The stench of sewage poured into the sea, and the rancid and moist smell went straight to the brain, choking people who could not breathe.

"Oh my God, it stinks in here, too! What's going on? Is it a direct access to the toilet? Just...... Hey, what's wrong with you!? ”

Matthew clenched his nose, burst into tears, and asked vaguely with stones, but as soon as he turned around, his heart was half cold.

In the pitch-black environment, everyone only saw Bi Fang leaning against the wall and retching, his face was pale, his eyes were bloodshot, and sticky saliva flowed out unconsciously and dripped to the ground.

"Hey, hey, are you alright?"

Matthew was so frightened that he was about to jump up, and he stepped forward to support Bi Fang, which was much more terrifying than his own vomiting, and if Bi Fang had an accident now, he would have to be finished with him.

I'm a little pendant, and Matthew knows it very well.

"It's okay, I'll take it easy!"

Bi Fang leaned against the wall and slowly sat on the ground, cut off a section of the clothes under his waist, soaked it with water, and covered his mouth and nose to feel better.

Even normal people feel disgusting when they smell it is amplified a hundred times in Bi Fang's nasal cavity, the nasal mucosa is as if it has been burned, and every olfactory cell is wailing wildly, which is no different from facing a stink bomb!

Turning out the memory of going to the most smelly toilet, and then thickening the smell dozens of times at that time, it is probably how Bi Fang feels now, and it is already a manifestation of his strong willpower to be able to persist until now.

After ventilating a few times in a row, Bi Fang's mind was slightly clearer, and the remaining distance was less than a hundred meters, but unless he didn't ventilate from now on, he could no longer move forward.

But a round trip is 200 meters, and you have to find a suitable position to make a bomb in the middle.

Hearing Bi Fang say that he couldn't handle it, Matthew panicked: "What should I do then?" ”

"Don't worry, let me think, think about ......"

Bi Fang's mind was still a little confused, the plan was perfect, but he never expected that he would be stumped by this section of sewer, the taste here was too exciting.

"It's hard for a normal sewer smell to push the limits of human physiology, and I suspect there may be hydrogen sulfide and maybe methane. Very large factories are equipped with septic tanks to avoid the accumulation of sewage, etc., and after several months of abandonment, the gas filtration system here may have failed, coupled with the failure of the exhaust fan, the sewer air is not circulated, resulting in the air content of hydrogen sulfide far exceeding the normal standard. ”

"In July last year, a 19-year-old girl died of hydrogen sulfide poisoning in Busan, a country of bangguo, when the 19-year-old went to a public toilet near the swimming pool and never came out.

Twenty minutes later, the companion saw that the situation was not good, and rushed into the toilet to find the girl lying on the ground, unconscious. The smell of the toilet was unbearable, and even my companions were so smoked that they almost fainted, and they kept vomiting while saving people. The girl was not rescued afterwards, and the cause of death was hydrogen sulfide poisoning. ”

"It was also a malfunction of the gas filtration system, which produced a large amount of hydrogen sulfide, which was later released from the exhaust hole of the public toilet where the girl was killed. In cramped toilets, hydrogen sulfide concentrations are as high as 1,000 ppm, which is 60 times higher than the 15 ppm specified by the safety standard. At high concentrations, hydrogen sulfide can even cause an 'electric shock' death in a matter of seconds. The mechanism of cyanide poisoning is similar. ”

Matthew's eyes widened and his breathing became slight, he looked around, looked at Bi Fang's example, and quickly tore off a piece of cloth from his body, wet it and covered his mouth and nose.

"It's useless." Bi Fang shook his head, "I cover my mouth and nose to relieve the irritation, the wet towel is just a fiber fabric, it can't block these gas molecules, and it has no anti-poison effect, if it can really effectively block smoke and poisonous gas, the air will also be isolated, making people unable to breathe." ”

[Damn, so dangerous? I'll never go to a public toilet again]

[Scary, too scary]

[The old man knows too much, a chemist]

[Ah, I found it!] When hydrogen sulfide enters the bloodstream, it quickly finds an oxidizing cytochrome oxidase enzyme that binds to the trivalent iron ions of heme. The ferric of this enzyme is supposed to be reduced to ferric reduced cytochrome oxidase, which transports electrons during the redox process to utilize molecular oxygen. 】

[Continued: However, hydrogen sulfide will rob the ferric iron, which will also block the human respiratory chain and cause hypoxia of tissue cells. In addition to this, hydrogen sulfide also has a strong cytotoxic effect on the lungs in the respiratory system, resulting in severe damage to lung tissue and pulmonary edema!! 】

Netizens who have reacted quickly have begun to find out the dangers of hydrogen sulfide.

"So what now?"

Seeing that the wet towel was useless, Matthew didn't know what to do, and he, a photographer, didn't know how to save himself in this situation.

Unexpectedly, Bi Fang waved his hand and signaled Matthew to be calm: "Don't worry, there will be toxic gases in the sewers many times, so I was prepared before I came down, in this case, we can make a simple gas mask, do you remember what I asked you to do before you came down?" ”

"You mean the charcoal?"

Matthew hurriedly put down his backpack and took out a large handful of black charcoal pellets from it, which Bi Fang asked him to make this morning, but he didn't explain why, and now he vaguely understands.

Bi Fang took the packet of charcoal and explained: "Gas masks are generally composed of four parts: poison filtering materials, smoke filter materials, isolation materials and strong sealing materials. ”

"What we encounter is toxic gas, so the poison filter material must be indispensable, and there are only a few kinds that can be found in the wild, one is limestone particles, the other is activated carbon, and the third is charcoal."

Bi Fang took out an empty plastic bottle, used a screwdriver to tie a small hole at the bottom as the air intake hole of the poison filter canister, and cut out an arc at the other end, and placed it on his face to fit to ensure that it was in the shape of the human nose and face.

"The three materials are very easy to obtain, especially charcoal, but I processed it a little to make better activated carbon, and the preparation of activated carbon is also very simple, as long as you use firewood to make charcoal, and then knock it into small pieces of charcoal, put the small pieces of charcoal into a clean and fine nylon mesh bag, pierce it into the mouth of the bag, put it in an acidic solution and boil for more than 30 minutes, and wash out the oil."

Matthew on the side suddenly realized. "No wonder you asked me to put vinegar in the morning! It's acetic acid in it, right? ”

"That's right." Bi Fang nodded, "Vinegar contains acetic acid, and other acids can be used without vinegar, hydrochloric acid, sulfuric acid, and even citric acid, citric acid is added in many foods, and even some cosmetics are available, and alkaline sodium carbonate can also be used." If there really is nothing, you can even induce vomiting and cook it with stomach acid. ”

Bi Fang nodded, put a sponge at the bottom of the hole in the plastic bottle, followed by sawdust, put 7cm, compacted to 5cm, and then put a layer of gauze, at this time put in activated carbon 3cm, and then put a layer of sponge.

A simple gas mask is made.

"Let's use that sealing material as a mask, a plastic bag is fine, pay attention to be soft, thick, transparent, and must not leak."

Bi Fang extruded the tank from the inside of the bag to the outside, sealed the interface firmly with tape and paper, and added a fixed belt through the tank and handed it to Matthew.

"The rest of the road is up to you."

"Good...... Well? Matthew took the gas mask and was putting it on his head, when he heard this, he was stunned and pointed at himself, "Me? ”

Bi Fang nodded: "It's you, don't hide it, my sense of smell is much more developed than ordinary people, and the smell I smell is several times that of you, and I can't walk in." ”

"And don't detonate it with antifreeze, you sprinkle it directly on the ground, only don't use an open flame to ignite, use the way I taught you last time to wrap the newspaper with potassium permanganate and antifreeze to ignite, the ignition process takes about thirty seconds, and after making it, throw it directly on the ground and run towards me, be fast, understand?"

Bi Fang's expression was serious, and the appearance of hydrogen sulfide made him change some of his minds.

Nine out of ten of the gases in the sewers were flammable and explosive, so he never used an open flame.

If it weren't for the fact that the flashlight in your hand was a military flashlight with a strong seal, you might not even be able to use the flashlight.

The power of the explosion depends on the amount of explosives, and a complete explosion of a barrel of antifreeze and half a barrel of gasoline may attract some people, but it is absolutely limited.

But what about hydrogen sulfide and methane throughout the sewer?

Blow up half a street, how many people will be attracted to it?