Holme signal uses chemical compound

In case of emergency help to a ship. a box containing CaC2 and Ca3P2 is thrown in water using a canon. The reaction with water produces Ca2H2,  PH3 and P2H4. The compound P2H4 is self  combustible and burns PH3 and C2H2, White smoke of P2O5 and black smoke (incomplete combustion of C2H2) is visible at long distance indicating demand for help.CaC2+2H2O→ CaOH2+C2H2Ca3P2+6H2O→ 3CaOH2+2PH3