Image principale

Explosimeter: 6 laws to know

Date de l'actualité

What is an explosimeter?

It is a gas detector that measures the presence of gases (explosive or flammable) according to their Lower Explosive Limit or LEL.

It is used to detect gas leaks such as natural gas, butane, propane, etc.

Gas leaks can occur during a fire department intervention, during an intervention of gas operators in the field, in a factory handling gas, etc.

> Find at the end of this article an exclusive infographic!


The portable flammable gas, explosive gas and oxygen detectors measure the risk of explosion and the lack or excess of oxygen, and combined with a vibrator, an audible and optical alarm reacts immediately when the gas concentration exceeds the preset alarm thresholds.

1. In healthy areas, you should be

Before using an explosimeter, it is imperative to perform a zero measurement in a safe area and not in the presence of a flammable gas.

This step is essential, because if it is not done correctly or even totally forgotten, it can lead to negative values and an underestimation of the risk.

2. Thou shalt avoid dust

Beware of dust! Indeed, you should know that your explosimeter will not detect the explosive risk linked to dusts, it is even the opposite, they clog the filter of the device, so it is imperative to avoid them.

On the other hand, a dust explosion can occur when the elements of the fire triangle (a fuel: material such as wood, plastic, etc. / an oxidizer: oxygen in the air / and a heat source: a match or electricity for example) are present. Most dusts are of organic origin such as grain, flour, wood, etc.

3. Thou shalt not saturate

Of course, your explosimeter will react to stresses such as lighter fluid or a gas line.

But do you think it is really necessary to subject it to such concentrations? As you can imagine, the answer is no... Indeed, a saturated device, thus certainly in high alarm, becomes blind and can take time to be functional again.

4. Thou shalt forget conversions

Your device indicates a percentage of the Lower Explosive Limit. However, you must take into account the gas on which your explosimeter is calibrated, and know which gas or vapor it is facing!

As long as your explosimeter indicates a value, it is sufficient to affirm the presence of a risk at your location. You must take the necessary measures without delay. Forget conversion curves, don't waste time!

Just think of your explosimeter as a flammable gas detector, avoiding approximate calculations.

5. Twenty seconds, you will wait

The catalytic oxidation explosimeter provides a measurement of the concentration of a flammable gas between 0% and 100% of the lower flammable limit (LFL). The instrument is set up with a reference gas, and the response of the instrument is based on this standard gas. Typically, methane (CH₄) is the gas used to calibrate an explosimeter.

Catalytic oxidation explosimeters do not indicate the presence of combustible gases in an oxygen-inerted environment: below 15% O₂ in air, the measurement is likely to be in error.

Other factors are likely to influence the operation of the explosimeter and lead it to false responses:

  • Ambient humidity
  • High or very low temperatures,
  • electromagnetic waves,
  • silicon, lead or sulfur substances

Other explosimeter technologies exist: thermal conductivity, or infrared detection.

6. You will love catalytic oxidation

This is the time required for your explosimeter to react in the presence of a flammable gas in the atmosphere. This reaction time depends on the gas concentration and the model of the explosimeter.

When taking samples, give the explosimeter time to react.

> Thermal conductivity :

Thermal conductivity detectors are detectors used to analyze inorganic gases and hydrocarbon molecules.

The thermal conductivity detector compares the thermal conductivity of two gas streams, the pure carrier (reference) gas and the sample. The temperature change of the heating wire in the detector is affected by the thermal conductivity of the surrounding gas. This change in thermal conductivity is detected as a change in electrical resistance and is measured for gas detection.

Advantage: This type of sensor offers a very wide measurement range from a few ppm to 100%.

> Infrared detection :

The sensor emits an infrared beam whose wavelength is defined according to the target gas. When this gas passes in front of the beam, it absorbs part of the radiation. The measured intensity will drop. Compare this to a reference intensity to establish the concentration.

Since no chemical reaction is involved, infrared sensors do not suffer from saturation problems and are not affected by oxygen concentrations. In the event of a malfunction, the beam intensity decreases, which the sensor interprets as the presence of gas.

Advantage: It can either be used as a point detector, or it can be used to monitor a large area over several dozen meters.

> MPS cell:

Designed for multi-gas environments such as waste energy, wastewater, green energy, biogas, petrochemical, oil and gas and industrial manufacturing. MPS sensors are designed for today's multi-gas environments, preventing contamination and preventing sensor poisoning.

The MPS fuel gas sensor can detect gas mixtures as accurately as a single gas. It even classifies gas mixtures into one of six categories based on the size of the hydrocarbon molecules and the presence of hydrogen. The result is a truly comprehensive response and exceptional visibility into the safety of the work environment and employee confidence.

Advantage: It can quickly detect more than 15 characterized flammable gases at a time.