Gas Detection

While measuring the concentration of gas in any use of gas detectors. What are the things they need to keep in mind? What is the difference between ppm and the LEL. where to measure and where to use ppm lel?

*... LEL 'LEL' which is a percentage of the air concentration at which the gas mixture ignites.
(There is also a HEL (or (UEL) or upper (Upper) Explosive Limit).
The% of gas in the air should be between these limits in order to burn. LIE example of propane is 2.1% in air and HEL was 10.4% in air. Below or above these limits, propane will not ignite.

*... Ppm ... parts per million is usually used to detect harmful gases such as hydrogen sulfide (H2S).
*.. H2S is a flammable, toxic, and acid gas, which irritates the eyes and mucous membranes at concentrations of 20-150 ppm. Slightly higher concentrations cause irritation of upper respiratory tract.
*.. Inhalation of 500 ppm for 30 minutes causes headaches, dizziness, agitation and gastric disorders.
*.. Concentrations above 600 ppm can be fatal within 30 minutes due to respiratory paralysis.
*.. Smell can not be invoked to detect the presence of H2S, because of the chilling effect it has on the olfactory nerves. The gas destroys the sense of smell at low concentrations.
As a matter of interest, flammable (explosive) limits for H2S is 4.3% and 46% in the air ... A wide range flammable.

I thought that two responders were very clear on the question: if this is not a question of burning gas or light use ppm. Toxicity is not a problem of ignition, so use ppm. Report Abuse

ppm = parts per million.
LEL = lower explosive.

The extent of the LEL would be used only when the gas is suspected explosives (such as propane, for example). For each type of explosive gases mixed in the air when a certain concentration is reached, it becomes explosive, but below this concentration can not explode. Each gas has a LEL different explosives.

PPM will normally be measured if the gas is toxic.

Hope this helps.
Bill