The silent mine whistle

An original fiction passage set in the nineteenth century.

At six o’clock, the men assembled beside the winding shed. Daniel stood among them with his lamp hooked to his belt, watching the dark mouth of the shaft. The engine man pulled the rope, but the whistle released only a faint breath. Until it was repaired, the foreman would allow nobody below. The older men cursed the delay and stamped their boots against the cold. Daniel said nothing. For a few precious minutes, the voiceless whistle stood guard between him and the shaft.

From the extract, identify the phrase that presents the broken whistle as protecting Daniel from entering the mine.