You are testing a tank that contained...

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Question 1 of 2066636eec28f7522a1c51cf14

You are testing a tank that contained gasoline by using a combustible gas indicator. Under testing, the tank sample caused the needle to move rapidly to 100 on the dial then fall to zero. What is the concentration of flammable gas?

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Question 1 of 20

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🔍 Key Concepts

• How a combustible gas indicator (explosimeter) scale is usually marked (percent of the lower explosive limit – LEL). • What it means when the reading quickly pegs at the top of the scale and then drops back to zero on this type of instrument. • The relationship between instrument range and whether a sample is too lean, within, or too rich to burn.

💭 Think About

• Think about what would physically cause the meter to slam to 100% and then immediately fall to 0% when exposed to a strong sample. • Consider whether the sensor is being overwhelmed (saturated) or not detecting anything at all — how would each condition look on the dial? • Ask yourself: if the concentration is far above the range the instrument is calibrated to measure, how will the reading behave?

✅ Before You Answer

• Recall that most explosimeters are calibrated in % of LEL, not in actual percent gas by volume. • Decide whether a transient spike to full scale, followed by a drop to zero, better represents a condition above, within, or below the instrument’s measurement range. • Confirm that a truly defective instrument would likely show inconsistent or no movement at all, not a repeatable, characteristic pattern with a strong vapor sample.

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