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WTC OSHA Silica Sampling Data for Northwest Area

The PEL for Respirable Dust containing crystalline silica (quartz) is determined individually for each sample, using the following formula:

PEL = 10mg/m3 ÷ (%SiO2+2), where %SiO2 refers to the amount of crystalline silica measured in that sample.

This calculated PEL is compared with the Respirable Dust sample result to determine whether there is an overexposure. According to this formula, if there is no crystalline silica found in a sample, the PEL for that Respirable Dust sample is 5.0 mg/m3. As the formula implies, the PEL for respirable dust containing crystalline silica varies depending on the concentration of crystalline silica in the sample. The higher the concentration of crystalline silica the lower the PEL. (Click here for more information on the crystalline silica and the OSHA PEL.)

The Particulates not otherwise regulated (Respirable Fraction) OSHA permissible exposure limit (PEL) is 5.0 mg/m3.

aOther forms of crystalline silica (cristobalite) have not been detected in WTC samples. bResults are averaged and reported for the time duration stated. cND = Crystalline Silica None Detected.

 Date Taken Operation Sample Type Duration (min) Respirable Dust TWAb mg/m3 Crystalline Silicaa (Quartz)c %b PEL mg/m3 (based on formula) Respirable Dust TWAb >PEL? 05/29/02 AREA SAMPLE Personal 455 0.100 ND 5.000 05/29/02 AREA SAMPLE Area 465 0.100 ND 5.000 05/13/02 AREA SAMPLE Area 450 0.026 ND 5.000 05/04/02 DOCKBUILDER Personal 390 0.430 6.40 1.190 05/04/02 LABORER Personal 420 0.190 ND 5.000 05/03/02 Area 414 0.043 ND 5.000 05/03/02 Personal 412 0.410 13.00 0.667 05/03/02 Area 444 1.300 4.00 1.667 05/01/02 Personal 445 0.160 ND 5.000 04/27/02 NY FIRE DEPARTMENT Personal 420 0.065 ND 5.000 04/27/02 NY FIRE DEPARTMENT Personal 420 0.082 ND 5.000 04/27/02 AREA SAMPLE Area 375 0.058 ND 5.000 04/27/02 NY POLICE DEPARTMENT Personal 410 0.077 ND 5.000 04/27/02 AREA SAMPLE Area 373 0.063 ND 5.000 04/24/02 NY FIRE DEPARTMENT Personal 435 0.150 ND 5.000 04/24/02 NY FIRE DEPARTMENT Personal 437 0.110 13.00 0.667 04/24/02 NY FIRE DEPARTMENT Personal 435 0.160 18.00 0.500 04/24/02 AREA SAMPLE Personal 475 0.110 16.00 0.556 04/24/02 AREA SAMPLE Area 470 0.096 ND 5.000 04/24/02 DOCKBUILDER Personal 299 0.420 11.00 0.769 04/24/02 DOCKBUILDER Personal 267 0.150 ND 5.000 04/23/02 NY FIRE DEPARTMENT Personal 463 0.160 ND 5.000 04/23/02 NY FIRE DEPARTMENT Personal 470 0.061 ND 5.000 04/23/02 NY FIRE DEPARTMENT Personal 472 0.070 ND 5.000 04/23/02 NY FIRE DEPARTMENT Personal 461 0.099 ND 5.000 04/23/02 Personal 444 0.083 ND 5.000 04/23/02 Personal 232 0.380 ND 0.627 04/23/02 Personal 124 0.380 26.00 0.627 04/23/02 Personal 423 0.310 ND 5.000 04/23/02 Personal 516 0.150 17.00 0.526 04/21/02 AREA SAMPLE Area 485 0.052 ND 5.000 04/21/02 AREA SAMPLE Area 19 0.000 ND 5.000 04/21/02 AREA SAMPLE Area 475 0.130 22.00 0.417 04/21/02 AREA SAMPLE Area 514 0.034 ND 5.000 04/21/02 AREA SAMPLE Area 513 0.015 ND 5.000 04/21/02 AREA SAMPLE Area 480 0.000 ND 5.000 04/20/02 Personal 419 0.074 22.00 0.417 04/19/02 Area 462 0.330 4.90 1.449 04/19/02 Personal 462 0.740 3.60 1.786 04/19/02 Area 460 0.270 9.60 0.862 04/18/02 Area 497 0.057 ND 5.000 04/18/02 Area 446 0.059 ND 5.000 04/18/02 Area 466 0.041 ND 5.000 04/18/02 Personal 477 0.100 ND 5.000 04/16/02 AREA SAMPLE Personal 507 0.120 ND 5.000 04/16/02 DOCKBUILDER Personal 90 0.072 ND 5.000 04/16/02 DOCKBUILDER Personal 440 0.150 8.60 0.943 04/09/02 GRAPPLER Personal 472 0.035 ND 5.000 04/09/02 GRAPPLER Personal 479 0.025 ND 5.000 04/06/02 AREA SAMPLE Area 375 0.035 72.00 0.135 04/06/02 AREA SAMPLE Area 405 0.059 34.00 0.278 04/05/02 DOCKBUILDER Personal 422 0.280 ND 5.000 04/05/02 DOCKBUILDER Area 422 0.110 ND 5.000 04/04/02 NY FIRE DEPARTMENT Personal 457 0.100 ND 5.000 04/04/02 NY FIRE DEPARTMENT Personal 450 0.050 ND 5.000 03/09/02 NY FIRE DEPARTMENT Personal 440 0.080 ND 5.000 03/09/02 NY FIRE DEPARTMENT Personal 439 0.280 5.90 1.266 03/09/02 NY FIRE DEPARTMENT Personal 437 0.059 ND 5.000 03/08/02 DRILLER Personal 410 2.200 9.90 0.840 YES 03/08/02 DRILLER Personal 370 0.530 4.60 1.515 02/25/02 Personal 450 0.240 ND 5.000 02/24/02 Personal 410 0.065 ND 5.000 02/24/02 Area 480 0.210 14.00 0.625 02/24/02 Area 480 0.047 ND 5.000 02/22/02 Personal 480 0.100 ND 5.000 02/22/02 Area 435 0.046 ND 5.000 02/21/02 Area 460 0.022 ND 5.000 02/20/02 DOCKBUILDER Personal 225 0.160 ND 5.000 02/20/02 DOCKBUILDER Personal 285 1.800 8.40 0.948 YES 02/20/02 DOCKBUILDER Personal 210 1.800 8.60 0.948 YES 02/19/02 LABORER Personal 86 3.100 7.60 1.042 YES 02/19/02 LABORER Personal 538 0.530 4.30 1.587 02/01/02 GRAPPLER Personal 450 0.035 ND 5.000 01/29/02 Personal 495 0.140 ND 5.000 01/18/02 LABORER Personal 433 0.300 8.70 0.935 01/18/02 AREA SAMPLE Area 431 0.050 ND 5.000 01/18/02 LABORER Personal 430 0.066 ND 5.000 01/12/02 SURVEY ENGINEER Area 489 0.028 ND 5.000 11/17/01 AREA SAMPLE Area 292 0.130 ND 5.000 11/17/01 AREA SAMPLE Area 24 0.049 ND 5.000 10/26/01 Area 402 0.610 ND 5.000 10/26/01 CAT OPERATOR Personal 403 0.000 ND 5.000 10/23/01 OPERATING ENGINEER Personal 285 0.063 ND 5.000 10/21/01 "BOBCAT" OPERATOR Personal 260 0.250 ND 5.000 10/19/01 KEEPING ROADWAY CLEAR ON NORTH SIDE OF #7 WTC. Personal 386 0.110 ND 5.000 10/18/01 BOBCAT OPERATOR Personal 378 0.057 ND 5.000 10/16/01 POLICE OFFICER Personal 354 0.028 ND 5.000 10/14/01 CSHO Personal 355 0.037 ND 5.000 10/14/01 LABORER Personal 345 0.000 ND 5.000 10/11/01 Area 324 0.086 ND 5.000 10/10/01 OPERATING ENGINEER Personal 343 0.250 ND 5.000 10/10/01 GRAPPLER OPERATOR Personal 435 0.180 ND 5.000 10/10/01 IRONWORKER-BURNER/CUTTER Personal 111 2.300 ND 5.000 10/10/01 "BOBCAT" OPERATOR Personal 152 0.230 ND 5.000 10/10/01 LABORER Personal 140 0.970 ND 5.000 10/09/01 GRAPPLER/CLAW OPERATOR/OPERATING ENGINEER Personal 336 0.033 ND 5.000 10/09/01 GRAPPLER/CLAW OPERATOR/OPERATING ENGINEER Personal 296 0.016 ND 5.000 10/07/01 EXCAVATOR OPERATOR/OPERATING ENGINEER Personal 210 0.220 ND 5.000 10/05/01 Area 357 0.073 ND 5.000 10/04/01 Area 349 0.210 ND 5.000 10/04/01 Area 325 0.110 ND 5.000 10/02/01 GENERAL LABORER Personal 345 0.210 ND 5.000 10/02/01 TORCH CUTTER/BURNING Personal 335 0.160 ND 5.000 09/30/01 TORCH CUTTER/BURNING Personal 335 0.310 ND 5.000 09/30/01 EXCAVATOR OPERATOR/OPERATING ENGINEER Personal 74 0.000 ND 5.000 09/30/01 LABORER Personal 290 0.063 ND 5.000 09/27/01 GRAPPLER OPERATOR Personal 285 0.056 ND 5.000 09/27/01 Area 200 0.120 ND 5.000 09/22/01 BLDG 7, EAST CORNER Area 269 2.900 < 1.00 3.333