Sol 38. Watney comes up with a way to get the hydrogen out of the Hab: Hydrogen only burns in the presence of oxygen, so he’ll trick the Hab’s oxygen regulator into pulling all the oxygen out of the Hab. While wearing a space suit, he’ll use an oxygen tank to burn the hydrogen in controlled bursts. However, the absence of oxygen will kill the bacteria in the soil. Watney takes a break, planning to listen to whatever music he finds from Commander Lewis’ personal USB drive. He signs back in for a log entry, Sol 38 (2), to inform us that the music is, disastrously, disco.
Though Watney relies on the Hab’s life support technology, he will, ironically, have to intentionally cause the oxygen regulator to malfunction in order to make the Hab habitable again. Once again, a solution gives rise to another problem: how to keep the soil alive? Watney’s second log entry is another nod to the running joke he’s creating between himself and the reader.
Sol 39. Watney realizes the soil bacteria will be OK if he lowers the Hab temperature enough to trick them into hibernating due to the wintry temperatures. He’ll leave the Hab at 1 percent oxygen content—enough to keep the bacteria alive, but not enough to maintain a fire. The cold will kill the potatoes, though, so Watney needs to put them in bags of soil and move them to the rover, where they’ll stay warm.
Weir uses this log entry to show how Watney thinks through the details of his plan in order to avoid another life-threatening mistake. Temperature and atmosphere—aspects of daily life people on Earth take for granted—are now critical variables in Watney’s plans.
Sol 40. The first steps of Watney’s plan work, but he’s only able to lower the oxygen content to fifteen percent. This keeps the atmospheric pressure tolerable, so Watney decides to wear multiple layers of clothing and put on an oxygen mask instead of a space suit, which allows him more mobility. Watney cuts the power to the oxygen regulator and starts burning hydrogen. Then, he’s suddenly knocked backwards by an explosion. His oxygen mask comes off.
Many “safety features” of NASA equipment are now working against Watney. The oxygen regulator can’t be “tricked” into removing all oxygen from the Hab, but this actually makes Watney’s current situation riskier. The EVA suit is designed to keep astronauts safe, but it’s also too cumbersome to work in. The reader is just as shocked by the explosion as Watney is.
Watney manages to turn the regulator back on, and the Hab’s oxygen returns to a normal level. From his burnt outer layers of clothing and the Hab’s computers, which show a rapid temperature spike in the Hab, Watney realizes that he survived a very hot explosion, but he isn’t sure what happened. He decides to spend the night in the rover and check the Hab’s equipment in the morning.
Watney usually has clear, scientific explanations for the problems that arise—and he often anticipates those problems before they occur. Now, this unexpected explosion makes it clear to readers that even with careful planning, Watney is not safe from the consequences of human error.
Sol 41. Watney is relieved to find that the oxygenator, atmospheric regulator, and the Hab’s other important equipment are still working perfectly. The soil is still alive, too. He realizes that he caused the explosion by wearing an oxygen mask, not a space suit, while burning off the hydrogen. Humans exhale a mixture of carbon dioxide and oxygen, so every time, Watney exhaled, his mask leaked a bit of oxygen into the system—in the presence of this extra oxygen, the hydrogen combusted. Watney is lucky to have survived, but the Hab is now once again safe. He settles in for an episode of Dukes of Hazzard from Lewis’ memory stick. On Sol 42, Watney moves the potato plants back into the Hab. He still has to make another 470 liters of water, but he’ll do so more cautiously, taking breaks to burn off all the excess hydrogen.
Watney’s intricate precautions earlier in the chapter may have seemed like overkill, but the fact that the explosion was caused by Watney’s hasty decision to breathe through the oxygen mask rather than the EVA suit shows exactly why careful planning is necessary. In order to survive on Mars, Watney must think through the consequences of things even as seemingly simple as breathing. Watney’s reference to The Dukes of Hazzard can be read as a play on words, highlighting how he himself is mastering the occupational hazards that come with living on Mars.