left in the tanks.
4. At lunch or work breaks and at the end of the shift are the times when it is most likely someone will leave a burning or cutting torch in the tank, perhaps turned on and leaking oxygen or an inert gas.

Since the former can produce an oxygen-enriched atmosphere, and the latter an oxygen-deficient atmosphere, tanks should be checked for equipment left behind, and atmosphere, monitored if necessary prior to re-entering and resuming work. In an oxygen-enriched atmosphere, the flammable range is severely broadened.

This means that an oxygen-enriched atmosphere can promote very rapid burning.6. Ballasting or trimming, Changing the position of the ballast, or trimming or in any way moving the vessel so as to expose cargo that had been previously trapped, can produce a change in the atmosphere of the tank. The atmosphere should be retested after any such move and prior to entry or work.

Section 1915.14 (a) and (b) Hot work, This is a reminder that other sections of the OSHA shipyard safety and health standards in part 1915 should be reviewed prior to starting any hot work. Most notably, subpart D, Welding, Cutting and Heating, places additional restrictions on hot work.

The requirements of §§ 1915.51 and 1915.53 must be met before hot work is begun on any metal that is toxic or is covered by a preservative coating respectively; the requirements of § 1915.54 must be met before welding, cutting, or heating is begun on any hollow containers or structures not covered by § 1915.12.

Section 1915.12(a)(2), During hot work, more than 20.8 percent oxygen by volume can be unsafe since it extends the normal flammable range. The standard permits the oxygen level to reach 22 percent by volume in order to account for instrument error. However, the cause of excess oxygen should be investigated and the source removed.

What does 5% LEL mean?

The Lower Explosive Limit (LEL) varies from gas to gas, but for most flammable gases it is less than 5% by volume. This means that it takes a relatively low concentration of gas or vapour to produce a high risk of explosion.

What is the meaning of 1% LEL?

Lower and Upper Explosive Limits – The values shown in the table below are valid only for the conditions under which they were determined (usually room temperature and atmospheric pressure using a 2 inch tube with spark ignition). The flammability range of most materials expands as temperature, pressure and container diameter increase. All concentrations in percent by volume.

One of the many requirements for entering confined spaces is the measurement for flammable gases. Prior to entry of a confined space, the level of flammable gases must be below 10% of LEL. The most common sensor used for measuring LEL is the Wheatstone bridge/catalytic bead/pellistor sensor (“Wheatstone bridge”).

1. A Wheatstone bridge LEL sensor is simply a tiny electric stove with two burner elements.
2. One element has a catalyst (such as platinum) and one doesn’t.
3. Both elements are heated to a temperature that normally would not support combustion.
4. However, the element with the catalyst “burns” gas at a low level and heats up relative to the element without the catalyst.

The hotter element has more resistance and the Wheatstone bridge measures the difference in resistance between the two elements, which correlates to LEL. Unfortunately, Wheatstone bridge sensors fail to an unsafe state; when they fail, they indicate safe levels of flammable gases. Failure and/or poisoning of Wheatstone bridge LEL sensor can only be determined through challenging Wheatstone bridge sensors with calibration gas.

1. Gases burn with different heat outputs Some gases burn hot and some burn relatively cool. These differing physical characteristics lead to difficulties when using LEL sensors. For example, 100% of LEL Methane (5% methane by volume) burns with twice the heat of 100% of LEL Propane (2.0 propane by volume).
2. Heavier hydrocarbon vapors have difficulty diffusing into LEL sensors and reduce their output Some Heavier hydrocarbon vapors have difficulty diffusing through the sintered metal flame arrestor on LEL sensors. This flame arrestor is necessary to prevent the sensor itself from starting a fire and does not prevent gases like methane, propane and ethane from reaching the Wheatstone bridge. However, hydrocarbons like gasoline, diesel, solvents, etc, diffuse through the flame arrestor slower so that less vapor reaches the Wheatstone bridge and the sensor gives less output.

Many Volatile Organic Compounds (VOCs) are flammable and may be detected by the LEL or combustible gas sensors found in virtually every multigas monitor. However, LEL sensors are not particularly useful in measuring toxicity because they do not have enough sensitivity. What are Some common VOC? VOCs are the chemical compounds that keep industry going and include.

• Fuels
• Oils, °reasers, Heat Transfer Fluids
• Solvents, Paints
• Plastics, Resins and their precursors
• and many others

VOCs are found throughout industry, from the obvious applications in the petro-chem industry to not-so-obvious applications such as sausage manufacturing. What is meant by PPM? Parts per million (ppm) is a commonly used unit of concentration for small values. One part per million is one part of solute per one million parts solvent or 10 -6, Parts per million and other “parts per” notations (e.g., parts per billion or parts per trillion) are dimensionless quantities with no units.

1. Preferred methods for expressing parts per million include μV/V (microvolume per volume), μL/L (microliters per liter), mg/kg (milligram per kilogram), μmol/mol (micromole per mole), and μm/m (micrometer per meter).
2. The “parts per” notation is used to describe dilute solutions in chemistry and engineering, but its meaning is ambiguous and it is not part of the SI system of measurement.

The reason the system is ambiguous is because the concentration depends on the original unit fraction that is used. For example, comparing one milliliter of a sample to a million milliliters is different from comparing one mole to a million moles or one gram to one million grams.

• one inch in 16 miles
• one second in 11.5 days
• one minute in two years
• one car in bumper-to bumper traffic from Cleveland to San Francisco

Other visualization of scale involved with PPB One PPB is like.

• adding a pinch of salt to a 10 ton bag of potato chips
• One ppb is like one sheet in a roll of toilet paper stretching from New York to London.

LEL Sensors Measure Explosivity, Not Toxicity LEL sensors measure percent of LEL. For example, Gasoline has an LEL of 1.4%. Therefore, 100% of LEL is 14,000 ppm of gasoline, 10% of LEL is 1,400 ppm of gasoline and 1% of LEL is 140 ppm of gasoline.140 ppm of gasoline is the lowest amount of vapor that the LEL monitor can “see.” Gasoline has a TWA of 300 ppm and a STEL of 500 ppm; this does not make LEL sensors well suited for measuring gasoline vapors because they simply don’t provide adequate resolution.

• One of the many requirements for entering confined spaces called is the measurement of confined spaces for flammable gases.
• Prior to entry of a confined space, the level of flammable gases must be below 10% of LEL.
• The most common sensor used for measuring LEL is the Wheatstone bridge/catalytic bead/pellistor sensor (“Wheatstone bridge”).
• While useful in a wide variety of applications, in some settings Wheatstone bridge LEL sensors either don’t have enough sensitivity to a particular chemical, or chemicals used in the environment can render the Wheatstone bridge sensor inoperable.
• In these types of circumstances, PIDs (photoionization detectors) can provide an alternative, highly accurate, and poison-free means of measuring 10% of LEL for confined space entry.

What is a PID? A Photo-Ionization Detector measures VOCs and other toxic gases in low concentrations from ppb (parts per billion) up to 10,000 ppm (parts per million or 1% by volume). A PID is a very sensitive broad-spectrum monitor, like a “low-level LEL monitor.

1. A Photo-Ionization Detector measures VOCs and other toxic gases in low concentrations from ppb (parts per billion) up to 10,000 ppm (parts per million or 1% by volume).
2. A PID is a very sensitive broad-spectrum monitor, like a “low-level LEL monitor.
3. How does a PID Work? A Photo Ionization Detector (PID) uses an Ultraviolet (UV) light source (Photo= light) to break down chemicals to positive and negative ions (Ionization) that can easily be counted with a Detector.

Ionization occurs when a molecule absorbs the high energy UV light, which excites the molecule and results in the temporary loss of a negatively charged electron and the formation of positively charged ion. The gas becomes electrically charged. In the Detector these charged particles produce a current that is then amplified and displayed on the meter as “ppm” (parts per million) or even in “ppb” (parts per billion).

1. The ions quickly recombine after the electrodes in the detector to “reform” their original molecule.
2. PIDs are non-destructive; they do not “burn” or permanently alter the sample gas, which allows them to be used for sample gathering.
3. What does a PID measure?

The largest group of compounds measured by a PID are the Organics. compounds containing Carbon (C) atoms. These include.

• Aromatics – compounds containing a benzene ring including benzene, toluene, ethyl benzene and xylene
• Ketones and Aldehydes – compounds with a C=O bond including acetone, methyl ethyl ketone (MEK) and acetaldehyde
• Amines and Amides – Carbon compounds containing nitrogen, like diethylamine
• Chlorinated hydrocarbons – trichloroethylene (TCE), perchloroethylene (PERC)
• Sulfur compounds – mercaptans, sulfides
• Unsaturated hydrocarbons – like butadiene and isobutylene
• Alcohol’s- like isopropanol (IPA) and ethanol
• Saturated hydrocarbons – like butane and octane. In addition to organic compounds, PIDs can be used to measure some Inorganics. These are compounds without carbon and include.
• Ammonia
• Semiconductor gases. Arsine, Phosphine
• Hydrogen sulfide
• Nitric Oxide
• Bromine and Iodine

Sources.

1. Data extracted from Gas Data Book, 7th edition, copyright by Matheson Gas Products, and from Bulletin 627
2. Flammability Characteristics of Combustible Gases and Vapors, copyright by U.S.Department of the Interior, Bureau of Mines

Related Post(s) What is a confined space? Generally speaking, a confined space is a fully or partially enclosed space that is not primarily designed or intended for continuous human occupancy. : Lower and Upper Explosive Limits for Flammable Gases and Vapors

What does 20 LEL mean?

20% LEL is the High Alarm, a distress signal. Not explosive yet.100% LEL means the gas concentration has reached the lower explosive limit and became explosive.

What does 0 100 LEL mean?

If you spend much time working with calibration gas, it’s very likely that you will see the term “LEL” used extensively. LEL, short for “Lower Explosive Limit”, is defined as the lowest concentration (by percentage) of a gas or vapor in air that is capable of producing a flash of fire in presence of an ignition source (arc, flame, heat, etc.).

Concentrations lower than the Lower Explosive Limit are ‘too lean’ to burn; those above the Upper Explosive Limit (UEL) are too rich to burn. In gas-detection systems, the amount of gas present is specified as a percentage (%) of LEL. Zero percent Lower Explosive Limit (0% LEL) denotes a combustible gas-free atmosphere.

One hundred percent lower explosive limit (100% LEL) denotes an atmosphere in which gas is at its lower flammable limit. The relationship between percent LEL and percent by volume differs from gas to gas. The example below demonstrates the flammability of Methane (Natural Gas) in Air.

In concentrations of 0-5% Methane in air, the mixture is too lean to ignite or burn. Methane concentrations between 5% and 17% in will support ignition and are considered highly flammable. At levels above 17%, the atmosphere is too rich for the methane to ignite. To compute the LEL of any gas in air, divide the unknown concentration by the LEL listed in the NFPA Handbook.100% LEL’s for 9 of Gasco’s more common gasses are shown in the Table 1A here.

For example, if you take 2.5% Methane in air and divide it by 100% LEL of methane (5%), the result is 50% LEL. (2.5% ÷ 5% = 50%) The same theory can be applied to any of the gasses listed here. Conversely, you can multiply the % LEL of the unknown concentration by the 100% LEL to obtain the % by volume. Table 1A Since air is made up primarily of 20.9% Oxygen with the balance being nitrogen, if you take Oxygen out of the equation, the methane is no longer flammable at any concentration. This is important when ordering mixtures with no oxygen content; without oxygen, LEL is not a factor. If you need help determining the correct calibration gas for your application, our experts are here to help!

What is 100% LEL in ppm?

1% means 1 part out of a 100: Eventually, we go down to 0.1%, 0.01%, 0.001%, but these numbers get kind of cumbersome, so it becomes convenient to change scale.100% also means 1 million out of a million. Therefore, 10% is the same as 100,000 parts of a million (ppm).1% is the same as 10,000 parts per million.

How many ppm is 20% LEL?

20% of LEL = 1 % (= 10000 ppm ).

What is the LEL limit in a confined space?

Monitor The LELs In Confined Spaces With GDS Corp GDS Corp. is a respected gas and flame detection company for the commercial and industrial sectors. When you need to monitor the LELs within your facility, come to us. What Is LEL and Confined Space? A Confined Space is an enclosed area such as a storage tank, fuel vessel or other containment enclosure, where monitoring and detecting LEL as well as other hazardous materials is regulated by Federal Law.

An LEL Confined Space will be a containment vessel that contains combustible gas or solvent, which when emptied poses an explosive and toxic gas risk to the personnel that have to enter the Confined Space for maintenance or other purposes that may be related to the process with which the materials in the Confined Space is used.

An LEL Confined Space refers to Lower Explosive Limit within the confined space, which will be a percentage of combustible material in a gas or vapor state, that if mixed in the right proportion with air can create a hazardous fuel/air mixture that can be ignited and explode.

Since personnel entering the Confined Space for maintenance may be performing actions such as welding, or other maintenance where ignition sources could be present, it is critical that the LEL level be monitored and that if any LEL level exists within the Confined Space, that alarms immediately occur to warn the personnel to take immediate safety action.

Typically, an LEL Confined Space will be well ventilated and even purged with an inert gas such as nitrogen so that if a hazardous combustible gas or solvent vapor is in the confined space, these additional safety measures will protect personnel and keep confined space LEL levels from being present.

1. An LEL Confined Space will also require not only monitoring and the detection and alarm of combustible materials inside the confined space, but that an attendant be outside the confined space to monitor the conditions inside.
2. Should a person inside the confined space be in danger, or overcome by vapors or gases, proactive safety measures will be taken immediately upon an alarm condition.

Fixed Gas Detection Systems are available to monitor inside an LEL Confined Space on a continuous basis. There are also sample draw gas detection systems that can sample the atmosphere inside an LEL Confined Space, and indicate on an instrument outside of the confined space the hazardous levels of combustible and toxic gas or vapor, or the deficiency of oxygen if inert gas is pumped into the LEL Confined Space.

Get in Touch with GDS Corp. Today Contact GDS Corp., a U.S. manufacturer of Industrial Gas Detection Equipment using sensor technologies such as Catalytic Bead sensors, electrochemical sensors, photoionization sensors and infrared sensors located in Houston, Texas. Our many years of experience with Industrial Gas Detection, and Fixed Gas Detection solutions using these various sensor technologies can assist with decisions for the system required to protect employees entering an LEL Confined Space.

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What percent of LEL is explosive?

The lower explosive limit (LEL) is the minimal amount of concentration needed of a particular chemical to cause an explosion. The LEL is determined empirically for each pure chemical and air mixture at a given temperature. If more than than one chemical is dispersed in the air, as is normally the case, then LeChatelier’s mixing rule can be applied to get the cumulative LEL for the mixture.

• Concentrations lower than the Lower Explosive Limit are ‘too lean’ to burn; those above the Upper Explosive Limit (UEL) are too rich to burn.The a mount of gas present is specified as a percentage (%) of LEL.
• Zero percent Lower Explosive Limit (0% LEL) denotes a combusti ble gas-free atmosphere.
• One hundred percent lower explosive limit (100% LEL) denotes an atmosphere in which gas is at its lower flammable limit.

The relationship between percent LEL and percent by volume differs from gas to gas.The example below demonstrates the flammability of Methane (Natural Gas) in Air. In concentrations of 0-5% Methane in air, the mixture is too lean to ignite or burn. Methane concentrations between 5% and 17% will support ignition and are considered highly flammable. –

What is 10% of the LEL?

Methane LEL – Let’s have a look at how we can interpret this measurement. Methane LEL is 4.4% volume-per-volume, which means that if the concentration of methane in 1 cubic metre of air exceeds 4.4%, the mixture will explode. If the alarm goes off at 10% LEL, it means that the detector will calculate 10% of 4.4%, being 0.44% of the cubic metre of air.

What is 4% LEL in ppm?

Percent to ppm conversion table

What does 50% LEL mean?

The LEL of a gas is the lowest concentration of that gas which can combust. A reading in %LEL measures the percentage of that LEL value. For example, for methane, the LEL is 5% by volume.50% LEL is half of that value, or 2.5% by volume.

What is 4% LEL hydrogen?

The LEL (lower explosive level) of Hydrogen is generally considered to be 4% by volume (4% v/v). That means the mixture is too lean to burn if there is less than 4% Hydrogen present. But at 4%, we can burn or explode if there is an ignition source.

What is an example of a LEL?

2) How is the LEL of gas measured? – The LEL of a gas is measured as a percentage of volume. If you’re using an LEL gas detector, the display will show a 0-100% LEL readout. For example, hydrogen gas has an LEL of 4% by volume in the air. When the volume of hydrogen gas has reached the point of 2% by volume, then the detector will read 50% LEL.

Will LEL detect natural gas?

LEL Gas Detectors: Learn How They Work | GDS GDS Corp. is proud to provide the commercial and industrial sectors with high quality LEL detectors and LEL analyzers to ensure LEL safety. An LEL Detector or LEL Meter detects dangerous levels of a combustible gas or solvent vapor in air, expressed in percent Lower Explosive Limit, or LEL.

1. An LEL Detector is an integral part of a complete gas detection system and can be referred to as a Gas Detector or just a fixed gas detection system.
2. How Do LEL Detectors Work? Combustible gas and solvents that create explosive vapor in air when spilled, or leak into an area, have a Lower Flammable Limit found on a specific Material Safety Data Sheet materials (MSDS).

LFL is the same as LEL. Combustible Gases and Solvents also have an Upper Flammable Limit (UFL), which is the same as with UEL, or Upper Explosive Limit. An LEL Detector simply detects, indicates and alarms for levels between 0-100% LEL of materials it is calibrated to monitor and detect.

Using methane in air as an example, the LEL of methane is 5% by volume. So an LEL Detector or an LEL analyzer, working as part of a complete LEL Gas Detection System, that’s calibrated to detect methane in air in a range of 0-100% LEL Methane will detect the presence of methane in air between 0-100% LEL, or 0-5% by volume.

An LEL Meter in a fixed gas detection system calibrated for 0-100% LEL methane when reading 50% LEL methane will read the equivalent of 2.5% Methane by volume in air. Because LEL analyzers are detecting combustible gas or solvent vapor in the LEL range above, the LEL Detector is functioning in a safe range, before the LEL level reaches 100% LEL, or the minimum level needed to support ignition or combustion.

1. An LEL Detector is an essential component of a fixed gas detection safety instrument for LEL safety and so monitors, indicates and alarms when levels of LEL exceed 0% to indicate the presence of combustible gas or solvent vapor.
2. This is well before a combustible fuel/air mixture exists near the LEL analyzer.

Generally, the dangerous areas where these combustible materials remain or get used are regulated by local, state and federal entities, and designated as hazardous locations. LEL Detectors and the fixed gas detection system that they work within are also classified for use in the hazardous locations where these materials are kept or interacted with, to maintain LEL safety.

It is also important to understand the differences and apply the correct LEL Meter sensor technology to the application for LEL safety. Catalytic Bead sensors and Infrared sensors are used in LEL Detection, and each has advantages and disadvantages that need to be fully understood before selecting the proper technology to be used in a fixed gas detection system that uses an LEL analyzer.

Contact GDS Corp. Today If you have any questions about LEL safety, the LEL detector working principle or the LEL analyzer wiki, feel free to give us a call, using one of the many provided phone numbers. Our application engineers look forward to hearing from you!

GDS Gas Detection Products Our CSA and ATEX certified fixed and transportable gas detectors, gas sensors, flame detectors and alarm and display controllers are truly ‘state of the art’ devices offering unparalleled features and capabilities.

: LEL Gas Detectors: Learn How They Work | GDS

What is LEL and H2S?

LEL / CO / H2S / O2 (Standard 4-Gas Configurations) The store will not work correctly in the case when cookies are disabled. Shop here for gas detectors with the standard four gas configuration. This includes LEL (lower explosive limit, CO (carbon monoxide), H2S (hydrogen sulphide) and O2 (oxygen).

What is max ppm?

The American Conference of Governmental Industrial Hygienists (ACGIH) recommends an 8- hour TWA Threshold Limit Value (TLV) of 5,000 ppm and a Ceiling exposure limit (not to be exceeded) of 30,000 ppm for a 10-minute period. A value of 40,000 is considered immediately dangerous to life and health (IDLH value).

Is methane ppm or LEL?

– The basics of measuring ranges – – The abbreviation LEL stands for Lower Explosion Limit and it corresponds to the concentration of a substance in the air above which there is a risk of explosion. The LEL of flammable gases such as methane, ethane, propane and butane is relevant for us.

In this article we will limit ourselves to the LEL of methane. Methane is measured in % LEL or % by volume ( vol.-%), Methane is also measured in ppm (parts per million). The LEL monitoring serves the safety of individuals, because it can be stated that 100% LEL corresponds to 100% risk of explosion. When working in an area above the LEL, an ignition source in combination with oxygen can cause an explosion.

In Europe, we have set the LEL of methane at 4.4 vol.-%. Below this limit, ignition is not possible because the mixture of air and methane is too lean. However, since measurements are only monitored at specific points, it is necessary to work at high safety levels.

For example, if we measure in front of the body, the concentration in the room could increase significantly towards the ceiling. Another reason for low alarm levels is that natural gas is always a gas mixture and contains other components besides methane. For example, propane and butane are often found in addition to ethane.

Since these gases are explosive even at lower concentrations, the LEL of natural gas is usually slightly below 4.4 vol.-%, For this reason, the alarm levels in Germany are set at 20% LEL or often already at 10% LEL for the first alarm.

What does 50% LEL mean?

The LEL of a gas is the lowest concentration of that gas which can combust. A reading in %LEL measures the percentage of that LEL value. For example, for methane, the LEL is 5% by volume.50% LEL is half of that value, or 2.5% by volume.

What is 10% of the LEL?

Methane LEL – Let’s have a look at how we can interpret this measurement. Methane LEL is 4.4% volume-per-volume, which means that if the concentration of methane in 1 cubic metre of air exceeds 4.4%, the mixture will explode. If the alarm goes off at 10% LEL, it means that the detector will calculate 10% of 4.4%, being 0.44% of the cubic metre of air.

What is 4% LEL in ppm?

Percent to ppm conversion table

What percent of LEL is explosive?

The lower explosive limit (LEL) is the minimal amount of concentration needed of a particular chemical to cause an explosion. The LEL is determined empirically for each pure chemical and air mixture at a given temperature. If more than than one chemical is dispersed in the air, as is normally the case, then LeChatelier’s mixing rule can be applied to get the cumulative LEL for the mixture.

• Concentrations lower than the Lower Explosive Limit are ‘too lean’ to burn; those above the Upper Explosive Limit (UEL) are too rich to burn.The a mount of gas present is specified as a percentage (%) of LEL.
• Zero percent Lower Explosive Limit (0% LEL) denotes a combusti ble gas-free atmosphere.
• One hundred percent lower explosive limit (100% LEL) denotes an atmosphere in which gas is at its lower flammable limit.

The relationship between percent LEL and percent by volume differs from gas to gas.The example below demonstrates the flammability of Methane (Natural Gas) in Air. In concentrations of 0-5% Methane in air, the mixture is too lean to ignite or burn. Methane concentrations between 5% and 17% will support ignition and are considered highly flammable. –

Jack Gloop