What Happens If You Fall into a Pit Toilet: The Real Danger Isn't the Filth but "Invisible Gas"

According to the video, a pit toilet is a type of toilet that stores human waste beneath the bowl rather than flushing it into the sewer system. There are several ways to dispose of the stored waste, but in Japan the dominant method was the "kumitori" (pump-out) system, in which waste is accumulated to a certain level and then pumped out to be processed elsewhere. At one time, almost all household toilets in Japan were the pump-out type, but their numbers plummeted as sewer systems spread. As of 2019, they reportedly accounted for less than 5%. Even so, they are still used today in rural areas without sewer service and in temporary toilets during disasters.

The video explains that modern pit toilets almost never have a structure where waste drops straight down. For reasons such as odor control, they use either a bent pipe through which waste flows diagonally, or a valve called a "flapper valve" that seals the contents to some degree. The tank is connected to the outside through a pump-out port or manhole, and it's common for a vacuum truck to pump out the waste once or twice a month.

In developing countries, there are also toilets called "pit latrines." In these, waste falls directly into a large underground pit; liquids seep into the surrounding soil, but solids keep accumulating. As a result, the pit must eventually be sealed off or emptied by some means. The video stresses that with either type, hygiene measures such as physically separating the toilet from water sources and kitchens are essential, and that touching the contents with bare skin is out of the question.

The first barrier is a physical one. Whether a squat toilet or a Western-style toilet, the hole leading beneath the bowl is very narrow—too small for a person to pass through. The same is true of pit toilets; even for simple pit latrines in developing countries, it is reportedly recommended that the hole be no larger than 25 cm to prevent falls.

Still, several people have actually fallen into waste tanks. According to the video, they didn't fall through the toilet hole. They fell through outdoor pump-out ports or manholes, through collapsed tank lids, or through toilets with large openings of a kind not seen in Japan. The video says that if someone were to actually fall in, these routes are far more realistic. From there on, the discussion proceeds on the assumption that someone opened the lid of a pump-out port and fell into the tank.

The first thing to hit you upon entering the tank is the smell of accumulated excrement. The video lists its components as methyl mercaptan, indole, skatole, butyric acid, hydrogen sulfide, and others. Ordinarily, it's a stench strong enough to make your nose curl.

However, according to the video, the odor itself is not very likely to harm you while you're falling. Humans can detect odors at extremely low concentrations—sometimes at levels just a few thousandths of the concentration that causes harm. For this reason, the video explains, it's more accurate to think of odor as basically an alarm rather than a poison.

The danger rises sharply just before you reach the bottom of the tank. The video finds the key in the environment inside the tank. Inside many waste tanks, oxygen is extremely scarce—a condition known as "anaerobic."

The video explains that this is because the oxygen supply can't keep up with consumption. Oxygen is not a gas that dissolves easily in water to begin with. Human waste, on the other hand, is a mass of organic matter that readily consumes oxygen as it decomposes. The small amount of oxygen entering from the surface is quickly used up, and it barely reaches the dark, unstirred depths. As a result, anaerobic microorganisms that can live without oxygen take center stage in the accumulated waste. These microorganisms feed on the sulfur and organic matter in the waste and produce hydrogen sulfide, methane, and other gases. The video describes the bottom of a pit toilet as a "natural fermentation chamber" that quietly and continuously produces toxic and flammable gases.

Among these gases, the video singles out hydrogen sulfide as particularly dangerous. Its smell, often likened to rotten eggs, can reportedly be detected by some people at just 0.01 ppm—an airborne concentration of roughly one part in 100 million.

But the video says that as long as you can smell it, you're still only at the beginning. Hydrogen sulfide has the property of paralyzing the sense of smell once its concentration rises to dangerous levels, so the odor disappears. According to the figures cited in the video, that concentration is about 100–150 ppm. At 500–700 ppm, a person collapses within five minutes, and at 1,000 ppm, just one or two breaths are said to cause a coma. In other words, you can rely on smell as an alarm only at low concentrations; at truly dangerous concentrations, the alarm stops sounding.

The video explains the mechanism of its toxicity as follows. When hydrogen sulfide is inhaled, the mitochondria that produce energy inside cells become unable to use oxygen. Then, no matter how much oxygen is around, the body suffocates from the inside. And the organs that need oxygen most—the brain and heart—are the first to stop functioning.

Hydrogen sulfide isn't the only dangerous gas. The video also points to methane and carbon dioxide. These are less toxic than hydrogen sulfide, but they push out the oxygen in the same space. In other words, even if hydrogen sulfide doesn't get you, you could suffocate from simple lack of oxygen.

There is also the risk of infection. Referring to a previous episode, the video states that humans perceive poop as foul-smelling because humanity evolved to avoid things that serve as breeding grounds for infectious disease. It lists pathogens that may be present in feces, including norovirus, hepatitis viruses, dysentery, and parasite eggs. Although many of these don't act as immediately as suffocation, the video says the threat definitely exists.

According to the video, accidents involving falls into waste tanks happen all over the world. One relatively lucky example it introduces is an accident in Norway in 2016. A man in his twenties went into a toilet to retrieve a smartphone his friend had dropped, and couldn't get back out. He vomited from the smell and spent about an hour submerged up to his thighs in waste while being bitten by animals inside. In the end, firefighters who rushed to the scene rescued him by cutting apart the entire toilet with a chainsaw, and he was prescribed antibiotics at the hospital. The video adds that the smartphone apparently could not be recovered.

On the other hand, the video cites an accident in China in 2014 as an example with the worst possible outcome. Here too, it began with a woman dropping her smartphone into a toilet. Her husband went into the tank and lost consciousness, and upon seeing this, his mother, his wife, and his father went into the tank one after another, and all of them collapsed. Within just about five minutes, the husband and his mother died; the father was left with paralysis, and the wife fell into a coma in the hospital.

The video points out that a characteristic of this type of accident is that secondary disasters—where would-be rescuers collapse one after another—are likely to occur. Comparing it with the Norwegian case shows that even the same action of "going into a waste tank to retrieve a smartphone" can lead to vastly different outcomes depending on the condition of the air inside.

The video's conclusion is that what you should worry about if you fall into a pit toilet is neither the visible feces nor the overpowering stench. The real threats are oxygen deprivation and toxic gases that can take a life in an instant, and even the human kindness of trying to help someone who has collapsed can literally prove fatal.

At the end, the video asks viewers to remember, if only a little, when they sit on a warm toilet seat: that once there was a dark, bottomless hole beneath it, and that behind the wisdom that keeps us from falling in lies a pile of countless no-laughing-matter failures by those who came before us. These are its closing words.