[Dan0353]

Can anyone clarify how to calculate the lower explosion limit (LEL) of Methane?

For example, the LEL of Methane is 4.4 volume percent. Does this mean that 4.4% by volume of the air (or headspace of a container) is Methane at the LEL?

If this is the case, how would you calculate the volume percent of methane, since the methane gas would spread out and evenly occupy the entire headspace?

Are you able to use Methane's approximate density as a gas (assume 20C and 1atm) of 0.656 g/L to calculate this? If so, a headspace of 1000 Liters could have 4.4% Methane gas by volume or 44 Liters. To gain 44 Liters of methane, about 28.86 grams of Methane would need to be vaporized (i.e. 44L times 0.656 g/L).

Lastly, if you want to operate at 25% or less of LEL, this would restrict methane's volume percent to 1.1 (i.e. 4.4% divided by 4)? Therefore only a maximum of 7.215 g of methane (28.86 grams divided by 4) would be allowed?

[Borek]

Apart from the fact you are not "calculating LEL", but calculating amount of methane at LEL - your numbers look more or less correct. Actually from the ideal gas equation I got 29.3 g of methane in 1000 L.

[Dan0353]

Apart from the fact you are not "calculating LEL", but calculating amount of methane at LEL - your numbers look more or less correct. Actually from the ideal gas equation I got 29.3 g of methane in 1000 L.

Hi Borek,

Do you mind showing your work, so I can see where I went wrong with the calculation? And yes, I am just calculating the amount of methane present at LEL.

Thanks so much.

[Borek]

Do you mind showing your work, so I can see where I went wrong with the calculation? And yes, I am just calculating the amount of methane present at LEL.

There is not much to show, I just used PV=nRT plugging all knowns and solving for n, then multiplying by molar mass. You result is different as you started with a given density - hard to say which method gives a more correct result. If the density value is reliable, it should give a better value, as methane doesn't have to behave like an ideal gas.