NYC-WTC_000199582

NYC 9/11 Public Portal Document

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Table 9. Crystalline silica - respirable fraction of alpha-quartz

Tier Action Crystalline Silica (settled Crystalline Silica (indoor air) dust) Level Basis Level Basis I Aggressive cleaning. If 10.0 pg/m’ OSHA PEL of levels persist, take * 100 pg/m’ (see additional action to narrative reduce exposure. below).

Evaluate conditions in the area including representativeness of air samples, asbestos settled dust levels and loading. II Maintain recommended above 10.0 pg/m’ cleaning methods. background to 1 pg/m’ Consider additional (or monitoring. background) * Evaluate conditions in the area including representativeness of air samples, fibrous glass settled dust levels and loading. III No further action background Level is set at 1 pg/m^ or OSHA PEL of required. that found in backjp-ound 100 pg/m’ (see background, or narrative unaffected, areas. below). In this way, no increase in risk due to the silica in settled dust would be expected. * Silica measured in airborne respirable dust, by NIOSH 7500.

The benchmarks for silica in indoor air were derived from the Occupational Safety and Health Administration’s (OSHA) permissible exposure limit (PEL) for dust containing 100% respirable silica in air of 100 pg/m^ (0.1mg/m^)as a time weighted average for an 8 hour exposure.

Silica exposure poses risk of both cancer and non-cancer respiratory health effects. Although no

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