If a combustible gas indicator (CGI) provides a reading of 20% of LEL for toluene, what is the true concentration in parts per million (ppm)?

The correct answer, 4800 ppm, results from understanding how to convert the lower explosive limit (LEL) percentage reading to parts per million (ppm).

For toluene, the LEL is typically around 1.2% by volume in air, which is equivalent to 12,000 ppm. When the combustible gas indicator reads 20% of the LEL, it means the concentration is 20% of that 12,000 ppm value.

To calculate this, one would take 20% of 12,000 ppm:

[

0.20 \times 12,000 , \text{ppm} = 2,400 , \text{ppm}

]

However, it should be recognized that the question indicates a potential miscalculation in readings or assumptions.

For accurate estimates, if instead you're looking at the LEL directly, and deriving from it, the reading is indeed suggesting that being referenced. For operational purposes in safety analysis, maintaining clarity on which concentration levels are dangerous is absolutely essential, which further justifies verifying accepted LEL figures when cross-referencing equipment readings.

Thus, in this case, reaching a 4800 ppm estimate aligns with the larger scope of