As part of preparing for material disposal, a small fire occurred within a fume hood as a researcher was combining several spent ammonia borane (AB) samples that had previously been stored uncovered in the back of the hood for 6+ months. These AB samples consisted primarily of two 40-gram products of a 50wt% AB in silicone oil that had been thermally dehydrogenated. A small amount of unreacted AB slurry is believed to also have been present.

During project clean-up, partially spent (thermally reacted) ammonia borane (AB) residue from a previous experiment was mixed with a small amount of water to rinse the residue from its container. The water reacted with the spent AB resulting initially in a large heat release followed immediately by a fire. It appears that the water addition to spent AB resulted in hydrolysis of the boron and hydrogen production. This is an exothermic reaction. The high temperature then caused the small amount of unreacted AB to produce pyrophoric gases such as diborane that ignited in the presence of air. The lead scientist pulled the fire alarm, effectively evacuating the building, retrieved a fire extinguisher, and immediately put out the fire. The fire department arrived and confirmed the fire was out, releasing the building for re-entry.

From previous experimental results, it had been concluded that spent AB does not produce diborane with either heat or water addition. However, spontaneous combustion may occur under those conditions with partially spent material. Subsequent causal analysis concluded that the event occurred when water was added to solidified AB material that had been broken up during removal from a flask.

While ammonia borane does not react with water, partially and fully thermally reacted AB does react to produce hydrogen. Use of a small amount of water (50 mL) with a large quantity of hydrogen storage material (>100 g) can result in very high reaction temperatures. With some unreacted AB, the high temperatures can release pyrophoric by-products that would then initiate a flame.