it may not be the sed only solution but this does what you need (and it still uses sed)
LINE=`grep -n "Special Installation Instructions" PHSS_37232|cut -d: -f1`
cat PHSS_37232|sed -e "1,${LINE}d" > PHSS_37232.meat
2 lines instead of one for simplistic understanding. they can be combined into a single line if needed by command substitution.
HTH
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UNIX because I majored in cryptology...