People have being asking me about Beirut and the Tiwai Ouvea dross stored in Southland.
Professor Allan Blackman, School of Science at Auckland University of Technology:
“Of the ouvea premix materials, Professor Allan Blackman says the “most potentially hazardous” compound is aluminium nitride, which is what makes ammonia when mixed with water.He also has concerns about heat produced from the reaction when ammonia is made. This is because heat aids in the formation of hydrogen gas and could cause a potential explosion. But this will only happen if “large enough quantities” of hydrogen are generated. But the reaction time of aluminium nitride with water is relatively slow, he says. Which means the release rate of ammonia would be similarly slow, as would the production of hydrogen”. Newhub.
Associate Professor Sally Gaw and Professor Brett Robinson says “they believe the worst case scenario is the heat released by the reaction with water, which could generate a fire at the paper mill along with releasing ammonia gas. “The actual impacts will depend on how much of the ouvea comes into contact with water.” Newshub.
PS That’s summary all comes from the Newshubs link below and I think is the best answer I can find to-date. I must say on this occasions Newshub deserve a large hand clap, for a Job well done, as this only news organisation, asides from myself, who ever bothred to explained the full risks of the dross in depth. I am not sure how missed this one but good on yah Newshub and thanks to Jason (Newhubs cameraman) who was at the Mataura meeting back in Feb & to John at TVNZ for getting the important point I made to you guys when other media present were trying to down play the risk.
PPS As I understand the issue, visa risk of an explosion, its a question of how much hydrogen builds up and how quickly that hydrogen released comes in contact with water.
In most location short of a sudden deluge of water, causing a sudden chemical reaction, the risk is very low to below middling.
However one location in Invercargil (Liddle St) CBD does concern me. Because;
A) The small of ammonia was clear when I visited. There was not lot opportunity for fumes to escape as there was no ventilation aside from wee cracks in door were
B) the Ouvea bags could be seen piled roof high and far back into a large ware house space.
C) This Liddle Street location us about 200 metres from a fuel depot and is on the verge of Invercargils inner CBD. (All areas were Ouvea was found to be stored in Southland were in areas proned to flash flooding).
To recap risk = speed of build up of hydrogen and speed with which it comes in contact with water triggering chemical reaction.
If released slowly there is not much risk as dilution defuses the risk and limits heat generation. If however that reaction happens quickly, as the hydrogen is already there (as it has built up as the ammonia converts to nitrate and has no where to go) then yes the risk becomes very real.