Explosion meter

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The explosion-meter is used to determine whether the gas/vapour-air mixtures are safe against the possibility of fire or explosion.


Measurement Type Detection of gas clouds
Output Reading of the % of the LEL
Principle Heat of burning
Suitable for substance types Explosive gases/vapours
Measurement range 0 – 100 % LEL
Measurement units In % of LEL
Operator experience level Medium
Operation - Ship (handheld)
Dimensions (LxHxW)
Weight
Accuracy Indicative
Mobilisation Time Minutes
Mobilisation requirements None
Secondary equipment None
Environmental requirements None
Mean time before failure N/A

Operating Principle

The explosion-meter is based on the combustion of the substance to be measured inside the apparatus; the heat liberated being a measure of the concentration.

Air is drawn into the unit through a flow regulating opening, filter and flashback arrestor into the combustion chamber by an aspirator bulb. In the combustion chamber a platinum filament is heated until the gas combusts thus raising the temperature of the filament. The filament is an integral part of a resistor circuit called a Wheatstone Bridge, the temperature imbalance of which is measured and directly read on a voltmeter as a concentration

Directly proportional to its proximity to the lower explosion limit of the substance. There are several types of commercially available explosion meters, some of which are shown on the right hand side of the page.

Use

Explosion meters are available as handheld or portable devices to perform on scene measurements.


Explosion meter readings are generally only accurate for the gas for which the apparatus has been calibrated.


Appropriate conversion factors should be used when checking for a vapour other than the test vapour.

Limitations

Explosion meters utilizing a platinum filament will not operate properly in the presence of lead and silicon compounds and the filament will probably be destroyed.

Potentially hazardous areas have to be entered to perform the measurement.

The instrument only functions properly when sufficient oxygen is available.


Measurement in high concentrations could give false readings because at concentrations above the LEL, the meter goes to the end of the scale and then backs to a final rest position of zero. Consequently, it is extremely important to watch the meter constantly while testing.

Performance

This instrument measures the concentration as a percentage of the LEL (Lower Explosion Limit) or the percentage by volume, but these percentages are based on calibrations with some standard gas, often methane. For other gases, readings are only approximates.


Picture 120, Picture 121, Picture 122 Some examples of explosion meters Copyright photo ASCC