The Lower Explosive Limit

What is a safe LEL reading?

If a gas concentration is below its LEL, it cannot ignite, and the confined space is considered safe. If the gas concentration is above its UEL, the gas is too rich and there’s not enough oxygen for combustion. … Methane, for example, has an LEL of 5% vol and a UEL of 15% vol.

How does an LEL meter work?

A catalytic bead LEL sensor senses a combustible gas through flameless combustion that occurs with the help of electrically produced heat and a catalyst material coating on the sensing bead. In other words, a CB LEL sensor detects gas through the actual burning of the gas.

What is a safe LEL level natural gas?

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.

What is the difference between LEL and LFL?

Lower flammability limit (LFL): The lowest concentration (percentage) of a gas or a vapor in air capable of producing a flash of fire in the presence of an ignition source (arc, flame, heat). The term is considered by many safety professionals to be the same as the lower explosive level (LEL).

At what percent is natural gas explosive?

Natural gas has a flammability range of approximately 5 to 15 percent. That means that any mixture containing less than 5 percent or greater than 15 percent natural gas to air would not support combustion.

What is the upper explosive limit?

The highest concentration of a gas or vapor (percentage by volume in air) above which a flame will not spread in the presence of an ignition source (arc, flame, or heat). Concentrations higher than UEL are “too rich” to burn.

What's the difference between LEL and percent by volume?

The Percent by Volume means that in a total sample of any given gases equivalent to the 100%, while percentage of a Explosive/flammable gas within that total will mean a risk. … Meaning this that the %LEL is the total needed percentage out of a 100% of a flammable gas.

What are the lower and higher explosive levels of natural gas?

The minimum concentration of a particular gas necessary to support its combustion in air is defined as the Lower Explosive Limit (LEL). Below this level, the mixture is too “lean” to burn. The maximum concentration of a gas or vapour that will cause an explosion is defined as the Upper Explosive Limit (UEL).

How do you read a gas meter LEL?

In other words, 100% LEL = 5% volume. When methane concentration levels reach 100% LEL, the gas will explode if an ignition source is present. For propane, 100% LEL = 2.1% volume, and for hydrogen, 100% LEL = 4.0% volume. So the %LEL scale is based entirely on explosive limits.

Article first time published on

What is the meaning of LEL OSHA?

Lower explosive limit (LEL) means the minimum concentration of vapor in air below which propagation of a flame does not occur in the presence of an ignition source.

Is LEL and LEL the same?

GasLELUELXylene1.16.6GasLELUEL

What is the maximum allowable lower explosive level LEL?

The Lower Explosive Limit (LEL) is the lowest concentration of a gas or vapour that will burn in air. The Lower Explosive Limit (LEL) varies from gas to gas, but for most flammable gases it is less than 5% by volume.

What does LEL mean in confined space?

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.

How is LEL measured?

How is LEL measured? Known combustible gasses have a determined LEL expressed as a volume %Vol. As the amount of detectable combustible gas rises, an LEL sensor will display a readout from 0 – 100% LEL. For example: Methane has an LEL of 5.0% Vol in air.

What is difference between LEL and UEL?

Lower explosive limit (LEL): the lowest concentration of gas or vapour which will burn or explode if ignited. Upper explosive limit (UEL): the highest concentration of gas or vapour which will burn or explode if ignited.

What is a low flashpoint?

Flash point is the lowest temperature at which a chemical can vaporize to form an ignitable mixture in air. A lower flash point indicates higher flammability. … At the flash point, the vapor may cease to burn when the ignition source is removed. You can often find it in the section 9 of a safety data sheet (SDS).

Which gas has the widest flammable range?

Fuel Gas”Lower Explosive or Flammable Limit” (LEL/LFL) (% by volume of air)”Upper Explosive or Flammable Limit” (UEL/UFL) (% by volume of air)Carbon monoxide1275Carbon oxysulfide1229Chlorobenzene1.39.6Chloroethane3.815.4

What is a safe LEL level UK?

For leak detection purposes (ie not process monitoring), the first alarm level should be set as low as practicable, preferably no higher than 10% of the lower explosion limit (LEL). The second alarm level should be no more than 25% LEL.

How many ppm is 1 LEL natural gas?

So, 1.0% LEL hydrogen = 40,000 ppm X 0.01 = 400 ppm.

What is the difference between LEL and PPM?

LEL stands for the Lower Explosive Limit of a gas. It is the minimal concentration of the gas required for the gas to ignite. It is normally expressed as a percentage of the total air. PPM stands for parts per million.

How many ppm of propane is explosive?

Propane has a lower explosive limit (LEL) of 2.1% and an upper explosive limit (UEL) of 9.5% at room temperature. At elevated temperatures these numbers could be different. The IDLH concentration is 10% of LEL or 2100 parts per million (ppm). A 2.1% concentration of propane in air is equivalent to 21,000 ppm.

How do you do a bump test?

Alternatively, you can perform a manual bump test simply by applying gas to the instrument while it is on the main gas reading screen. If each sensor shows readings in response to the gas and the detector goes into alarm, then that instrument is good to go.

What does a 4 gas monitor detect?

What LELs does a 4 gas monitor read? Aside from 4 gas monitors assessing the presence of main gasses which include oxygen, carbon monoxide, hydrogen sulfide, they also detect lower explosive levels (LELs) of flammable, combustible gasses.

How often does a gas detector need to be calibrated?

Most manufacturers do recommend re-calibration at least every six months or 180 days.

Which gas is the calibration of gas detector?

Auto Span: – Oxygen sensor, use pure air calibration gas (20.9% O2) in case of deficient to enriched atmosphere.

What is the minimum oxygen level for a confined space?

19.5 % Minimum acceptable oxygen level. 15 – 19% Decreased ability to work strenuously. Impair coordination. Early symptoms.

What is the most combustible gas?

1) Chlorine Trifluoride is the most flammable gas Of all the dangerous chemical gases, chlorine trifluoride is known to be the most flammable.

What is the minimum oxygen concentration for combustion?

Fig. 1 shows a minimum oxygen concentration (LOC) of 4.6% that is independent of hydrogen concentration in the range of 10–30%. More typically, however, the minimum oxygen concentration for an inert fuel–air mixture occurs at a narrow range of fuel concentra tions.

What happens if a gas or vapor goes below its lower explosive limit?

The minimum concentration of a specific gas or vapor that will support combustion is defined as the Lower Explosive Limit (LEL) for that gas. Below this level, the mixture is considered too lean to burn. … But between the range of the LEL and the UEL, combustible and flammable gases will burn or explode.