Consider Analysis Error When Determining Flammable Gas Concentration

flammable-gas-detectorBefore starting welding work at an existing flammable gas facility, nitrogen substitution is the first step to do. Flammable gas inside the facility has to be replaced by nitrogen, in order to move its concentration beyond its explosion limit or explosion range.

Explosion limit data should be referred to MSDS of the flammable gas. It is described in MSDS in terms of Lower Explosion Limit (LEL) and Upper Explosion Limit (UEL).

Then, after nitrogen substitution finished, take gas sample and analyze it by using Gas Chromatography. Let’s take an example, suppose hydrogen gas is inside the facility. Hydrogen explosion limit is 4% to 75%. Suppose analysis result shows that hydrogen concentration remains in the facility is 3.2%.

Will you accept this result and allow welding work? Don’t do it too fast. Why? Because we have to consider analysis error due to analyzer problem or unsatisfied sampling technique.

It will be safer if we set target of remaining hydrogen concentration nearly to zero. It will only cost you nitrogen, not your safety.

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