You have been carrying a liquid with flammable limits of 1% to 7% mixture with air. If your instructions say that no one shall enter the tank if the vapor concentration is over 15% of the LEL, what is the maximum allowable percentage of vapors for men to enter?
• Lower Explosive Limit (LEL) and what it represents • How to calculate a percentage of the LEL when the LEL is expressed as a gas concentration in air • Difference between absolute vapor concentration (%) and percent of the LEL
• First, determine what the actual LEL value is in percent based on the flammable limits given in the question. • Next, calculate what 15% of that LEL value would be as an absolute vapor percentage in air. • Compare your calculated value with the multiple-choice options to see which one matches your result.
• Verify you are using the lower flammable limit (not the upper) when interpreting the LEL. • Make sure you correctly convert 15% of the LEL into an absolute concentration percentage (multiply, don’t add or subtract). • Double‑check that your final number is less than the LEL value itself, since 15% of the LEL must be a smaller concentration than the full LEL.
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