Toxic Materials* To date, no systematic identification of toxic materials involved in SPS deployment has been made. This materials list must be developed first, and then an assessment of the potential effects of SPS deployment can be made. It is expected that some of the materials will have a significant base of information upon which to carry out an assessment (e.g., mercury); however, there may be other materials where the dose-response relationships and the source-receptor pathways are unknown and additional research will be needed to carry out the assessment. The details of the research plan for toxic materials are presented in Appendix 2A. 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. Reference 2.8.9 describes some of the problems with accidental hydrogen release based on projections for the space shuttle program. Liquid hydrogen spills can ignite immediately or have a delayed ignition. Upon immediate ignition there is a flash as the gaseous hydrogen is consumed followed by a burning of the liquid pool. The flash from a 3200 m3 (850, 000 gal) spill can produce thermal radiation sufficient to cause first degree burns and ignite light combustibles such as paper at a distance of 300 m. Radiation from a liquid pool fire is about a factor of 5 less. This sized spill is based on a launch pad accident of the space shuttle. A transport accident would probably not involve as much liquid hydrogen in one incident. If immediate ignition did not occur, Ref. 2.8.9 indicates that the cloud of gaseous hydrogen could be dispersed downwind and ignited by some remote spark. However, this is limited by the lower flammable limit (the lowest concentration for which ignition could occur) and by the fact that an accident would likely involve some violent event sufficient to cause immediate ignition. Other explosive and/or highly flammable materials include monomethylhydrazine, hydrazine, and nitrogen tetroxide used in chemical liquid propellants. These are of more concern for their highly toxic effects than for their flammability.
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