Complex sentence: In 1892 he became an assistant fireman, and a regular fireman in 1896, qualifying him to join his trade union, the Associated Society of Locomotive Engineers and Firemen (ASLEF).
Split into simpler sentences: In 1892 he became an assistant fireman, and a regular fireman in 1896. Becoming a fireman qualified him to join his trade union, the Associated Society of Locomotive Engineers and Firemen (ASLEF).