Combustibles Meter, Gas Leak Detector - June 24, 2021

Best Gas Leak Detector (%LEL versus PPM)

Gas leak detectors are used to find leaks in natural gas pipes, fittings, and connectors. In industrial settings or homes gas leaks tend to occur with natural gas. They can also happen with propane when cooking on the grill, traveling in an RV, or camping. To ensure safety in occupational spaces, gas leak detectors are used to monitor confined spaces, silos, and tanks for any combustible residue. A gas leak detector is an affordable tool used by plumbers, HVAC, technicians, handymen, and homeowners.

Pros	Cons
Gas leak detectors are affordable tools, less than $100. Gas leak detectors can last for over five years. Gas leak detectors are very sensitive to many combustibles.	Gas leak detectors do not show which gas is being detected. Gas leak detectors find leaks at the source, it may take time to track all the pipes and connectors. Does not detect carbon monoxide.

What Is Natural Gas, Methane, and Propane Gas?

Natural gas is the gas we use at home that is supplied by the utility company. It powers our stovetops, ovens, furnaces, boilers, and heaters.

Natural gas is primarily made up of methane. With a chemical formula of CH4, methane is the most basic hydrocarbon compound. It is used around the world in homes and in many industrial applications as a fuel source.

Propane is very similar to methane with a chemical formula of C2H5. It is also an excellent fuel source and used throughout the globe. Propane can be liquified to produce liquified petroleum gas (LPG).

Natural gas methane is used as a domestic gas to fuel appliances.
Natural gas methane is used by gas-burning power plants to generate electricity.
Natural gas methane is used in industrial applications to produce chemicals, fertilizers, hydrogen, etc.
Propane is used in compressed cylinders for fueling grills and BBQs.
Propane is used to power vehicles as a "clean fuel" in comparison to gasoline.
Propane is used in RVs, camping, and many portable cooking appliances.

Natural gas, methane, and propane are all combustibles.

What Are Combustible Gases?

A combustible gas is one that can be used as a fuel source. In other words, these gases can be ignited and combustion can take place.

Examples of combustibles gases include the following:

Acetone, industrial solvents, alcohol, jet fuel, ammonia, lacquer, thinners, benzene, methane, butane, naphtha, ethylene oxide, natural gas, gasoline, propane, halon, refrigerants, hydrogen sulfide, and toluene.

What Does a Natural Gas Leak Detector Do?

How Does a Gas Leak Detector Work?

A gas leak detector is an electronic device that is made up of two parts. The first is the electronic system that performs computation and signal processing. The second is the gas sensor, which converts the detected combustible gas concentration to an electronic signal for analysis by the processor.

What Are the Different Types of Gas Leak Detectors?

Gas Leak Detector

This gas leak detector has a gooseneck and display. The gooseneck contains the sensor and is designed to be placed up against gas piping to pinpoint a leak. It is sometimes called a gas sniffer or gas leak tester.

Combustible Gas Leak Detector

This gas detector is made for a home or RV to alarm if there is a gas leak. Combustible gas detectors are designed to be stationary and always on. For example, if a stovetop is left on, gas will accumulate. This gas leak detector is made to alarm home or RV occupants of imminent danger.

Personal Gas Detector

The personal protection gas leak detector is typically used in industrial or occupational settings. This detector is set to alarm and protects the user. They are used for silos, tanks, and other confined spaces. It is sometimes called an EX LEL explosives gas detector, combustibles meter, or combustible gas detector.

How Does a Combustibles Sensor Work?

The most popular combustibles sensor is the catalytic bead sensor, often referred to as a pellister sensor. This detects combustibles by oxidizing or “burning” the combustible gas on an active bead. The heating effect changes the sensor's conductivity, which is proportional to the amount of combustible gas detected. Integrated with a heating element to operate at about 500F, this device is often very small. The sensor contains two beads, one active and one not. It is typically placed in a Wheatstone bridge configuration.

pellister catalytic bead combustibles sensor

Another popular combustibles sensor is a semiconducting metal oxide sensor. Located in Japan, the Figaro company is recognized for popularizing this technology. The sensor is based on a redox reaction with a metal oxide semiconducting material. From there, the sensor changes conductivity in proportion to the concentration of the combustible.

The most popular combustible sensors are summarized below.

Combustibles Sensor Technology	Working Principle	Pros	Cons
Catalytic Bead Pellister Sensor	Combustible gas oxidizes on the bead, changing the conductivity of the element. The resistance change is proportional to the combustible concentration.	Low cost Very reliable & simple Best for methane and propane 5 to 10 year lifespan Best for %LEL range	Not selective Consumes power for heating Requires startup time for heating Not desirable for high % absolute volume
Semiconducting Metal Oxide	Combustible molecules interact with a film of metal oxide material, causing surface redox reactions to take place. As a result, a power-law relationship between combustible concentration and conductivity of the sensor occurs.	Long lifetime over 5 years Best for ppm range Low cost Robust	5-minute warm-up time Influenced by temperature and humidity
Photoionisation Detectors (PID)	Ultraviolet (UV) light dislodges an electron from the VOC molecules, producing a current proportional to the combustible concentration.	Best for VOCs and large hydrocarbon molecules Robust Very reliable 5 to 10 year lifepan	Expensive Complicated due to UV source
Thermal conductivity (TCD) sensors	The sensor contains two coils of wire coated with ceramic. The molecular weight of different combustibles will affect the temperature of the sensing bead. The temperature change will change resistance proportionally to the amount of combustible detected.	High range, 0-100% volume Simple design	Not common Not used in low concentration applications
Non-Dispersive Infrared (NDIR)	Infrared light is emitted and then absorbed by combustible gas molecules. The absorption is detected with a photodetector. Using the Beer-Lambert law, the IR absorption and gas concentration is determined.	Accurate High dynamic range Long life	Expensive Not common Non-linear output

What Are Safe Combustible Levels?

Various government agencies recommend exposure limits to different combustible gases. As an example, levels pertaining to methane (CH4) and propane (C2H5) are shown below.

	Recommendation / Requirement
Occupational Safety and Health (OSHA)	1,000 ppm 8 hour TWA [Propane]
National Institute for Occupational Safety and Health (NIOSH)	1,000 ppm 8 hour TWA [Methane] 50,000 ppm (5%vol) IDHL Immediately Dangerous To Life or Health [Methane] 1,000 ppm 8 hour TWA [Propane] 21,000 ppm (2.1%vol) IDHL Immediately Dangerous To Life or Health [Propane]
The American Conference of Governmental Industrial Hygienists (ACGIH)	1,000 ppm 8 hour TWA [Propane]

Is Methane an Asphyxiant?

Yes, the primary cause of human toxicity from methane is the displacement of oxygen. If methane leaks in a closed indoor space, it may reduce oxygen and asphyxiate occupants.

Do Gas Leak Detectors Indicate Which Gas Is Being Detected?

No, they do not. Gas leak detectors cannot discriminate from the hundreds of different combustible gases that may be present in your sample. A typical combustibles gas detector is calibrated to methane. Therefore, the values presented during your detection will be in ppm, %LEL, or %volume with respect to methane. However, if you know you are detecting other combustible gases, such as propane, a correcting factor must be taken into consideration for the most accurate results.

What Is a Gas Leak Detector Used For?

There are a plethora of gas leak detector applications. Some popular options are highlighted below.

Industrial Tank: A gas leak detector with a gooseneck is placed in a tank before the worker enters to sniff for any residual combustibles that may have accumulated. After the readings are within safe limits, the worker may enter. They will also carry a personal protection combustible meter that is set to a %LEL alarm threshold.
Plumber: A plumber has a few ways to determine gas leaks, such as gas leak soap. In some cases, it may not be desirable to use a liquid as it can stain or create a mess. In this case, a gas leak detector showing ppm readings is used to pinpoint the gas leak that the homeowner can smell.
Personal Protection Equipment: The oil and gas industry employs many people that work around tanks, pipes, and refineries. Personal protection combustible gas detectors are required that alarm at predetermined %LEL levels.
RV Travel: When traveling in the RV, propane is often used as the go-to fuel source. Since the propane tank resides on the RV, leaks can quickly enter the RV. Therefore, it is imperative that a continuous and stationary gas leak detector is operating. This is very important for an RV because it is a small, confined space which will quickly accumulate gas to dangerous levels in the event of a leak. In this case, a wall plug gas leak detector would be fitting to alarm RV occupants of a build-up of propane.

Do Plumbers Use Gas Leak Detectors?

Yes, this is an important tool for plumbers and HVAC technicians.

Can I Use a Natural Gas Leak Detector for Sewer Gas?

Yes, using a gas leak detector is a fantastic tool as a starting point to try to locate a sewer gas leak. Most sewer gas is also composed of methane and hydrogen sulfide.

Will a Gas Leak Detector Detect LPG?

Yes, LPG is propane and will be detected by your gas leak detector.

Can It Detect a Leak from a Gas Pipe Hidden Behind Drywall?

No. For a gas leak detector to find a leak, the actual leak must be accessible to the sensor head of the device. If the leak is behind drywall, the air and space around the leak dilutes the gas that is leaking, making it impossible to find using a gas leak detector. In this situation, we would advise trying an ultrasonic leak detector.

Can a Gas Leak Detector Be Used for a Car Fuel Leak?

Yes. Gas leak detectors can help find a fuel leak in transport vehicles. In fact, they have also been known to find and confirm head gasket leaks.

Will a carbon monoxide detector detect a gas leak?

No, they do not.

Do not confuse a carbon monoxide detector with a gas leak detector. Gas leak detectors cannot detect carbon monoxide gas. Carbon monoxide detectors are not sensitive to combustibles.

How Can I Test My Gas Leak Detector?

The best way to test your gas leak detector is to expose it to a known gas source. This type of testing is generally referred to as bump testing and is a good practice, especially in personal protection applications where safety is paramount.

What Is the Best Gas Leak Detector?

There are many gas leak detectors on the market. The reputable brands include the following:

How Do I Select a Gas Leak Detector?

To select the best gas leak detector for your needs, follow this guide.

What type of combustibles are you targeting? Methane? VOC? Gasoline vapors?
Would a gooseneck be desirable?
Do I need the ppm range or the LEL% range?
Do I need to incorporate any correcting factors (CR)? CRs may be build in (calibrated offset) or be calculated on the fly by the user.

Can I Use a Gas Leak Alarm for the Kitchen?

Yes, a kitchen is a great place to install a gas leak detector. These devices are sometimes also referred to as kitchen gas leak alarms.

How Long Do Gas Leak Detectors Last?

Gas leak detectors based on catalytic bead and semiconducting metal oxide sensors will last over 5 years. UV and NDIR will be limited by the source emitters, but usually will also last over 5 years.

What Is Gas Leak Detector Calibration?

When purchasing a gas leak detector ask when and how was the unit calibrated. This should be mentioned in the product literature.
It is good practice to calibrate you gas leak detector between 6 to 12 months. More on calibration best practice can be found here.
It is important to understand the range (ppm, %LEL, or %volume) and calibration point that is appropriate. The calibration is typically performed at a concentration in the middle range. For example, if the gas leak detector has a 0-10,000 ppm range, then a 5,000 ppm methane gas concentration will be used.
You may need to calibrate more often if:

The user employs the device as an analytical tool where accuracy is paramount.
The device is used at extreme temperatures and humidities.
The user is performing a dangerous or extreme task. In this case, calibration and bump testing are mandatory since imminent injury or death will occur if the device fails.

What Is Gas Leak Detector Bump Testing?

Bump testing is a procedure where the user exposes the detector to a small amount of “blast” target gas to ensure the detector operates and alarms as programmed.
The function of this test is to verify proper operation and build user confidence, particularly in hazardous applications.
It is recommended to bump test when first purchased, with subsequent testing every week. It is especially important in LIFE THREATENING and / or DANGEROUS applications to verify detector operation. See video explanation here.
Methane bump test gas is here.

How Do I Properly Use a Gas Leak Detector?

When operating a gas leak detector, there are some important tips. Read your product manual and:

Ensure the gas leak detector is within its calibration period.
Ensure the gas leak detector has been bump tested and validated as operational.
Turn ON the gas leak detector in the fresh air.
Let the gas leak detector to warm up. It may take a few minutes, and it is always good practice to wait a few extra minutes.
When using a personal protection combustibles meter, turn it ON, and keep it on you. Set your alarms as desired.
If undertaking analytical measurements, keep the unit stationary. Ensure humidity and temperature are also tracked and are as constant as possible.
If the gas leak detector shows a small residual level in the fresh air, perform a zero calibration.

What Is the Difference Between ppm and %vol Gas Leak Detector Readings?

The typical scales of concentration for combustibles such as methane or propane are ppm and %vol. Both of these values are interchangeable.

Conversion Example

Methane % value = (methane ppm / 1,000,000) x 100%

For example, if we have 5,000 ppm of methane, then we obtain:

Methane % value = (5,000 / 1,000,000) x 100%

Methane % value = 0.5%

Quick Conversion from ppm to %vol

100 ppm = 0.01%

1,000 ppm = 0.1%

10,000 ppm =1%

100,000 ppm =10%

1,000,000 ppm =100%

What Is the Difference Between ppm and %LEL Gas Leak Detector Readings?

%LEL is very different than %vol. %LEL represents a percentage of the lower explosive limit of a particular combustible.

Each combustible has a different explosive limit in air and different low explosive levels (LEL).

For example, methane will explode in air at 5% volume (which is 50,000 ppm). This is called te 100% Lower Explosive Limit. In other words, 100% LEL = 5% volume. When the methane concentration reaches 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 if our gas detector is reading 5% LEL and it has been calibrated to methane, then 5% of [5%vol] = 0.25% vol or 2,500 ppm.

What Are Correction Factors for %LEL and Combustible Meters?

Methane is the most common gas used to calibrate gas leak detectors and combustible meters. Correction factors (CFs) have been determined that allow the user to quantify a large number of chemicals using only a single calibration gas, such as methane. There are two ways one can use these factors.

First, operate your gas leak detector as normal. Let us assume it has been calibrated to methane. So if the device reads 10% LEL registering from a propane source, we will use the correction factor for propane, which is 1.4. Multiply 10% LEL to propane CF (1.4), which gives 14% LEL. This means the corrected (real) reading is 14% LEL.
Calibrate the unit with methane. Assume you are calibrating it to 25% LEL methane. You are certain you will exclusively use it for an ethanol system (for example). In that case, your span point will not be 25% LEL but will be 25% LEL x 1.8 = 45% LEL. The unit has been calibrated with and adjustment to read and display %LEL of ethanol.

The below table includes some common combustible gases and their correcting factors. These and others can be found here.

Gas	Correcting Factor (Multiply)
Acetone	1.9
Ammonia	1.0
Ethanol	1.8
Ethylene Oxide	1.7
Gasoline	2.6
Hydrogen	1.0
Isopropanol	2.2
Propane	1.4
Toluene	2.4

Final Words

Gas leak detectors are very useful to find leaks in natural gas pipes, fittings, and connectors. In addition, combustible meters are used for personal protection to warn users about dangerous indoor accumulation. There are many considerations when it comes to gas leak detectors since they are a non-specific gas detector. A gas leak detector is an affordable tool used by plumbers, HVAC, technicians, handymen, and homeowners. It is a fast and inexpensive way to find sewer gas, propane, and methane leaks.

About The Author

Dr. Koz is the President of FORENSICS DETECTORS, where the company operates from the scenic Palos Verdes Peninsula in Los Angeles, California. He is a subject matter expert on gas sensor technology, gas detectors, gas meters, and gas analyzers. He has been designing, building, manufacturing and testing toxic gas detection systems for over 20 years.

Every day is a blessing for Dr. Koz. He loves to help customers solve their unique problems. Dr. Koz also loves spending time with his wife and his three children going to the beach, grilling burgers, and having a cold beer.

Read more about Forensics Detectors here.

Email: drkoz@forensicsdetectors.com
Phone: +1 424-341-3886

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