Contents
Chapter 4
Overview
Watney implements his hazardous plan to make water by decomposing hydrazine and burning the released hydrogen with oxygen, successfully producing about 50 liters and humidifying the Hab. After accelerating oxygen production and continuing the process, he realizes unburned hydrogen has accumulated to dangerous levels and evacuates. The Hab becomes an explosion risk, forcing an immediate new survival plan.
Summary
On Sol 32, Mark Watney refines his water plan: generate oxygen slowly via the MAV fuel plant and oxygenator, then decompose hydrazine over an iridium catalyst to release hydrogen and nitrogen. Lacking safe storage, he decides to form water immediately by burning hydrogen in the Hab, accepting major fire and explosion risks.
On Sol 33, Watney extracts hydrazine tanks and the MDV reaction chamber, builds a plastic-bag enclosure with a makeshift chimney, and fashions a pilot flame from a wooden cross splinter. Wearing protective gear, he starts a cautious hydrazine flow and successfully produces water while monitoring temperature. He plans to stop after consuming half his oxygen reserves for roughly 50 liters of water.
By Sol 34, after an all-night run, the Hab becomes hot and humid as he creates about 50 liters, which the water reclaimer collects until full, with excess stored in a gutted space suit. Encouraged, Watney boosts the fuel plant’s compressor (higher pump voltage) and continues making water at the oxygen production rate, keeping at least 25 liters of O2 in reserve.
On Sol 37, reconciling water yields with expectations, Watney notices a net oxygen gain between reserve tanks and deduces incomplete hydrogen combustion. Sampling the Hab air confirms 64% hydrogen, 9% oxygen, 22% nitrogen—an explosive mix. He evacuates to Rover 2, realizing the Hab is a bomb and he has limited time before CO2 filters saturate to devise a safe fix.
Who Appears
- Mark WatneyAstronaut and botanist; devises and executes a risky hydrazine-to-water process, makes ~50 L, then discovers dangerous hydrogen buildup and evacuates to a rover.
- Melissa LewisCommander mentioned; her geology sampling bags are repurposed to build a plastic tent over the reaction setup.
- Rick MartinezPilot mentioned; his wooden cross is splintered to create a pilot flame for burning hydrogen.
- Alex VogelChemist mentioned; Watney uses goggles from Vogel’s kit for protection during hydrazine handling.
- Beth JohanssenSystems operator mentioned; clothing threads used as ties and seals in the reaction tent setup.