2.1.2 Unconventional Effects Toxic Materials. To date, no systematic identification of any toxic materials involved in SPS deployment has been made. Until this materials list is developed, the potential public health effects of exposure to these substances cannot be assessed. The continuing environmental assessment will attempt to compile such a list, review the state of knowledge of health effects, quantify the potential for public exposure, and evaluate alternative control measures. Transport Accidents. A sizable quantity of highly explosive rocket propellants will need to be transported to the launch site in the course of SPS launch operations. The one of most serious concern is liquid hydrogen, which is currently transported by tank truck to launch sites but is under consideration for transport by barge or rail car. Liquid hydrogen spills can ignite immediately or have a delayed ignition. Upon immediate ignition a flash occurs that can produce thermal radiation sufficient to cause first- degree burns and ignite light combustibles, such as paper, some distance away. If immediate ignition does not occur, the cloud of gaseous hydrogen could be dispersed downwind and ignited by some remote spark. However, this possibility is limited by the dilution of the cloud through mixing with the air. Other explosive and/or highly flammable materials include monomethylhydrazine, hydrazine, and nitrogen tetroxide, used in chemical liquid propellants. These are of more concern because of their high toxicity rather than their flammability. Spills of liquid oxygen could also create significant local impacts, notably on ecosystems. The extreme cold is the principal cause of damage. Although data are available on the results of transportation accidents, they have not been translated into actual health and safety effects, i.e., injury rates. To do so would require an analysis of accident probability and an evaluation of probable transport corridors to determine public exposure hazards. An evaluation of these problems will be included as part of the ongoing assessment.
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