Your belief is unfounded. There is no relationship between the subjunctive and urgency. Your sentences should read in the indicative: 1.
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... your friend needs to get away from that flammable substanceThis is a main clause. Subjunctives are used in subordinate clauses. And in any case, danger and similar ideas are not associated with the use of the subjunctive in English.
You be here at 9 tomorrow to work on what is left.This is a form of the imperative mood-- a command.
2. He warned that his friend needed to get away from the flammable substance.He warned that the toy building might tumbl