Floor Tile Mastic and a Dry Grinder
A school corridor has 900 ft2 of 9-inch by 9-inch floor tile. The tile itself is non-asbestos, but the black mastic contains 6% chrysotile. The contractor plans to pop the tile with a walk-behind scraper, then remove the mastic using a methylene chloride-based solvent and a floor grinder. The corridor will be separated from occupied classrooms only by plastic sheeting on the walls; there is no negative-pressure enclosure. Workers will wear half-face air-purifying respirators with P100 filters. One worker intends to use the grinder dry because the solvent makes the floor slippery and slow. The school will remain open for summer programs, and the corridor is on the same HVAC zone as two classrooms. The contractor asks whether the plan is acceptable and what must be changed before work starts.
1. Classify the flooring work and identify the main flaws in the proposed plan.
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The tile is non-asbestos, but the mastic is asbestos-containing material. Removal of resilient flooring and mastic is generally Class II asbestos work. That classification does not make the plan acceptable. Dry grinding of mastic is a major flaw: it abrades the material into fine dust, converts a nonfriable material into a dust-generating operation, and can make it RACM under NESHAP. The chemical solvent adds a methylene chloride exposure hazard, and the half-face P100 respirator does not protect against that chemical.
Other flaws include no negative-pressure enclosure, no critical barriers at openings, and an HVAC zone shared with occupied classrooms. The plastic on the walls does not prevent fiber migration. The grinder must not be used dry, and the solvent method needs a separate hazard review.
2. What controls and monitoring should be required for this job?
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The contractor should use wet methods or HEPA-equipped grinding equipment with local exhaust, not dry grinding. A negative-pressure enclosure with HEPA air machines and critical barriers should isolate the corridor from occupied spaces. The HVAC serving the corridor should be shut down or isolated. Workers need appropriate respiratory protection for asbestos and for methylene chloride if that solvent is used; a P100 filter alone is not adequate for solvent vapor.
Work practices should include HEPA vacuuming, wet wiping, prompt bagging of mastic debris, and no eating or drinking in the work area. Personal air monitoring should cover asbestos and solvent exposure. The school should be informed of the schedule and access restrictions. Waste must be packaged and labeled properly, and the area should be cleaned and cleared before students or staff re-enter.
3. Is a NESHAP notification required for the 900 ft2 of mastic removal?
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It depends on how the mastic is removed, but the proposed dry grinding would likely make notification required. If the mastic is removed as a nonfriable Category I material and remains nonfriable, it may not be RACM, and the 160 ft2 RACM threshold may not be triggered. But grinding, sanding, or abrading the mastic can render it friable and regulated. At 900 ft2, that exceeds the 160 ft2 threshold.
The contractor should not assume the job is exempt because the tile is non-asbestos. The compliance decision must be based on the mastic's condition and removal method. If the mastic will be ground, the contractor should treat it as RACM, provide the required renovation notification, and use RACM work practices.