why is calcium carbide used in holme's signal

Containers containing calcium carbide and calcium phosphide are pierced and thrown in the sea when the gases evolved burn and serve as a signal. It is also used in smoke screens.

 

After making two holes these container are thrown in sea on reacting with water calcium carbide produce scetylene and calcium phosphide produce phosphine,along with phosphine,some amount of P2H4 is also produced,and it catches fire instantly,along with other two gases,luminous flame of acetylene serve as a signal