Gas detection

Using a portable gas detector or gas monitor provides clarity on air quality in the working environment.

A gas detector emits a clear warning signal if the amount of harmful gas reaches a hazardous level or if the oxygen content drops too low. Depending on the model, gas detectors also provide the user with an insight into the type and amount of gas present at the location where the reading is being taken. Whether a gas detector is used as a warning system only or for exact readings, reliability is vitally important!

Besides portable gas detectors there are also systems that continuously monitor ambient air. These gas detectors are connected to a central alarm system and are set up where air quality needs to be monitored continuously. Readings can be tracked from a single point on a PC. These specialist systems do not appear on this website. Should you wish to find out more about them, our specialists can provide you with information about them.

Intersafe supplies a comprehensive range of gas monitors, gas detector tubes and accessories. Hire is also an option. Intersafe offers more management and maintenance programmes. See iNet for complete outsourcing.

Find out more about gas detection

Intersafe brands

  • MSA 
  • Honeywell 
  • Industrial Scientific 
  • Uniphos 

Areas of application for gas detection

Portable gas detectors can be categorised on the basis of three areas of application.

Explosive gases and vapours

In order to be able to assess an explosion hazard it is important to know beforehand whether the three elements required for it are present:

  1. A fuel (a flammable gas or liquid)
  2. Heat or a source of ignition
  3. Oxygen


If one of these three elements is missing, then an explosion cannot occur. If all these element are present, then the ratio in which they occur matters. In most cases the percentage of oxygen in the atmosphere will be normal, i.e. 21%. If this is the case, then the amount of flammable gas in the air is relevant. An explosion cannot take place unless the atmosphere contains a certain percentage of this gas. An explosion can no longer occur either if the proportion of this gas is above a certain percentage. These are known as the explosive limits. It is more important usually to know what the lower explosive limit is. This is referred to as LEL (or OEG in Dutch). This is the minimum concentration of a gas or vapour in an atmosphere that constitutes an explosive vapour or gas/air mixture. A flammable gas or liquid will also have an upper explosion limit, referred to as UEL. This is the maximum concentration of a gas or vapour in an atmosphere that still constitutes an explosive vapour or gas/air mixture. The explosive range of a flammable gas or vapour is therefore between the LEL and the UEL. If the percentage of oxygen in the atmosphere is other than normal, then the explosive limits will also vary. Flammable gases are usually measured in a percentage of the lower explosive limit (%LEL). This means that 100% LEL is equal to the percentage by volume of the gas in the atmosphere that constitute the lower explosive limit.


Oxygen level is measured in order to be able to alert users about danger of suffocation and to monitor the presence of oxygen in inert atmospheres from which oxygen has been removed intentionally, such as in storage tanks. Oxygen content is shown in percentages by volume.

Toxic gases

Apart from flammable gases and oxygen, there are countless toxic gases that can contaminate the environment. They constitute a hazard to health and to the environment. The most common toxic gases can be measured with one or more of the measuring instruments from the Intersafe range. For the remaining toxic gases there are gas detection tubes that provide an indication of the amounts of these gases in the ambient air. The unit of measurement for toxic gases is ppm (parts per million) or mg/m³.

Measuring principles

There are various types of sensor on the market for measuring gases. Each of these relies on its own measurement principle. Without going into detail, we can give you an idea of the most common principles and their application:

  • Catalytic combustion

The gas being observed is combusted in a safe enclosure (in the sensor). In order to be able to measure correctly, it must be known which gas is being observed. This principle is used to measure flammable gasses, especially where an explosion hazard is involved.

  • Thermal conductivity

Gas flows along a heated sensor and brings about a temperature difference relative to a shielded sensor. This methodology is often used to measure flammable gases in higher concentrations.

  • Electrochemical

Precious metal electrodes in an electrolyte (usually an acid) generate an electrical current in a sensor if there is any of the gas being measured present. This principle is used for measuring oxygen and toxic gases.

  • Infrared (IR)

The gas flows past an infrared lamp which detects the gas due to the changes that the gas causes in the wavelength of the infrared light. These sensor can be used to measure flammable gases and carbon dioxide. Unlike catalytic sensors,

IR sensors are not susceptible to poisoning.

  • Photoionisation detector (PID)

Photoionisation utilises a special lamp that detects a gas based on the ionisation potential (IP) of this gas. The ionisation potential of a gas is the energy required to remove an electron from an atom of that gas. It is therefore a measure of how tightly an electron is bound to its atom. This method enables very accurate and rapid measurements to be made. The measure is suitable primarily for measuring hydrocarbons.

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