ANFO can combust when in contact with iron oxides.

• A. True
• B. False
• C. Only under high pressure
• D. Only if wet

Answer: (A)

ANFO is a mixture of an oxidizer (ammonium nitrate) and a fuel (fuel oil), designed to detonate under proper initiation. However, it can also burn (deflagrate) if conditions allow a rapid oxidation to propagate on a surface. Iron oxide surfaces can act as catalysts for oxidation, providing a reactive site where the hydrocarbon fuel can burn more readily and where any heat released can be more easily sustained. When ANFO is in contact with iron oxides, this catalytic effect can promote combustion rather than requiring the high-energy shock needed for detonation. So the statement is true: contact with iron oxides can enable ANFO to combust.