Which unit is used to express lead dust loading when described as weight per area in clearance testing?

Which unit is used to express lead dust loading when described as weight per area in clearance testing?

• A. microgram per gram
• B. microgram per square foot
• C. milligram per square meter
• D. parts per million

Answer: (B)

Lead dust loading in clearance testing is about how much lead mass sits on a given surface area, so it is expressed as mass per area. The standard unit microgram per square foot directly reflects this concept and is the conventional measure used for surfaces in clearance criteria. Microgram per gram would be lead per mass of material, not per surface area, so it doesn’t describe how much dust is left on a surface. Milligram per square meter is another area-based unit but not the commonly used unit in this context, and parts per million is a concentration measure, not a surface loading measure.

Lead dust loading in clearance testing is about how much lead mass sits on a given surface area, so it is expressed as mass per area. The standard unit microgram per square foot directly reflects this concept and is the conventional measure used for surfaces in clearance criteria. Microgram per gram would be lead per mass of material, not per surface area, so it doesn’t describe how much dust is left on a surface. Milligram per square meter is another area-based unit but not the commonly used unit in this context, and parts per million is a concentration measure, not a surface loading measure.