What was the nature of the signalman's duty? What did the narrator think of the way it was being carried out?

The signalman's duty is to ring the bell signaling approaching trains, as well as to receive and send messages. The narrator believed the signalman was being overly cautious..... even zealous in his duties.

He was several times interrupted by the little bell, and had to read off messages, and send replies. Once, he had to stand without the door, and display a flag as a train passed, and make some verbal communication to the driver. In the discharge of his duties I observed him to be remarkably exact and vigilant, breaking off his discourse at a syllable, and remaining silent until what he had to do was done.

In a word, I should have set this man down as one of the safest of men to be employed in that capacity, but for the circumstance that while he was speaking to me he twice broke off with a fallen colour, turned his face towards the little bell when it did NOT ring, opened the door of the hut (which was kept shut to exclude the unhealthy damp), and looked out towards the red light near the mouth of the tunnel.