8.3 ASSESSMENT OF POTENTIAL CONSEQUENCES ON THE SELECTED ROUTES

This section evotiuotes the potential consequences of hazardous materials caormrier accidents on the tour selected hozzzmot route segments in Wayne County, including the Detroit Windsor Tunnel, the Ambassador Bridge, the segment of NMHT 0 under Cobo Haell, and the lowerted section 0oft NH 0 between the tunction oit the interchange with Wyoming Road and the interchange with 8 Mile Rood.

The consequences of hozmoti releases or spills werte onotyzed without addrreesssmthg the likeiéhood of occurrence Some assumptions were made rtegoarding the consequences 0! the rteleoases, The thtrtst assumption rteloated to the toxic end point used to estimate consequences. Additional assumptions cCoOnDcCeGrHnIeGd tlirtst responder [emergency personnell}] r«esponuse titme, the response behavior aotf people in vehicles who would be at rtisk aoti exposute to the potential hozmoet phmuntec., and the r(esponse behavior ofi people rtesidxrng [0!t prioesent] neawr the mute that would be in the release plume,.

The probability of total exposure given the concentrtoatiton c0mnd duonration oil exposurte was applied in conducting the corhtsequettce assessment. The numbert o0ft itndividuals in vehicles, in rtesidences, o0rt othecrt nearby lIaOcCiIlhiItItGesh tin thoe ultieccted area was assumed with a 50 percent potential toatoality exposure role and was used to estimate the consequences ot a rteilease. Regutdtttg rtestidents a0nd ottheertss. in the vicinity 0oFt the highway, It was assumed that emertgenCy r«essponders would be abtle to notify them tIon shelter mIn place Oo:r to evacuate betore the hozmqt plume could rteach the otitected rtesudences ond/or othert facilities, or

Some uncertainties were inherent in the evaluation, and these uncertainties could have impacted the risk assessment results One of the motor uncertainties was associated with the accident rate for each of the route segments. The route segment evaluated was less than 0 mile. Troutlihic doto averaged over a much Ilonget rmoute segment may not be rtepresentoative oft the traoftftic density in the short route segment that was evaluated, Varying traffic density oiso posed a significant unkitoWn

The

yecaurs, might increase the accuracy oti the estimattee, However,

collecting historical data tor: the past live years o01r longert may pose other choitenges because accident r(a0t'0e5s havvee: been dechnting. Trotttic counts [or each of the evaluated segments might incrweoase the accuracy of the accident rate estimate.

Anothert uncertainty was associated with the quantity and disttibution among the closses/divisions o0Ti haozartdous maotertiacls being transported through Wayne County. While some itnftmormoation was collected on the volume and the cloasses/ divisions of hauzamrdous materials trmavelitng into and out 0o!i Wayne County, the available collection points often were distant lhrormn Wayne County, making

On

exact count of hazardous materials shipments imn Wayne County cdtt•ttiiccult to

determine.

The uncertainty in the distribution of shipments among the various hazardous materials classes and divisions presents acmn uncerttuainty |ththat might be mitigated by collecting moerte data, In spite oft the stated uncertainties, a serious attempt was mode to pertftorm on obijective analysis. While the exact shipment risk data might be uncertain, the relative risk numbers should provide a valid undertstoanditng ol the classes and divisions oi haozamrdous material shipments that travel through Wayne County.