What units are commonly used to report floor dust lead loading in clearance criteria?

• A. mg/m2
• B. Micrograms per square foot (µg/ft2)
• C. Micrograms per square meter (µg/m2)
• D. Nanograms per square inch

Answer: (B)

Dust lead loading on floors is measured as how much lead is present per area after a wipe, and the common reporting unit in clearance criteria is micrograms per square foot (µg/ft²). This imperial unit lines up with how floor space is measured in U.S. regulations, making the numbers directly comparable to the clearance thresholds (for example, a typical floor criterion is around 40 µg/ft²). If you ever encounter metric units, you’d convert them to µg/ft² to compare with the standard values, since 1 ft² corresponds to about 0.0929 m². Other units like µg/m² or ng/in² exist, but they’re not the standard for U.S. clearance criteria, so using µg/ft² keeps interpretation straightforward and avoids extra conversions.