Name a typical clearance criterion for interior window sill dust lead loading.

• A. 25 micrograms per square foot
• B. 2,500 micrograms per square foot
• C. 2.5 micrograms per square foot
• D. 250 micrograms per square foot (µg/ft2) or as specified by jurisdiction

Answer: (D)

Lead dust clearance uses surface-loading limits to decide if cleanup is sufficient. For interior window sills, a common threshold is 250 micrograms per square foot, though some places may set their own limit. This reflects a balance between protecting occupants from lead exposure and what is practically achievable on that surface. After cleaning, wipe samples from the sill are analyzed; if the lead loading is at or below 250 µg/ft2 (or the local jurisdiction’s value), the area passes clearance. The other numbers aren’t standard for window sills because they’re either far too low or far too high to serve as protective, practical limits for that surface.