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1·When vapors of flammable liquid or combustible gas stagnate in job site , reaching 30% or more of the lower explosion limit, dangers such as explosion and fire may occur imminently;

四于作业场所有引火性液体之蒸气或可燃性气体滞留，达爆炸下限值之百分之三十以上，致有立即发生爆炸、火灾危险之虞时。