Maguire John F, Woodcock Leslie V
Scientific Simulation Systems Inc., San Antonio, TX 78249, USA.
Department Physics, University of Algarve, 8005-139 Faro, Portugal.
Entropy (Basel). 2019 Dec 20;22(1):14. doi: 10.3390/e22010014.
We review the thermodynamics of combustion reactions involved in aluminum fires in the light of the spate of recent high-profile tower-block disasters, such as the Grenfell fire in London 2017, the Dubai fires between 2010 and 2016, and the fires and explosions that resulted in the 9/11 collapse of the World Trade Center twin towers in New York. These fires are class B, i.e., burning metallic materials, yet water was applied in all cases as an extinguisher. Here, we highlight the scientific thermochemical reasons why water should never be used on aluminum fires, not least because a mixture of aluminum and water is a highly exothermic fuel. When the plastic materials initially catch fire and burn with limited oxygen (O in air) to carbon (C), which is seen as an aerosol (black smoke) and black residue, the heat of the reaction melts the aluminum (Al) and increases its fluidity and volatility. Hence, this process also increases its reactivity, whence it rapidly reacts with the carbon product of polymer combustion to form aluminum carbide (AlC). The heat of formation of AlCl is so great that it becomes white-hot sparks that are similar to fireworks. At very high temperatures, both molten Al and AlC aerosol react violently with water to give alumina fine dust aerosol (AlO) + hydrogen (H) gas and methane (CH) gas, respectively, with white smoke and residues. These highly inflammable gases, with low spontaneous combustion temperatures, instantaneously react with the oxygen in the air, accelerating the fire out of control. Adding water to an aluminum fire is similar to adding "rocket fuel" to the existing flames. A CO-foam/powder extinguisher, as deployed in the aircraft industry against aluminum and plastic fires by smothering, is required to contain aluminum fires at an early stage. Automatic sprinkler extinguisher systems should not be installed in tower blocks that are at risk of aluminum fires.
鉴于近期一系列备受瞩目的高层建筑火灾灾难，如2017年伦敦的格伦费尔火灾、2010年至2016年间迪拜的火灾以及导致纽约世界贸易中心双子塔在9·11事件中倒塌的火灾和爆炸，我们回顾了铝火灾中涉及的燃烧反应的热力学。这些火灾属于B类，即燃烧金属材料，但在所有情况下都使用了水作为灭火剂。在此，我们强调绝不应在铝火灾中使用水的科学热化学原因，尤其是因为铝和水的混合物是一种高度放热的燃料。当塑料材料最初着火并在有限的氧气（空气中的O）中燃烧生成碳（C）时，碳以气溶胶（黑烟）和黑色残渣的形式出现，反应产生的热量会熔化铝（Al）并增加其流动性和挥发性。因此，这个过程也会增加其反应活性，从而使其迅速与聚合物燃烧产生的碳产物反应形成碳化铝（AlC）。AlC的生成热非常大，会变成类似烟花的白热火花。在非常高的温度下，熔融的Al和气态AlC气溶胶都会与水剧烈反应，分别生成氧化铝细粉尘气溶胶（AlO）+氢气（H）和甲烷（CH）气体，同时伴有白烟和残渣。这些易燃气体的自燃温度很低，会立即与空气中的氧气反应，使火势迅速失控。向铝火灾中加水类似于给现有的火焰添加“火箭燃料”。在航空工业中用于扑灭铝和塑料火灾的CO泡沫/粉末灭火器，通过窒息作用，需要在早期阶段控制铝火灾。不应在有铝火灾风险的高层建筑中安装自动喷水灭火系统。
