This is because a zombie’s downpour is not guaranteed to kill it quickly. Suppose you are pumping massive amounts into a bog, like the fire department did in North Carolina. This does not mean that water gets to the right places when it flows underground. “It creates a channel, and the fire in that channel is removed, but the water isn’t going anywhere else,” says Rein. Other parts of the fire can become infected without being touched. And so the zombie lives.
If firefighters do not have enough water at their disposal, they may try to compact the soil with heavy machinery in an attempt to cut off the oxygen supply to the fire. But this equipment is not always available for a crew. Even then, such a maneuver is dangerous work, since it requires driving on an active fire. In addition, these fires can be huge, and heavy machinery can only cover a limited amount of land.
So in the lab, Rein and his colleagues experimented with a new anti-zombie weapon: water mixed with a non-toxic, readily available fire extinguisher. surfactant, also known as a wetting agent or suppressor. “It’s a bit like soap – it just reduces the surface tension of the water and allows the water to better penetrate a porous medium,” says Rein. “Peat is a porous medium.”
Using a small, custom-built “peat reactor” filled with plant material and lined with ceramic insulators, they could start a zombie fire and watch it as it burned. Above the box they placed a nozzle for spraying ordinary water or their special mixture on different fires. Compared to the same amount of plain water, water with a surfactant reduced the time required to extinguish the fire by 40 percent. Thanks to this decrease in surface tension, instead of creating channels, the mixture penetrated the ground more evenly, so that small patches of zombie fire had nowhere to hide.
It’s not that the surfactant had some kind of chemical effect on the fire – for example, lowering oxygen levels. Instead, it was more of a thermal effect, “in the sense that the surfactant allows the water to reach more hot spots and get to them faster,” says Rein.