Four Deaths in a Wastewater Tank: Toxic Gas at a Joss Paper Workshop, China, 2025

On May 14, 2025, four members of one family died in an underground wastewater tank at a small workshop in southwestern China that made ceremonial paper. The workshop was operating without the safety and environmental approvals the law requires, and had no protective equipment, gas monitoring or ventilation. A report by Chinese public health investigators, published in CDC's MMWR, describes what happened and what it shows about the dangers of confined spaces.

What ceremonial paper is

Ceremonial paper, or joss paper, is used in Chinese and other East Asian ancestor worship: sheets and paper effigies are burned at funerals and festivals to honor ancestors. It is made cheaply, from bamboo pulp, rice paper or recycled paper, and is often printed with gold or silver foil to look like money. The raw material is ground into pulp, blended into a slurry, drained, formed, pressed, bleached and dried. Pulping and bleaching often use sulfuric acid, sodium sulfate and sodium hydroxide, and the wastewater is usually stored in a sedimentation tank before treatment. Hydrogen sulfide can be released from that wastewater through the decomposition of sulfur-containing organic compounds and anaerobic sulfate reduction.

What happened

The workshop had been making trial runs for about a year; some paper had been produced but none sold. It had a business license obtained online, but no safety production license, occupational health pre-assessment, environmental assessment or fire inspection certificate — all required.

Timeline of the incident (MMWR).

• About 5:50 p.m. The operator's wife, 54, climbed down a ladder about 7.3 feet (2.2 m), without protective equipment, into an underground tank to drain it and remove sediment — the first time in at least a year. She used an electric pump because the tank had no drain. Within minutes she lost consciousness.
• Over the next 20 minutes, her son (28), her husband — the workshop operator (57) — and her daughter (31) went in to rescue her, also without protection. Each quickly collapsed.
• 6:21 p.m. The operator's daughter-in-law had a neighbor call for emergency help. Township health center staff arrived within 10 minutes, noticed an unusual smell and, lacking protective gear themselves, called for more help.
• 7:10 p.m. County hospital emergency staff and firefighters arrived. By 7:25 p.m. firefighters had pulled all four out — cyanotic, unconscious, with no detectable pulse, breathing, blood pressure or reflexes.
• 8:30 p.m. All four were pronounced dead at the county hospital after resuscitation failed.

What investigators found

The workshop was a one-story building of about 5,400 square feet (500 m²) with four unventilated underground tanks, each about 494 cubic feet (14 m³) and 7.3 feet deep, reached one person at a time by ladder through small openings. The tank where the deaths occurred held 6.7 inches (17 cm) of wastewater; the other three were nearly full.

About 22 hours later, provincial investigators in protective suits and breathing apparatus sampled the tank's air:

Taken together, the gases gave a mixed exposure ratio of 106 — a combined measure that should be 1 or less — meaning the atmosphere could kill immediately. The victims' signs matched poisoning by these gases. No autopsies were done.

• Hydrogen sulfide is heavier than air and pools in low places. At high concentrations (above 800 ppm) it quickly causes olfactory fatigue and respiratory failure. In China, suffocating gases — especially hydrogen sulfide — cause about half of work-related poisoning deaths.
• Hydrogen fluoride and phosphine were a surprise, as they aren't usually linked to papermaking. Minerals in the tank may have reacted with alkaline chemicals such as bleach to produce hydrogen fluoride, and the anaerobic decay and fermentation of organic matter can produce phosphine.
• Because the tank had gone uncleaned for at least a year, the gases had built up to deadly levels. The readings may understate them: the tank had been open to the air for nearly a day before sampling.

The response

Officials classified the incident as a major (level III) public health emergency and responded within hours. Police closed the workshop and sealed the toxic residue; environmental authorities traced the gas to the tank and treated the remaining wastewater. Interviews and health checks of all 10 residents of the village's six households found no signs of exposure, and the nearest home was about 200 meters away.

Lessons

Entering a confined space at work requires a plan in advance. Here, an untrained worker with no protection entered an unmonitored, unventilated tank, and untrained relatives with no protection followed her in — the same pattern as a 2018 incident in China in which a rescue attempt ended in multiple deaths. In a 2013 case at another papermaking business in China, five people were poisoned by hydrogen sulfide while working without protection; all survived, though two had pulmonary and cerebral edema.

The authors also point to regulatory failure: the workshop had operated for at least a year on self-reported permit applications rather than documented approvals and inspections, and authorities lack the staff to inspect small workshops. They recommend:

• stronger safety approvals by emergency management, environmental and health authorities for businesses that produce toxic byproducts;
• better supervision to prevent oversight gaps;
• training for workers in safe practices, hazard recognition and protective equipment.

Sources

• Jiang Z, Luo S, Wu D, et al. "Poisoning Deaths in a Workshop for Ceremonial Papermaking — China, May 2025," MMWR Vol. 75, No. 30, CDC; published by CDC and in the public domain. The report calls all four who died employees in one place but says the daughter was not an employee in another, so this page does not say which of them worked there. Its photographs of the tank openings are not reproduced.