Ammonium Nitrate (AN) Incompatibility with Common Alloys

The recent Ammonium Nitrate (AN) explosion in Beirut has brought home the dangers of AN storage, but did you know that the copper based alloys commonly used in Lightning Protection and Grounding applications, are incompatible with AN, and can negatively react with AN making it highly unstable?

Brass and copper must never be used anywhere where these metals could ever come into contact with;

• ammonium nitrate
• solutions of ammonium nitrate solutions
• ammonium nitrate-based explosives.

This reaction between AN and copper brass can lead to the formation of a complex salt known as Tetraamminecopper(II) Nitrate , or TACN, where any contact between TACN and AN, can lead to AN becoming highly unstable, resulting in a higher sensitivity to mechanical and thermal stimuli, and presenting significant explosive properties. 

A detailed white paper on the subject by Martin Künzel,1* Ond?ej Vodochodsky,1 Robert Matyá?,1 Zdeněk Jalovy,1 Jiri Pachman,1 Jaroslav Maixner is linked below.

Lightning protection and grounding systems commonly use copper and brass componentry, yet no guidance is offered within the the current Australian Standard AS1768 Lightning Protection that would highlight this incompatibility of Ammonium Nitrate with these common metals.  

Where the use of brass or copper is unavoidable, i.e as may be required in some fire suppression/ extinguishing systems, then it is recommended that all exposed metal be protected by some suitable coating, i.e. paint, although such painting should not interfere with any required function, i.e, the nozzles of the fire extinguisher system.

The safest option is the use of 316 grade stainless steel componentry such as the 316 Stainless Steel earthing plates pictured above that can be placed in the formwork prior to concrete pour and which bond to the steel reinforcement mesh within the slab and which can terminate Lightning protection system components and grounding systems that are suitably compatible, all of which are available from your friendly neighborhood Lightningman.

Lightningman has recently submitted this issue as a proposed inclusion within the upcoming AS1768 Lightning Protection standard revision, which hopefully will be released later this year.

Grant Kirkby- Lightningman