Ventilate septic tanks, sewer manholes, cesspools, vegetable cellars, and fermentation tanks before entering; if someone collapses inside, never jump in after them—call emergency services immediately

Septic tanks, manholes, cesspools, and sealed vegetable cellars accumulate lethal concentrations of toxic gases (like hydrogen sulfide) and suffer severe oxygen deficiency, knocking an entrant unconscious within seconds. Across official industrial accident registries, a single worker collapses, and coworkers or relatives rush in consecutively to rescue them, only to die alongside them. Official statistics show over half of all confined space fatalities are would-be rescuers. If someone collapses inside, never enter: call emergency dispatch (such as 119 and 120) immediately.

Zero financial cost. Opening all covers and ventilation shafts and waiting upwind takes some extra time. Household septic tanks are safest when emptied by licensed professional service teams with proper equipment. The main difficulty is overcoming the instinct to rush in when a companion or family member collapses.

A "confined space" refers to enclosed or partially enclosed spaces not designed for continuous human occupancy, including septic tanks, sewage pits, manholes, storage cellars, and industrial vats. An analysis by the Ministry of Emergency Management of China of major confined space accidents since 2013 showed that poisoning and asphyxiation accounted for 96.8% of accidents and 96.9% of fatalities, driven primarily by hydrogen sulfide, carbon monoxide, nitrogen, and carbon dioxide. Accidents involving blind, unequipped rescue attempts accounted for 87.4% of incidents and 86.8% of deaths. The Ministry's 2020 Safety Guidance Manual highlighted that nearly 80% of confined space disasters saw casualties escalate due to impromptu, unprotected rescue attempts, and over 50% of total fatalities were would-be rescuers. In 2018, the State Council Work Safety Committee reported eight separate confined space incidents that initially involved only one worker in distress, but due to successive unequipped rescue entries, resulted in 3 to 4 deaths each. In 2019, during a sewage pit cleaning at a paper mill in Dongguan, three workers collapsed from hydrogen sulfide; six workers entered consecutively to attempt a rescue, resulting in seven deaths. In 2020 at a noodle manufacturing plant in Jiaozuo, one worker fell into a fermentation tank; five coworkers rushed in to assist, resulting in six deaths. The U.S. National Institute for Occupational Safety and Health (NIOSH) investigated 70 fatal confined space incidents between 1983 and 1993 involving 109 deaths: 39 victims (36%) entered specifically to rescue others, and only 4 of those 39 were trained emergency personnel. A 1986 NIOSH alert estimated that approximately 60% of confined space fatalities were would-be rescuers. Safety manuals explain that while hydrogen sulfide smells like rotten eggs at low levels, high concentrations rapidly cause olfactory paralysis—the human nose completely loses the ability to smell it. Concentrations exceeding 1,000 mg/m³ cause instantaneous "knockdown" and death within seconds. Similarly, extreme carbon dioxide concentrations induce loss of consciousness in seconds. Emergency guidelines strictly mandate: if local personnel lack breathing apparatus and retrieval gear, immediately call 119/120; "under no circumstances should forced entry be attempted." Rescuing an occupant from the outside requires that the entrant was already wearing a full-body harness attached to an external retrieval winch line. Ministerial Order No. 13 mandates that industrial work strictly follow the rule: "ventilate first, test next, enter last." Unventilated subterranean vegetable cellars also pose acute asphyxiation risks because stored root vegetables consume oxygen and release dense carbon dioxide; authorities advise opening all cellar hatches for prolonged natural ventilation, testing air, wearing safety ropes, and maintaining surface observers before entry.

Grade C is assigned because data stem from occupational casualty registries and safety engineering codes rather than clinical intervention trials. Benefit magnitude is rated Moderate: while the event outcome is frequently fatal (often taking multiple lives at once), exposure is concentrated among individuals who access these subterranean structures. Common domestic encounters include cleaning septic or biogas tanks and descending into winter vegetable storage cellars. Never rely on smell to judge atmospheric safety; absence of odor does not mean toxic gas is absent. If assigned by an employer to enter shafts or tanks without mechanical ventilation, gas testing equipment, continuous surface monitoring, or safety harnesses, workers have the statutory right to refuse, as detailed in Chapter 19, Rule 10. If someone collapses inside, shout for help and dial emergency dispatch (119 and 120); external actions are limited to removing covers and using fans or blowers from outside. Once an unconscious victim is extracted to fresh air, check for breathing and initiate chest compressions if breathing is absent, as outlined in Chapter 13, Rule 1. The protocol remains identical whether the victim is a coworker, neighbor, or stranger, adhering to the same safety boundary as Chapter 13, Rule 25 (do not jump into water if you see someone drowning). Carbon monoxide risks from indoor fuel burning are covered in Chapter 1, Rule 3. Primary beneficiaries are yourself (as the prospective rescuer) and coworkers or family members.

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