Clearance After Window Abatement: Mass per Wipe, Not Loading
You are conducting clearance after a window-component abatement (14 window components removed and replaced) in a vacant 1925 apartment. Final cleaning is complete and the crew has left the site. The laboratory reports mass per wipe only. Your sampler's template areas were 1.0 ft² for floors, 0.5 ft² for interior sills, and 0.25 ft² for troughs. Results in micrograms: Room A - floor 22, sill 90, trough 65. Room B - floor 52, sill 155, trough 155. Room C - floor 38, sill 120, trough 87.5. In Room B the crew wiped two floor locations and the laboratory analyzed them as a single composite, reporting one value of 52 µg. The property manager wants to move the new tenant in tomorrow morning.
1. Convert the results to dust-lead loadings and determine which rooms pass or fail clearance.
Read the worked answer
Loading = mass ÷ sampled area. Clearance criteria are less than 40 µg/ft² (floors), less than 250 µg/ft² (interior sills), and less than 400 µg/ft² (window troughs).
Room A: 22 ÷ 1.0 = 22 (pass) · 90 ÷ 0.5 = 180 (pass) · 65 ÷ 0.25 = 260 (pass).
Room B: 52 ÷ 1.0 = 52 (FAIL, >40) · 155 ÷ 0.5 = 310 (FAIL, >250) · 155 ÷ 0.25 = 620 (FAIL, >400).
Room C: 38 ÷ 1.0 = 38 (pass) · 120 ÷ 0.5 = 240 (pass) · 87.5 ÷ 0.25 = 350 (pass).
Conclusion: the unit fails clearance because Room B fails on all three surfaces. Rooms A and C individually pass.
Reasoning notes worth stating: the failure would have been invisible if you had compared raw micrograms to the criteria - a 155 looks harmless next to a 250 criterion until you divide by 0.5 ft². Also watch the boundary: criteria are strict inequalities, so a trough at exactly 400 µg/ft² fails, and Room C's 350 and Room A's 260 are close enough to the sill/trough limits that a re-clean before re-clear is prudent.
2. What is the status of the Room B floor composite, and how does it affect the clearance decision?
Read the worked answer
The composite is unusable for clearance. Clearance dust samples must be collected and analyzed as individual samples, one per surface per location; compositing is an option for some risk-assessment dust sampling, not for clearance, because a composite cannot tell you which of the sampled surfaces failed.
The Room B floor therefore has no valid clearance result, regardless of the 52 µg composite value. That has two consequences:
- Room B cannot be cleared on the basis of that data even if the reclean happens to pass the sill and trough.
- After recleaning Room B, collect fresh individual floor wipes at the required number of locations and analyze each separately.
Practically, this also means you should review how the crew collected dust throughout the unit - if the compositing error was procedural rather than a one-off, samples in Rooms A and C deserve scrutiny before they are relied upon. Document the discard and the reason in the clearance record.
3. The property manager asks whether the tenant can move in tomorrow if only Room B is recleaned and re-wiped. What do you say?
Read the worked answer
No. Clearance is determined for the unit as a whole; a unit that has failed clearance cannot be reoccupied until it passes, and the re-clearance has to cover what the failed clearance covered, not just the room that blew the numbers.
Recommended path:
- Reclean Room B in full (HEPA vacuum, wet wash, HEPA again), including the window trough, which failed at 620 µg/ft² and is the hardest surface to clean.
- Re-clear Room B with the full set of surfaces and separate samples per location.
- Because Rooms A and C passed with margin but were cleaned by the same crew that produced the composite error and the Room B failure, consider re-cleaning and re-wiping them as well; at minimum, re-inspect them visually and re-wipe any surface that looks disturbed. Trough values of 260 and 350 are not comfortable margins.
- Do not certify occupancy on a partial clearance, and do not accept a cleanup done by the abatement crew as a substitute for your own post-cleaning clearance sampling.
State plainly in writing that the unit remains uncleared until a passing re-clearance is documented. The schedule pressure belongs to the manager, not to the data.