Silver fire - Definition

Silver fire is a phenomenon that occurs when a DC voltage is applied across ethylene glycol, such that the positive electrode is made of silver. The resultant reaction can best be described as a hypergolic electrochemical reaction, i.e. it produces flame.

The voltage can be as low as 3 volts.

This was the cause of the disastrous fire on board Apollo 1 which killed three astronauts during a ground pressurisation test. The capsule wiring was almost entirely Teflon-insulated copper wire; this demands that the copper conductors be silverplated to prevent chemical reactions with the Teflon. Also, the Apollo environmental control system uses ethylene glycol as a heat transfer agent, and the system was leaking. As a result, there were plenty of opportunities for the requisite conditions to occur, which they did. The situation was worsened by the fact that the capsule was pressurised with pure oxygen.

Ethylene glycol is commonly used to de-ice aircraft before takeoff, causing a problem as aircraft frequently contain silver-plated electronic components. In order to reduce corrosion, corrosion inhibitors are usually added, making the reaction worse in that another byproduct of the reaction is fulminate of silver, an explosive. The problem can be eliminated by the addition of chelating agents to the mixture.