An explosimeter is a

gas detector A gas detector is a device that detects the presence of gases in an area, often as part of a safety system. A gas detector can sound an alarm to operators in the area where the leak is occurring, giving them the opportunity to leave. This type of d ...

which is used to measure the amount of combustible gases present in a sample. When a percentage of the

lower explosive limit Mixtures of dispersed combustible materials (such as gaseous or vaporised fuels, and some dusts) and oxygen in the air will burn only if the fuel concentration lies within well-defined lower and upper bounds determined experimentally, referred to a ...

(LEL) of an atmosphere is exceeded, an alarm signal on the instrument is activated. The device, also called a

combustible gas detector A combustible material is something that can burn (i.e., ''combust'') in air. A combustible material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort and a flammable mat ...

, operates on the principle of resistance proportional to heat—a wire is heated, and a sample of the gas is introduced to the hot wire. Combustible gases burn in the presence of the hot wire, thus increasing the resistance and disturbing a

Wheatstone bridge A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. The primary benefit of the circuit is its ability to provid ...

, which gives the reading. A

flashback arrestor A flashback arrestor or flash arrestor is a gas safety device most commonly used in oxy-fuel welding and cutting to stop the flame or reverse flow of gas back up into the equipment or supply line. It protects the user and equipment from damage ...

is installed in the device to avoid the explosimeter igniting the sample external to the device. Note, that the detection readings of an explosimeter are only accurate if the gas being sampled has the same characteristics and response as the

calibration gas A calibration gas is a reference gas or gas mixture used as comparative standard in the calibration of analytical instruments, like gas analysers or gas detectors A gas detector is a device that detects the presence of gases in an area, often as ...

. Most explosimeters are calibrated to

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

References

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External links

* https://web.archive.org/web/20050910075254/http://www.marineengineering.org.uk/testequipment/explosimeter.htm (select explosimeter from the left frame)
Explosimetry
Explosion protection Gas technologies Measuring instruments