The flammable limits of benzene are 1.4% to 8.0% by volume in air. If a reading of 50% of the lower explosive limit is obtained, using the meter shown in the illustration, the vapor concentration at the sample point is __________. See illustration SF-0002.
• Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL) for benzene (1.4% to 8.0% by volume in air) • How an explosimeter/meter scale is usually calibrated (often as percent of the LEL, not percent by volume) • Meaning of too lean, flammable range, and too rich in relation to LEL and UEL
• What actual percent-by-volume concentration in air corresponds to 100% of the LEL for benzene, given in the question? • If the meter in the illustration reads 50% of the LEL, how would you calculate the corresponding percent-by-volume concentration? • Once you know that concentration, is it between the LEL and UEL, below the LEL, or above the UEL?
• Confirm that 100% LEL for benzene = 1.4% by volume in air, based on the data given • Carefully distinguish between % of LEL on the meter scale and % by volume in the space; do not mix them up • After converting 50% of LEL to % by volume, check whether that value lies inside or outside the 1.4%–8.0% flammable range
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