Combustible gas indicators measure the...

Question 1 / 205eccef9ebacbc34ba4d465aa

Question 1 of 205eccef9ebacbc34ba4d465aa

Combustible gas indicators measure the concentration of combustible gases as a percentage of the lower explosive limit of the gas. If the hydrocarbon content of the sample exceeds the upper explosive limit __________.

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5eccef9ebacbc34ba4d465aa

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🔍 Key Concepts

• Lower Explosive Limit (LEL) vs Upper Explosive Limit (UEL) and what they mean for flammability • How a combustible gas indicator (CGI) is calibrated and what its scale actually measures • What happens to a flame- or heat-based sensor when there is too much fuel (rich mixture) in the sample

💭 Think About

• Think about what the CGI scale is referenced to: is it showing percent gas in air, or percent of LEL? How would readings behave if the mixture goes beyond the flammable range? • Consider what happens inside the sensor if the gas concentration gets richer than the UEL. Does the combustion in the sensor increase, stop, or change in some other way? How would that affect the needle movement? • Compare each option with the idea of a sensor that can become effectively "off-scale" or unable to burn the sample gas properly—what needle behavior best matches that condition?

✅ Before You Answer

• Be clear on the definitions of LEL (too lean) and UEL (too rich) and the range in between where gas is actually flammable. • Confirm how a typical catalytic-type CGI responds when the gas concentration is high enough that it no longer supports combustion in the sensor element. • Check whether an over-rich mixture would cause the instrument to show a steady full-scale reading, a spike then drop, or no reliable reading at all. Focus on which behavior matches physical combustion limits.

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Question 1 of 20

the needle will rise slowly to and remain at the maximum reading

the needle will move rapidly to and remain at the maximum reading

the needle will move to the maximum reading and return back to zero

it will not be detected

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Question 1 / 205eccef9ebacbc34ba4d465aa

Question 1 of 205eccef9ebacbc34ba4d465aa

Back

Question 1 of 20

5eccef9ebacbc34ba4d465aa

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🔍 Key Concepts

💭 Think About

✅ Before You Answer

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