So, I build this grand fortress dome which I hewed from the mountainside itself, hollow out the topside of the dome and fill it with 2 z-levels of magma. Beforehand I built magma-safe floodgates that open up the flow all over the entire front of my fortress, where my hastily built Trade Depot is.
No, that's not the good part. I decide to move the trade depot on top of the dome, and make a path up to it accordingly, as well as an opening to the roof of my fortress from the inside. Finally, the Merchants from the mountainhomes arrive and begin to make their trek to my fortress. Little did I know, Bug 850 had different ideas on the fate of the supplies from the Mountainhomes and their merchants.
While putting the finishing touches on my pumpstacks that will pump water through the center of my fortress giving everyone happy mist thoughts and possibly flooding everything if it goes awry, I get a message.
Urist McHauler has died in the heat.
...What?
I look for his body around the usual suspect areas, smelting room and such. Nothing, search around the barra-
Urist McHauler has died in the heat.
Urist McHauler has died in the heat.
Urist McHauler has died in the heat.
Urist McHauler has died in the heat.
Urist McHauler has died in the heat.
Urist McHauler has died in the heat.
Urist McHauler has died in the heat.
Urist McHauler has died in the heat.
Urist McHauler has died in the heat.
Urist McHauler has died in the heat.
Urist McHauler has died in the heat.
Urist McHauler has died in the heat.
Urist McMayor has died in the heat.
Urist McChampion has died in the heat.
Urist McCat has died in the heat.
Urist McMason has died in the heat.
Everything is on fire, the barracks, the trade depot, and all the haulers which caught fire are now running through my fortress to their wooden beds to rest, and asking for water from soon to be flaming dwarves, who give them water, catch fire, catch the bucket they're holding on fire, and proceed to take the wooden bucket back to the stockpile room full of wooden bins, barrels, alcohol, and buckets.
Needless to say, my entire fortress was alit within a matter of seconds, all because my Merchants walked up a ramp with only a single wall separating them from magma. Because of such, the pack animals caught fire, the wagon pushed them to the Trade Depot full of wooden bins. Fun ensued.
/facepalm