My Apocalypse System Arrives 10 Years Early

The rulers of this Underground City, the Upper Caste, had been slaughtering or expelling the Lower Caste en masse. This led to a labor shortage for menial jobs. As a result, feces began to accumulate more and more. In just one or two months, tens of thousands of tons of it had collected in the cesspool at the bottom of the city.

Tens of thousands of tons of feces piled up and fermented, producing an extremely high concentration of methane. The ventilation system was also in disrepair and broken, allowing the gas to become increasingly dense.

Biogas is primarily produced by the anaerobic fermentation of organic matter. Its main component is methane (CH4), typically making up 50-70% of its volume, followed by carbon dioxide (CO2) and other gases like hydrogen sulfide.

Among these, methane is the main flammable component. Other gases, such as hydrogen sulfide, are toxic, and inhaling too much can be fatal.

According to some sources, each ton of organic waste (such as feces) can produce approximately 20-30 cubic meters of biogas during anaerobic fermentation, with a methane content of about 50-70%.

Let’s assume an average value—say, 25 cubic meters of biogas per ton of feces, with a methane content of 60%. The total biogas production would then be 50,000 tons × 25 m³/ton = 1,250,000 cubic meters of biogas. The methane portion would be 1,250,000 × 0.6 = 750,000 cubic meters.

The heat of combustion for methane is approximately 55.5 MJ/kg, or about 15.4 kWh/kg. The density of methane under standard conditions (0°C, 1 atm) is approximately 0.717 kg/m³. Therefore, the mass of 750,000 cubic meters of methane is 750,000 × 0.717 kg ≈ 537,750 kg, which is about 537.75 tons of methane.

The total combustion energy of the methane is 537,750 kg × 55.5 MJ/kg ≈ 29,840,625 MJ.

One ton of TNT is equivalent to about 4.184 GJ (or 4184 MJ). Therefore, the total TNT equivalent is 29,840,625 MJ ÷ 4184 MJ/ton ≈ 7,130 tons of TNT.

Of course, not all the biogas would be fully combusted or detonated upon ignition. But even if we take just one-tenth of that, it’s equivalent to 713 tons of TNT. Two-tenths would be 1,426 tons of TNT.

For comparison, a small tactical nuclear weapon (like the United States’ W54 warhead) has a yield of about 1,000 tons of TNT.

At that moment, in a district near the bottom of the Underground City, a man from the third caste went to use the toilet with a cigarette dangling from his lips. He noticed a strange smell but could tolerate it. It was a dry latrine, after all, and he was used to them from back in the age of peace.

In India, proper toilets were scarce even in the age of peace; dry latrines were everywhere.

After the man squatted down, he flicked his lighter, intending to light his cigarette. But he never could have imagined that with a FWOOSH~, he had just ignited the biogas.

Instantly, a massive combustion and explosion occurred!

Furthermore, it happened in the relatively enclosed space at the very bottom of the Underground City, so the force of the explosion may have been even greater than that of a small tactical nuclear weapon.

This kind of Underground City was already cramped, and the construction quality of the Indian Underground City was mediocre at best. And so, disaster struck.

In truth, incidents in underground cities caused by safety hazards like fires were not uncommon in any country. But one caused by an exploding mountain of feces? That was truly a first.