AFTER ALL, WHICH IS
LEL?

BEFORE A FIRE OR
EXPLOSION MAY OCCUR,
SHOULD BE CHECKED
THREE CONDITIONS
SIMULTANEOUSLY:

Um combustível, ou seja, um gás infamável + Oxigénio + Uma fonte de ignição, como uma faísca ou chama

The proportion of fuel and oxygen needed to combustion occurs varies with each combustible gas or vapor.

Minimum concentration of a given combustible gas necessary to sustain its combustion in the air. Below that level, the mixture is too poor to burn.

Maximum concentration of a given fuel gas to support its combustion in the air. Above that level, the mixture is too rich to burn.

The interval between the LEL and the UEL is known as the: FLAMMABLE INTERVAL > for that gas

Considering the case of Methane:

Consider the LEL scale as illustrated in a figure 1:

So, the minimum percentage of methane volume in the air for an explosion to occur is 4,4%, this being the LEL value.
When it comes to security, the reference value will be% LEL (percentage of LEL value) and not% CH4 (percentage of CH4 by volume in air).

When the lower explosive limit for Methane is reached (4,4%), we are facing an explosive atmosphere. This is, if the atmosphere reaches 100% of LEL and a spark or any other ignition source occurs, the air and gas mixture will ignite and an explosion may occur.

EXAMPLES OF EQUIPMENT

Our CROWCON flammable gas detection equipment is set to alert the user when the mixture reaches 20% LEL (low alarm), triggering a second alarm when the mixture reaches 40% LEL (loud alarm).

CROWCON flammable gas detection equipment

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