NYC-WTC_000164840

NYC 9/11 Public Portal Document

APPENDIX A Contaminants Not Expected to be Found Around the WTC Benzene

Benzene is a volatile organic chemical (VOC) that was found in emissions from the open flames and smoldering debris left after the collapse of the WTC. The benzene may have originated from the airplanes’ residual jet fuel or from the continuous burning of plastics and other materials contained within the collapsed towers.

Since the fires and smoldering debris persisted long after the collapse of the WTC towers, there is a possibility that harmful levels of benzene vapor could have accumulated in nearby indoor environments. However, because benzene is very volatile and dissipates into ambient air quickly, the vapor plumes would have had to contain high concentrations of benzene, and the indoor area would have had to be relatively close to the fire source in order for indoor amounts of benzene to build up to harmful levels. In addition, unlike dioxin, benzene cannot become adsorbed by dust particles and transported indoors to settle as a long-term potential hazard. Once the source of the benzene is extinguished completely from the area, then benzene can no longer be a hazard.

Results of samples taken within the immediate WTC work zone from September 11 through mid­ January 2002, show benzene levels of up to 180,000 parts per billion (ppb). However, tests during the same time period outside the work zone show levels of benzene that were below the established EPA screening level of 20 ppb, indicating how quickly benzene dissipates in the air. A specific example, for the day of October 3, is shown below:

From debris pile at From debris pile at From Liberty & WTC North Tower WTC South Tower Greenwich Streets 28,000-39,000 ppb 4,300 ppb less than 20 ppb

From January 26, 2002 through April 23, 2002 (the most recent test date available) levels of benzene in ambient air have remained below the 20 ppb screening level, except for one grab sample from the immediate work zone on February 9 and another sample from the same location on February 12. These tests indicate that the source of harmful ambient benzene levels has been extinguished, and therefore there is no source of benzene available to accumulate in any indoor environment. It is recommended that benzene not be monitored in any further indoor testing.

Polychlorinated Biphenyls (PCBs)

PCBs were historically used as coolants and lubricants in transformers, capacitors, and other electrical equipment. It is possible that, with the collapse of the WTC towers, PCBs could have been dispersed into the ambient air and then transported indoors. However, to date, all measurements of ambient air around the WTC work zone have been significantly below EPA’s screening level (730 nanograms per cubic meter). This indicates that PCBs in ambient air are not considered harmful. Therefore, it is recommended that PCBs not be monitored in any indoor testing.

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