A combustible gas instrument (CGI) displays a 2% of LEL reading for methyl ethyl ketone. If its LEL is 1.4, what is the true concentration in parts per million?

To determine the true concentration of methyl ethyl ketone (MEK) in parts per million (ppm) based on the lower explosive limit (LEL) and the reading from the combustible gas instrument (CGI), you can use the following relationship:

1. Calculate the percentage of LEL in decimal form. In this case, a 2% LEL reading translates to 0.02.

2. Next, multiply the decimal representation of the LEL percentage by the LEL value of the substance. For MEK, the LEL is 1.4. So, you calculate:

[

\text{True concentration in ppm} = \text{LEL value} \times 1000 \times \text{percentage of LEL}

]

Substituting the values:

[

\text{True concentration in ppm} = 1.4 \times 1000 \times 0.02 = 28

]

However, to find the concentration in ppm, it is important to remember that for combustible gases, the LEL is typically expressed in percentage and you multiply the LEL percentage times the LEL value, then further multiply by 1000